Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546
(OP) 5-89
OP
1.31.1 Directionalizing the negative phase sequence overcurrent element
Directionality is achieved by comparison of the angle between the negative phase sequence
voltage and the negative phase sequence current and the element may be selected to
operate in either the forward or reverse direction. A suitable relay characteristic angle
setting (2> Char Angle) is chosen to provide optimum performance. This setting should be
set equal to the phase angle of the negative sequence current with respect to the inverted
negative sequence voltage (– V2), in order to be at the center of the directional
characteristic.
For the negative phase sequence directional elements to operate, the relay must detect a
polarizing voltage above a minimum threshold, 2> V2pol Set. The logic diagram for
negative sequence overcurrent protection (shown with directional operation) is attached as
Figure 61 below.
CTS Block
I2> Start
I2> Timer Block
Current Above I2> Setting
I2> Protection Inhibit
&
P1605ENb
Directional Check
I2> Trip
DT
0
Polarising Voltage Above V2> Setting
Slow VTS Block
&
&
Figure 61 Directionalizing the negative phase sequence overcurrent element
1.32 Undervoltage protection
Both the und
er and overvoltage protection functions can be found in the relay menu Volt
Protection. The measuring mode (ph-N or ph-ph) and operating mode (single phase or 3
phase) for both stages are independently settable.
Stage 1 may be selected as either IDMT, DT or Disabled, within the V<1 function cell.
Stage 2 is DT only and is enabled/disabled in the V<2 status cell.
Two stages are included to provide both alarm and trip stages, where required.
Alternatively, different time settings may be required depending upon the severity of the
voltage dip.
Outputs are available for single or three phase conditions via the V<Operate Mode cell.
When the protected feeder is de-energized, or the circuit breaker is opened, an undervoltage
condition would be detected. Therefore, the V<Polehead nh cell is included for each of the
two stages to block the undervoltage protection from operating for this condition. If the cell is
enabled, the relevant stage will become inhibited by the inbuilt pole dead logic within the
relay. This logic produces an output when it detects either an open circuit breaker via
auxiliary contacts feeding the relay opto inputs or it detects a combination of both
undercurrent and undervoltage on any one phase.
The IDMT characteristic available on the first stage is defined by the following formula:
t = K/(1 - M)
Where:
K = Time multiplier setting
t = Operating time in seconds
M = Measured voltage / relay setting voltage (V< Voltage Set)
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