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be tested for immediate system conditions by reading the current change
when one tap is changed on either transformer.
The ΔVAR2 I Ratio is used to adjust the sensitivity to the line current input versus the
circulating current input (opposite transformer load current) to compensate for unequal
CT ratios between transformers. For proper operation with a ratio setting of 1, the ratio of
the CT ratios must be equal to the ratio of the transformer ratings (CT1/CT2=MVA1/
MVA2).
TX1 Rating
TX2 Rating TX2 CT Ratio
TX1 CT Ratio 










 =
T T
Ratio TX 1
GUID-B2A8BFE8-DF9C-482A-A7A6-66CD23E437B4 V1 EN
(Equation 7)
TX2 Rating
TX1 Rating TX1 CT Ratio
TX2 CT Ratio 










 =
T T
Ratio TX 2
GUID-63BF9653-000A-43C9-A5A2-0E61A95FF8BA V1 EN
(Equation 8)
Example:
A 20 MVA transformer is being paralleled with a 15 MVA transformer. If the CT ratios
are 2000 A and 1500 A to 0.2 A, no compensation would be required (both transformers
are fully loaded when the CT outputs are 200 mA.) However, if they each had 2000 A to
0.2 A CTs, the ΔVAR2 I Ratio on the 20 MVA transformer control should be 1.34, and the
ΔVAR2 I Ratio on the 15 MVA transformer control should be 0.75.
The settings for this ratio are 0.50 to 2.00, in 0.01 increments. When the setting is 0.50, the
control will be 0.50 times as sensitive to the VArs from the circulating current input versus
the load input current. The default setting for the sensitivity is 1.00, indicating the ratio of
the CT ratios are equal to the ratio of the transformer ratings.
This feature can also be used to replace the need for auxiliary transformer for matching
transformer CT ratios. No correction is necessary to compensate for impedance
differences in the transformers with ΔVAR operation.
For ΔVAR2 applications (without KeepTrack
™
), paralleling will be disabled if either
current input drops to less than approximately 10 mA or if a neutral input is present. When
ΔVAR2 operation is configured, the normal neutral input is directed to this duty rather
than the normal neutral light operation. It is highly recommended that this input be
connected to operate whenever any breaker opens which isolates the transformer from
parallel operation.
For ΔVAR2 Paralleling mode the Auxiliary Input A1 will be the ΔVAR2 Disable Input.
This is needed since the Neutral Position Input is used for KeepTrack.
Section 6
1VAC388793-MB A
Configuration
408 TCC300
User Manual