Measurement Techniques - Megger SCITS100 Mode D'emploi

Measurement Techniques

Testing I.D.M.T. Relays
1. CREEP TEST — The SCITS100 is used to measure the current required to just move the disc. Any of the three
main a.c. outputs may be used. Note:— the 100 A output gives the greatest sensitivity although the impedance
of the load under test may preclude its use.
2. TRIP TEST — The SCITS100 is used to measure the time taken from the instigation of the current to the
contacts closing (normally open) or opening (normally closed) in the relay. Any of the three main a.c. outputs may
be used for injection, and the counter should be used in the 'Normal' mode.
3. RUNBACK TEST — The SCITS100 is used to inject a current into the relay to cause it to trip, and then measure
the time taken for the disc to reset back to its starting point, (Runback time). Any of the three main outputs may
be used for injection, and the counter should be used in the 'Runback' mode.
4. TAP CHANGING TEST — The SCITS100 is used to inject a current into the current transformer whilst its tapping
plug is moved in turn to all positions. During this procedure, the Test Set's ammeter is watched to check that the
current never falls to zero. Any of the main a.c. outputs may be used.
Testing Instantaneous Relays
These relays are tested by simply injecting current and visually inspecting whether the relays have tripped. These
types of relays may require up to 100 A, hence the range of the SCITS100. Any of the three main a.c. outputs may
be used.
The 240 V d.c. output can be used to test d.c. voltage instantaneous relays.
Testing Directional Relays
These relays comprise both voltage and current elements. To test these relays therefore, a voltage and current
element in phase with one another is required. The SCITS100 has a separate 120 V a.c. output, with auxiliary output
control, for this purpose. The current may be injected from any of the three main a.c. outputs.
Testing Thermal Overload Relays
The SCITS100 is used to test the trip characteristics. The current required is typically 0,5 A. Any of the three main a.c.
outputs may be used.
Testing Earth Fault Relays
Relay
Testing an earth fault relay
The SCITS100 is used to inject a current through a resistor (R) in the Earth Fault measurement circuit to trip the relay
(see above). The voltage and current at which this occurs are then measured. The test will need to be performed twice
since only one measurement can be made at a time. Any of the main a.c. outputs may be used.
Testing d.c. Voltage Relays
These relays are similar to the Instantaneous type, except that a d.c. voltage is required. The 240 V d.c. output on the
SCITS100 should be used.
Testing Analogue Meters
The SCITS100 can be used as an a.c. supply to check the calibration of analogue meters such as those used in Sub-
stations. Any of the three main a.c. outputs may be used.
R V
I
Earth Fault
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