I.L. 40-201.9
Power Automation and Protection Division
5-8
REL 352 Version 1.00
7.
ZONE 2 AND ZONE 3 SETTINGS
Settings for Zone 2 and Zone 3 protective systems are similar. Application of the distance units
follow the standard application for a conventional step distance, non-pilot relaying system.
The impedance units are always to be used as time delayed Zone 2 and Zone 3 protective
zones.
Following the traditional step distance, Zone 2 is set to under-reach any Zone 1 covering the
adjacent lines coming out of the remote terminal, if possible. It is also expected that Zone 2 will
always cover at least 100 percent of the protected line plus 10 percent of the shortest adjacent
line under all operating conditions.
Zone 2 timers, for phase and ground, should be set to coordinate with the forward and reverse
adjacent high speed trips. Moreover, the timer should include the breaking time of the slowest
adjacent breaker and a tolerance of two to three cycles. Typical Zone 2 timers range between
0.2 to 0.3 seconds.
For Zone 3, it is recommended to be set under-reaching any Zone 2 from the remote terminal,
if possible. Zone 3 should include at least 100 percent of the protected line plus 100 percent
of the adjacent shortest line plus 10 percent of the next shortest line.
Zone 3 timers, for phase and ground, should be set to coordinate with the forward and reverse
adjacent Zone 2 trips. Generally two times the Zone 2 timer may be chosen for the Zone 3 timer
setting. Zone 3 timer ranges between 0.4 and 0.6 seconds.
Applicable parameters and settings for the characteristics of the zones have been discussed
already. These are the PANG, GANG and ZR settings discussed in previous paragraphs since
they are commonly used in other parts of the relay algorithms, for example the fault locator.
Ground units in both zones have a forward (ZGf) and a reverse (ZGr) reach. Therefore, phase
to ground, three phase and some phase to phase to ground faults have a forward and a reverse
reach.
The phase to phase unit in REL 352 has only a forward reach (ZP). This unit is inherently di-
rectional and its characteristics, which are dependent on the source impedance. This implies
that all phase to phase and some phase to phase to ground faults have a forward reach only
determined by the phase to phase unit.
7.1
Zone 2 phase unit reach (Z2P)
This setting controls the Zone 2 reach for phase to phase faults in secondary ohms. It is always
forward looking.
For Example:
If Z2 reach is 30 ohms at 75
°
, set Z2P = 30.
7.2
ZONE-2 PHASE TIMER (T2P)
Selects the time delay for Zone 2 Phase fault detection in seconds. Set T2P = 0.15 if the mini-
mum time delay for step distance coordination is 150 milliseconds.
