ABB REG670 Applications Manual page 571

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
is positive and its modulus is greater than DU, then initiate an ULOWER
1. If U
di
command. Tapping will then take place after appropriate t1/t2 timing.
is negative and its modulus is greater than DU, then initiate an URAISE
2. If U
di
command. Tapping will then take place after appropriate t1/t2 timing.
modulus is smaller than DU, then do nothing.
3. If U
di
The binary output signal ADAPT on the TR8ATCC function block will be activated
to indicate that this TR8ATCC is adapting to another TR8ATCC in the parallel group.
It shall be noted that control with adapt mode works as described under the condition
that only one transformer in the parallel group is set to manual mode via the binary
input MANCTRL or, the local HMI Main menu/Control/Commands/
TransformerVoltageControl(ATCC,90)/TR8ATCC:x.
In order to operate each tap changer individually when the circulating current method
is used, the operator must set each TR8ATCC in the parallel group, in manual.
Adapt mode (operation with the master follower method)
When in master follower mode, the adapt situation occurs when the setting
OperationAdapt is On, and the master is put in manual control with the followers still
in parallel master-follower control. In this situation the followers will continue to
follow the master the same way as when it is in automatic control.
If one follower in a master follower parallel group is put in manual mode, still with the
setting OperationAdaptOn, the rest of the group will continue in automatic master
follower control. The follower in manual mode will of course disregard any possible
tapping of the master. However, as one transformer in the parallel group is now
exempted from the parallel control, the binary output signal ADAPT on TR8ATCC
function block will be activated for the rest of the parallel group.
Plant with capacitive shunt compensation (for operation with the
circulating current method)
If significant capacitive shunt generation is connected in a substation and it is not
symmetrically connected to all transformers in a parallel group, the situation may
require compensation of the capacitive current to the ATCC.
An asymmetric connection will exist if for example, the capacitor is situated on the
LV-side of a transformer, between the CT measuring point and the power transformer
or at a tertiary winding of the power transformer, see figure 289. In a situation like this,
the capacitive current will interact in opposite way in the different ATCCs with regard
to the calculation of circulating currents. The capacitive current is part of the
imaginary load current and therefore essential in the calculation. The calculated
circulating current and the real circulating currents will in this case not be the same,
and they will not reach a minimum at the same time. This might result in a situation
when minimizing of the calculated circulating current will not regulate the tap
changers to the same tap positions even if the power transformers are equal.
However if the capacitive current is also considered in the calculation of the
circulating current, then the influence can be compensated for.
Section 15
Control
565