P54x/EN OP/La4 Operation
(OP) 5-124
MiCOM P543, P544, P545 & P546
OP
3. OPERATION OF NON PROTECTION FUNCTIONS
The protection functionality of the P543, P544, P545, and P546 are very similar, and a
common operational description can be applied. For the non-protection functions, some of
the functionality is the same and, similarly, a common operational description can be applied.
The principal difference between different models is that the P543 and P545 can control only
a single circuit breaker,, whereas the P544 and P546 can control two.
For this reason, the circuit breaker monitoring and control software differs between the
P543/P545 and the P544/P546, and a common operational description cannot be applied.
This section describes the operation of the non-protection functions common to all models
and that are not associated with circuit breaker monitoring and control.
Separate sections are assigned to describe the P543/P545 operational control of a single
circuit breaker, and the P544/P546 operational control of dual circuit breakers.
3.1 Voltage transformer supervision - fuse fail
The volta
ge transformer supervision (VTS) feature is used to detect failure of the ac voltage
inputs to the relay. This may be caused by internal voltage transformer faults, overloading,
or faults on the interconnecting wiring to relays. This usually results in one or more VT fuses
blowing. Following a failure of the ac voltage input there would be a misrepresentation of
the phase voltages on the power system, as measured by the relay, which may result in
maloperation.
The VTS logic in the relay is designed to detect the voltage failure, and automatically adjust
the configuration of protection elements whose stability would otherwise be compromised. A
time-delayed alarm output is also available.
A setting VTs Connected Yes/No (Voltage transformers connected to the relay) under
CT AND VT RATIOS will:
When set to yes this setting will have no effect.
When set to No it causes the VTS logic to set the VTS Slow Block and VTS Fast Block
DDBs, but not raise any alarms. It will also override the VTS enabled setting should the user
set it. The effect of this is to stop the pole dead logic working incorrectly with the presence of
no voltage and no current but not the CB open part of the logic and also block the distance,
under voltage and other voltage dependant functions.
VTS can be declared by a mini circuit breaker (MCB) status input, by an internal logic using
relay measurement or both. A setting VTS Mode (Measured + MCB /Measured Only/MCB
Only) is available to select the method to declare VT failure.
For the measured method, there are three main aspects to consider regarding the failure of
the VT supply. These are defined below:
1. Loss of one or two phase voltages
2. Loss of all three phase voltages under load conditions
3. Absence of three phase voltages upon line energization
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