Block protection generator

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Section 3. Protection and automation

Relay protection. Block protection generator - transformer

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Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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3.2.72. For generator-transformer units with generators with a power of more than 10 MW, relay protection devices must be provided against the following types of damage and abnormal operating modes:

1) earth faults on the generator voltage side;

2) multi-phase short circuits in the generator stator winding and on its terminals;

3) short circuits between turns of one phase in the turbogenerator stator winding (according to 3.2.76);

4) multi-phase short circuits in the windings and at the transformer terminals;

5) single-phase earth faults in the transformer winding and its terminals connected to the network with high earth fault currents;

6) short circuits between turns in the transformer windings;

7) external short circuit;

8) generator overload by negative sequence currents (for units with generators with a capacity of more than 30 MW);

9) symmetrical overload of the generator stator winding and transformer windings;

10) overload of the generator rotor winding with excitation current (for turbogenerators with direct cooling of winding conductors and for hydrogenerators);

11) increasing the voltage on the generator stator and unit transformer (for units with turbogenerators with a capacity of 160 MW or more and for all units with hydro generators);

12) earth faults at one point of the excitation circuit (in accordance with 3.2.85);

13) ground faults at the second point of the excitation circuit of a turbogenerator with a power of less than 160 MW;

14) asynchronous mode with loss of excitation¹⁾ (in accordance with 3.2.86);

15) lowering the oil level in the transformer tank;

16) partial breakdown of the insulation of the inputs of 500 kV transformers.

1. To prevent asynchronous operation without loss of excitation, see Ch. 3.3.

3.2.73. Instructions for the protection of generators and step-up transformers related to their separate operation are also valid for the case when they are combined into a generator-transformer unit (autotransformer), taking into account the requirements given in 3.2.74 - 3.2.90.

3.2.74. On units with generators larger than 30 MW, as a rule, earth fault protection in the generator voltage circuit must be provided, covering the entire stator winding.

When the unit generator power is 30 MW or less, devices should be used that protect at least 85% of the stator winding. The use of such devices is also allowed on units with turbogenerators with a power of 30 to 160 MW, if additional equipment is required to be connected to the generator circuit to protect the entire stator winding.

Protection must be performed with a tripping action with a time delay of not more than 0,5 s on all units without taps on the generator voltage and with taps to auxiliary transformers. On units having an electrical connection with the auxiliary network or consumers fed through the lines from the taps between the generator and the transformer, if the capacitive earth fault current is 5 A or more, protection against earth faults in the generator stator winding and against double earth faults, as provided for on generators operating on busbars (see 3.2.38 and 3.2.39), should be installed; if the capacitive earth fault current is less than 5 A, then the earth fault protection can be performed in the same way as on the units without taps on the generator voltage, but with action on the signal.

If there is a circuit breaker in the generator circuit, an additional ground fault alarm must be provided on the generator voltage side of the unit transformer.

3.2.75. On a unit with an indirectly cooled generator, consisting of one generator and one transformer, in the absence of a circuit breaker in the generator circuit, it is recommended to provide one common longitudinal differential protection of the unit. If there is a circuit breaker in the generator circuit, separate differential protection must be installed on the generator and transformer.

When using two transformers in the unit instead of one, as well as when operating two or more generators without circuit breakers in a unit with one transformer (enlarged unit), each generator and transformer with a capacity of 125 MVA and more must be provided with a separate longitudinal differential protection. In the absence of built-in current transformers at the low voltage inputs of these transformers, it is allowed to use a common differential protection for two transformers.

On a unit with a generator having direct cooling of the winding conductors, a separate longitudinal differential protection of the generator should be provided. At the same time, if there is a circuit breaker in the generator circuit, then a separate differential protection of the unit transformer must be installed (or each transformer if two or more transformers work in the unit with the generator; in the absence of built-in current transformers at the low voltage inputs of these transformers, it is allowed to use a common differential protection for the unit transformers); in the absence of a switch to protect the transformer of the unit, either a separate differential protection or a common longitudinal differential protection of the unit should be installed (for units consisting of one generator and one transformer, the general differential protection of the unit is preferable).

From the higher voltage side, the differential protection of the transformer (block) can be connected to the current transformers built into the block transformer. In this case, to protect the busbar, a separate protection must be installed between the switches on the high voltage side and the transformer of the unit.

Separate differential protection of generators shall be three-phase, three-relay, with a trip current similar to that specified in 3.2.36.

To reserve the indicated differential protections on units with generators with a power of 160 MW or more, having direct cooling of the winding conductors, it is necessary to provide a backup differential protection covering the generator and the transformer of the unit, together with busbars on the high voltage side.

It is recommended to install backup differential protection of units even if the power of generators with direct cooling of winding conductors is less than 160 MW.

When using backup differential protection on units without a circuit breaker in the generator circuit, it is recommended to provide separate main differential protections for the generator and transformer.

If there is a switch in the generator circuit, the backup differential protection must be performed with a time delay of 0,35-0,5 s.

3.2.76. On turbogenerators with two or three parallel branches of the stator winding, a single-system transverse differential protection against winding short circuits in one phase, operating without time delay, must be provided.

3.2.77. On units with generators with a power of 160 MW or more with direct cooling of the winding conductors, negative sequence current protection with an integral dependent characteristic corresponding to the characteristic of permissible overloads of the protected generator by negative sequence currents must be provided. The protection should act to turn off the generator switch, and in its absence, to turn off the unit from the network. To reserve the protection of elements adjacent to the blocks, the specified protection must have an element with an independent time delay, acting to disconnect the block from the network and a two-stage action in accordance with 3.2.81.

On units with generators with a power of less than 160 MW, which have direct cooling of the winding conductors, as well as on units with hydro generators with a power of more than 30 MW, which have indirect cooling, negative sequence current protection should be performed with a step or dependent time delay. In this case, different stages of protection may have one or more time delays (see 3.2.81, clause 4). The indicated step or dependent time delay shall be consistent with the characteristic of permissible negative sequence current overloads of the generator (see 3.2.41).

On units with indirectly cooled turbogenerators with a power of more than 30 MW, protection must be carried out in accordance with 3.2.41.

In addition to tripping protections, all units with turbogenerators with a power of more than 30 MW shall be provided with an overload signaling by negative sequence currents, carried out in accordance with 3.2.41.

3.2.78. On units with generators with a power of more than 30 MW, protection against external symmetrical short circuits must be carried out as specified in 3.2.42. At the same time, for hydrogenerators, the protection operation voltage should be taken about 0,6-0,7 nominal. On units with turbogenerators having a backup exciter, the specified protection must be supplemented by a current relay connected to the current from the unit's higher voltage side.

On units with generators of 60 MW or more, it is recommended to use distance protection instead of the specified protection. On units with generators having direct cooling of the winding conductors, instead of backup differential protection (see 3.2.75), it is allowed to install two-stage distance protection against phase-to-phase short circuits.

The first stage of this protection, which provides short-range redundancy, must be performed with blocking during swings and operate as specified in 3.2.81, paragraph 3, with a time delay of not more than 1 s. The first stage must securely surround the block transformer while providing selectivity with adjacent element protections. Redundancy by the first stage of generator protection is mandatory if separate transformer and generator differential protections are used on the unit.

The second stage providing long-range backup shall operate as specified in 3.2.81, paragraph 2.

It is recommended to install a two-stage distance protection and in the presence of a backup differential protection in order to increase the effectiveness of long-range backup. Both stages of distance protection in this case shall operate as specified in 3.2.81, paragraph 2.

3.2.79. Protection against external short circuits on units with generators with a capacity of 30 MW or less should be carried out in accordance with 3.2.43. The protection operation parameters on units with hydro generators should be taken in accordance with 3.2.42, 3.2.43 and 3.2.78.

3.2.80. On generator-transformer units with a circuit breaker in the generator circuit, in the absence of backup differential protection of the unit, maximum current protection from the high voltage side of the unit should be provided, designed to back up the main protection of the unit transformer when working with the generator turned off.

3.2.81. Back-up protection of the generator-transformer units must be carried out taking into account the following:

1. No protection is installed on the generator voltage side of the transformer of the unit, but generator protection is used.

2. In case of long-range redundancy, the protection should act, as a rule, with two time delays: from the first - for dividing the circuit on the side of the higher voltage of the unit (for example, for turning off the bus-connecting and sectional switches), from the second - for disconnecting the unit from the network.

3. In case of close redundancy, the unit (generator) must be disconnected from the network, the generator field must be extinguished and the unit stopped if required by 3.2.89.

4. Separate stages or backup protection devices, depending on their purpose and expediency of use for long-range and short-range redundancy, can have one, two or three time delays.

5. It is recommended to provide protection voltage release devices according to 3.2.78 and 3.2.79 on the side of the generator voltage and on the side of the network.

6. For the main and backup protections of the unit, as a rule, separate output relays and power supply with operational direct current from different circuit breakers should be provided.

3.2.82. On units with turbogenerators, protection against symmetrical stator overloads should be carried out in the same way as on generators operating on busbars (see 3.2.47).

At hydroelectric power stations without constant duty of operational personnel, in addition to signaling symmetrical overloads, protection with an independent characteristic should be provided, acting with a longer time delay for turning off the unit (generator) and with a shorter time delay for unloading. Instead of the specified protection, appropriate devices in the excitation control system can be used.

3.2.83. On generators with a power of 160 MW or more with direct cooling of the winding conductors, protection against overload of the rotor winding by the excitation current must be performed with an integral dependent time delay, which corresponds to the characteristic of the permissible overloads of the generator by the excitation current. This protection must act on tripping.

If it is impossible to turn on the protection for the rotor current (for example, with brushless excitation), it is allowed to use protection with an independent time delay that reacts to an increase in voltage in the excitation circuit.

The protection must be able to act with a shorter time delay to reduce the excitation current. If there are overload limiting devices in the excitation regulator, the unloading action can be carried out simultaneously from these devices and from the rotor protection. It is also allowed to use the overload limiting device in the AVR to act on unloading (with two time delays) and tripping. In this case, the protection with integral dependent time delay may not be installed.

On turbine generators with a power of less than 160 MW with direct cooling of the winding conductors and on hydrogenerators with a power of more than 30 MW with indirect cooling, protection should be carried out in the same way as indicated in 3.2.46.

In the presence of group excitation control devices on generators, it is recommended to perform protection with IDMT.

When generators are operated with standby exciter, the rotor overload protection must remain in operation. If it is impossible to use protection with an independent time delay, it is allowed to provide protection with an independent time delay on the backup exciter.

3.2.84. On units with turbogenerators with a capacity of 160 MW or more, in order to prevent an increase in voltage in idle mode, protection against overvoltage must be provided, which is automatically disabled when the generator is running on the network. When the protection is in effect, the field of the generator and exciter must be suppressed.

On units with hydro generators, voltage surge protection must be provided to prevent voltage increase during load shedding. The protection should act to turn off the unit (generator) and extinguish the generator field. The protection action to stop the unit is allowed.

3.2.85. Protection against earth faults at one point of the excitation circuit must be provided for hydro generators, turbo generators with water-cooled rotor windings and all turbo generators with a capacity of 300 MW and above. On hydrogenerators, the protection should act on shutdown, and on turbogenerators - on a signal.

Protection against earth faults at the second point of the excitation circuit of turbogenerators must be installed on units with a power of less than 160 MW in accordance with 3.2.48.

3.2.86. On units with turbogenerators with a capacity of 160 MW or more, having direct cooling of the winding conductors, and with hydrogenerators, protection devices against asynchronous operation with loss of excitation should be provided.

These devices are also recommended for use on turbogenerators with a power of less than 160 MW with direct cooling of the winding conductors. On these turbogenerators, it is also allowed to provide for automatic detection of the asynchronous mode only by the disabled position of the automatic field damping devices (without the use of protection against the asynchronous mode).

When transferring a turbogenerator that has lost excitation to asynchronous mode, the above protection devices or automatic field damping should act on the signal of loss of excitation and automatically switch the auxiliary load in the branch of the unit whose generator has lost excitation to a backup power source.

All hydrogenerators and turbogenerators that do not allow asynchronous operation, as well as other turbogenerators in conditions of a shortage of reactive power in the system under the action of these devices, must be disconnected from the network.

3.2.87. If there is a circuit breaker in the generator circuit with direct cooling of winding conductors, redundancy should be provided in case of failure of this circuit breaker (for example, using breaker failure).

3.2.88. The breaker failure level of 110 kV and above at power plants must be carried out taking into account the following:

1. In order to prevent unnecessary shutdown of several backup protection units in the event of an open-phase mode on one of them as a result of a failure of a circuit breaker with a single-phase drive when it is turned off at power plants with generators that have direct cooling of the winding conductors, an accelerated launch of the breaker must be provided (for example, from the zero-sequence current protection of the unit transformer from the network side with a large earth fault current).

2. For power plants where the generator-transformer units and the lines have common switches (for example, when using a one-and-a-half scheme or a polygon scheme), it is necessary to provide a teleswitching device to turn off the switch and prohibit automatic reclosure at the opposite end of the line under the action of the breaker failure if it is started from the unit protection. In addition, the action of the breaker failure to stop the high-frequency protection transmitter should be provided.

3.2.89. When the protection of the stator of the generator and the transformer of the unit against internal damage, as well as the protection of the generator rotor, is acted upon, the damaged element must be disconnected from the network, the generator and exciter fields must be extinguished, the breaker start and the technological protections must be affected.

If a trip from the protection results in a de-energization of the auxiliary load connected by a branch to the unit, the protection must also act to open the circuit breakers in the working auxiliary power supply circuit in order to transfer them to the backup source using the ATS.

Backup protections of the generator and transformer of the unit in case of external damages shall operate in accordance with 3.2.81, paragraph 2-4.

At thermal power plants with a block diagram in the thermal part, in cases of shutdown of the unit due to internal damage, a complete shutdown of the unit must be ensured. In case of external damages, as well as under the action of protections in cases where the operation of the unit can be quickly restored, the unit must be switched to idle mode, if this mode is allowed by thermal and mechanical equipment.

At hydroelectric power plants, in case of internal damage to the unit, in addition to shutting down the unit, the unit must be stopped. The action to stop the unit can also be carried out when the unit is turned off as a result of external damage.

3.2.90. On the generator - transformer - line units, the main line protection and backup protection from the power system side must be performed in accordance with the requirements of this chapter on line protection, and from the side of the unit, the backup line protection functions must be performed by the backup protection of the unit.

The protection of the unit must be performed according to the above requirements.

The action of the block protection to open the circuit breaker and start the breaker from the side of the power system must be transmitted using two mutually redundant teledisconnect devices via a high-frequency channel or via communication wires. In addition, it is recommended to provide for the simultaneous action of the block protection to stop the high-frequency protection transmitter.

On units with turbogenerators (with a block diagram in the thermal part), from the side of the power system, the busbar protection action (with a double busbar system) or the breaker failure action (with a one-and-a-half circuit or a polygon circuit) must be transferred from the power system using a teleswitching device to the opposite end of the line, respectively, to transfer the unit to idle mode or to extinguish the generator field and stop the unit. In addition, it is recommended to use a teleswitching device to accelerate the extinguishing of the generator field and shutdown of auxiliary needs when backup protections are in place on the part of the power system.

In case of non-full-phase disconnection of the circuit breaker from the side of the network with a large earth fault current, an accelerated launch of the breaker shall be carried out in the same way as provided for in 3.2.88, paragraph 1.

See other articles Section Rules for the installation of electrical installations (PUE).

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