ABB RELION REX640, Техническое руководство, Страница: 1385 / 1960

K Load factor
I_A, I_B and I_C RMS value of input phase currents (Amperes)
I
rated
Rated current (Amperes)
If
Transformer type is set to “Single phase”, the denominator consists only of I 2
rated
instead of 3×I
2
rated
.
Equation 321
assumes that voltage is constant and tap changer position is not
considered.
For a star-delta transformer, it is recommended to use the function on
the star winding, since the circulating zero sequence currents (in case of
unbalance) cannot be measured on the delta winding of the transformer.
Transformer parameter selection
The transformer parameters are selected based on the
Parameter Sel method,
Cooling mode, Transformer type, and Transformer rating settings.
If the
Parameter Sel method setting is set to "IEC", the transformer parameters'
values are automatically selected as per the IEC 60076-7 guidelines based on
Table
1323
.
Table 1323: Constants based IEC guidelines
Distribution
Transformers Medium and Large power transformers
Cooling mode ONAN ONAN ONAF OFAF ODAF
Oil Exponent (x) 0.8 0.8 0.8 1.0 1.0
Winding Exponent (y) 1.6 1.3 1.3 1.3 2.0
Constant K11 (k
11
) 1.00 0.50 0.50 1.00 1.00
Constant K21 (k
21
) 1.00 2.00 2.00 1.30 1.00
Constant K22 (k
22
) 2.00 2.00 2.00 1.00 1.00
Oil Time Constant
(
Շ
0
) [minutes]
180 210 150 90 90
Winding Tm Constant
(
Շ
w
) [minutes]
4 10 7 7 7
If
Parameter Sel method is set to "IEEE", the constants are selected as per the IEEE
C57.91
™
-2011 standard based on
Table 1324
.
Table 1324: Constants based on IEEE guidelines
Distribution
Transformers Medium and Large power transformers
Cooling mode ONAN ONAN ONAF OFAF ODAF
Oil Exponent (x) 0.8 0.8 0.8 0.8 1.0
Winding Exponent (y) 0.8 0.8 0.9 0.9 1.0
Constant K11 (k
11
) 1.00 1.00 1.00 1.00 1.00
Table continues on the next page
1MRS759142 F Condition monitoring functions
REX640
Technical Manual
1385