ABB RELION REX640 - Page 1713

the HV side voltage constant despite of variations in the load current and the MV
side voltage. This is achieved by monitoring the HV side voltage.
“Bi-dir(meas)” or “Bi-dir(calc)” set values should be used only when it is
clear that the source of reverse power flow is a strong source.
If HV side measurements are directly available, “Bi-dir(meas)” mode can be used. If
it is not available, “Bi-dir(calc)” can be set and HV side values are calculated (after
power reversal) from MV side measurements with the help of settings Step of tap ,
Tap nominal and Impedance voltage as given below.
If Raise block tap > Lower block tap , then HV side voltage and current are calculated
as
= 1 + ( _ − _
)
∗
∆
∗ { − ∗ }
}
{
(Equation 380)
1 + (
_ − _ ) ∗ ∆
=
}
{
(Equation 381)
If Raise block tap < Lower block tap , then HV side voltage and current are calculated
as
= 1 + ( _ − _ ) ∗ ∆ ∗
{
− ∗
}
}
{
(Equation 382)
=
1 + ( _ − _ ) ∗ ∆
}
{
(Equation 383)
U
HV
HV side voltage which will be compared with control voltage U
p
for HV side
regulation
I
HV
HV side current
U
MV
MV side measured voltage
I
MV
MV side measured current
TAP_NOM Tap nominal
TAP_POS Own tap position
ΔU
step
Step of Tap
ZV Impedance voltage referred to MV side
When “Bi-dir(calc)” set value is used, it is mandatory that own tap
position information should be connected.
Since it is not always possible to know the source strengths on either side of
the transformer, an additional setting option “Auto select” is also provided. If
the Regulation mode is set as “Auto select”, the direction of regulation will be
automatically selected by OL5ATCC function as below. A power ratio factor (PRF) is
calculated by the OL5ATCC function utilizing HV and MV side voltage and current
1MRS759142 F
Control functions
REX640
Technical Manual
1713