3 Mounting and Commissioning
248
7ST6 Manual
E50417-G1176-C251-A3
3.3.6
Current and Voltage Test
Load Current
≥
[10% I N ]
The connections of the current and voltage transformers are tested using primary
quantities. Secondary load current of at least 10 % of the nominal current of the device
is necessary. The line is energized and will remain in this state during the measure-
ments.
With proper connections of the measuring circuits, none of the measured values su-
pervision elements should pick up in the device. If an element detects a problem, the
causes which provoked it may be viewed in the Event Log.
If current or voltage summation errors occur, then check the matching factors (see
Section 2.1.3.1).
Indications from the symmetry monitoring could occur because there are actually
asymmetrical conditions in the network. If these asymmetrical conditions are normal
service conditions, the corresponding monitoring functions should be made less sen-
sitive (see Section 2.16).
Current and Voltage
Values
Currents and voltages can be viewed in the display field on the front of the device or
the operator interface using a PC. They can be compared to the actual measured
values, as primary and secondary quantities.
If the measured values are not plausible, the connection must be checked and correct-
ed after the line has been isolated and the current transformer circuits have been
short-circuited. The measurements must then be repeated.
Voltage Transform-
er Miniature Circuit
Breaker (VT mcb)
Open the miniature circuit breaker of the feeder voltage transformers. The measured
voltages in the operational measured values appear with a value close to zero (small
measured voltages are of no consequence).
Check in the spontaneous indications that the VT mcb trip was entered (indication
„>FAIL:Feeder VT“
„ON“ in the spontaneous indications). It has to be assured be-
forehand that the position of the VT mcb is connected to the device via a binary input.
Close the VT mcb again: The above indication appears in the spontaneous indications
as „OFF“, i.e.
„>FAIL:Feeder VT“
„OFF“.
If one of the indications does not appear, the connection and allocation of these
signals must be checked.
If the „ON“ state and the „OFF“ state are swapped, the contact type (H–active or L–
active) must be checked and remedied.
If a busbar voltage is used (for voltage or synchronism check) and the assigned VT
mcb is connected to the device, the following function must also be checked:
If the VT mcb is open the indication „ON“ appears, if it is closed the indication „OFF“
is displayed.
Switch off the protected power line.
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