DPR-400 User Manual Rev_01 Firmware V-1.0
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Cold load pickup operation is used to prevent unwanted conditions while energizing after long duration
power losses. Temporary pulse currents which exceed protection threshold values may be formed when
restoring power, depending on the characteristics of the network’s load. These current transients may be
due to the following reasons:
- Pulse magnetization currents of transformers
- Starting currents of asynchronous motors
- Collective activation of air conditioning of heating loads
Protections should normally be configured so as not to trip the breaker in similar transient situations.
However, configuring the protection functions to consider such transient current fluctuations will not
always be possible as it will require setting very high values or very long timers. Instead, cold load pickup
will temporarily inhibit protection threshold values to prevent faulty breaker trips.
On the field, long term loads which are not high enough to trip cause faults and heating in the wires. The
amount of heating can be calculated using formulas which are determined by network characteristics,
current flow, and time. According to the IEC 60255-8 standard, this thermal loading can be calculated as
follows:
Here;
t → Time remaining for protection at given current value
Te → Thermal constant coefficient, entered as a parameter
I → Maximum phase current
Iflc → Current threshold, entered as a parameter
K → 1.05 constant, continuous operation permitted up to 105% of Iflc
Ip → Stable current value before going into overload
The controller offers 2 levels of under voltage protection. These protections can be configured as phase-
phase as well as phase-neutral. In addition, protection may be desired if any or all of the three phases are
below the threshold value. Voltage protections can be disabled if breaker is open or the voltage and
current values of one phase are simultaneously zero. Protections can be configured as constant timer or
variable timer.
The controller offers 2 levels of high voltage protection. These protections can be configured as phase-
phase as well as phase-neutral. In addition, protection may be desired if any or all of the three phases are
above the threshold value. Protections can be configured as constant timer or variable timer.
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