Section 14 Primary injection testing
About this chapter
This chapter describes tests with primary current through the protected zone to
determine that connections and settings are correct.
14.1
Primary injection testing
Whenever it becomes necessary to work on primary equipment, it is
essential that all the necessary switching, locking,
earthing and
safety procedures are observed and obeyed in a rigid and
formalized manner. Operating and testing procedures should be
strictly followed in order to avoid exposure to the substation
equipment that has not been properly de-energized.
A test with primary current through the protected zone is usually a final check that
the current circuits are correctly connected to the IED protection scheme. It is
important to have an appropriate source, which is able to inject sufficient current in
the primary circuit in order to distinguish between noise and real injected current.
Therefore it is recommended that the injection current should be at least 10% of
rated CT primary current.
14.1.1
Voltage control VCTR
14.1.1.1 Load drop compensation function, LDC
The load drop compensation function can be tested directly with operational
currents, that is, with the power transformer in service and loaded.
When the system is carrying load there will be a difference between the busbar
voltage (UB) and the voltage at the load point (UL). This difference is load
dependent and can be compensated by the VCTR function.
The load current is fed into the VCTR function where parameters corresponding to
the line data for resistance and inductance are set. The voltage drop calculated by
the LDC will be proportional to the voltage drop in the system up to the load point.
In the IED this voltage will be subtracted from the measured busbar voltage (UB)
and the result, corresponding to the voltage at the load point (UL) will be presented
1MRK 504 088-UEN C Section 14
Primary injection testing
205
Installation and commissioning manual
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