Busbar protection, protection at bypass, bus coupler and sectionalizers

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

Relay protection. Busbar protection, protection at bypass, bus coupler and sectionalizers

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

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3.2.119. For busbars 110 kV and higher at power plants and substations, separate relay protection devices must be provided:

1) for two bus systems (double bus system, one and a half scheme, etc.) and a single sectioned bus system;

2) for a single non-partitioned busbar system, if the shutdown of faults on the busbars by the action of the protection of the connected elements is unacceptable under conditions that are similar to those given in 3.2.108, or if there are branches on the lines supplying the busbars in question.

3.2.120. For 35 kV busbars of power plants and substations, separate relay protection devices must be provided:

under the conditions given in 3.2.108;
for two busbar systems or sections, if when using for their separation the protection installed on the bus-coupling (sectional) switch, or the protections installed on the elements that feed these busbars, the requirements for consumer power supply reliability are not met (taking into account the capabilities provided by automatic reclosing devices and AVR).

3.2.121. As a protection for busbars of power plants and substations of 35 kV and above, as a rule, differential current protection without time delay should be provided, covering all elements that are connected to the system or busbar section. Protection should be carried out using special current relays, detuned from transient and steady unbalance currents (for example, relays connected through saturable current transformers, relays with braking).

When connecting a transformer (autotransformer) of 330 kV and higher through more than one switch, it is recommended to provide for differential current protection of the busbar.

3.2.122. For double busbar systems of power plants and substations of 35 kV and above with one circuit breaker per connected element, differential protection must be provided in the version for a fixed distribution of elements.

In the protection of busbars 110 kV and above, it should be possible to change the fixation when transferring the connection from one busbar system to another on the rows of clamps.

3.2.123. The differential protection specified in 3.2.121 and 3.2.122 must be implemented with a device for monitoring the health of the secondary circuits of the involved current transformers, acting with a time delay to disable the protection and signal.

3.2.124. For sectioned buses of 6-10 kV power plants, a two-stage incomplete differential protection should be provided, the first stage of which is made in the form of a current cutoff for current and voltage or distance protection, and the second - in the form of overcurrent protection. The protection should act to turn off the supply elements and the auxiliary transformer.

If the specified performance of the second stage of protection does not provide the required sensitivity in case of short circuit at the end of the supplied reactive lines (the load on the generator voltage buses is large, the switches of the supplied lines are installed behind the reactors), it should be performed in the form of separate sets of overcurrent protections with or without voltage start installed in reactor circuits; the effect of these kits on disconnecting the supply elements must be controlled by an additional device that operates when a short circuit occurs. In this case, the sectional switch must be provided with protection (designed to eliminate damage between the reactor and the switch), which is put into effect when this switch is turned off. When allocating part of the supply elements to the redundant busbar system, incomplete differential busbar protection in the design for a fixed distribution of elements should be provided.

If frequent operating modes are possible with the separation of the supply elements into different busbar systems, it is allowed to provide separate distance protections installed on all supply elements, except for generators.

3.2.125. For sectioned tires 6-10 kV of power plants with generators with a capacity of 12 MW or less, it is allowed not to provide special protection; in this case, the elimination of a short circuit on the tires should be carried out by the action of the maximum current protections of the generators.

3.2.126. Special relay protection devices for single sectioned and double busbar systems of 6-10 kV step-down substations, as a rule, should not be provided, and the elimination of short circuits on the buses should be carried out by the action of transformer protection against external short circuits and protections installed on the sectional or bus-coupling switch. In order to increase the sensitivity and speed up the protection of busbars of powerful substations, it is allowed to use protection included in the sum of the currents of the supply elements. In the presence of reactors on lines extending from substation buses, it is allowed to protect the tires by analogy with the protection of power plant buses.

3.2.127. If there are current transformers built into the circuit breakers, for the differential protection of the busbars and for the protection of connections extending from these busbars, current transformers located on different sides of the circuit breaker must be used so that the faults in the circuit breaker are included in the coverage of these protections.

If the circuit breakers do not have built-in current transformers, then for the sake of economy, remote current transformers should be provided only on one side of the circuit breaker and installed, if possible, so that the circuit breakers are included in the zone of operation of the busbar differential protection. At the same time, in the protection of a double busbar system with a fixed distribution of elements, the use of two cores of current transformers in the circuit of a bus coupling circuit breaker must be provided.

When using separate distance protections as busbar protection, the current transformers of these protections in the circuit of the sectional switch must be installed between the busbar section and the reactor.

3.2.128. Busbar protection should be carried out in such a way that when testing a damaged system or busbar section, selective shutdown of the system (section) without time delay is ensured.

3.2.129. On a bypass switch of 110 kV and above, in the presence of a bus-connecting (sectional) switch, protection must be provided (used when checking and repairing protection, a switch and current transformers of any of the elements connected to the tires:

three-stage remote protection and current cutoff from multi-phase short circuits;
four-stage current directional zero-sequence earth fault protection.

At the same time, protections must be provided on the bus-connecting (sectional) switch (used to separate systems or bus sections in the absence of breaker failure or to disable it or bus protection, as well as to increase the efficiency of long-range redundancy):

two-stage current protection against multi-phase short circuits;
three-stage zero sequence current protection against earth faults.

It is allowed to install more complex protections on the bus-coupling (sectional) switch, if this is required to improve the efficiency of long-range redundancy.

On the bus-coupling (sectional) circuit breaker 110 kV and above, which is also intended to perform the function of a bypass switch, the same protections must be provided as on the bypass and bus-coupling (sectional) circuit breakers when they are separate.

It is recommended to provide for the transfer of the main high-speed protection lines of 110 kV and above to a bypass switch.

On the bus-connecting (sectional) circuit breaker 3-35 kV, a two-stage current protection against multi-phase short circuits must be provided.

3.2.130. A separate protection panel, designed specifically for use instead of a line that is displayed for protection testing, should be provided for electrical connection diagrams in which there is no bypass switch (for example, a quadrilateral, one and a half circuit, etc.); such a separate protection panel should be provided for 220 kV lines that do not have a separate main protection; for lines 330-500 kV.

It is allowed to provide a separate protection panel for 110 kV lines that do not have a separate main protection, with electrical connection schemes "bridge" with switches in the circuits of the lines and "polygon", if, when checking the protection of the line, eliminate damage on it in accordance with the requirements by simpler means technically impossible.

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

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