Options for the implementation of protection kits for 110-220 kV overhead lines.

1. The simplest set of protections is used on dead-end overhead lines: two-stage current protection against phase-to-phase short circuits (MTZ and MFTO) and a three-stage ZZ. At the same time, there is no short-range redundancy of the overhead line protection, and it is possible that in the event of a short circuit on a dead-end overhead line and a failure of its protection, the entire SS of a large system substation is extinguished when the long-range protection redundancy is operating. That is, even on simple dead-end overhead lines extending from the buses of large substations and power plants, it would be desirable to use basic and backup protection to increase the reliability of the substation or power plant, but this practice is not accepted.

2. The simplest option for backbone overhead lines with two-way power supply: three-stage DZ, four-stage ZZ and MFTO. DZ and ZZ provide protection of overhead lines from all types of short circuits and long-range redundancy of protection. MFTO is used as an additional protection due to its simplicity, low cost, high reliability and speed.

Serially produced are typical relay protection devices for overhead lines 110-220 kV, containing a three-stage DZ, a four-stage ZZ and MFTO:

The electromechanical panel of the EPZ-1636 type has been produced by the Cheboksary Electrical Apparatus Plant (CHEAZ) since 1967. Installed on most of the 110-220 kV overhead lines of the power system of the Chelyabinsk region.
- an electronic cabinet of the ShDE-2801 type, manufactured by CHEAZ since 1986, installed in the power system of the Chelyabinsk region on only a few dozen 110-220 kV overhead lines.
- microprocessor cabinets of the ШЭ2607 series, produced by NPP Ekra since the 1990s: ШЭ2607 011, ШЭ2607 016 (breaker control with a three-phase drive, three-stage DZ, four-stage ZZ, MFTO), ШЭ2607 012 (breaker control with a single-phase drive, three-stage DZ, four-stage ZZ , MFTO), SHE2607 021 (three-stage DZ, four-stage ZZ, MFTO).

No near redundancy.
- disconnection of a short circuit at the end of the protected overhead line with the time of the second or third stages of protection.

3. A more complex protection option for overhead lines with two-way power supply is the use of a protection cabinet of the ShDE-2802 type (ChEAZ has been produced since 1986). The cabinet contains two sets of protections: main and backup. The main set of protections includes a three-stage DZ, a four-stage DZ and a MFTO. Reserve set - simplified two-stage DZ and ZZ. Each set provides protection for overhead lines from all types of short circuits. At the same time, the reserve set provides short-range redundancy of protections, the main set - long-range redundancy.

Disadvantages of this set of protections:

a) Not quite full-fledged short-range redundancy, since the main and backup sets of protection:

They have common devices (for example, a remote sensing blocking device during swings), the failure of which can lead to the simultaneous failure of both the main and backup sets.
- made on the same principle, which means the possibility of simultaneous failure of both of them for the same reason. - are located in the same cabinet, which means that they can be damaged at the same time.

b) Disconnection of short circuit at the end of the protected overhead line with the time of the second or third steps.

Networks with a voltage of 110-220 kV operate in a mode with an effective or dead-earthed neutral. Therefore, an earth fault in such networks is a short circuit with a current sometimes exceeding the current of a three-phase short circuit and must be disconnected with the shortest possible time delay.

Air and mixed (cable-air) lines are equipped with automatic reclosing devices. In some cases, if the circuit breaker used is made with phase-by-phase control, phase-by-phase tripping and automatic reclosure are used. This allows you to open and close the damaged phase without disconnecting the load. Since in such networks the neutral of the supply transformer is grounded, the load practically does not feel short-term operation in open-phase mode.

On purely cable lines, reclosing, as a rule, is not used.

High voltage lines operate with high load currents, which requires the use of protections with special characteristics. On transit lines that can be overloaded, as a rule, distance protections are used to effectively decouple from load currents. On dead-end lines, in many cases, current protection can be dispensed with. As a rule, it is not allowed that the protections operate during overloads. Overload protection, if necessary, is carried out on special devices.

According to the PUE, overload prevention devices should be used in cases where the permissible current flow duration for the equipment is less than 1020 minutes. Overload protection should act on the unloading of equipment, the break in transit, the disconnection of the load, and only last but not least, the disconnection of overloaded equipment.

High voltage lines are usually long, which makes it difficult to find the fault location. Therefore, the lines must be equipped with devices that determine the distance to the fault. According to the directive materials of the CIS, lines with a length of 20 km or more should be equipped with weapons of mass destruction.

A delay in disconnecting a short circuit can lead to a violation of the stability of the parallel operation of power plants, due to a long voltage drop, equipment can stop and the production process can be disrupted, additional damage to the line on which a short circuit has occurred can occur. Therefore, on such lines, protections are very often used that disable short circuits at any point without time delay. These can be differential protections installed at the ends of the line and connected by a high-frequency, conductor or optical channel. These can be ordinary defenses, accelerated upon receipt of a permissive, or removal of a blocking signal from the opposite side.

Current and distance protection, as a rule, are performed stepwise. The number of steps is at least 3, in some cases 4 or even 5 steps are necessary.

In many cases, all required protections can be performed on the basis of one device. However, the failure of this one device leaves the equipment unprotected, which is unacceptable. Therefore, it is advisable to carry out protection of high voltage lines from 2 sets. The second set is a reserve one and can be simplified in comparison with the main one: it does not have automatic reclosure, OMA, it has fewer stages, etc. The second set must be powered by another control current circuit breaker and a set of current transformers. If possible, be powered by another battery and a voltage transformer, act on a separate circuit breaker trip solenoid.

High-voltage line protection devices must take into account the possibility of circuit breaker failure and have a breaker failure, either built into the device itself or organized separately.

To analyze an accident and the operation of relay protection and automation, it is necessary to register both analog values ​​and discrete signals in case of emergency events.

Thus, for high-voltage lines, protection and automation kits must perform the following functions:

Protection against phase-to-phase short circuits and short circuits to earth.

Single-phase or three-phase automatic reclosure.

Overload protection.

ROV.

Determining the location of damage.

Oscillography of currents and voltages, as well as registration of discrete signals of protection and automation.

Protective devices must be redundant or duplicated.

For lines with switches with single-phase control, it is necessary to have protection against open-phase operation, which acts to turn off its own and adjacent switches, since long-term open-phase operation in LPG networks is not allowed.

7.2. FEATURES OF CALCULATION OF CURRENTS AND VOLTAGES DURING A SHORT CIRCUIT

As indicated in Chap. 1, in networks with a grounded neutral, two additional types of short circuit must be taken into account: single-phase and two-phase short circuits to earth.

Calculations of currents and voltages in case of short circuits to earth are carried out by the method of symmetrical components, see Ch. 1. This is important, among other things, because the protections use symmetrical components, which are absent in symmetrical modes. The use of negative and zero sequence currents allows not to adjust the protection against the load current, and to have a current setting lower than the load current. For example, for earth fault protection, zero sequence current protection is mainly used, which is included in the neutral wire of three current transformers connected in a star.

When using the method of symmetrical components, the equivalent circuit for each of them is compiled separately, then they are connected together at the place of the short circuit. For example, let's make an equivalent circuit for the circuit in Figure 7.1.

X1 system =15 ohm
X0 syst. =25 ohm	L1 25km AS-120	L2 35 km AS-95

T1 - 10000/110

UK \u003d 10.5 T2 - 16000/110 UK \u003d 10.5

Rice. 7.1 Example of a network for drawing up an equivalent circuit in symmetrical components

When calculating the parameters of a line of 110 kV and higher for an equivalent circuit, the active resistance of the line is usually neglected. The direct sequence inductance (X 1 ) of the line according to the reference data is: AC-95 - 0.429 ohms per km, AC-120 - 0.423 ohms per km. Zero sequence resistance for a line with steel torso

themselves equal to 3 X 1 i.e. respectively 0.429 3 = 1.287 and 0.423 3 = 1.269.

Define the line parameters:

	L 1 \u003d 25 0, 423 \u003d 10.6 ohms;		L 1 \u003d 25 1.269 \u003d 31.7 ohms
	L 2 \u003d 35 0.423 \u003d 15.02 Ohm;		L 2 \u003d 35 1.269 \u003d 45.05 ohms

Let's define the parameters of the transformer:

T1 10000kVA.

X 1 T 1 \u003d 0, 105 1152 10 \u003d 138 ohms;

X 1 T 2 \u003d 0.105 1152 16 \u003d 86.8 ohms; X 0 T 2 \u003d 86, 8 ohms

The negative sequence resistance in the equivalent circuit is equal to the positive sequence resistance.

The zero-sequence resistance of transformers is usually assumed to be equal to the positive-sequence resistance. X 1 T \u003d X 0 T. Transformer T1 is not included in the zero sequence equivalent circuit, since its neutral is grounded.

We draw up a replacement scheme.

X1C=X2C=15 ohm

X1L1 \u003d X2L1 \u003d 10.6 Ohm

X1L2 \u003d X2L1 \u003d 15.1 Ohm

X0C =25 ohm

X0L1 \u003d 31.7 Ohm

X0L2 \u003d 45.05 Ohm

X1T1 \u003d 138 Ohm

X1T2 \u003d 86.8 ohms

X0T2 \u003d 86.8 ohms

The calculation of three-phase and two-phase short circuits is carried out in the usual way, see table 7.1. Table 7.1

	resistance up to a month			Short circuit three-phase			Short circuit two-phase
	and short circuit X 1 ∑ = ∑ X 1			= (115 3) X 1			0.87 I
	15+10.6 = 25.6 ohms
	25.6 + 15.1 \u003d 40.7 ohms
	25.6+ 138=163.6 ohm
	40.7 + 86.8 \u003d 127.5 ohms

To calculate the earth fault currents, it is necessary to use the method of symmetrical components. According to this method, the equivalent resistances of the positive, negative and zero sequence are calculated relative to the fault point and are connected in series in the equivalent circuit for single-phase earth faults in Fig. 7.2, and in series / parallel for two-phase to the ground Fig.7.2, b.

X 1E

X 2E

X 0E

X 1E

X 2E

X 0E I 0

I 0b

Rice. 7.2. Scheme for switching equivalent resistances of direct, negative and zero sequence for calculating short-circuit currents to earth:

a) - single-phase; b) - two-phase; c) - distribution of zero sequence currents between two neutral grounding points.

Let's calculate the short circuit to the ground, see tables 7.2, 7.3.

The positive and negative sequence circuit consists of one branch: from the power supply to the short circuit. In the zero sequence circuit, there are 2 branches from grounded neutrals, which are sources of short circuit current and must be connected in parallel in the equivalent circuit. The resistance of parallel connected branches is determined by the formula:

X 3 \u003d (X a X b) (X a + X b)

The current distribution in parallel branches is determined by the formulas:

I a \u003d I E X E X a; I in \u003d I E X E

Table 7.2 Single-phase fault currents

X1 E

X2 E

X0 E \u003d X0 a //X0 b *

HE

Ikz1

Ikz2

Ikz0

Ikz0 a *

Ikz0 b

I short circuit

I1 +I2 +I0

*Note. The resistance of two sections of the zero-sequence circuit connected in parallel is determined by formula 7.1.

**Note. The current is distributed between two sections of the zero sequence according to the formula 7.2.

Table 7.3 Two-Phase Earth Fault Currents

	X1 E	X2 E	X0 E *	X0-2 E ** =	HE	I KZ1	I short circuit 2 ***	I KZ0	I short circuit 0 a ****	I KZ0 b	IKZ *****≈
				X0 E //X2							I1 +½ (I2 +I0 )

*Note. The resistance of two sections of the zero-sequence circuit connected in parallel is determined according to formula 7.1, the calculation is made in table 7.2.

**Note. The resistance of two resistances of the negative and zero sequence connected in parallel is determined by the formula 7.1.

***Note. The current is distributed between two resistances of the negative and zero sequence according to the formula 7.2.

****Note. The current is distributed between two sections of the zero sequence according to the formula 7.2.

*****Note. The two-phase earth fault current is given by an approximate formula, the exact value is determined geometrically, see below.

Determination of phase currents after calculation of symmetrical components

With a single-phase short circuit, the entire short circuit current flows in the damaged phase, and no current flows in the remaining phases. The currents of all sequences are equal to each other.

To comply with such conditions, the symmetrical components are arranged as follows (Fig. 7.3):

Ia 1

Ia 2

I a 0 I b 0 I c 0

ia 0

Ia 2

Ib 1

Ic 2

Ia 1

Ic 1

Ib 2

Direct currents

Reverse currents

Zero currents

Ic 1

Ib 1

Ic 0

Ib 0

follow.

follow.

follow.

Ic 2

Ib 2

Fig.7.3. Vector diagrams for symmetrical components with a single-phase short circuit

With a single-phase short circuit, the currents I1 \u003d I2 \u003d I0. In the damaged phase, they are equal in magnitude and coincide in phase. In undamaged phases, equal currents of all sequences form an equilateral triangle and the resulting sum of all currents is 0.

In a two-phase earth fault, the current in one undamaged phase is zero. The positive sequence current is equal to the sum of the zero and negative sequence currents with the opposite sign. Based on these provisions, we build the currents of the symmetrical components (Fig. 7.4):

Ia 1

Ia 1

Ia 2

Ic 2

Ib 2

ia 0

I a 0 I b 0 I c 0

Ic 2

Ib 2

Ic 1

Ib 1

Ia 2

Ic 0

Ic 1

Ib 1

Ib 0

Rice. 7.4 Vector diagrams of symmetrical current components of a two-phase earth fault

It can be seen from the constructed diagram that it is quite difficult to build phase currents during earth faults, since the angle of the phase current differs from the angle of the symmetrical components. It should be built graphically or use orthogonal projections. However, with sufficient accuracy for practice, the current value can be determined by a simplified formula:

I f \u003d I 1 + 1 2 (I 2 + I 0) \u003d 1.5 I 1

The currents in Table 7.3 are calculated using this formula.

If we compare the two-phase earth fault currents according to table 7.3 with the two-phase and three-phase fault currents according to table 7.1, we can conclude that the two-phase fault currents are slightly lower than the two-phase earth fault current, therefore the protection sensitivity should be determined by the two-phase fault current. The currents of a three-phase short circuit are respectively higher than the current of a two-phase short circuit by

earth, therefore, the determination of the maximum short circuit current for protection detuning is carried out according to a three-phase short circuit. This means that the two-phase earth fault current is not needed for protection calculations, and there is no need to calculate it. The situation changes somewhat when calculating short-circuit currents on the buses of powerful power plants, where the resistance of the negative and zero sequence is less than the direct resistance. But this has nothing to do with distribution networks, and for power plants, currents are counted on a computer according to a special program.

7.3 EXAMPLES OF CHOICE OF EQUIPMENT FOR DEAD-END OHL 110-220 KV

Scheme 7.1. Dead end overhead line 110–220 kV. There is no power supply from PS1 and PS2. T1 PS1 is connected through a separator and a short circuit. T1 PS2 is switched on through the switch. The neutral side of the HV T1 PS2 is grounded, on PS1 it is isolated. Minimum protection requirements:

Option 1 . A three-stage protection against phase-to-phase short circuits should be applied (the first stage, without time delay, is detuned from short circuits on the HV PS2 buses, the second, with a short time delay, from short circuits on the PS1 and PS2 LV buses, the third stage is maximum protection). Ground fault protection - 2 stages (the first stage, without time delay, is detuned from the current sent to the buses by the grounded PS2 transformer, the second stage with a time delay ensuring its coordination with the protection of the external network, but not detuned from the short-circuit current sent by the PS2 transformer ). Two or one AR must be applied. The sensitive steps must be accelerated during reclosure. The protections start up the breaker failure of the supply substation. Additional requirements include protection against phase failure, determining the location of damage on the overhead line, monitoring the life of the switch.

Option 2. Unlike the first, the earth fault protection is directional, which allows it not to be detuned from the reverse fault current and, thus, to perform more sensitive protection without time delay. In this way, it is possible to protect the entire line without time delay.

Note. This and the following examples do not give precise recommendations on the choice of protection settings, references to setting protections are used to justify the choice of types of protection. In real conditions, a different protection setting can be applied, which is required to be determined in a specific design. Protections can be replaced by other types of protection devices having suitable characteristics.

A set of protections, as already mentioned, should consist of 2 sets. Protection can be implemented on 2 devices selected from:

MiCOM P121, P122, P123, P126, P127 from ALSTOM,

F 60, F650 from GE

two ABB REF 543 relays - selected 2nd suitable modifications,

7SJ 511, 512, 531, 551 SIEMENS - selected 2nd suitable modifications,

two SEL 551 relays from SEL.

Scheme 7.2. Open transit at substation 3.

A double-circuit overhead line enters substation 2, the sections of which operate in parallel. The possibility of transferring the section to PS2 in the repair mode is envisaged.

IN In this case, the sectional switch on PS3 is turned on. The transit is closed only for the time of switching and, when choosing protections, its closing is not taken into account. 1 section PS3 includes a transformer with a grounded neutral. There is no current source for a single-phase short circuit at substations 2 and 3. Therefore, the protection on the non-powered side only works in a "cascade", after the line is disconnected from the power side. Despite the absence of power from the opposite side, the protection must be made directional both for earth faults and for phase-to-phase short circuits. This allows the receiving side to correctly determine the damaged line.

IN In general, in order to provide selective protection with short time delays, especially on short lines, it is necessary to apply a four-stage protection, the settings of which are selected as follows: 1 stage is detuned from short circuit

V at the end of the line, the 2nd stage is coordinated with the first stage of the parallel line in the cascade and the first stage of the adjacent line, the 3rd stage is coordinated with the second stages of these overhead lines. When coordinating protection with an adjacent line, the mode one with two is taken into account: in the first section - 1 overhead line, in the second section - 2, which significantly coarsens the protection. These three steps protect the line, and the last, 4th step, reserves the adjacent section. When the protections are coordinated in time, the time of the breaker failure action is taken into account, which increases the time delays of the coordinated protections by the time of the breaker failure action. When choosing the current protection settings, they must be detuned from the total load of the two lines, since one of the parallel overhead lines can turn off at any time, and the entire load will be connected to one overhead line.

IN as part of the protection devices, both sets of protections must be directional. You can apply the following protection options:

MiCOM, P127 and P142 from ALSTOM,

F60 and F650 from GE,

two ABB REF 543 relays - directional modifications are selected,

relays 7SJ512 and 7SJ 531 from SIEMENS,

two SEL 351 relays from SEL.

In some cases, for reasons of sensitivity, detuning from load currents or ensuring selective operation, it may be necessary to use a remote

Z=LZ

onnoy protection. For this purpose, one of the protections is replaced by a remote one. Distance protection can be applied:

MiCOM P433, P439, P441 from ALSTOM,

D30 from GE,

REL 511 from ABB - directional modifications are selected,

relay 7SA 511 or 7SA 513 from SIEMENS,

relay SEL 311 from SEL.

7.4. REMOTE PROTECTIONS

Purpose and principle of operation

Distance protections are complex directional or non-directional protections with relative selectivity, made using minimum resistance relays that react to the line resistance to the fault point, which is proportional to the distance, i.e. distances. This is where the name distance protection (DZ) comes from. Distance protections respond to phase-to-phase short circuits (except for microprocessor-based remote sensing). For proper operation of the distance protection, it is necessary to have current circuits from the connection CT and voltage circuits from the VT. In the absence or malfunction of voltage circuits, excessive operation of the DZ during a short circuit in adjacent sections is possible.

In networks of complex configuration with several power supplies, simple and directional overcurrent protection (NTC) cannot provide selective short circuit disconnection. So, for example, with a short circuit on W 2 (Fig. 7.5), NTZ 3 should act faster than RZ I, and with a short circuit on W 1, on the contrary, NTZ 1 should act faster than RZ 3. These conflicting requirements cannot be met with the help of NTZ. In addition, MTS and NTS often do not meet the requirements for speed and sensitivity. Selective short circuit disconnection in complex ring networks can be provided using remote relay protection (RD).

DZ time delay t 3 depends on the distance (distance) t 3 \u003d f (L PK) (Fig. 7.5) between

the installation site of the RZ (point P) and the point of the short circuit (K), i.e. L PK, and increases with an increase in this

distance. The remote sensing closest to the damage site has a shorter time delay than the more distant remote sensing.

For example, during a short circuit at point K1 (Fig. 7.6), D32, located closer to the fault site, operates with a shorter time delay than the more distant D31. If a short circuit also occurs at point K2, then the duration of D32 increases, and the short circuit is selectively turned off by the remote sensing zone closest to the damage site.

The main element of the remote control is a remote measuring body (DO), which determines the distance of the short circuit from the installation site of the relay protection. Resistance relays (PC) are used as DOs, reacting to the total, reactive or active resistance of the damaged section of the power transmission line (Z, X, R).

The resistance of the power line phase from the installation site of the relay R to the place of the short circuit (points K) is proportional to the length of this section, since the resistance value to the place of the short circuit is equal to the length

section multiplied by the resistivity of the line: beats. .

Thus, the behavior of a remote element that reacts to line resistance depends on the distance to the fault. Depending on the type of resistance to which the DO reacts (Z, X or R), DZ are divided into RZ total, reactive and active resistances. Resistance relays used in remote sensing to determine the

resistance Z PK to the short circuit point, control the voltage and current at the installation site of the DZ (Fig. 7.7.).

∆ – distance protection

TO PC terminals are supplied with secondary values U P and I P from VT and CT. The relay is designed so that its behavior generally depends on the ratio of U P to I P . This ratio is some resistance Z P . With a short circuit Z P = Z PK , and at certain values ​​of Z PK , PC is triggered; it responds to a decrease in Z P, since during short circuit U P decrease

fluctuates, and I P increases. The highest value at which the PC operates is called the relay operation resistance Z cp .

Z p = U p I p ≤ Z cp

To ensure selectivity in networks of complex configuration on power lines with two-way power supply, it is necessary to perform remote sensing, acting when the power is directed from the busbars to the power transmission line. The directionality of the action of the remote protection is provided with the help of additional RHMs or the use of directional PCs capable of responding to the direction of the short circuit power.

			Time dependence characteristics
	Rice. 7.7. Connection of current circuits and	distance protections t = f (L
	resistance relay voltage
		a - inclined; b - stepped; c - combined
	Delay characteristics	distance protection

The dependence of the duration of the remote protection on the distance or resistance to the place of the short circuit t 3 \u003d f (L PK) or t 3 \u003d f (Z PK) is called the time delay characteristic of the remote sensing. By ha-

According to the character of this dependence, DZs are divided into three groups: with increasing (sloping) characteristics of the time of action, stepwise and combined characteristics

(Fig. 7.8). Stepped DZs operate faster than DZs with inclined and combined characteristics and, as a rule, are simpler in design. Remote sensing with a stepwise characteristic of the production of CHEAZ was usually performed with three steps of time corresponding to three zones of remote sensing (Fig. 7.8, b). Modern microprocessor protections have 4, 5 or 6 levels of protection. Slope relays were developed specifically for distribution networks (for example, DZ-10).

Principles for performing selective network protection using distance protection devices

On power lines with two-way power supply, remote sensing devices are installed on both sides of each power line and must operate when power is directed from the tires to the power line. Remote relay protection devices operating in one direction of power must be coordinated with each other in time and in coverage area so that selective short circuit disconnection is ensured. In the scheme under consideration (Fig. 7.9.), D31, remote sensing, D35 and D36, D34, D32 are consistent with each other.

Taking into account the fact that the first stages of remote sensing do not have a time delay (t I \u003d 0), according to the selectivity condition, they should not operate outside the protected transmission line. Based on this, the length of the first stage, which does not have a time delay (t I \u003d 0), is taken less than the length of the protected transmission line and is usually 0.8–0.9 of the length of the transmission line. The rest of the protected transmission line and the bus of the opposite substation are covered by the second stage of the DZ of this transmission line. The length and delay of the second stage are consistent (usually) with the length and delay of the first stage of the remote sensing of the next section. For example, at the second stu-

Fig.7.9 Coordination of time delays of remote relay protection with a step characteristic:

∆z – remote relay error; ∆ t – selectivity step

The last third stage of the remote protection is a backup, its length is selected from the condition of coverage of the next section, in case of failure of its relay protection or switch. Exposure time

The minimum is taken to be ∆ t more than the duration of the second or third remote sensing zone of the next section. In this case, the coverage area of ​​the third stage should be rebuilt from the end of the second or third area of ​​the next section.

Line protection structure using distance protection

In domestic power systems, remote sensing is used for operation with phase-to-phase short circuits, and for operation with single-phase short circuits, a simpler stepped zero-sequence overcurrent protection (NP) is used. Most microprocessor equipment has a distance protection that operates in case of all types of damage, including earth faults. The resistance relay (RS) is switched on through the VT and CT for primary voltages in

the beginning of the protected transmission line. Secondary voltage at PC terminals: U p = U pn K II , and secondary current: I p = I pn K I .

The resistance at the input terminals of the relay is determined by the expression.

Uninterrupted and reliable transportation of electricity to consumers is one of the main tasks constantly solved by power engineers. To ensure it, electric networks have been created, consisting of distribution substations and power lines connecting them. To move energy over long distances, supports are used, to which connecting wires are suspended. They are isolated between themselves and the ground by a layer of ambient air. Such lines are called air lines by the type of insulation.

If the distance of the transport highway is short or for safety reasons it is necessary to hide the power line in the ground, then cables are used.

Overhead and cable power lines are constantly under voltage, the magnitude of which is determined by the structure of the electrical network.

Purpose of relay protection of power lines

In the event of damage to the insulation of any place of a cable or extended overhead power transmission line, the voltage applied to the line creates a leakage or short circuit current through the broken section.

The reasons for the violation of isolation can be various factors that are able to eliminate themselves or continue their destructive effect. For example, a stork flying between the wires of an overhead power line created a phase-to-phase short circuit with its wings and burned down, falling nearby.

Or a tree that grew very close to the support, during a storm, was thrown down by a gust of wind on the wires and shorted them out.

In the first case, a short circuit occurred for a short period of time and disappeared, and in the second case, the insulation violation is of a long-term nature and requires elimination by the maintenance electrical personnel.

Such damage can cause great damage to energy enterprises. The currents of the resulting short circuits have a huge thermal energy that can burn not only the wires of the supply lines, but also destroy the power equipment at the supply substations.

For these reasons, all damage that occurs on power lines must be immediately eliminated. This is achieved by removing voltage from the damaged line on the supply side. If such a power line receives power from both sides, then both of them must turn off the voltage.

The functions of continuous monitoring of the electrical parameters of the state of all power lines and removing voltage from them from all sides in the event of any emergency situations are assigned to complex technical systems, which are traditionally called relay protection.

The adjective "relay" is formed from the element base based on electromagnetic relays, the designs of which arose with the advent of the first power lines and are being improved to this day.

Modular protective devices, which are widely introduced into the practice of power engineers, do not yet exclude the complete replacement of relay devices and, according to the established tradition, are also included in relay protection devices.

Relay protection principles

Network status controls

To monitor the electrical parameters of power lines, it is necessary to have their measuring bodies that are able to constantly monitor any deviations in the normal mode in the network and, at the same time, meet the conditions for safe operation.

In power lines of all voltages, this function is assigned to instrument transformers. They are divided into transformers:

current (CT);

voltage (TN).

Since the quality of the protections is of paramount importance for the reliability of the entire electrical system, the measuring CTs and VTs are subject to increased requirements for accuracy, which are determined by their metrological characteristics.

Accuracy classes of measuring transformers for use in RPA devices (relay protection and automation) are normalized by the values ​​"0.5", "0.2" and "P".

Measuring voltage transformers

A general view of the installation of voltage transformers on a 110 kV overhead line is shown in the picture below.

It can be seen here that VTs are not installed anywhere in the long line, but on the switchgear of the electrical substation. Each transformer is connected by its primary terminals to the corresponding wire of the overhead line and the ground loop.

The voltage converted by the secondary windings is output through the 1P and 2P switches through the corresponding cores of the power cable. For use in protection and measurement devices, the secondary windings are connected in a "star" and "delta" scheme, as shown in the picture for TN-110 kV.

To reduce and accurately operate relay protection, a special power cable is used, and increased requirements are imposed on its installation and operation.

Measuring VTs are created for each type of voltage of the power line and can be switched on according to different schemes to perform certain tasks. But they all work according to the general principle - the conversion of the linear voltage of the power transmission line into a secondary value of 100 volts with exact copying and highlighting all the characteristics of the primary harmonics on a certain scale.

The VT transformation ratio is determined by the ratio of the line voltages of the primary and secondary circuits. For example, for the considered 110 kV overhead line, it is written as follows: 110000/100.

Measuring current transformers

These devices also convert the primary load of the line into secondary values ​​with the maximum repetition of all changes in the harmonics of the primary current.

For ease of operation and maintenance of electrical equipment, they are also mounted on substation switchgears.

They are included in the overhead line circuit in a different way than VTs: with their primary winding, which is usually represented by only one turn in the form of a direct current lead, they simply cut into each wire of the line phase. This is clearly seen in the photo above.

The CT transformation ratio is determined by the ratio of the choice of nominal values ​​at the stage of designing the transmission line. For example, if the power line is designed to transport currents of 600 amperes, and 5 A will be removed on the secondary side of the CT, then the designation 600/5 is used.

In the energy sector, two standards for the values ​​\u200b\u200bof secondary currents are accepted, which are used:

5 A for all CTs up to and including 110 kV;

1 A for lines 330 kV and above.

CT secondary windings are connected for connection to protection devices according to different schemes:

full star;

incomplete star;

triangle.

Each compound has its own specific features and is used for certain types of protection in various ways. An example of connecting line current transformers and current relay windings in a full star circuit is shown in the picture.

This simplest and most common harmonic filter is used in many relay protection schemes. In it, the currents from each phase are controlled by an individual relay of the same name, and the sum of all vectors passes through the winding included in the common neutral wire.

The method of using measuring current and voltage transformers allows transferring the primary processes occurring on power equipment to the secondary circuit on an exact scale for using them in the hardware of relay protection and creating algorithms for the operation of logic devices to eliminate emergency processes on equipment.

Bodies for processing the information received

In relay protection, the main working element is a relay - an electrical device that performs two main functions:

monitors the quality of a controlled parameter, for example, current, and in normal mode stably maintains and does not change the state of its contact system;

upon reaching a critical value, called the setpoint or threshold, it instantly switches the position of its contacts and is in this state until the controlled value returns to the range of normal values.

The principles of formation of circuits for switching current and voltage relays into secondary circuits helps to understand the representation of sinusoidal harmonics by vector quantities with their representation on the complex plane.

At the bottom of the picture is a vector diagram for a typical distribution of sinusoids in three phases A, B, C in the operating mode of power supply to consumers.

Monitoring the status of current and voltage circuits

Partially, the principle of processing secondary signals is shown in the circuit for switching on the CT and relay windings according to the full star circuit and VT on the outdoor switchgear-110. This method allows you to assemble vectors in the ways shown below.

The inclusion of the relay winding in any of the harmonics of these phases allows you to fully control the processes occurring in it and disable the circuit from operation in case of accidents. To do this, it is enough to use the appropriate designs of current or voltage relay devices.

The above schemes are a particular case of the diverse use of various filters.

Ways to control the power passing through the line

RPA devices control the power value based on the readings of the same current and voltage transformers. In this case, well-known formulas and ratios of the total, active and reactive powers to each other and their values ​​expressed through the vectors of currents and voltages are used.

Here it is taken into account that the current vector is formed by the applied EMF to the line resistance and equally overcomes its active and reactive parts. But at the same time, a voltage drop occurs in sections with Ua and Up components according to the laws described by the voltage triangle.

Power can be transferred from one end of the line to the other and even change its direction when transporting electricity.

Changes in its direction result from:

switching loads by operating personnel;

power swings in the system due to the effects of transients and other factors;

occurrence of emergencies.

The power relays (PM) operating as part of the RPA take into account fluctuations in its directions and are configured to operate when a critical value is reached.

Ways to control line resistance

Relay protection devices that estimate the distance to the place of a short circuit based on the measurement of electrical resistance are called remote, or abbreviated DZ protection. They also use current and voltage transformer circuits in their work.

To measure the resistance, it is used, which is described for the section of the circuit under consideration.

When a sinusoidal current passes through active, capacitive and inductive resistances, the voltage drop vector on them deviates in different directions. This is taken into account by the behavior of the relay protections.

According to this principle, numerous types of resistance relays (RS) operate in RPA devices.

Ways to control the frequency on the line

To maintain the stability of the period of oscillation of the harmonics of the current transmitted through the power line, frequency control relays are used. They work on the principle of comparing the reference sinusoid generated by the built-in generator with the frequency received from the line measuring transformers.

After processing these two signals, the frequency relay determines the quality of the controlled harmonic and, when the set value is reached, changes the position of the contact system.

Features of control of line parameters by digital protections

Microprocessor developments that replace relay technologies also cannot work without secondary values ​​of currents and voltages, which are taken from CT and VT measuring transformers.

For the operation of digital protections, information about the secondary sinusoid is processed by sampling methods, which consist in superimposing a high frequency analog signal and fixing the amplitude of the controlled parameter at the intersection of the graphs.

Due to the small discretization step, fast processing methods and the use of the mathematical approximation method, a high accuracy of measuring secondary currents and voltages is obtained.

The digital values ​​calculated in this way are used in the operation algorithm of microprocessor devices.

Logic part of relay protection and automation

After the primary values ​​of currents and voltages of electricity transmitted through power lines are modeled by instrument transformers, selected for processing by filters and perceived by the sensitive organs of relay devices of current, voltage, power, resistance and frequency, it is the turn of the logical relay circuits.

Their design is based on relays operating from an additional source of direct, rectified or alternating voltage, which is also called operational, and the circuits fed by it are operational. This term has a technical meaning: very quickly, without undue delay, perform your switching.

The speed of operation of the logic circuit largely determines the speed of shutting down an emergency, and, consequently, the degree of its destructive consequences.

According to the way they perform their tasks, relays operating in operational circuits are called intermediate: they receive a signal from the protection measuring body and transmit it by switching their contacts to executive bodies: output relays, solenoids, electromagnets of trips or switching on of power switches.

Intermediate relays usually have several pairs of contacts that work to close or open the circuit. They are used for simultaneous duplication of commands between different RPA devices.

A time delay is often introduced into the operation algorithm of relay protection to ensure the principle of selectivity and the formation of the order of a certain algorithm. It blocks the operation of the protection for the period of the setting.

This delay input is created using special time relays (RT), which have a clock mechanism that affects the speed of operation of their contacts.

The logical part of the relay protection uses one of the many algorithms created for different cases that may occur on a power line of a specific configuration and voltage.

As an example, we can give just some of the names of the work of the logic of two relay protections based on the control of the current of power transmission lines:

current cutoff (designation of speed) without time delay or with delay (ensuring selectivity of RV) taking into account the direction of power (due to the relay RM) or without it;

overcurrent protection, which can be endowed with the same controls as the cutoff, complete with or without checking the minimum voltage on the line.

Elements of the automation of various devices are often introduced into the operation of the relay protection logic, for example:

single-phase or three-phase reclosing of the circuit breaker;

turn on backup power;

acceleration;

frequency load.

The logical part of the line protection can be made in a small relay compartment directly above the power circuit breaker, which is typical for outdoor packaged switchgear (KRUN) with voltage up to 10 kV, or occupy several 2x0.8 m panels in the relay room.

For example, the protection logic of a 330 kV line can be placed on separate protection panels:

reserve;

DZ - remote;

DFZ - differential phase;

VChB - high-frequency blocking;

OAPV;

acceleration.

output circuits

The output circuits serve as the final element of the relay protection of the line. Their logic is also based on the use of intermediate relays.

The output circuits form the order of operation of the line circuit breakers and determine the interaction with neighboring connections, devices (for example, breaker failure - back-up shutdown of the circuit breaker) and other elements of the RPA.

Simple line protections may have only one output relay, the operation of which leads to the opening of the circuit breaker. In complex systems of branched protection, special logical circuits are created that work according to a certain algorithm.

The final removal of voltage from the line in the event of an emergency is carried out by a power switch, which is actuated by the force of the shutdown electromagnet. For its operation, special power circuits are supplied that can withstand powerful loads. ki.

Complain

Section 3. Protection and automation

Chapter 3.2. Relay protection

Protection of overhead lines in networks with a voltage of 110-500 kV with an effectively grounded neutral

3.2.106. For lines in 110-500 kV networks with an effectively grounded neutral, relay protection devices against multi-phase short circuits and earth faults must be provided.

3.2.107. Protections must be equipped with devices that block their action during oscillations, if oscillations or asynchronous operation are possible in the network, in which excessive operation of the protection is likely. It is allowed to perform protection without blocking devices if it is tuned out from swings in time (about 1.5-2 s).

3.2.108. For lines of 330 kV and above, protection should be provided as the main one, acting without slowing down in case of short circuit at any point of the protected section.

For lines with a voltage of 110-220 kV, the question of the type of main protection, including the need to use protection that operates without deceleration in case of short circuit at any point of the protected section, should be addressed primarily taking into account the requirement to maintain the stability of the power system. At the same time, if, according to the calculations of the stability of the operation of the power system, no other, more stringent requirements are imposed, it can be assumed that this requirement is usually satisfied when three-phase short circuits, at which the residual voltage on the buses of power plants and substations is below 0.6-0, 7 U nom, are switched off without time delay. Lower value of residual stress (0.6 U nom) can be allowed for 110 kV lines, less critical 220 kV lines (in highly branched networks, where consumers are reliably supplied from several sides), as well as for more critical 220 kV lines in cases where the considered short circuit does not lead to a significant discharge loads.

When choosing the type of protection installed on 110-220 kV lines, in addition to the requirement to maintain the stability of the power system, the following should be taken into account:

1. On the lines of 110 kV and above, extending from the NPP, as well as on all elements of the adjacent network, on which, in case of multi-phase short circuits, the residual voltage of the positive sequence on the high voltage side of the NPP units can decrease to more than 0.45 nominal, redundancy of high-speed protection with a time delay not exceeding 1.5 s, taking into account the action of the breaker.

2. Damage, the disconnection of which with a time delay can lead to a disruption in the operation of critical consumers, must be disconnected without a time delay (for example, damage in which the residual voltage on the buses of power plants and substations will be below 0.6 U nom, if switching them off with a time delay can lead to self-unloading due to a voltage avalanche, or damage with a residual voltage of 0.6 U nom and more, if switching them off with a time delay can lead to a violation of the technology).

3. If it is necessary to implement a fast-acting automatic reclosure, a fast-acting protection must be installed on the line, which ensures disconnection of the damaged line without time delay on both sides.

4. When switching off with a fault time delay with currents several times higher than the rated current, unacceptable overheating of the conductors is possible.

It is allowed to use high-speed protection in complex networks and in the absence of the above conditions, if it is necessary to ensure selectivity.

3.2.109. When evaluating the assurance of stability requirements, based on the residual stress values ​​according to 3.2.108, the following should be taken into account:

1. For a single connection between power plants or power systems, the residual voltage specified in 3.2.108 must be checked on the buses of substations and power plants included in this connection, in case of short circuit on the lines extending from these tires, except for the lines forming the connection; for a single connection containing part of the sections with parallel lines - also in case of a short circuit on each of these parallel lines.

2. If there are several connections between power plants or power systems, the residual voltage value specified in 3.2.108 should be checked on the buses of only those substations or power plants where these connections are connected, in case of short circuit on the connections and on other lines powered by these tires, as well as on lines powered by buses of communications substations.

3. Residual voltage must be checked for short circuit at the end of the zone covered by the first stage of protection in the mode of cascading fault trip, i.e. after opening the circuit breaker from the opposite end of the line by protection without time delay.

3.2.110. On single lines with one-sided supply from multi-phase faults, step current protection or step current and voltage protection should be installed. If such protections do not meet the requirements of sensitivity or fault disconnection speed (see 3.2.108), for example, in the head sections, or if it is expedient under the condition of matching the protections of adjacent sections with the protection of the section under consideration, stepped distance protection should be provided. In the latter case, as an additional protection, it is recommended to use current cutoff without time delay.

From earth faults, as a rule, stepped current directional or non-directional zero sequence protection should be provided. As a rule, protection should be installed only on those sides from which power can be supplied.

For lines consisting of several consecutive sections, for the purpose of simplification, it is allowed to use non-selective stepped current and voltage protections (against multi-phase faults) and stepped zero-sequence current protections (against earth faults) in combination with alternate automatic reclosure devices.

3.2.111. On single lines that are powered from two or more sides (the latter - on lines with branches), both in the presence and in the absence of bypass connections, as well as on lines included in a ring network with one power point, against multi-phase short circuits should be distance protection is used (mainly three-stage), used as a backup or main (the latter - only on 110-220 kV lines).

As an additional protection, it is recommended to use current cutoff without time delay. In some cases, it is allowed to use the current cutoff for action in case of erroneous switching on to a three-phase short circuit at the place where the protection is installed, when the current cutoff made for operation in other modes does not meet the sensitivity requirement (see 3.2.26).

From earth faults, as a rule, stepped current directional or non-directional zero sequence protection should be provided.

3.2.112. As the main protection against multi-phase short circuits at the receiving end of the head sections of the ring network with one power point, it is recommended to use a single-stage current directional protection; on other single lines (mainly 110 kV), it is allowed in some cases to use stepped current protection or stepped current and voltage protection, making them directional if necessary. As a rule, protection should be installed only on those sides from which power can be supplied.

3.2.113. On parallel lines fed from two or more sides, as well as on the supply end of parallel lines with one-sided supply, the same protections as on the corresponding single lines can be used (see 3.2.110 and 3.2.111).

To accelerate the disconnection of earth faults, and in some cases, faults between phases on lines with two-sided power supply, additional protection with control of the direction of power in a parallel line can be applied. This protection can be made in the form of a separate transverse current protection (with the inclusion of a relay for zero sequence current or phase currents) or only as an acceleration circuit for installed protections (zero sequence current, overcurrent, remote, etc.) with direction control power in parallel lines.

In order to increase the sensitivity of the zero sequence protection, it is allowed to provide for the deactivation of its individual stages when the parallel line switch is turned off.

At the receiving end of two single-ended parallel lines, as a rule, transverse directional differential protection should be provided.

3.2.114. If the protection according to 3.2.113 does not meet the speed requirements (see 3.2.108), as the main protection (when two parallel lines are operating) at the supply end of two parallel 110-220 kV lines with unilateral supply and at two parallel 110 kV lines with Bilateral power supply mainly in distribution networks can be applied transverse differential directional protection.

In this case, in the mode of operation of one line, as well as as a backup when operating two lines, protection according to 3.2.110 and 3.2.111 is used. It is allowed to turn on this protection or its individual stages for the sum of the currents of both lines (for example, the last stage of the zero sequence current protection) in order to increase its sensitivity to damage on adjacent elements.

It is allowed to use transverse differential directional protection in addition to the step current protection of 110 kV parallel lines to reduce the time of fault disconnection on the protected lines in cases where, according to the speed conditions (see 3.2.108), its use is not mandatory.

3.2.115. If the protection according to 3.2.111-3.2.113 does not meet the speed requirement (see 3.2.108), high-frequency and longitudinal differential protections should be provided as the main protections for single and parallel lines with two-sided supply.

For 110-220 kV lines, it is recommended to carry out the main protection using high-frequency blocking of remote and current directional zero sequence protection, when it is appropriate for sensitivity conditions (for example, on lines with branches) or protection simplification.

If it is necessary to lay a special cable, the use of longitudinal differential protection must be justified by a feasibility study.

To control the serviceability of the auxiliary protection wires, special devices must be provided.

On 330-350 kV lines, in addition to high-frequency protection, it is necessary to provide for the use of a device for transmitting a tripping or enabling high-frequency signal (to speed up the action of step backup protection), if this device is provided for other purposes. On 500 kV lines, it is allowed to install the specified device specifically for relay protection.

It is allowed in cases where it is required by the conditions of speed (see 3.2.108) or sensitivity (for example, on lines with branches), the use of transmission of a trip signal to accelerate the operation of step protections of 110-220 kV lines.

3.2.116. When performing the main protection according to 3.2.115, the following should be used as backup:

• from multi-phase short circuits, as a rule, distance protection, mainly three-stage;
• against earth faults stepped current directional or non-directional zero sequence protection.

In the case of a long-term deactivation of the main protection specified in 3.2.115, when this protection is set to the requirement of the fault disconnection speed (see 3.2.108), it is allowed to provide for non-selective acceleration of the backup protection against faults between phases (for example, with control of the direct voltage value sequences).

3.2.117. The main protections, high-speed backup protection stages against multi-phase short circuits and measuring elements of the OAPV device for 330-350 kV lines must be of a special design that ensures their normal functioning (with the specified parameters) under conditions of intense transient electromagnetic processes and significant capacitive conductivities of the lines. For this, the following must be provided:

• in sets of protections and measuring bodies of the OAPV - measures limiting the influence of transient electromagnetic processes (for example, low-frequency filters);
• in differential-phase high-frequency protection installed on lines longer than 150 km - devices for compensating currents due to line capacitance.

When switching on high-speed protections for the sum of the currents of two or more current transformers, if it is impossible to fulfill the requirements of 3.2.29, it is recommended to provide special measures to prevent excessive operation of protections in case of external damage (for example, coarsening of protections) or install a separate set of current transformers in the line circuit to power the protection .

In protections installed on 330-500 kV lines equipped with longitudinal capacitive compensation devices, measures must be taken to prevent excessive protection operation in case of external damage due to the influence of these devices. For example, a negative sequence power directional relay or enable signal transmission can be used. ¶ ×

The tasks of relay protection, its role and purpose are to ensure the reliable operation of power systems and the uninterrupted supply of electricity to consumers. This is due to the complication of schemes and the growth of power networks, the enlargement of power systems, the increase in the installed capacity of both stations as a whole and the nominal unit capacity of individual units. This, in turn, affects the operation of power systems: operation at the limit of stability, the presence of long intersystem communication lines, and an increased likelihood of chain accidents. In this regard, the requirements for speed, selectivity, sensitivity and reliability of relay protection are increasing. Relay protection devices using semiconductor devices are becoming more common. Their use opens up more opportunities for creating high-speed protections.

Currently, microprocessor-based relay protection devices have been developed and are beginning to be actively used, which makes it possible to further increase the speed and reliability of protection, and reduce the cost of their repair and maintenance.

1.2.2 Transformer parameters are summarized in Table 2.

TABLE 1.2

SELECTION OF PROTECTION DEVICE TYPES

Relay protection of overhead line 110 kV.

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Design scheme

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3. Calculation of short circuit currents.
3.1 Calculation of the resistance of a direct sequence of circuit elements.
The calculation of resistances is made in named units (Ohms), at the base voltage Ub=115 kV.
The equivalent circuit is shown in fig.

C1: X 1 \u003d X * s * \u003d 1.3 * \u003d 9.55 Ohms
X 2 \u003d X beats. *l* \u003d 0.4 * 70 * \u003d 28 Ohm
X 3 \u003d X beats. *l* \u003d 0.4 * 45 * \u003d 18 Ohm
X 4 \u003d X beats. *l* \u003d 0.4 * 30 * \u003d 12 Ohm
X 5 \u003d X beats. *l* \u003d 0.4 * 16 * \u003d 6.4 Ohm
T 6 \u003d * \u003d * \u003d 34.72 Ohm
T 7 \u003d * \u003d * \u003d 220.4 ohms
X 3.4 \u003d 18 + 12 \u003d 30 ohms

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X 2.4 = = 14.48 ohms

X 1-4 \u003d 9.55 + 14.48 \u003d 24.03 Ohm

X 1-5 \u003d 24.03 + 6.4 \u003d 30.34

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I (3) (k 1) \u003d \u003d 2.76 kA
I (3) (k 2) = = = 2.18 kA
I (3) (k 3) = = = 0.26 kA

3.2 Calculation of single-phase short-circuit currents to earth at point K-2.

C1: X 1 \u003d X * s * \u003d 1.6 * \u003d 11.76 Ohms
X 2 \u003d X beats. *l* \u003d 0.8 * 70 * \u003d 56 Ohm
X 3 \u003d X beats. *l* \u003d 0.8 * 45 * \u003d 36 Ohm
X 4 \u003d X beats. *l* \u003d 0.8 * 30 * \u003d 24 Ohm
X 5 \u003d X beats. *l* \u003d 0.8 * 16 * \u003d 12.8 Ohm

X 3.4 \u003d 36 + 24 \u003d 60 ohms

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X 2.3.4 \u003d (60 * 56) / (60 + 56) \u003d 28.97 Ohm

X 1-4 \u003d 11.76 + 28.97 ohms

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X 1-4.6 \u003d (40.73 * 34.72) / (40.73 + 34.72) \u003d 18.74 ohms

X 1-6 \u003d 18.74 + 12.8 \u003d 31.54 ohms

X res.0 (k2) \u003d 31.54 Ohm
3I 0(k2) = = = 2.16 kA

3.6 Calculation of short circuit currents at point K-4 and K-5.

Ub=Umin=96.6 kV	Ub=Umax=126 kV
X 10 \u003d X s1.2 \u003d X s1.2 cf. * = 24.03* = 16.96 ohms	X 10 \u003d X s1.2 \u003d X s1.2 cf. * = 24.03 * = 28.85 ohms
Xs \u003d Xs cf * \u003d \u003d 16.96 Ohm	Xs \u003d Xs cf * \u003d \u003d 28.85 Ohm
X T (-PO) = * = = 41.99	U to (+ N) \u003d U to nom. + \u003d 17.5 + \u003d 18.4 Xt (+ N) \u003d * * \u003d 71.44 Ohm
Z nw \u003d 0.3 * 1.5 * \u003d 38.01 Ohm	Z nw \u003d 0.3 * 1.5 * \u003d 64.8 Ohm
Point K-4
Khrez (k4) \u003d Xs + Xtv (-ro) \u003d 16.96 + 41.99 \u003d 58.95 Ohm	Khrez (k4) \u003d Xs + Xtv (+ N) \u003d 28.85 + 71.44 \u003d 100.29 Ohm
I (3) for max = = 0.95 kA	I (3) for max = = 0.73 kA
The actual value of the short circuit current at point K-4, referred to a voltage of 37 kV
I (3) for max = 0.95 * = 8.74 kA	I (3) for max =0.73* =8.76 kA
Point K-5
Value name 115 kV 10 kV I nom. = = =207,59 = =2099,74 K I 300/5 3000/5 I number, in = = =3,46 = =3,5 Accepted values Inom HV, Inom LV 3,4 3.5 RPN range, RPN span Sheet Document No. Signature date Sheet KP.140408.43.06.PZ 4. Relay protection. 4.1 Single-ended line protection. 4.1.1 Calculation of two-stage current protection against phase-to-phase short circuits of the W line. Calculation of the current cutoff without time delay from phase-to-phase short circuits (I stage). 1) I 1 sz Kots. * I (3) k-3max \u003d 1.2 * 0.26 \u003d 0.31 kA 2) Kch \u003d I (2) k-1min / Is.z. 1 \u003d 2.76 * 0.87 / 0.31 \u003d 7.74 Kch \u003d I (2) k-2min / Is.z. 1 1.5=2.18*0.87/0.31=6.12 3) I (1) c.r. \u003d I (1) cz * Ksh / K1 \u003d 0.31 * 1 / (100/5) \u003d 0.02 kA 4) The response time of the current cutoff is assumed to be 0.1s Calculation of the maximum current protection with time delay from phase-to-phase short circuits (stage II). 1) I II sz Kots * Ksz / Kv) * Iload. max \u003d (1.2 * 2 / 0.8) * 0.03 \u003d 0.09 kA Iload.max=Snom.t./=6.3/=0.03 kA 2) Kch \u003d I (2) k-3min / Is.z. I 1 1.2=0.26*0.87/0.09=2.51 3) I (11) c.r. = I (11) cz * Ksh / K1 = 0.09 * 1 / (100/5) = 0.0045 kA 4) The response time of the MTZ is selected according to the condition of agreement with the MTZ of the tr-ra. t II sz \u003d tsz (mtz t-raT) + t \u003d 2 + 0.4 \u003d 2.4s 4.1.2. Calculation of the two-stage earth fault protection of line W. Calculation of zero sequence cutoff currents without time delay (1 stage). 1) I (1) 0cz 3I0 (1) k-2min / Kch \u003d 2.16 / 1.5 \u003d 1.44 kA 2) I (1) 0cr I0 (1) sz * Ksh / K I \u003d 1.44 * 1 / (100/5) \u003d 0.072 kA 3) The response time of the current cutoff is assumed to be 0.1 s. Calculation of zero sequence current protection with time delay (2 stage). 1) I 11 0cz Kots*Inb.max=Kots*Kper*Knb*Icalc.=1.25*1*0.05*0.26=0.02 kA I accept I 11 0cz=60A 2) I (11) 0cr = I (11) 0cz * Ksh / K I \u003d 60 * 1 / (100/5) \u003d 3 kA 3) Kch \u003d 3I0k-2min / I (11) 0sz 1.5 \u003d 2.16 / 0.06 \u003d 36 4) tsz II \u003d tsz I + t \u003d 0.1 + 0.4 \u003d 0.5s 4.2 Calculation of transformer protection. 4.2.1 Gas protection. It is the main from all damages inside the transformer tank. Damage to transformers that occurs inside its casing is accompanied by an electric arc or heating of parts, which leads to the decomposition of oil and insulating materials and the formation of volatile gases. Being lighter than oil, the gases rise into the conservator, which is the highest part of the transformer. The gas relay is installed in the pipe connecting the transformer casing with the expander so that gas and oil flow pass through it, rushing into the expander in case of damage to the transformer. The gas relay responds to the speed of oil movement in case of damage in the transformer. With minor damage, the formation of gas occurs slowly, and it rises in small bubbles to the expander. In this case, the protection acts on the signal. If the damage to the transformer is significant, then gases are violently formed and the protection acts on the shutdown. For a transformer with an on-load tap-changer, 2 gas relays are provided: one for the transformer tank, the other for the tap-changer tank. Sheet Document No. Signature date Sheet KP.140408.43.06.PZ It is carried out by microprocessor protection type "Sirius-T". Value name Designation and method of definition Numeric value for side 115 kV 10 kV Primary current on the side of the protected transformer corresponding to its rated power, A I nom. = = =207,59 = =2099,74 Transformer ratio of current transformers K I 300/5 3000/5 Secondary current in the arms of the protection, corresponding to the rated power of the protected transformer I number, in = = =3,46 = =3,5 Accepted values Inom HV, Inom LV 3,4 3.5 RPN range, RPN span 100*(176-96,5)/(2*111,25)=13 Change Sheet Document No. Signature date Sheet KP.140408.43.06.PZ 4.2.2 Differential cutoff. The setpoint must be selected from two conditions: - detuning from the inrush of the magnetizing current of the power transformer. - detuning from the maximum primary unbalance current in the transient mode of the calculated external short circuit. Detuning from magnetizing inrush current. When the power transformer is switched on from the higher voltage side, the ratio of the magnetizing current surge to the amplitude of the rated current of the protected transformer does not exceed 5. This corresponds to the ratio of the amplitude of the magnetizing current surge to the effective value of the rated current of the first harmonic equal to 5 = 7. The cutoff responds to the instantaneous value, equal to 2.5*Idiff./Inom. The minimum possible setting for the first harmonic is Idiff/Inom=4, which contributes to 2.5*4=10 in terms of amplitudes. Comparison of the obtained values ​​indicates that the instantaneous cutoff is detuned from possible magnetization current surges. Calculations show that the effective value of the first harmonic of the magnetizing current inrush does not exceed 0.35 of the inrush amplitude. If the amplitude is equal to 7 effective values ​​of the rated current, then the effective value of the first harmonic is 7*0.35=2.46. Therefore, even with a minimum setting of 4 Inom. The cutoff is detuned from magnetizing current surges and when regulating the first harmonic of the differential current. Detuning from the unbalance current with an external short circuit. For detuning from the unbalance current with an external short circuit, there are formulas that take into account all three components of the unbalance current. But with small limiting multiplicity of domestic current transformers, the amplitude of the unbalance current can reach the amplitude of the maximum current of the external short circuit. Change Sheet Document No. Signature date Sheet KP.140408.43.06.PZ Under these conditions, it is recommended to select the setting according to the condition: Idiff/Inom Kots*Knb(1)*Ikz.in.max where Knb(1) is the ratio of the amplitude of the first harmonic of the unbalance current to the reduced amplitude of the periodic component of the external short circuit current. If a CT with a secondary rated current of 5A is used both on the HV side and on the LV side, Knb(1) = 0.7 can be taken. If a CT with a secondary rated current of 1A is used on the HV side, then Knb(1) = 1.0 should be taken. The detuning coefficient (Kots) is assumed to be 1.2. Ikz.vn.max-ratio of the current of the external calculated short circuit to the rated current of the transformer. If a through current Irms passes through the protected transformer, it can carry a differential current. Idiff.=(Nper*Codn*E+ Urpn+ fadd.)*Irm=(2*1.0+0.13+0.04)*Irm=0.37*Irm. When deriving this formula, it was assumed that one CT works exactly, the second has an error equal to Idiff. Let us introduce the concept of the braking current reduction factor. Ksn.t.=Ibr./Ickv.=1-0.5*(Nper*Codn.*E + Urpn + fadd) / Ksn.t. \u003d 100 * 1.3 * (2 * 1 * 0.1 + 0.13 + 0.04) / 0.815 \u003d 59 The second breaking point of the braking characteristic: It 2 ​​/Inom determines the size of the second section of the braking characteristic. In load and similar modes, the braking current is equal to the through current. The appearance of coiled short circuits only slightly changes the primary currents, so the braking current has not changed much. For high sensitivity to coil short circuits, the second section should include the rated load mode (Im / Inom = 1), the mode of permissible long-term overloads (Im / Inom = 1.3). It is desirable that the modes of possible short-term overloads also fall into the second section (self-starting of motors after ATS, starting currents of powerful motors, if any). Sheet Document No. Signature date Sheet KP.140408.43.06.PZ The second harmonic blocking setting I g / I g1, based on the experience of companies that have been using such protection for a long time, is recommended at the level of 12-15% I accept I g2 / I g1 \u003d 0.15 We calculate the sensitivity coefficient for the considered network. Primary tripping current of protection in the absence of braking: Ic.z \u003d Inom * (I 1 / Inom) \u003d 208 * 0.3 \u003d 62.4 A. When checking the sensitivity of protection, we take into account that due to the direction of braking with internal short circuits, there is no braking current. Sensitivity for two-phase short circuit on the LV side Kch=730*0.87/62.4=10.18 Conclusion: the sensitivity is sufficient. 4.3 Overload protection "Sirius-T". The overload signal setting is taken equal to: Isz \u003d Kots * Inom / Kv \u003d 1.05 * 3.4 / 0.95 \u003d 3.76, where detuning coefficient Kots=1.05; the return coefficient in this device is Kv = 0.95. The rated current Inom is recommended to be determined taking into account the possibility of increasing it by 5% when regulating the voltage. For a 40 MVA transformer, the rated secondary currents on the middle branch on the HV and LV sides are 3.4 and 3.5 A. The calculated values ​​of the load setting are equal. HV side: Ivn \u003d 1.05 * 1.05 * 3.4 / 0.95 \u003d 3.95 A HH side: Inn \u003d 1.05 * 1.05 * 3.5 / 0.95 \u003d 4.06 A If the transformer has a split LV winding, then overload control must be carried out by the input protection devices installed on the LV side circuit breakers. Protection operates on tires with tсз=6s. Change Sheet Document No. Signature date Sheet KP.140408.43.06.PZ 4.4.1 Maximum current protection on the Sirius-T type microprocessor relay on the HV side 110 kV. The calculation of the operation parameters (settings) of the overcurrent protection consists in choosing the protection operation current (primary); relay operation current. In addition, a design check of the current transformer is carried out. Choice of operating current. The current settings for the overcurrent protection must ensure that the protection does not trip during sequential overloads and the necessary sensitivity for all types of short circuits in the main zone and in the redundancy zone. Isz \u003d Ksz * Ksh / Ktt \u003d 265 * 1 / (300/5) \u003d 4.42 A Checking the sensitivity of overcurrent protection. Kch I (3) k.min.in/Isz=0.87*730/265=2.4 Kch I (3) k.min.in/Isz=0.87*5.28/265=1.73 1.2 Conclusion: the sensitivity of MTZ is sufficient, in accordance with the PUE. I choose the response time of the MTZ 1 second 4.4.2 Maximum current protection on the Sirius-UV type microprocessor relay on the LV side 10 kV. Protection operation current. Isz \u003d Cost / Kv * In.max \u003d 1.2 / 0.95 * 2099.74 \u003d 2652.3 2099.74 - selected according to the rated current of the transformer 0.95 is the return coefficient of the Sirius relay. I accept the current of protection operation Iсз=2652 A. Relay actuation current. Isz \u003d Ksz * Ksh / Ktt \u003d 2652 * 1 / (3000/5) \u003d 4.42A Checking the sensitivity of MTZ. Kch Ik (2) min.nn./Isz=0.87*7050/2652=2.31 1.5 Conclusion: the sensitivity of the MTZ is sufficient, in accordance with the PUE. Change Sheet Document No. Signature date Sheet KP.140408.43.06,PZ Bringing currents to the LV stage Isk.n.=Ik.vn*Uvn/Unn=730*(96.58/10)=7050 A Voltage start. Calculation of overcurrent protection with combined voltage start installed on the 10.5 kV side. The primary voltage of the protection operation for the undervoltage relay, according to the condition of detuning from the self-starting voltage when turning on from the AVR or AR of the inhibited load motors and according to the condition of ensuring the return of the relay after the external short circuit is turned off, is taken: Usz=0.6Unom=0.6*10500=6300V In this case, the operating voltage of the undervoltage relay will be: Uav=Usz/Kch=0.6*10500/(10500/100)=60 V. Relay RN-54/160 is accepted for installation For the voltage filter-relay, the inverse sequence of the protection operation voltage is taken according to the condition of detuning from the unbalance voltage in the load mode. U2сз 0.06*Unom=0.06*10500=630V Negative sequence voltage filter-relay actuation voltage. U2av=U2sz/K U=630/(10500/100)=6V It is taken to the setting of the RSN-13 filter relay. Voltage sensitivity test at short circuit at point-5-for undervoltage relay. KchU=Usz*Kv/Uz.max=6.3*1.2/4.1=1.84 1.2 where Uz.max= 3*I (3) k-4max*Zkw.min= *5280*0.45=4.1kV here I (3) k-4max is the current of a three-phase short circuit at the end of the cable line in the maximum operating mode (mode 9) - for negative sequence voltage relay filter. Change Sheet Document No. Signature date Sheet KP.140408.43.06.PZ KchU2=U2s.min/U2ss=3.2/0.63=5.08 1.2 where U2z.min=0.5*Unom.n.- *I 2 max*Zkw.min=0.5*10.5-( 2)*0.3*1.5=5.25-2.05 =3.2kV here I 2 max - negative sequence current at the place of installation of protection in case of a short circuit between two phases at the end of the cable line in the maximum operating mode. You can accept: I 2 max=I (3) k-4.max/2=I (2) k-4.max/2 The choice of protection time delays is made according to the stepwise principle tсz mtz-10=tсз.sv-10+ t=1+0.5=1.5s (РВ-128) tсz mtz-110=tсз.мтз-35+ t=2.3+0.3=2.6 (РВ-0.1) where tсз.св-10 is the protection response time on the sectional switch 10 kV The selectivity level t is adopted for the time relay RV-0.1 t=0.3s, for the time relay RV-128 t=0.5s. Change Sheet Document No. Signature date Sheet KP.140408.43.24.PZ 6. Calculation of 10% error of current transformers TFND-110. Transformation ratio =100/5 Estimated multiplicity of 10 percent error: K (10) calc.=1.1*Is/I1nom.=1.1*1440/100=15.84 according to the curve of 10 percent error, the permissible secondary load Z2adm is determined. Z2adm.=2 Ohm Z2adm.=Zp+Rpr+R 0.05 perv. Zp=0.25ohm Z2add.=Zp+Rpr.+Rtrans. Rpr \u003d 2-0.25-0.05 \u003d 1.7 Ohm q= *l/ Rpr=0.0285*70/1.7=1.17