7SG15 MicroTAPP Commissioning
©2012 Siemens Protection Devices Limited Chapter 7 Page 8 of 10
7.2 On-Load Tests
If a single transformer is commissioned and no load is connected, the relay should be set to ‘manual’ until such
time that sufficient load is available for the ‘on load’ tests to be completed.
It is important that final tests are carried out using load current in order to confirm correct operation of the voltage
control system as follows: -
1 Check VT/CT phase selection and polarity
2 Check LDC response for load boosting. This test is necessary even if LDC is not finally applied
3 Verify correct operation of tap change control for parallel transformers
For testing the control method should be selected to: -
TAPP in "menu/settings/setup/voltage control".
7.2.1 Settings
For the tests, settings should be applied as shown in table 2.
Menu Setting Value
Voltage Control Band
±1.0%
LDC 0%
Initial Delay DTL 180 sec
Inter-tap Delay 60 sec
Basic Balance the relay to the
system voltage
Table 2
7.2.2 Procedure
1 Switch all transformer tap change controls to Manual.
2 Adjust tap positions so that any circulating current is at a minimum and the system voltage level is
satisfactory.
3 If the transformers are dissimilar or are connected across a network, different tap positions may be
required in order to achieve minimum circulating current.
4 Measure the CT secondary current using a clip-on CT and note the reading.
5 Use the instrument display to establish the indicated load current and system power factor, confirm the
readings are as expected. If the indicated power factor is suspect the CT phase selection is probably
wrong. If the power factor is –ve the CT polarity is incorrect.
6 Set the system power factor in the settings/network menu.
7 Adjust the Basic level until the relay indicates LOW, note the reading.
8 Adjust the Basic level until the relay indicates HIGH, note the reading.
9 Set the basic level midway between the readings of 7 & 8 above, note the reading.
10 Confirm that basic balance point agrees with the power system voltage level.
Note: If the voltage set point does not appear to be correct the VT/CT phase angle selection may be incorrect.
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