values and respective compensating factors, and is therefore more complex for greater
than two transformers.
1. Confirm that OperationPAR is set to CC for the transformers in the parallel group.
2. For parallel operation, it is also recommended that settings be confirmed for parallel
group membership, governed by setting TnRXOP in the local HMI under Main
menu/Settings/Setting group N/Control/TransformerVoltageControl(ATCC,
90)/TR8ATCC:x/ParCtrl
The general parallel arrangement of transformers are defined by setting TnRXOP to
Enabled or Disabled. The following rules are applicable on the settings T1RXOP -
T4RXOP.
If IED T1 and T2 are connected,
• T1RXOP shall be set to Enabled in instance 2 of TR8ATCC (90), and
• T2RXOP shall be set to Enabled in instance 1 of TR8ATCC (90).
If T1 - T3 are available,
• T1RXOP and T2RXOP shall be set to Enabled in instance 3 of TR8ATCC
(90),
• T2RXOP and T3RXOP shall be set to Enabled in instance 1 of TR8ATCC (90)
and so on.
The parameter corresponding to the own IED must not be set.
T1RXOP should thus not be set in IED T1, T2RXOPnot in IED T2
and so on.
3. Review the settings for VDeadband (based on percentage of nominal bus voltage)
and calculate the upper (V2) and lower (V1) voltage regulation limits for which a tap
change command will be issued from the master transformer in the group.
4. Review the expected time for first (t1) and subsequent (t2) tap change commands
from the master transformer in the local HMI under Main menu/Settings/Setting
group N/TransformerVoltageControl(ATCC,90)/TR1ATCC:x/TR8ATCC:x/
Time/t1 and t2
5. Inject a voltage V
B
equal to VSet for each transformer.
6. Inject a load current for Transformer 1 that is equal to rated load current I2Base and
a load current for Transformer 2 that is equal to 95% of rated load current I2Base.
This will have the effect of producing a calculated circulating current that flows from
HV to LV side for Transformer 1 and LV to HV side for Transformer 2.
7. Confirm that a circulating current is measured on the local HMI that is equal in
magnitude to 5% of I2Base, with polarity as discussed in step
6.
8. Confirm the settings for Ci (Compensation Factor) and Xi (Transformer Short
Circuit Impedance). Using these setting values and the measured quantity of
circulating current from the local HMI (Icc_i), calculate the value for circulating
current voltage adjustment Vci.
1MRK 504 165-UUS - Section 11
Testing functionality by secondary injection
Transformer protection RET670 2.2 ANSI 255
Commissioning manual
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