Construction of substation 220 kV Lafarge. Volume 2. Relay protection and automation, страница 13

-     breaker failure protection that switches off circuit breakers at the input and sectionalising switch cabinet. Overcurrent protection

Overcurrent protection is connected to the current transformers at the input cabinet.

Two-stage overcurrent protection:

- first stage is a current cutoff, does not have any time delay;

- second stage has independent time delay, which can be regulated in range (0,1-10) seconds.

Overcurrent protection should have operating current setting, regulated in range (0,4-12) ∙Inom А.

Overcurrent protection starts breaker failure protection and switches off a circuit breaker.

Logical busbar protection blocks the overcurrent protection at the terminals of input cabinets when receives a signal (overcurrent protection) from feeder line terminals of switchgear 35 kV

There must be an acceleration of the protection (second stage) during manual (remote or local) switching on the circuit breaker. Acceleration of the protection is introduced for the time, which should be regulated in the range (0-1,5) second. Accelerated stage should not react to magnetizing inrush of power transformer.

 One-phase earth-fault protection

Protection connects to zero-sequence current transformer.

Range of used frequencies of high harmonics (150-1000) Hz.

Protection must not react to the currents of high harmonics in transient state.

Protection operates to switch off the circuit breaker. Breaker failure protection

Breaker failure protection operates when any stage of current protection starts.

Operating current range of protection should be within the limits (0,25-2,5) A.

Reset ratio of the current body of breaker failure protection should be at least 0,9.

The operating time of the current body of breaker failure protection must not exceed 0.03 in case when the input current is twice higher than operating current.

The return time of the current body with input current reset from 30 ∙ Is.r to zero should not exceed 0.03 s.

Breaker failure protection should have two-step operation:

- switching off circuit breaker of a feeder line without any time delay;

- switching off circuit breaker at an input cabinet and sectionalising switch cabinet.

Breaker failure protection direct time should be regulated in the range (0,1–0,6) sec.

4.2.4. Relay protection and automation at a voltage transformer cabinet at a busbar 35 kV

Voltage transformer cabinet of each section should have:

- undervoltage control at a busbar section for automatic load transfer;

- voltage control at a busbar section for automatic load transfer;

- operability control of a voltage transformer;

- earth-fault alarm;

- arc protection at voltage transformer cabinets that switches off circuit breakers at an input and sectionalising switch cabinets. Voltage and undervoltage control of switchgear busbars 35 kV

Requirements for these functions shall meet the requirements in Operability control of a voltage transformer

Operability control is connected to a voltage transformer of its section and should have ability to measure or calculate direct and negative sequence voltages.

Operability control should feel, if possible, faults both in primary and secondary circuits.

Operability control should operate on a signal with a time delay, regulated in range (0,1-10) seconds.

Requirements for this function shall meet the requirements in

4.2.5. Arc protection of the switchgear 35 kV

Protection use sensors that are sensitive to short-circuit current when arc presented in any switchgear compartment.

Type of sensor and its location depends on manufacturer of the switchgear.

Operating time of arc sensors should be no more than 0,05 seconds.

The liquidation time of arc circuit, including switching off the circuit breaker, should be no more than 0,2 sec.

Arc protection must have current check:

-  for input cabinets – overcurrent protection of LV side of the transformer;

-  for feeder lines – overcurrent protection of input and sectionalizing switch;