Application Notes; Clp For Resistive Loads; Clp For Motor Feeders; Clp For Switch Onto Fault Conditions - GE MiCOM P40 Agile Technical Manual

P14D
The CLP Operation signal indicates that CLP logic is in operation. This only happens when CLP is enabled AND CLP
is initiated either externally or from a CB Open condition after the tcold period has elapsed. The CLP Operation
indicator goes low when CLP is disabled or when the external CLP trigger is removed or when there is a CB closed
condition.
tcold and tclp are initiated via the CB open and CB closed signals generated within the device. These signals are
produced by connecting auxiliary contacts from the circuit breaker or starting device to the IED's opto-inputs
If dual CB contacts are not available (one for Open (52a) and for Close (52b)) you can configure the device to be
driven from a single contact (either 52a or 52b). The device would then simply invert one signal to provide the
other. This option is available using the CB status input cell in the CB CONTROL column. The setting can be set to
None, 52a, 52b or 52a and 52b.
9.3

APPLICATION NOTES

9.3.1

CLP FOR RESISTIVE LOADS

A typical example of where CLP logic may be used is for resistive heating loads such as such as air conditioning
systems. Resistive loads typically offer less resistance when cold than when warm, hence the start-up current will
be higher.
To set up the CLP, you need to select Enable from the I> status option to enable the settings of the temporary
current and time settings. These settings should be chosen in accordance with the expected load profile. Where it
is not necessary to alter the setting of a particular stage, the CLP settings should be set to the same level as the
standard overcurrent settings.
It may not be necessary to alter the protection settings following a short supply interruption. In this case a suitable
tcold timer setting can be used.
9.3.2

CLP FOR MOTOR FEEDERS

In general, a dedicated motor protection device would protect feeders supplying motor loads. However, if CLP logic
is available in a feeder device, this may be used to modify the overcurrent settings during start-up.
Depending on the magnitude and duration of the motor starting current, it may be sufficient to simply block
operation of instantaneous elements. If the start duration is long, the time-delayed protection settings may also
need to be raised. A combination of both blocking and raising of the overcurrent settings may be adopted. The CLP
overcurrent settings in this case must be chosen with regard to the motor starting characteristic.
This may be useful where instantaneous earth fault protection needs to be applied to the motor. During motor
start-up conditions, it is likely that incorrect operation of the earth fault element would occur due to asymmetric
CT saturation. This is due to the high level of starting current causing saturation of one or more of the line CTs
feeding the overcurrent/earth fault protection. The resultant transient imbalance in the secondary line current
quantities is therefore detected by the residually connected earth fault element. For this reason, it is normal to
either apply a nominal time delay to the element, or to use a series stabilising resistor.
The CLP logic may be used to allow reduced operating times or current settings to be applied to the earth fault
element under normal running conditions. These settings could then be raised prior to motor starting, by means of
the logic.
9.3.3

CLP FOR SWITCH ONTO FAULT CONDITIONS

In some feeder applications, fast tripping may be required if a fault is already present on the feeder when it is
energised. Such faults may be due to a fault condition not having been removed from the feeder, or due to
earthing clamps having been left on following maintenance. In either case, it is desirable to clear the fault
condition quickly, rather than waiting for the time delay imposed by IDMT overcurrent protection.
The CLP logic can cater for this situation. Selected overcurrent/earth fault stages could be set to instantaneous
operation for a defined period following circuit breaker closure (typically 200 ms). Therefore, instantaneous fault
clearance would be achieved for a switch onto fault (SOTF) condition.
P14D-TM-EN-8
Chapter 6 - Current Protection Functions
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