Schweitzer Engineering Laboratories SEL-701, Instruction Manual

Page: 269 / 468

Date Code 20010719
701 Motor Protection Relay
SEL
OGIC®
Control Equations & Relay Logic
Stop/Trip Logic
B.21
The relay automatically locks out the motor by asserting the trip signal under any
of the following conditions:
Antibackspin Lockout. The antibackspin timer has not expired since
the motor trip occurred. The trip signal is maintained until the
antibackspin timer expires.
Minimum Time Between Starts Lockout. A new start is not
permitted until after the minimum time between starts has passed.
The trip signal is maintained until a start is permitted.
Starts-Per-Hour Limit Lockout. If the starts-per-hour limit has
been met, a new start is not permitted until 60 minutes after the oldest
start. The trip signal is maintained until a start is permitted.
Thermal Element Lockout. The motor thermal element % Thermal
Capacity value is too high to permit a normal motor start without
tripping. The trip signal is maintained until the % Thermal Capacity
decreases to a level where a start can safely take place.
If any of the above protection functions is not enabled by the relay settings, that
function does not affect trip unlatch.
Also note that the relay automatically asserts the trip signal if the motor stops and
a lockout condition is true. The trip signal is maintained until all the enabled motor
lockout conditions are satisfied.
Trips initiated by the STOP command, the front-panel Stop Motor function, or by
Modbus operation are maintained for at least the duration of the Minimum Trip
Duration Time (TDURD) setting.