Schweitzer Engineering Laboratories SEL-352-1 - Lockout Relay Control

Date Code 20010731 Close Logic 4-17
SEL-352-1, -2 Instruction Manual
Our example uses Scheme 1 because of the lack of margin between the first attempt at tripping
the breaker and the breaker failure timer. A two-cycle breaker with a four-cycle breaker failure
setting does not leave enough time to initiate a time-delayed retrip. In our example, the
instantaneous retrip could be a completely redundant trip coil and circuit. Use time-delayed
retripping if there is adequate margin between the first trip and breaker failure tripping. If there
is not enough margin, use instantaneous retripping.
LOCKOUT RELAY CONTROL
Application Description
After detecting a breaker failure condition, all adjacent breakers must open to clear the fault if
one existed, the breaker must be isolated, and then the system must be restored appropriately.
There are many methods for accomplishing this, but two examples follow:
Example 1
1. Relay trips all adjacent breakers through a lockout auxiliary relay
2. Operator isolates the failed breaker with manual disconnects
3. Operator manually resets the lockout relay
4. Operator restores the system by closing breakers
Example 2
1. Relay trips all adjacent breakers through a lockout auxiliary relay
2. Relay trips motor-operated disconnects to isolate the breaker
3. Relay electrically resets the lockout relay
4. Automated reclosing restores the system
The two examples describe a range of control from a mostly manual system to a fully automated
system. The SEL-352 Relay lockout relay control supports either of these schemes and
variations of these schemes. To modify Scheme 1 or 2 for your application, use the SET
command.
Operating Characteristic
Lockout relay trip and reset logic is provided for installations with and without automatic
breaker isolation schemes.
Use Scheme 1 (Figure 4.12) for breaker failure tripping and “Safe to Reset Lockout Relay”
conditions.
Use Scheme 2 (Figure 4.14) to automatically isolate the failed breaker with motor-operated
disconnects (MOD). The SEL-352 Relay trips the MOD when current drops below a settable
threshold. This scheme also can be used to indicate “Safe to Disconnect” conditions for manual
disconnect switches.