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It is also desirable to check the operating voltage achieved with the setting resistor and all parallel CTs connected
but de-energised. A higher capacity test set will be required for this test. Adequate current must be supplied to
provide the magnetising current of all connected CTs.
Precautions should be taken to ensure that no personnel are at risk of contact with any of the energised
secondary wiring during the test and that the high impedance external components are adequately thermally
rated.
Settings Data:
Voltage Setting (V
87/50-1
87/50-2
To complete testing of the differential protection it is required to primary inject current through CTs to simulate an
out of zone fault and ensure stability of the relay.
The test can then be repeated with one set of CT secondary connections reversed to prove operation at the
correct primary operate current.
2.2.1.1
Element Blocking
The differential elements can be blocked by Binary Input Inhibit or from the CT supervision (CT50) function.
Where applied this functionality should be checked.
Element
BI Inhibits
87/50-1
87/50-2
Check correct indication, trip output, alarm contacts, waveform record.
Check that any shorting links are removed after testing.
©2013 Siemens Protection Devices Limited
Chapter 6) 7SR23 DAD Commissioning & Maintenance Guide
V
Measured
S
)
S
Checked
CT Supervision (CT50)
Settings Data:
Operate Current (I
)
OP
Checked
I
Measured
OP
Chapter 6 Page 15 of 26
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