- without any time delay: switching off the circuit breaker at the input cabinet;
- with a time delay: switching off the transformer and blocking auto-reclosing.
Breaker failure protection time delay should have regulation in the range (0,1–0,6) seconds.
4.2.2. Relay protection of busbar sectionalising switch 35 kV
Protections of sectionalising switch 35 kV:
- overcurrent protection with logical busbar protection;
- arc protection at the feeder line cabinets that switches off the circuit breaker at sectionalising switch cabinet and arc protection at the sectionalising switch cabinet that switches off the circuit breaker at the input cabinet;
- automatic load transfer (when the level voltage on one of the busbars drops);
22.214.171.124. Overcurrent project of busbar sectionalising switch 35 kV
Overcurrent protection should be connected to the current transformers at the sectionalising switch of switchgear 35 kV.
Logical busbar protection:
- blocks the overcurrent protection at the terminals of sectionalising switch cabinets when receives a signal (overcurrent protection) from feeder line terminals of switchgear 35 kV.
- sends a signal from sectionalising switch terminal (overcurrent project) to block overcurrent protection at the terminals of input cabinets 35 kV.
Overcurrent protection should have current operation setting which can be regulated in the range (0,4-12)∙Inom А.
Overcurrent protection should operate to switch the circuit breaker with time delay which should be regulated in the range (0-10) sec, breaker failure protection.
There must be an acceleration of the protection during the manual (remote or local) or automatic (automatic load transfer) 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.
126.96.36.199. Automatic load transfer of the switchgear 35 kV
Power lost on one of the busbars 35 kV should lead to switching off the circuit breaker at the input cabinet of this busbar and switching on the sectionalising switch.
The automatic load transfer for separate busbar needs: three-phase undervoltage control of this busbar, the voltage level control at the adjacent busbar, position (should be “off”) control of the circuit breaker at the input cabinet of this section, the absence control of “blocking auto-reclosing” signal from arc protection, overcurrent protection or breaker failure protection, overcurrent protection of the MV protections of the transformer T1(T2).
It shall be possible to restore automatically the original diagram (pre-damage condition).
Selector “on/off” of the automatic load transfer function should be in the sectionalising switchgear cabinet 35 kV.
Complete control of the undervoltage level at busbar includes undervoltage function which reacts to voltage between conductors Ubc drop and negative sequence voltage U2.
Complete control of the voltage level at busbar includes the overvoltage function which reacts to voltage between conductors Ubc and negative sequence voltage U2.
Regulation voltage range of undervoltage function:
- voltage between conductors (20 - 80) V;
- negative sequence voltage (6 - 24) V.
Regulation time delay range (0,2 - 10) sec.
Regulation voltage range of overvoltage function (80 - 110) V;
Reset ratio of undervoltage function should be no more than 1,05.
4.2.3. Relay protection of the feeder lines 35 кВ
Protections of feeder lines 35 kV:
- two-stage overcurrent protection, which contains current cutoff and overcurrent protection with automatic acceleration when switching on the transformer.
- arc protection at each feeder line cabinet of the switchgear 35 kV that switches off its own circuit breaker if electric arc presents in cable compartment. Arc protection that switches off the circuit breaker at sectionalising switch and input cabinet if electric arc presents in the circuit breaker or busbar compartment.
- one-phase earth-fault protection;
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