Toshiba GRT100 Series, Instruction Manual

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18
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6 F 2 S 0 7 8 9
current accurately. The kct range (from 2.00 to 8.00) is enough to operate the protection relay
correctly. When the value of the kct is set larger than 8 (that is, the kct value is set form 8.00 to
50.00), the protection relay can operate depending on the actual input of analog current and the
DIFT settings.
Figure 2.3.4 CT Ratio Matching
Setting for phase angle matching
The phase angle differences between line currents on each side of the power transformer are
corrected by setting according to the hands of a clock as follows:
Rule 1:
If all the windings are star-connected, then take one of the windings as a reference winding and
set 1 (= one o’clock) for it. For other winding(s), set the phase angle difference from the
reference winding by the expression of the leading angle. One hour corresponds to leading by
thirty degrees.
Example 1 If the setting winding leads the reference winding by 60

, set 3 (= three o’clock).
Example 2 If the setting winding is in phase with the reference winding, set 1 (= one
o’clock).
Example 3 If the setting winding lags the reference winding by 60

(that is leading by 300

),
set 11 (= eleven o’clock).
Rule 2:
If any of the windings are delta-connected, take one of the delta-connected winding(s) as a
Secondary
40MVA
66kV
Primary
40MVA
154kV
CT1
300/5
CT2
600/5
CT3
1200/5
GRT100
A B
C
kct1 kct3 kct2
Tertiary
12MVA
11kV