Networks with a voltage of 110 -220 kV operate in a mode with an effectively or solidly grounded neutral. Therefore, a ground fault in such networks is a short circuit with a current that sometimes exceeds the current of a three-phase short circuit, and must be disconnected with the minimum possible time delay.

Overhead and mixed (cable-overhead) lines are equipped with automatic reclosure devices. In some cases, if the circuit breaker used is made with phase-by-phase control, phase-by-phase shutdown and automatic reclosure are used. This allows you to turn off and turn on 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.

As a rule, autorecloser is not used on purely cable lines.

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

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

High voltage lines usually have a considerable length, which complicates the search for the location of the fault. Therefore, lines must be equipped with devices that determine the distance to the point of damage. According to CIS directive materials, 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 disruption of the stability of parallel operation of power plants; due to a long-term voltage drop, the equipment may stop and the production process may be disrupted; additional damage to the line on which the short circuit has occurred may occur. Therefore, protections are very often used on such lines that turn off short circuits at any point without a 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 protections, accelerated upon receipt of an enabling signal, or removal of a blocking signal from the opposite side.

Current and distance protection are usually carried out in stages. The number of steps is at least 3, in some cases 4 or even 5 steps are necessary.

In many cases, all required protection can be implemented on the basis of one device. However, 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 backup and can be simplified in comparison with the main one: do not have automatic reclosure, weapons of mass destruction, have a smaller number of stages, etc. The second set must be powered from another auxiliary circuit breaker and a set of current transformers. If possible, powered by a different battery and voltage transformer, act on a separate breaker trip solenoid.

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

To analyze the accident and the operation of relay protection and automation, registration of both analog values ​​and discrete signals during emergency events is required.

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 ground.

Single-phase or three-phase automatic reclosure.

Overload protection.

LEVEL

Determining the location of damage.

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

Protection devices must be redundant or duplicated.

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

7.2. FEATURES OF CALCULATING CURRENTS AND VOLTAGES DURING SHORT CIRCUITS

As stated 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 ground faults.

Calculations of currents and voltages during short circuits to ground are carried out using the method of symmetrical components, see Chapter. 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 makes it possible not to adjust the protection against load current, and to have a current setting less than the load current. For example, for protection against ground faults, the main use is the zero-sequence current protection, which is included in the neutral wire of three star-connected current transformers.

When using the method of symmetrical components, the equivalent circuit for each of them is drawn up separately, then they are connected together at the location of the short circuit. For example, let's create an equivalent circuit for the circuit in Fig. 7.1.

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

T1 – 10000/110

UK = 10.5 T2 – 16000/110 UK = 10.5

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

When calculating the parameters of a line of 110 kV and above for an equivalent circuit, the active resistance of the line is usually neglected. The positive sequence inductive reactance (X 1 ) of the line according to reference data is equal to: AC-95 - 0.429 Ohm per km, AC-120 - 0.423 Ohm per km. Zero sequence resistance for a line with steel cable torsos

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

Let's define the line parameters:

	L 1 = 25 0.423 = 10.6 Ohm;		L 1 = 25 1.269 = 31.7 ohms
	L 2 = 35 0.423 = 15.02 Ohm;		L 2 = 35 1.269 = 45.05 ohm

Let's determine the parameters of the transformer:

T1 10000kVA.

X 1 T 1 = 0.105 1152 10 = 138 Ohm;

X 1 T 2 = 0.105 1152 16 = 86.8 Ohm; X 0 T 2 = 86.8 Ohm

The negative sequence resistance in an 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 = X 0 T. Transformer T1 is not included in the zero-sequence equivalent circuit, since its neutral is ungrounded.

We draw up a replacement scheme.

X1C =X2C =15 Ohm

X1Л1 =X2Л1 =10.6 Ohm

X1Л2 =X2Л1 =15.1 Ohm

X0C =25 Ohm

X0Л1 =31.7 Ohm

X0Л2 =45.05 Ohm

X1T1 =138 Ohm

X1T2 =86.8 Ohm

X0T2 =86.8 Ohm

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 month			Three-phase short circuit			Short circuit two-phase
	ta short circuit X 1 ∑ = ∑ X 1			= (115 3) X 1			0.87 I
	15+10.6 = 25.6 Ohm
	25.6+15.1 =40.7 Ohm
	25.6+ 138=163.6 Ohm
	40.7+86.8 =127.5 Ohm

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

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

Let's calculate the ground fault, see tables 7.2, 7.3.

The positive and negative sequence circuit consists of one branch: from the power source 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 = (X a X b) (X a + X b)

Current distribution along parallel branches is determined by the formulas:

I a = I E X E X a; I in = I E X E

Table 7.2 Single-phase short circuit currents

X1 E

X2 E

X0 E = X0 a //X0 b *

HE

Ikz1

Iкз2

Ikz0

Ikz0 a *

Iкз0 b

I short circuit

I1 +I2 +I0

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

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

Table 7.3 Two-phase short circuit currents to ground

	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 using formula 7.1; the calculation is performed in Table 7.2.

**Note. The resistance of two parallel-connected negative and zero sequence resistances is determined using formula 7.1.

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

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

*****Note. The current of a two-phase short circuit to ground is indicated by an approximate formula, the exact value is determined geometrically, see below.

Determination of phase currents after calculating symmetrical components

With a single-phase short circuit, the entire short circuit current flows in the damaged phase; 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

sequential

sequential

sequential

Ic 2

Ib 2

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

For a single-phase short circuit, the currents are I1 = I2 = 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.

With a two-phase short circuit to ground, 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 construct the currents of the symmetrical components (Fig. 7.4):

Ia 1

Ia 1

Ia 2

Iс 2

Ib 2

Ia 0

I a 0 I b 0 I c 0

Iс 2

Ib 2

Iс 1

Ib 1

Ia 2

Ic 0

Iс 1

Ib 1

Ib 0

Rice. 7.4 Vector diagrams of symmetrical components of two-phase fault currents to ground

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

I f = I 1 + 1 2 (I 2 + I 0 ) = 1.5 I 1

The currents in Table 7.3 are calculated using this formula.

If we compare the currents of a two-phase short-circuit to ground according to Table 7.3 with the current of two-phase and three-phase short-circuits according to Table 7.1, we can conclude that the currents of a two-phase short-circuit to ground are slightly lower than the current of a two-phase short-circuit to ground, therefore the sensitivity of the protection should be determined by the current of a two-phase short-circuit. Three-phase short-circuit currents are correspondingly higher than two-phase short-circuit currents by

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

7.3 EXAMPLES OF SELECTION OF EQUIPMENT FOR DEAD-END OVERLINES 110-220 kV

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

Option 1 . Three-stage protection against phase-to-phase short circuits must be used (the first stage, without a time delay, is set up against short circuits on the PS2 HV buses, the second, with a short time delay, against short circuits on the PS1 and PS2 LV buses, the third stage is maximum protection). Ground fault protection - 2 stages (the first stage, without a time delay, is detuned from the current sent to the buses by the grounded transformer PS2, the second stage with a time delay, ensuring its coordination with the external network protections, but not detuned from the short-circuit current sent by the transformer PS2 ). A two-shot or one-time autorecloser must be applied. Sensitive stages must be accelerated during reclosure. The protections trigger a breaker failure of the supply substation. Additional requirements include protection against phase failure, determination of the location of a fault on an overhead line, and monitoring of the life of the circuit breaker.

Option 2. Unlike the first, the protection against ground faults is directional, which allows it not to be adjusted from the reverse short-circuit current and, thus, to perform more sensitive protection without a time delay. In this way, it is possible to protect the entire line without any time delay.

Note: This and subsequent examples do not provide precise recommendations on the choice of protection settings; references to setting up protection are used to justify the choice of protection types. In real conditions, a different protection setting may be applied, which is what needs to be determined during a specific design. The protections may be replaced by other types of protection devices having suitable characteristics.

The 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 REF 543 relays from ABB – selected 2 suitable modifications,

7SJ 511, 512, 531, 551 SIEMENS – selectable 2 suitable modifications,

two SEL 551 relays from SEL.

Scheme 7.2. Open-loop transit at substation 3.

A double-circuit overhead line enters substation 2, the sections of which operate in parallel. It is possible to transfer the cut to PS2 in repair mode.

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

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

V 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 one with two mode is taken into account: in the first section - 1 overhead line, in the second section - 2, which significantly roughens the protection. These three stages protect the line, and the last, 4th stage reserves the adjacent area. When coordinating protections over time, the duration of the breaker failure failure is taken into account, which increases the time delay of the coordinated protections for the duration of the breaker failure failure. When choosing current protection settings, they must be adjusted to 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. The following protection options can be applied:

MiCOM, P127 and P142 from ALSTOM,

F60 and F650 from GE,

two REF 543 relays from ABB - 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 control

Z = L Z

onal protection. For this purpose, one of the protections is replaced with 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 PROTECTION

Purpose and principle of operation

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

In complex configuration networks with several power supplies, simple and directional overcurrent protection (NTZ) cannot provide selective switching off of short circuits. 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 contradictory requirements cannot be met with the help of NTZ. In addition, MTZ and NTZ often do not meet the requirements for speed and sensitivity. Selective switching off of short circuits in complex ring networks can be achieved using remote relay protection (RD).

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

the installation location of the relay protection (point P) and the short circuit point (K), i.e. L PK, and increases with increasing this

th 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 action of D32 increases, and the short circuit is selectively turned off by the remote sensing protection closest to the place of damage.

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

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

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

Thus, the behavior of the remote element reacting to line resistance depends on the distance to the fault location. Depending on the type of resistance to which the DO reacts (Z, X or R), the DZ is divided into RE of total, reactive and active resistance. Resistance relays used in remote control to determine co-

resistance Z PK to the short-circuit point, control the voltage and current at the location of the remote control (Fig. 7.7.).

∆ – distance protection

TO PC terminals are supplied with secondary values U P and I P from TN 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 . During short circuit Z P = Z PK , and at certain values ​​of Z PK , PC is triggered; it reacts to a decrease in Z P, since during a short circuit U P decreases

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

Z p = U p I p ≤ Z cp

To ensure selectivity in networks of complex configurations on power lines with double-sided power supply, the faults must be directed, acting when the short-circuit power is directed from the buses to the power lines. The directionality of the action of the fault is ensured with the help of additional RNM or the use of directional PCs capable of responding to the direction of the fault power.

			Characteristics of time dependence
	Rice. 7.7. Connecting current circuits and	no distance protection t = f (L
	voltage relay resistance
		a – inclined; b – stepped; c – combined
	Time delay characteristics	distance protection

The dependence of the time of action of the fault on the distance or resistance to the fault location t 3 = f (L PK) or t 3 = f (Z PK) is called the time delay characteristic of the fault. By ha-

Based on the nature of this dependence, PDs are divided into three groups: with increasing (sloping) characteristics of the action time, stepwise and combined characteristics

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

Principles of selective network protection using distance protection devices

On power lines with double-sided power supply, PDs are installed on both sides of each power line and must act when directing power from the buses to the power line. Remote relays operating in one direction of power must be coordinated with each other in time and coverage area so that selective switching off of the short circuit 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 the remote control do not have a time delay (t I = 0), according to the selectivity condition, they should not operate outside the protected power line. Based on this, the length of the first stage, which does not have a time delay (t I = 0), is taken less than the length of the protected power line and is usually 0.8–0.9 times the length of the power line. The rest of the protected power line and the buses of the opposite substation are covered by the second stage of the protection of this power line. The length and time delay of the second stage are consistent (usually) with the length and time delay of the first stage of the remote sensing of the next section. For example, the second student

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

∆ z – distance relay error; ∆ t – selectivity level

The last third stage of the remote protection is a backup, its length is selected from the condition of covering the next section, in case of failure of its protective protection or circuit breaker. Exposure time

The value is taken to be ∆ t longer 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 must be built up from the end of the second or third zone of the next section.

Line protection structure using distance protection

In domestic power systems, DZ is used for action during interphase short circuits, and for action during single-phase short circuits, a simpler stepwise zero-sequence overcurrent protection (NP) is used. Most microprocessor equipment has distance protection that is valid for all types of damage, including ground faults. The resistance relay (RS) is connected through the VT and CT to the primary voltages in

the beginning of the protected power 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 relay input terminals is determined by the expression.

In accordance with the requirements of the PUE, the volume of power line relay protection devices is determined by the rated voltage level.

Lines of 110 kV and above are made with a grounded neutral. For a 110-500 kV line, relay protection devices against multiphase and single-phase ground faults must be provided.

To protect against multi-phase faults, distance protection is installed, and TO is installed as a backup.

Protection against short circuit protection is carried out using a zero-sequence current transformer and operates from capacitive current on the signal.

Block BMRZ-KL

Purpose of the BMRZ-KL block.

The BMRZ-KL digital relay protection unit is designed to perform the functions of relay protection, automation, control, measurement and signaling of cable and overhead power lines, distribution substations and power plants, and protection of electric motors. The function of determining the location of a fault (LMP) has been implemented - calculating the distance in kilometers to the location of a two-phase or three-phase short circuit on power lines. The presence of branches on a multi-terminal line leads to an increase in the OMP error. To calculate the distance to the fault location, the following parameters are used:

· specific reactance of the line (Ohm/km), which is set by the consumer in the form of a setting when setting up the BMRZ-KL;

· values ​​of current and voltage of the short-circuit loop obtained from oscillograms of the emergency process.

The current and voltage in the short-circuit loop are recorded in the section of the oscillogram with established electrical quantities. If during an accident a two-phase short circuit turns into a three-phase short circuit, the average distances to the short-circuit point are calculated. In this case, a decrease in the reliability of the WMD result is reflected on the BMRZ-KL display in the form of the message “The result is unstable.” The accuracy of calculating the distance to the fault location is proportional to the errors of the current and voltage measuring transformers and the accuracy of setting the parameters of the protected line. The result of the OMF does not depend on the transition resistance at the short-circuit location. Inaccuracies in determining line parameters have a significantly greater impact on the WMD. If WMD is not possible, for example, when protections are triggered without a time delay, the distance to the damage site is not displayed.

The BMRZ-KL block provides free assignment of backup discrete inputs and outputs. The block implements two options for protection against hazards:

· directional protection with control of the direction of zero-sequence power (analogue of ZZP - 1M and ZNZ);

· registration of the effective value of the sum of higher harmonics in the current 3 Iо (analogous to USZ-3M).

The second method is effective in networks with a compensated neutral and can be used to automatically or manually disconnect a damaged feeder, dramatically reducing the troubleshooting time. When BMRZ-KL units are combined into an automated control system, information about the values ​​of higher harmonics 3Iо in all feeders of the switchgear section appears on the computer of the relay operator or substation dispatcher 1-2 s after the occurrence of the fault.

The BMRZ-KL unit is available in four versions, differing in the communication channel and operating voltage.

Functions of the BMRZ-KL block.

· Directional three-stage overcurrent protection (MTZ) with combined voltage starting. For any stage, settings are selected individually.

· Directional protection against single-phase ground faults (SFG) with starting based on zero-sequence current and voltage. Registration of higher harmonics of current 3Iо.

· Minimum voltage protection (MVP) with control of two linear voltages and negative sequence voltage, with the possibility of blocking when starting the first and second stages of the overcurrent protection.

· Protection against unbalance and phase failure of the supply feeder (ZOP) with control of negative sequence current, as well as I 2 / I 1 .

· Redundancy in case of circuit breaker failure.

· Automatic restart.

· Execution of commands for automatic frequency unloading and automatic restart by frequency.

· Automatic oscillography of accident processes. (63 waveforms)

· Memory of emergency events.

· Counting pulses from active and reactive electricity meters (technical accounting).

· Measuring network parameters.

· Self-diagnosis.

· Two setting programs.

Distance protection BMRZ-LT

Three-stage distance protection (DZ) with a quadrangular response zone for all three stages (or a quadrangular response zone for the first two stages and a triangular response for the third) is designed to protect overhead lines (overhead line block - transformer) from phase-to-phase short circuits without ground faults and is made with three relays resistance in each stage, connected to circuits AB, BC, CA.

Four-stage zero-sequence current protection with independent time delays is designed to operate during single-phase and two-phase ground faults. The first three stages can be performed with detuning from the inrush current of the magnetizing current of the power transformer. Any stage can be configured by the user using software keys:

Non-directional;

Directional, with control of a zero-sequence power direction enabling relay;

Directional, with control of a blocking relay for the direction of zero-sequence power;

Overcurrent protection

Three-stage current protection can be configured by the user using software keys: - non-directional; - directional with permission or blocking based on power direction relay signals; - with combined triggering based on (U and U2) voltage; The current protection stage with a phantom voltage start circuit is designed for long-range backup during a short circuit on the low voltage side behind the transformers and monitoring the successful self-start of the remaining load after the short circuit is disconnected by the protection behind the transformer.

Phase loss protection

Unbalance and phase loss protection can be configured by the user using software keys:

Non-directional;

With negative sequence power direction control;

With zero sequence power direction control.

Redundancy in case of circuit breaker failure (CBF)

The "LVF" signal is issued a specified time after the signal to open the circuit breaker is issued while maintaining the current through the connection disconnected by the protection. The breaker failure failure algorithm is designed to control the position of the switch. Time settings: from 0.10 to 1.00 s, step 0.01 s.

Automatic reclosing (AR)

The block provides double automatic reclosure. The first and second autoreclose cycles can be disabled independently of each other using software keys. Automatic reclosure can be blocked when the cut-off is triggered and there is a voltage of 3Uo (ground in the network).

Multi-phase protection

We use maintenance as the main protection

Protection current

Relay operating current

Sensitivity factor

Therefore, the protection does not satisfy the sensitivity conditions

According to the PUE, step current protection should be installed on single lines with one-way power supply from multiphase faults. If such protections do not meet the requirements of sensitivity or speed of shutdown, stepwise distance protection must be provided. In the latter case, it is recommended to use current cut-off without a time delay as additional protection.

Distance protection

I Stage

Finding the response resistance of the first stage of protection

Line resistance (90%)

Transformer resistance

Relay response resistance

II Stage

Line resistance (10%)

Motor resistances:

where is the subtransient resistance, 0.2.

Protection response time

III Stage

Protection response resistance

Relay operation resistance according to formula (3.7)

Protection sensitivity factor as the main one

Ground fault protection

Performed using TTNP

Finding the capacitive current of overhead lines

Specific capacitive current of AC 70 wire - 0.045 A/km

Ground fault protection current

Ground fault current for overhead lines

Checking sensitivity

Therefore, the protection satisfies the sensitivity conditions

Selecting an operating current source

We use rechargeable batteries as a source of operating current, i.e. We use constant operating current sources. The main advantage of which is independence from the operating mode and state of the primary network. Therefore, direct operating current is more reliable during network disruptions.

110 kV substation Coal complex with 110 kV power line entries. Detailed design of relay protection and automation

2 Main technical solutions

2.1 Relay protection and automation

2.1.1 Relay protection and automation of power transformer
2.1.2 VV-10 kV protection
2.1.3 Protection of connections 10 kV
2.1.4 Protection SV-10 kV
2.1.5 Arc protection 10 kV
2.1.6 Logical protection of 10 kV buses
2.1.7 10 kV circuit breaker failure backup device
2.1.8 Automatic frequency shedding (AFS)

2.2 Automation of DGR control
2.3 Control, signaling, operational blocking and power supply of operational circuits

3 Development of EMC measures

Change registration sheet.

Explanatory note

The main technical decisions for the creation of a relay protection and automation complex were made on the basis of an assignment for the development of working documentation for the title: “Substation 110 kV Coal Complex with 110 kV power line entries.”

The quantitative and qualitative composition of the relay protection and automation functions complies with the requirements of the scientific and technical documentation (PUE, PTE, NTP PS and other industry normative documents).

2 Main technical solutions

This project provides for the creation of a complex of relay protection and automation of substation 110/6.6/6.3 kV “Inaglinsky Coal Complex”, made on modern microprocessor (MP)
devices produced by LLC NPP "EKRA" (Cheboksary) and LLC "RZA Systems" (Moscow), LLC "NTC Mekhanotronika" (St. Petersburg).

R&A of 110/6.6/6.3 kV power transformers is planned to be performed on the basis of MP devices produced by LLC NPP EKRA. Relay protection and automation of 6.6 kV and 6.3 kV equipment is planned to be performed on the basis of MP devices manufactured by RZA Systems LLC.

Protection of 6.6 kV and 6.3 kV switchgear equipment from arc faults is planned to be carried out on the basis of the “Duga” complex produced by LLC “NTC Mekhanotronika”.

Installation of 110 kV relay protection and automation cabinets, as well as general substation systems CS, OBR power supply is carried out in the relay panels room.

6.6 kV and 6.3 kV connection protection kits are installed in the relay compartments of the switchgear cells.
All used relay protection devices have the functions of oscillography, recording emergency processes and their subsequent storage in non-volatile memory. Also everyone
The devices have a standard RS-485 digital interface.

Solutions regarding connection to the secondary windings of CTs and VTs are shown in the distribution diagram for CTs and VTs of ITS devices, see P-15015-021-RZ.2.

To explain the principle of operation of the relay protection and automation complex at the facility, structural and functional diagrams of relay protection and automation were made. Schemes are presented graphically
materials P-15015-021-RZ.3.

2.1 Relay protection and automation

2.1.1 Relay protection and automation of power transformer
The project provides for the installation of cabinets of the type “ШЭ2607 045073”, manufactured by LLC NPP EKRA. The cabinet contains two sets:

1st - basic protection set a three-winding transformer based on a microprocessor terminal type “BE2704 V045”, which performs the following functions: - differential current protection (DCP) of the transformer from all types of short circuits inside the transformer tank;

MTZ of the HV side with the possibility of combined voltage starting on the LV side,
- MTZ of LV sides with the possibility of combined voltage starting on the LV side,
- overload protection on each side (OS),
- current relay for blocking the on-load tap-changer in case of overload,
- gas protection of the transformer and on-load tap-changer with insulation monitoring,
- receiving process signals from the transformer,

2nd - backup protection kit transformer and control automation
a switch based on a microprocessor terminal type "BE2704 V073" that performs
the following functions:

MT protection on the HV side with the possibility of combined voltage starting on the LV side;
- automatic circuit breaker control (ACC);
- gas protection of the transformer and on-load tap-changer with insulation monitoring.

To perform the functions of voltage regulation of the transformer, it is installed
SHE 2607 157 cabinet containing two sets based on BE2502A0501 terminals manufactured
LLC NPP "EKRA" Each kit performs the following functions:

Automatic maintenance of voltage within specified limits;
- control of the on-load tap-changer drive;
- monitoring the position of the on-load tap-changer;
- monitoring the serviceability of the on-load tap-changer drive.

Gas protection is used as a sensitive protection against internal damage to the transformer, reacting to the release of gases resulting from the decomposition of oil by an electric arc.

Gas protection of the transformer has two stages: the first stage is carried out with an effect on the signal with weak gas formation, the second stage is carried out with an effect without
time delay for turning off the transformer in case of strong gas formation.

Provision is made for transferring the shutdown stage of gas protection to a signal. The gas protection (jet relay) of the on-load tap-changer contactor has one stage, which operates without a time delay to turn off the transformer.

The operation of gas protection of the transformer and on-load tap-changer is provided through a set of main and a set of backup transformer protections. Insulation monitoring devices are provided in gas protection circuits. When the insulation level decreases, the gas protection is disabled and a fault signal is issued.

2.1.2 Protection of VV-6.6 kV and VV-6.3 kV

To protect explosives, it is planned to install “RS83-AV2” microprocessor terminals in the relay compartment of the cell, performing the following functions:

Three-phase overcurrent protection with time delay and combined voltage starting,

- minimum voltage protection (MVP),
- receiving a signal from the remote control,
- generation of the ATS signal to turn on the sectional switch.

2.1.3 Protection of 6.6 kV and 6.3 kV switchgear connections

To protect the connections, it is planned to install microprocessor terminals “RS83-A2M” in the relay compartments, which perform the following functions:

Three-phase overcurrent protection with time delay,
- automatic input of MTZ acceleration whenever the switch is turned on,
- determination of the feeder during single-phase ground faults (SFG),
- blocking of logical bus protection (LZSh),
- automatic circuit breaker control (ACC),
- receiving a signal from the remote control,
- circuit breaker failure backup device (CBF),
- disconnection from the AChR and inclusion from the ChAPV.

2.1.4 Protection SV-6.6 kV and SV-6.3 kV

To protect the SV, it is planned to install RS83-A20 microprocessor terminals in the relay compartments of the SV cells, which perform the following functions:

Three-phase MTZ-SV against phase-to-phase damage,
- automatic input of acceleration MTZ-SV whenever the switch is turned on,
- logical bus protection (LZSh),
- automatic circuit breaker control (ACC),
- receiving a signal from the remote control;
- circuit breaker failure backup device (CBF),
- automatic switching on of reserve (ATS)

2.1.5 Arc protection of 6.6 kV and 6.3 kV busbars

Arc protection is carried out using registration units "DUGA-O" and the central unit "DUGA-BC" produced by LLC "NTC Mekhanotronika". Protection reacts to light
radiation from an arc discharge and is made with current control. In the event of an arc fault in the input/output compartment in the cell of the outgoing connection, "DUGA-O" outputs a signal to
discrete input of the protection terminal, which, if there is current through the connection, turns off its own inhibit switch. In the event of an arc fault in the withdrawable compartment
element or busbar compartment of any of the cells, the device outputs a signal to the discrete input of the "DUGA-BC" block, which, in the presence of start signals for protection against input and
sectional switches, generates a signal to turn off these switches. When the arc sensors in the input/output compartment of the BB-6.6 (6.3) kV cell are triggered, the “DUGA-BC” block
generates a signal to turn off the power transformer and BB-6.6 (6.3) kV; in case of an arc fault in the PV compartment of the BB-6.6 (6.3) kV cell, the DUGA-BC block generates signals to
disconnection of the power transformer and SV-6.6 (6.3) kV with prohibition of automatic transfer switch.

2.1.6 Logical protection of buses 6.6 (6.3) kV

To protect 6.6 (6.3) kV buses, logical bus protection is used, blocking high-speed protection BB-6.6 (6.3) kV during a short circuit on the outgoing connection and allowing its operation during a short circuit on the busbars. Blocking is carried out by signals “Start MTZ” from outgoing line protection devices. The LZSh is assembled according to a sequential circuit to enable control of the LZSh circuits.

2.1.7 Circuit breaker failure backup device (CBF)

It is planned to organize a breaker failure protection system of 6.6 (6.3) kV, which is designed to disconnect with a time delay the upstream circuit breaker when its circuit breaker fails.
The breaker failure signal is generated when the protection is triggered and there is current through the switch. If the 6.6 (6.3) kV outgoing line switches fail, a breaker failure signal is generated to turn off the input breaker of the bus section and the sectional switch; if the sectional switch fails, a signal is generated to turn off both input switches; if the input breaker of the bus section fails, a signal is generated to turn off the sectional circuit breaker and to disconnect the power transformer through the main protection kit. If the 110 kV transformer switch fails, a signal is generated to turn off the transformer from all sides through the main protection set. The disconnection of a damaged transformer in the event of a failure of the 110 kV circuit breaker is carried out by the protection of 110 kV lines.

2.1.8 Automatic frequency shedding (AFS)

Automatic frequency unloading is used to eliminate active power shortages by automatically turning off consumers when the frequency decreases
(AFR) followed by automatic reconnection of disconnected consumers when frequency is restored (FARP). To implement these functions, it is planned to install 2 cabinets of the “ШЭЭ224 0611” type based on EKRA 221 0201 terminals. Each set provides AFR in the amount of 3 queues with subsequent FAPR (upon frequency restoration).

The selection of the AFR queue for the outgoing feeder protection terminal is made using a switch installed in the cell of each connection.

2.2 Registration of emergency events.

To perform the functions of recording emergency events at the substation, it is planned to install a cabinet of the “SEE 233 153” type based on the “EKRA 232” terminal, which ensures the collection, storage and possibility of transmitting data on emergency situations to the upper level.

2.3 Control, alarm, operational blocking and power supply of operationalchains.

Control and signaling of the position of the main switching devices is provided from the control panel. There is a mnemonic diagram on the control panel, on which
There are indicators for the position of disconnectors and grounding knives, signal lamps for the position of switches, switches for controlling switches, as well as panel instruments for measuring electrical quantities. The project provides for the installation of a central alarm cabinet. The cabinet provides for the organization of three signaling sections: the first - outdoor switchgear-110 kV and control unit, the second - KRUM-6.3 kV, the third - KRUM-6.6 kV. For each of the sections, pulse buses for emergency and warning alarms are organized, as well as the collection of discrete signals.

To power the operational blocking circuits of the disconnectors, the project provides for the installation of a power supply kit for the OBR circuits as part of the control panel. The power supply kit for the operational interlock circuits provides galvanic isolation of the power supply circuits and the OBR circuits. Control permission signals for each disconnector are generated by sequentially connecting the position contacts of switching devices, the actual position of which must be taken into account when switching the corresponding disconnector or grounding knife.

Networks, as a rule, operate with a solidly grounded neutral.

Therefore, protection is carried out against both multiphase (with the exception of double ground faults at different points) and single-phase short circuits. Networks often have complex configurations with multiple power sources. Therefore, to protect against multiphase short circuits (including double ground faults at one point), remote step protections with different characteristics of resistance elements, equipped with blocking devices against swings and violations of secondary circuits, are often used. Against ground faults, not distance protection is used, but multi-stage directional zero-sequence current protection.

In cases where, according to the conditions for ensuring the stability of the system and responsible consumers, protection is required along the entire length of the protected section without a time delay (on the buses of stations and node substations Uost with a 3-phase short circuit< 0,6-0,7Uном), возможны два решения вопроса: дополнение ступенчатых защит устройствами ВЧ блокировки или передачи отключающих сигналов и использование в качестве основной отдельной продольной защиты с абсолютной селективностью, предпочтение отдается второму варианту, обеспечивающему независимость в эксплуатации и более совершенное ближнее резервирование. На тупиковых линиях иногда удается использовать и более простые токовые ступенчатые защиты.

Topic 8. Protection of lines with voltage 110-220 kV

Lecture 12. Protection of lines with voltage 110-220 kV

Distance protection.

3. Purpose and principle of operation d station protections.

Characteristics of time delay of distance protection.

5. Principles of selective line protection using DZ. Structure of line protection using distance protection.

6. Swing blocking device (UBK)

7. Schemes for connecting remote controls for current and voltage. Requirements for connection circuits

8. Technical characteristics of digital protections

9. Acceleration of distance protection via the HF channel.

General information about protecting 110-220 kV lines

Networks with voltages of 110 - 220 kV operate in modes with an effectively or solidly grounded neutral. Therefore, any ground fault in such networks is a short circuit with a current sometimes exceeding the current of a three-phase short circuit. Such a short circuit must be disconnected with the minimum possible time delay.

High voltage lines operate with high load currents, which requires the use of protection with special characteristics. On transit lines that can be overloaded, distance protection is used to effectively isolate from load currents. On dead-end lines, in many cases, current protection can be used. Current and distance protection are carried out in stages. The number of steps must be at least 3, in some cases 4 - 5 steps are necessary.

According to the PUE, overload prevention devices must be used in cases where the permissible duration of the overload current for the equipment is more than 10...20 minutes. Overload protection should act on unloading equipment, interrupting transit, disconnecting load, and only last but not least on disconnecting overloaded equipment.

High voltage lines are long, making it difficult to find the location of the fault. Therefore, lines must be equipped with devices that determine the distance to the point of damage (DMP). According to CIS directive materials, lines with a length of 20 km or more should be equipped with weapons of mass destruction. Line protection on digital relays allows you to simultaneously perform the WMD function.

A delay in disconnecting the short circuit can lead to disruption of the stability of parallel operation of power plants. Due to a long-term voltage drop, the equipment of power plants may stop and the technological process of electricity production may be disrupted; additional damage to the line on which the short circuit occurred may occur. Therefore, on such lines protection is used that turns off the short circuit at any point without a time delay. Such protections include differential protections installed at the ends of the line and connected by a high-frequency, wire or optical communication channel, or conventional protections that are accelerated upon receipt of an enabling signal or removal of a blocking signal from the opposite side.

All required protections are performed on the basis of one digital device. However, failure of this one device leaves the equipment unprotected, which is unacceptable. Therefore, it is advisable to protect high voltage lines from two sets: main and backup. The backup set can be simplified compared to the main one: have no automatic reclosure, no weapons of mass destruction, have fewer stages, etc. The backup set must be powered by another auxiliary circuit breaker, other sets of current transformers and voltage transformers and act on a separate circuit breaker trip solenoid.

High-voltage line protection devices must take into account the possibility of circuit breaker failure and therefore must have a breaker failure protection device.

To analyze the accident and the operation of relay protection and automation, registration of signals during emergency events is required.

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 ground.

Three-phase or phase-by-phase automatic reclosure.

Overload protection.

Determining the location of damage.

Oscillography of currents and voltages when a short circuit occurs, as well as recording of discrete protection and automation signals.

Protection devices must be redundant or duplicated.

For lines that have switches with phase control, it is necessary to have protection against open-phase operation, since long-term open-phase operation in networks with a voltage of 110 - 220 kV is not allowed.

Distance protection (Dz)

Purpose and principle of operation. Distance protections are complex directional or non-directional protections with relative selectivity, implemented using minimal resistance relays.

The faults react to the value of the line resistance to the fault location, which is proportional to the distance, i.e. distances. This is where the name distance protection comes from. For distance protection to work, it is necessary to have current circuits from the CT connection and voltage circuits from the VT.

Rice. 12.1. Ring network with two power supplies. О – maximum current directional protection; ∆ – distance protection