Tests; Inspection; Secondary Injection Tests; Primary Injection Tests - Siemens 7SR242 Duobias Technical Manual

1.3

Tests

1.3.1

Inspection

Ensure that all connections are tight and correct to the relay wiring diagram and the scheme diagram. Record any
deviations. Check that the relay is correctly programmed and that it is fully inserted into the case. Refer to
'Section 2: Settings and Instruments' for information on programming the relay.
1.3.2

Secondary Injection Tests

Select the required relay configuration and settings for the application.
Isolate the auxiliary D.C. supplies for alarm and tripping from the relay and remove the trip and intertrip links.
Carry out injection tests for each relay function, as described in this document
For all high current tests it must be ensured that the test equipment has the required rating and stability and that
the relay is not stressed beyond its thermal limit.
1.3.3

Primary Injection Tests

Primary injection tests are essential to check the ratio and polarity of the current transformers as well as the
secondary wiring. Primary injection testing of the 87BD Biased Differential protection is recommended to avoid
relay operation during first energisation of the transformer if incorrect values are applied to the ICT Connection
protection setting.
Note. If the current transformers associated with the protection are located in power transformer bushings it may
not be possible to apply test connections between the current transformer and the power transformer windings.
Primary injection is needed however, to verify the polarity of the CTs. In these circumstances primary current
must be injected through the associated power transformer winding. It may be necessary to short circuit another
winding in order to allow current to flow. During these primary injection tests the injected current is likely to be
small due to the impedance of the transformer.
Phase current transformer polarities and connections can be checked by examination of the relay Current Meters
and Differential Meters in the Instruments Menu when the protected plant is carrying load but Earth Fault CT
polarity can only be checked during primary injection.
1.3.4

Putting into Service

After tests have been performed satisfactorily the relay should be put back into service as follows:-
Remove all test connections.
Replace all secondary circuit fuses and links, or close m.c.b.
Ensure the Protection Healthy LED is on, steady, and that all LED indications are correct. If necessary press
CANCEL until the Relay Identifier screen is displayed, then press TEST/RESET to reset the indication LEDs.
The relay meters should be checked in Instruments Mode with the relay on load
The relay settings should be downloaded to a computer and a printout of the settings produced. The installed
settings should then be compared against the required settings supplied before testing began. Automated setting
comparison can be carried out by ReyDisp using the Compare Settings Groups function in the Edit menu. Any
modified settings will be clearly highlighted.
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Chapter 6) 7SR242 Duobias Commissioning & Maintenance Guide
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