On-Line Compensation For On-Load Tap-Changer Position - ABB REG670 Applications Manual

1MRK 502 071-UEN -
7.1.3.7
7.1.3.8
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
If one of the windings is not connected, the algorithm automatically reduces to the
two-winding version. Nevertheless, the whole power transformer is protected,
including the non-connected winding.

On-line compensation for on-load tap-changer position

The Transformer differential function in the IED has a built-in facility to on-line
compensate for on-load tap-changer operation. The following parameters which are
set under general settings are related to this compensation feature:
• Parameter LocationOLTC1 defines the winding where first OLTC (OLTC1) is
physically located. The following options are available: Not Used / Winding 1 /
Winding 2 / Winding 3. When value Not Used is selected the differential function
will assume that OLTC1 does not exist and it will disregard all other parameters
related to first OLTC
• Parameter LowTapPosOLTC1 defines the minimum end tap position for OLTC1
(typically position 1)
• Parameter RatedTapOLTC1 defines the rated (for example, mid) position for
OLTC1 (for example, 11 for OLTC with 21 positions) This tap position shall
correspond to the values for rated current and voltage set for that winding
• Parameter HighTapPsOLTC1 defines the maximum end tap position for OLTC1
(for example, 21 for OLTC with 21 positions)
• Parameter TapHighVoltTC1 defines the end position for OLTC1 where highest
no-load voltage for that winding is obtained (for example, position with
maximum number of turns)
• Parameter StepSizeOLTC1 defines the voltage change per OLTC1 step (for
example, 1.5%)
The above parameters are defined for OLTC1. Similar parameters shall be set for
second on-load tap-changer designated with OLTC2 in the parameter names, for
three–winding differential protection.
Differential current alarm
Differential protection continuously monitors the level of the fundamental frequency
differential currents and gives an alarm if the pre-set value is simultaneously exceeded
in all three phases. This feature can be used to monitor the integrity of on-load tap-
changer compensation within the differential function. The threshold for the alarm
pickup level is defined by setting parameter IDiffAlarm. This threshold should be
typically set in such way to obtain operation when on-load tap-changer measured
value within differential function differs for more than two steps from the actual on-
load tap-changer position. To obtain such operation set parameter IDiffAlarm equal to
two times the on-load tap-changer step size (For example, typical setting value is 5%
to 10% of base current). Set the time delay defined by parameter tAlarmDelay two
times longer than the on-load tap-changer mechanical operating time (For example,
typical setting value 10s).
Section 7
Differential protection
135