ABB RELION REX640, Technical Manual, Page: 1711 / 1960

2 x Ici
I
TR1
x sin(
φ
1
)
I
TR2
x sin(
φ
2
)
φ
1
φ
2
U_A
Ici = circulating current
I
TR1
I
TR2
Figure 919: The circulating current between two parallel transformers
In this case, the circulating current can be calculated with the equation
I
I I
ci
TR TR
=
⋅ − ⋅
(sin sin ) φ φ
1 1 2 2
2
(Equation 378)
I
TR1
Current magnitude of regulator 1
I
TR2
Current magnitude of regulator 2
φ
1
Phase angle between U_A and I_A in regulator 1
φ
2
Phase angle between U_A and I_A in regulator 2
The circulating current can be read from the monitored data I_CIR.
Using the circulating current, the compensation term U
ci
can be calculated with the
equation
U
I
I
U
ci
ci
CT n
n
=
−
⋅ ⋅
_ 1
100
Stability factor
(Equation 379)
I
ci
Circulating current
I
CT_n1
Nominal primary current of the CT
Stability
factor
Stability setting (the recommended value depends on the loop impedance)
The value of U
ci
, which can be positive or negative, is added to the
Band center
voltage Us ( Equation 373
). According to
Figure 919
and
Equation 378
, the phasor
information from the other protection relays is needed.
1MRS759142 F Control functions
REX640
Technical Manual
1711