ABB ret650, Technical Manual

Page: 348 / 670

TR8ATCCis designed to automatically maintain the voltage at the LV-side side of a
power transformer within given limits around a set target voltage. A raise or lower
command is generated whenever the measured voltage, for a given period of time,
deviates from the set target value by more than the preset deadband value that is,
degree of insensitivity. A time-delay (inverse or definite time) is set to avoid
unnecessary operation during shorter voltage deviations from the target value, and in
order to coordinate with other automatic voltage controllers in the system.
TCMYLTC is an interface between TR8ATCC and the transformer load tap changer.
More specifically this means that it receives information fromTR8ATCC and based
on this it gives command-pulses to a power transformer motor driven on-load tap
changer and also receives information from the load tap changer regarding tap
position, progress of given commands, and so on.
12.3.4.1 Automatic voltage control for tap changer TR8ATCC
The LV-side of the transformer is used as the voltage measuring point. If necessary,
the LV side current is used as load current to calculate the line-voltage drop to the
regulation point. This current is also used when parallel control with the circulating
current method is used.
In addition, all three-phase currents from the HV-winding (usually the winding where
the tap changer is situated) are used by the Automatic voltage control for tap changer
TR8ATCC for parallel control function for over current blocking.
The setting MeasMode is a selection of single-phase, or phase-phase, or positive
sequence quantity. It is to be used for voltage and current measurement on the LV-
side. The involved phases are also selected. Thus, single-phases as well as phase-
phase or three-phase feeding on the LV-side is possible but it is commonly selected for
current and voltage.
The analog input signals are normally common for other functions in the IED for
example, protection functions.
The LV-busbar voltage is designated UB, load current I
L
and for load
point voltage U
L
will be used in the text to follow.
Automatic control for tap changer, parallel control TR8ATCC
Parallel control of power transformers means control of two or more power
transformers connected to the same busbar on the LV side and in most cases also on
the HV side. Special measures must be taken in order to avoid a runaway situation
where the tap changers on the parallel transformers gradually diverge and end up in
opposite end positions.
Three alternative methods can be used for parallel control with Automatic control for
tap changer, parallel control TR8ATCC:
Section 12
1MRK 504 135-UEN A
Control
342
Technical manual