Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
272
3.3.8 Checking the Instrument Transformer Connections of One Line End
If secondary test equipment is connected to the device, it is to be removed or, if applying, test switches should
be in normal operation position.
Note
It must be taken into consideration that tripping can occur even at the opposite end of the protected object if
connections were made wrong.
Before energizing the object to be protected at one end, short-circuit protection must be ensured at least at the
feeding ends. If a separate backup protection (e.g. time overcurrent protection) is available, it has to be put into
operation and switched to alert first.
Voltage and Phase Rotation Check
If the device is connected to voltage transformers, these connections are checked using primary values. For
devices without voltage transformer connection the rest of this margin heading may be omitted.
The voltage transformer connections are individually tested at either end of the object to be protected. At the
other end, the circuit breaker initially remains open.
• Having closed the circuit breaker, none of the measurement monitoring functions in the device must re-
spond.
– If there was a fault indication, however, the Event Log or spontaneous indications could be checked to
investigate the reason for it.
– At the indication of balance monitoring there might actually be asymmetries of the primary system. If they
are part of normal operation, the corresponding monitoring function is set less sensitive (see Section
2.14.1 under margin heading „Symmetry Monitoring“).
The voltages can be read as primary and secondary values on the display at the front, or called up in the
PC via the operator or service interface, and compared with the actual measured quantities. Besides the
magnitudes of the phase-to-ground and the phase-to-phase voltages, the phase differences of the voltages
are also displayed so that the correct phase sequence and polarity of individual transformers can also be
seen.
• The voltage magnitudes should be almost equal. All three angles ϕ (V
Lx
–V
Ly
) must be approximately 120°.
– If the measured quantities are not plausible, the connections must be checked and revised after switching
off the line. If the phase difference between two voltages is 60° instead of 120°, one voltage must be po-
larity-reversed. The same applies if there are phase-to-phase voltages which are almost equal to the
phase-to-ground voltages instead of having a value that is √3 larger. The measurements are to be repeat-
ed after correcting the connections.
– In general, the phase rotation is a clockwise phase rotation. If the system has an anti-clockwise phase
rotation, this must be identical at all ends of the protected object. The phase assignment of the measured
quantities has to be checked and, if required, corrected after the line has been isolated. The measure-
ment must then be repeated.
• Open the miniature circuit breaker of the feeder voltage transformers. The measured voltages in the opera-
tional measured values appear with a value close to zero (small measured voltages are of no consequence).
– Check in the Event Log and in the spontaneous indications that the VT mcb trip was noticed (indication
„>FAIL:Feeder VT“ „ON“, no. 361). It has to be assured beforehand that the position of the VT mcb
is connected to the device via a binary input.
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