Page 51 - Energize June 2022

TECHNICAL

The interpretation of circuit breaker operations. The control relay is manually or remotely operated and this provides the start
operating coil signatures may provide reference to the test gear, which then analyses the time between the start operation of the
information about the condition of the relay and a change in the voltage on the output contacts of the switch.
latching systems. Measured current curves
can be compared with the curve obtained Minimum pick-up measurement (minimum voltage to operate circuit breaker)
during commissioning of the switch. This test is intended to determine the minimum voltage at which the breaker is able to
Figures 4a-e show common problems operate. The contact timing parameters are not of interest, only whether the breaker
which such comparisons can reveal. In operates or not. It is a measure of how much force is needed to move the coil armature.
each case, the reference trace is shown in Testing begins at a low voltage, sending a control pulse to the breaker. The voltage is
black and the first-trip trace in red. 5 increased by small increments (5 V) until the breaker operates; this voltage is recorded and is
expected to remain unchanged through future dates. 5
Voltage based timing measurement Minimum voltage: This test is specified and recommended in international standards.
In this test the voltage on the output The objective of this test is to make sure that the breaker can operate at the lowest voltage
phases is used to measure the operating level provided by the station battery when the breaker has to operate during a power
time of the switch during open and close outage. The test is performed by applying the lowest specified operating voltage and

(a) Problem with coil plunger (b) Problem with link system

(c) Problem with coil plunger and link system (d) Low control voltage or bad wiring

(e) Shorted turns in coil winding
Figure 4: Common problems identified from coil current trace (Megger)

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