currents for each transformer based on impedance 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 /IED
Settings/Control /TransformerVoltageControl(90, U↕)/TR8ATCC(90, U↕||):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 /IED Settings/
TransformerVoltageControl(90, U↕) /TR1ATCC(90, U↕):x/TR8ATCC(90, U↕||):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.
EQUATION2089-ANSI V1 EN-US (Equation 126)
The voltage regulation algorithm then increases (for transformer T2) or decreases (for transformer
T1) the measured voltage by Vdi and compares Vi against the voltage deadband limits V1 and V2
for the purposes of voltage regulation.
EQUATION2091-ANSI V1 EN-US (Equation 127)
9. To cause a tap change, the calculated value for circulating current voltage adjustment must offset
the injected quantity for bus voltage V
B
so that Vi is outside the voltage deadband created by
setting VDeadband. Expressed by equation
128 and equation 129.
Section 11 1MRK 504 165-UUS Rev. J
Testing functionality by secondary injection
260 Transformer protection RET670
Commissioning manual
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