Switchgear 35 kV is an metal-clad installation designed for indoor installation. The RPA complex of switchgear 35 kV shall be fully implemented with the use of MP devices. Below we consider the structure of protection and technical requirements for MP devices of the RPA complex which is used at next elements of switchgear 35 kV:
- inputs of busbars 35 кВ;
- busbar sectionalising switch 35 кВ;
- feeder lines 35 кВ;
- voltage transformers at busbars 35 кВ.
Suggested MP devices, in addition to the RPA functions, should have automatic control function of circuit breaker:
- remote (through PCS) and local control of circuit breakers 35 kV;
- remote control of position of all the switchgears (circuit breakers, earthing switches, etc.);
- remote control of serviceability of the control and protection circuits, and condition of the MP device;
- registration and transferring of digital and analog emergency signals through PCS;
- possibility of local and remote configuration and changing the settings.
4.2.1. Relay protection of inputs 35 kV
Protections of inputs 35 kV:
- overcurrent protection with logical busbar protection;
- undervoltage protection;
- arc protection at the input cabinets of switchgear 35 kV (with switching off the circuit breakers);
- breaker failure protection.
4.2.1.1. Overcurrent protection of inputs 35 kV
Overcurrent protection should be connected to the current transformers at the input cabinets of switchgear 35 kV.
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
Overcurrent protection of the inputs 35 kV should include voltage level check.
Overcurrent protection should have current operation setting which can be regulated in the range (0,4-12)∙Inom А.
Overcurrent protection has independent characteristic of time delay. Setting range (0-10) sec.
Overcurrent protection should have two time delays with independent regulation of each.
Overcurrent protection should act to:
- with the first time delay: switching off the circuit breaker (35 kV) and starting his breaker failure protection;
- with the second time delay: switching off the transformer (using output relays of the kit of transformer main protection) and starting breaker failure protection on the HV (220 kV) and MV (35 kV) sides of the transformer with the blocking auto-reclosing;
There must be an acceleration of the protection during the 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.
4.2.1.2. Undervoltage protection of inputs 35 kV
Undervoltage protection is connected to the voltage transformers of busbars 35 kV. The functions of putting undervoltage protection and automatic load transfer are presented in one switch.
Undervoltage protection controls:
- the absence of voltage at its busbar 35 kV;
- the absence of voltage at the adjacent busbar 35 kV;
- closed position of the cutout of the voltage transformer secondary circuits at its busbar.
Undervoltage protection switches off the circuit breaker at the input 35 kV at its busbar.
Range of time delays regulation of this protection is (1-20) sec.
4.2.1.3. Breaker failure protection of inputs 35 kV
Breaker failure protection starts with overcurrent protection operates.
Operate current of the breaker failure protection should be regulated in the range (0,25 – 2,5) А.
Reset ratio of the current body of breaker failure protection at any setting should be at least 0,9.
Operation time of the current body of breaker failure protection should be no more than 0,03 seconds in case when the current exceeds twice the value of the operation current.
The return time of the current body of breaker failure protection with input current reset from 30 ∙ Is.r to zero should not exceed 0.03 s.
Breaker failure protection should have two stages:
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