ABB RELION REX640 Technical Manual page 1560

Section 9
Control functions
1554
φ
1
I
LOAD
GUID-8FD20B92-ED4E-407E-9DC8-AFF48A7E8B23 V1 EN
Figure 814: The expected phase angle of the load supplied by the transformers
operating in parallel is entered as a setting value φ
The regulators calculate the circulating current with the equation
I (sin tan cos
ϕ ϕ
= − ⋅
ci 1 Load
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I Average of the currents I_A, I_B and I_C
TR1
φ Phase angle between U_A and I_A
1
Load phase angle of the load current
φ Set
Load
In the negative reactance method, the circulating current is minimized by changing the
control voltage according to the measured circulating current. The regulator
calculates the circulating current compensation term U
MCC
I Stability factor
−
ci
U
= ⋅
ci
I 100
n
GUID-960695A1-192B-42D0-8422-BF8C561E6617 V1 EN
I Circulating current
ci
Stability factor Stability setting (the recommended value depends on the loop impedance)
If the transformers operating in parallel have different rated currents, the value of the
Stability factor setting of the regulator should be proportional to the rated currents,
that is, the higher the rated current, the higher the Stability factor setting value.
φ
LOAD
I
LOAD
I
LOAD
Ici = circulating
current
I
TR1
= I x │cos(φ )│/cos(φ
TR1 1
) I
ϕ
⋅
1 TR 1
U
⋅
n
1MRS759142 C
U_A
x sin(φ )
LOAD
I
TR1
)
LOAD
Load
(Equation 341)
(Equation 338) as in the
ci
(Equation 342)
Technical Manual
x sin(φ )
1
REX640