ABB REG650 Technical Manual page 94

Section 6
Differential protection
88
By using this table we can derive a complete calculation for all common transformer
configuration. For example when considering a YNd5 power transformer the following
can be concluded:
1. HV wye (Y) connected winding will be used as reference winding and zero
sequence currents shall be subtracted on that side
2. LV winding is lagging for 150°
With help of table 27, the following matrix equation can be written for this power
transformer:
- -
é ù é
ID A _ 2 1
ê ú 1 ê
= × - -
ID B _ 1 2
ê ú ê
3
ê ú ê
- -
ë ID C _ û ë 1 1 2
EQUATION1810-ANSI V1 EN
where:
ID_A is the fundamental frequency differential current in phase A (in W1 side primary amperes)
ID_B is the fundamental frequency differential current in phase B (in W1 side primary amperes)
ID_C is the fundamental frequency differential current in phase C (in W1 side primary amperes)
I_A_W1 is the fundamental frequency phase current in phase A on W1 side
I_B_W1 is the fundamental frequency phase current in phase B on W1 side
I_C_W1 is the fundamental frequency phase current in phaseC on W1 side
I_A_W2 is the fundamental frequency phase current in phase A on W2 side
I_B_W2 is the fundamental frequency phase current in phase B on W2 side
I_C_W2 is the fundamental frequency phase current in phaseC on W2 side
Vn_W1 is transformer rated phase-to-phase voltage on W1 side (setting parameter)
Vn_W2 is transformer rated phase-to-phase voltage on W2 side (setting parameter)
As marked in equation 1
equation, represents the total contribution from the individual phase currents from 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 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 W3 side to the fundamental frequency differential
currents compensated for eventual power transformer phase shift and transferred to the
power transformer reference side. .
ù é ù
1 I _ A W _ 1
ú ê ú Vr W _ 2
× + ×
1 I _ B W _ 1
ú ê ú
Vr W _ 1
ú ê ú
û ë I C W _ _ 1 û
and equation 2, the first term on the right hand side of the
1MRK 502 043-UUS B
-
é ù é
1 0 1 I _ A W _
1 ê ú ê
× - ×
1 1 0 I _ B W _
ê ú ê
3
ê ú ê
-
ë 0 1 1 û ë I C W _ _
Technical Manual
ù
2
ú
2
ú
ú
2 û
(Equation 21)