Woodward HighPROtec MCDLV4, Manual

Page: 774 / 1275

Protective Elements
CLPU - Cold Load Pickup
Available Elements:
CLPU
When the electric load is freshly started or restarted after a prolonged outage, the load current tends to have a
temporary surge that could be several times the normal load current in magnitude due to motor starting. This
phenomena is called cold load inrush. If the overcurrent pickup threshold is set according to the maximum possible
load inrush, the overcurrent protection may be insensitive to some faults, thus making whole protection systems
coordination difficult or even impossible. On the other hand, the overcurrent protection could trip on load inrush if it
is set based on the fault current studies. The
CLPU module is provided to generate a temporary
blocking/desensitizing signal to prevent overcurrent protections from unwanted tripping. The cold load pickup
function detects a warm-to-cold load transition according to the four selectable cold load detection modes:
•
CB POS (Breaker state);
•
I< (Undercurrent);
•
CB POS AND I< (Breaker state and undercurrent); and
•
CB POS OR I< (Breaker state OR undercurrent).
After a warm-to-cold load transition has been detected, a specified load-off timer will be started. This User-settable
load-off timer is used in some cases to make sure that the load is really “cold” enough. After the load-off timer times
out, the CLPU function issues an “enable” signal »CLPU.
ENABLED
« that can be used to block some sensitive
protection elements like instantaneous overcurrent elements, current unbalance, or power protection elements at
User´s choice. Using this enable signal, some time inverse overcurrent elements may also be desensitized at the
User's choice by means of activating adaptive settings of the corresponding overcurrent elements.
When a cold load condition is finished (a cold-to-warm load condition is detected) due to, for example, breaker
closing or load current injection, a load inrush detector will be initiated that supervises the coming and going of the
load inrush current process. A load inrush is detected if the coming load current exceeds a User-specified inrush
current threshold. This load inrush is considered as finished if the load current is decreased to 90% of the inrush
current threshold. After the inrush current is diminished, a settle timer starts. The cold load pickup enable signal
can only be reset after the settle timer times out. Another max-Block timer, which is started parallel with the load
inrush detector after a cold load condition is finished, may also terminate the CLPU enable signal if a load inrush
condition is prolonged abnormally.
The cold load pickup function can be blocked manually by external or internal signal at the User´s choice. For the
devices with Auto-Reclosing function, the
CLPU function will be blocked automatically if auto-reclosure is initiated
(AR is running).
This module issues a signal only (it is not armed).
In order to influence the tripping settings of the overcurrent protection, the
User has to assign the signal “CLPU
.
ENABLED
“ to an adaptive parameter set.
Please refer to the Parameter / Adaptive Parameter Sets section. Within the
adaptive parameter set, the User has to modify the tripping characteristic of
the overcurrent protection according to the needs.
774 MCDLV4 DOK-HB-MCDLV4-2E