Cold Load Protection
51 elements are affected by the setting of the
51CL Cold Load
function.
51CL can be configured for any
51 Time-Delayed Overcurrent
element to automatically apply modified
settings following a CB close after an extended open state to pick up
Cold Load
at an elevated level which
could exceed the normal protection tripping level and then revert to normal settings after a configurable
period of time or if the load current reduces to below a set level.
The setting of each shaped overcurrent element (51-n) can be inhibited and alternative
Cold Load
settings
can be applied for a period following circuit switch in.
During
Cold Load
settings conditions any directional settings applied in the phase overcurrent menu are still
applicable.
A CB
Don’t Believe It
(DBI) condition is not acted on, causing the element to remain operating in accord-
ance with the relevant 51-n settings. Where the
Reduced Current
setting is disabled, reversion to 51-n
settings will only occur at the end of the
Drop-off
time. If any element is picked up on expiry of
Drop-off
time, the relay will issue a trip and lockout.
If the circuit-breaker is re-opened before expiry of the
Drop-off
time, the drop-off timer is held but not reset.
Resetting the timer for each trip could result in damaging levels of current flowing for a prolonged period
during a rapid sequence of trips/closes.
Cold load trips use the same binary output(s) as the associated 51-n element.
Protection and Automation Functions
5.14 51 Time-Delayed Overcurrent – Phase
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