3.2 Checking Connections
475
7SD5 Manual
C53000-G1176-C169-1
– Are the polarities of the voltage transformers correct (if used)?
– Is the phase relationship of the voltage transformers correct (if used)?
– Is the polarity for current input I
4
correct (if used)?
– Is the polarity for voltage input U
4
correct (if used, e.g. with open delta winding or
busbar voltage)?
• Check the functions of all test switches that are installed for the purposes of sec-
ondary testing and isolation of the device. Of particular importance are test switches
in current transformer circuits. Be sure these switches short-circuit the current
transformers when they are in the „test mode“.
• The short-circuit feature of the current circuits of the device is to be checked. This
may be performed with secondary test equipment or other test equipment for check-
ing continuity. Make sure that terminal continuity is not wrongly simulated in reverse
direction via current transformers or their short circuit links.
– Remove the front cover of the device (see also Figure 3-3 and 3-4).
– Remove the ribbon cable connected to the C–I/O-2 board and pull the board out
until there is no contact between the board and the rear connections of the
device.
– At the terminals of the device, check continuity for each pair of terminals that re-
ceives current from the CTs.
– Firmly re-insert the I/O module. Carefully connect the ribbon cable. Be careful not
to bend connecting pins! Do not apply force!
– At the terminals of the device, again check continuity for each pair of terminals
that receives current from the CTs.
– Attach the front panel and tighten the screws.
• Connect an ammeter in the supply circuit of the power supply. A range of about 2.5
A to 5 A for the meter is appropriate.
• Switch on mcb. for auxiliary voltage (supply protection), check the voltage level and,
if applicable, the polarity of the voltage at the device terminals or at the connection
modules.
• The measured steady-state current should correspond to the quiescent power con-
sumption of the device. Transient movement of the ammeter merely indicates the
charging current of capacitors.
• Remove the voltage from the power supply by opening the mcb.
• Disconnect the measuring equipment; restore the normal power supply connec-
tions.
• Apply voltage to the power supply.
• Close the mcb for the voltage transformers.
• Verify that the voltage phase rotation at the device terminals is correct.
• Open the mcb's for the transformer voltage (VT mcb) and the power supply.
• Check the trip circuits to the power system circuit breakers.
• Check the close circuits to the power system circuit breakers.
• Verify that the control wiring to and from other devices is correct.
• Check the signalling connections.
•Close mcb.
• If communication converters are used: check the auxiliary voltages for the commu-
nication converters.
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