Areva MiCOM P125, Техническое руководство

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Application Guide P12y/EN AP/D32
MiCOM P125/P126 & P127 Page 49/74
5.3.2 Example Setting
The following information was recorded by the relay during commissioning:
full load = 500A
I2 = 50A
therefore the quiescent ratio for I2/I1 is given by:
I2/I1 = 50/500 = 0.1
To allow for tolerances and load variations a setting of 200% of this value may be typical:
Therefore set RATIO I2/I1 = 20%
Set tBC = 60 s to allow adequate time for short circuit fault clearance by time delayed
protections.
5.4 Cold Load Pick-up (P126 & P127)
The Cold Load Pick-up feature enables the selected settings of the MiCOM P126 and P127
relays to be changed to react to temporary overload conditions that may occur during cold
starts.
This condition may occur by switching on large heating loads after a sufficient cooling period,
or loads that draw high initial starting currents.
When a feeder is energised, the current levels that flow for a period of time following
energising may differ greatly from the normal load levels. Consequently, overcurrent settings
that have been applied to give short circuit protection may not be suitable during this period.
The Cold Load Pick-up (CLP) logic included in the MiCOM P126 & P127 relays raises the
settings of selected stages for a set duration. This allows the protection settings to be set
closer to the load profile by automatically increasing them after energising. The CLP logic
provides stability, without compromising protection performance during starting.
Cold Load Pick-up (CLP) setting is described in the Technical Data (TD), the CLP menu in
the User Guide (FT).
The timer tCL in the CLP menu controls the time for which the relevant protections elements
in CLP menu (%) are altered following an external input signal (e.g. circuit breaker closure.
When the set tCL time has elapsed, all of the relevant settings revert back to their original
values or become unblocked.
tCL is initiated via a dedicated logic input signal (refer to AUTOMAT. CTRL/INPUTS menu),
generated by connecting an auxiliary contact from the circuit breaker (52a or 52b) or starting
device to the logic relevant inputs of the relay.
The following sections describe applications where the CLP logic may be useful and the
settings that need to be applied.
5.4.1 Air Conditioning / Resistive Heating Loads
Where a feeder is used to supply air conditioning or resistive heating loads there may be a
conflict between the "steady state" overcurrent settings and those required following
energizing. This is due to the temporary increase in load current that may arise during
starting.
With the Cold Load Pick-up function enabled, the affected thresholds are selected to be
adjusted for the required time to allow the start condition to subside. A percentage value is
selected as the amount by which the selected threshold is increased or decreased.
The time for which the adjusted thresholds are valid is defined by the tCL setting. After this
time, the settings return to normal.
It may not be necessary to alter the protection settings following a short supply interruption.
In this case the CLP function is not activated.