P54x/EN AP/La4 Application Notes
(AP) 6-22
MiCOM P543, P544, P545 & P546
AP
2.3.13.1 Recommended polarizing settings (Distance option only)
Cable applications
- In line with LFZP123 or LFZR applications for cable feeders,
use only minimum 20% (0.2) memory, which results in
minimum mho expansion. This keeps the protected line
section well within the expanded mho, thereby ensuring
better accuracies and faster operating times for close-up
faults.
Series compensated lines
- Use a mho with maximum memory polarizing (setting = 5).
The large memory content will ensure correct operation even
with the negative reactance effects of the compensation
capacitors seen either within Zs, or within the line
impedance.
Short lines
- For lines shorter than 10 miles (16 km), or with an SIR higher
than 15, use maximum memory polarizing (setting = 5). This
ensures sufficient characteristic expansion to cover fault arc
resistance.
General line applications
- Use any setting between 0.2 and 1.
2.3.14 Distance elements basic scheme setting (Distance option only)
The Zon
e 1
time delay (tZ1) is generally set to zero, giving instantaneous operation.
The Zone 2
time delay (tZ2) is set to co-ordinate with zone 1 fault clearance time for
adjacent lines. The total fault clearance time will consist of the downstream zone 1 operating
time plus the associated breaker operating time. Allowance must also be made for the zone
2 elements to reset following clearance of an adjacent line fault and also for a safety margin.
A typical minimum zone 2 time delay is of the order of 200 ms.
The Zone 3
time delay (tZ3) is typically set with the same considerations made for the zone
2 time delay, except that the delay needs to co-ordinate with the downstream zone 2 fault
clearance. A typical minimum zone 3 operating time would be in the region of 400 ms.
The Zone 4
time delay (tZ4) needs to co-ordinate with any protection for adjacent lines in the
relay’s reverse direction.
Note (1): The MiCOM P54x allows separate time delays to be applied to both
phase and ground fault zones, for example where ground fault delays
are set longer to time grade with external ground/earth overcurrent
protection.
Note (2): Any zone (“#”) which may reach through a power transformer
reactance, and measure secondary side faults within that impedance
zone should have a small time delay applied. This is to avoid tripping
on the inrush current when energizing the transformer. As a general
rule, if: Z# Reach
setting
> 50% X
T
transformer reactance, set: tZ#
100 ms. Alternatively, the 2
nd
harmonic detector that is available in
the Programmable Scheme Logic may be used to block zones that
may be at risk of tripping on inrush current. Settings for the inrush
detector are found in the SUPERVISION menu column.
To Next Page
Loading...
