ABB RET650 Technical Manual page 98

Section 6
Differential protection
92
1. HV star (Y) connected winding will be used as reference winding and zero
sequence currents shall be subtracted on that side
2. The LV winding is lagging for 150°
With the help of table 34, the following matrix equation can be written for this power
transformer:
- -
é IDL 1 ù é 2 1
1
ê ú ê
= × - - ×
IDL 2 1 2
ê ú ê
3
ê ú ê - -
IDL 3 1 1 2
ë û ë
EQUATION2015 V1 EN
where:
IDL1 is the fundamental frequency differential current in phase L1 (in W1 side primary amperes)
IDL2 is the fundamental frequency differential current in phase L2 (in W1 side primary amperes)
IDL3 is the fundamental frequency differential current in phase L3 (in W1 side primary amperes)
IL1_W1 is the fundamental frequency phase current in phase L1 on the W1 side
IL2_W1 is the fundamental frequency phase current in phase L2 on the W1 side
IL3_W1 is the fundamental frequency phase current in phase L3 on the W1 side
IL1_W2 is the fundamental frequency phase current in phase L1 on the W2 side
IL2_W2 is the fundamental frequency phase current in phase L2 on the W2 side
IL3_W2 is the fundamental frequency phase current in phase L3 on the W2 side
Ur_W1 is transformer rated phase-to-phase voltage on the W1 side (setting parameter)
Ur_W2 is transformer rated phase-to-phase voltage on the W2 side (setting parameter)
As marked in equation 1
equation, represents the total contribution from the individual phase currents from the
W1 side to the fundamental frequency differential currents, compensated for eventual
power transformer phase shift. The second term on the right hand side of the equation,
represents the total contribution from the individual phase currents from the W2 side
to the fundamental frequency differential currents, compensated for eventual power
transformer phase shift and transferred to the power transformer reference side. The
third term on the right hand side of the equation, represents the total contribution from
the individual phase currents from the W3 side to the fundamental frequency
differential currents, compensated for eventual power transformer phase shift and
transferred to the power transformer reference side. .
The fundamental frequency differential currents are the magnitudes which are applied
in a phase segregated manner to the operate - restrain characteristic of the differential
protection. The magnitudes of the differential currents can be read as service values
from the function and they are available as outputs IDL1MAG, IDL2MAG,
IDL3MAG from the differential protection function block. Thus they can be
connected to the disturbance recorder and automatically recorded during any external
or internal fault condition.
1 ù é IL W 1_ 1 ù
Ur W _ 2 1
ú ê ú
+
1 IL 2 _ 1 W
ú ê ú
Ur W _ 1
ú ê ú
IL 3_ 1 W
û ë û
and equation 2, the first term on the right hand side of the
1MRK 504 135-UEN A
-
é 1 0 1 ù é IL W 1_ 2
ê ú ê
× × - ×
1 1 0 IL 2 _ 2
ê ú ê
3
ê - ú ê
0 1 1 IL 3_ 2
ë û ë
Technical manual
ù
ú
W
ú
ú
W
û
(Equation 21)