Checking The Instrument Transformer Connections Of One Line End - Siemens SIPROTEC Manual

3.3.7

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 ends of the protected object if
wrong connections were made.
Before energizing the protected object at any 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, this has to be put
into operation and switched to alert first.
Voltage and phase rotation check
If the device has been connected to voltage transformers, these connections are checked using primary values.
For devices without voltage transformer connection, the rest of this section can be ignored.
The voltage transformer connections are individually tested at either end of the object to be protected. At the
other end(s) the circuit breaker(s) first remains opened.
• 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.
– Indications of symmetry monitoring could occur because there are actually assymmetrial conditions in the
primary system. If they are part of normal operation, the corresponding monitoring function is set less sen-
sitive (see Section 2.24.1 under side title „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-earth 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 voltages can also be read with the „WEB-Monitor" (see below, „Current test").
• The voltages have to be almost equal. All three angles ϕ (U
– If the measured quantities are not plausible, the connections must be checked and corrected after switch-
ing off the line. If, for example, the phase difference between two voltages is 60° instead of 120°, one
voltage must be polarity-reversed The same applies if there are phase-to-phase voltages which are
almost equal to the phase voltages instead of having a value that is √3 larger. The measurements have
to be repeated after correcting the connections.
– In general, the phase rotation is clockwise. 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 switched off. The measurement must then
be repeated.
• Open the circuit breaker for voltage transformers of the feeder. The measured voltages in the operational
measured values appear with a value close to zero (small measured voltages are of no consequence).
– Check the Event Log and the spontaneous indications to make sure that the VT mcb trip was noticed (in-
dication „>FAIL:Feeder VT" „ON", no. 361). This requires the position of the circuit breaker for voltage
transformers to be communicated to the device via a binary input.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Mounting and Commissioning
–U ) must be approximately 120°.
Lx Ly
3.3 Commissioning
547