ABB Relion 670 series, Technical Manual

Page: 876 / 1432

Automatic voltage control for tap changer, single control TR1ATCC (90)
SEMOD158887-4 v5
Automatic voltage control for tap changer, single control TR1ATCC (90) measures the magnitude
of the busbar voltage V
B
. If no other additional features are enabled (line voltage drop
compensation), this voltage is further used for voltage regulation.
TR1ATCC (90) then compares this voltage with the set voltage,
VSet and decides which action
should be taken. To avoid unnecessary switching around the setpoint, a deadband (degree of
insensitivity) is introduced. The deadband is symmetrical around VSet, see figure 461 , and it is
arranged in such a way that there is an outer and an inner deadband. Measured voltages outside
the outer deadband start the timer to initiate tap commands, whilst the sequence resets when the
measured voltage is once again back inside the inner deadband. One half of the outer deadband is
denoted ΔV. The setting of ΔV, setting
Vdeadband should be set to a value near to the power
transformer’s tap changer voltage step (typically 75–125% of the tap changer step).
Voltage Magnitude Vmax V
2
Vset V
1
Vmin Vblock 0
Raise Cmd
*) Action in accordance with setting
Security Range
Lower Cmd
ANSI06000489-2-en.vsd
D D
V V
D
V
in
D
V
in
*) *) *)
ANSI06000489 V2 EN-US
Figure 461: Control actions on a voltage scale
During normal operating conditions the busbar voltage V
B
, stays within the outer deadband
(interval between V1 and V2 in figure 461 ). In that case no actions will be taken by the TR1ATCC
(90). However, if V
B
becomes smaller than V1, or greater than V2, an appropriate lower or raise
timer will start. The timer will run as long as the measured voltage stays outside the inner
deadband. If this condition persists longer than the preset time delay, TR1ATCC (90) will initiate
that the appropriate VLOWER or VRAISE command will be sent from Tap changer control and
supervision, 6 binary inputs TCMYLTC (84), or 32 binary inputs TCLYLTC (84) to the transformer
load tap changer. If necessary, the procedure will be repeated until the magnitude of the busbar
voltage again falls within the inner deadband. One half of the inner deadband is denoted ΔV
in
. The
inner deadband ΔV
in
, setting
VDeadbandInner should be set to a value smaller than ΔV. It is
recommended to set the inner deadband to 25-70% of the ΔV value.
This way of working is used by TR1ATCC (90) while the busbar voltage is within the security range
defined by settings
Vmin and Vmax
A situation where V
B
falls outside this range will be regarded as an abnormal situation.
Instead of controlling the voltage at the LV busbar in the same substation as the transformer
itself, it is possible to control the voltage at a load point out in the network, downstream from the
transformer. The Line Voltage Drop Compensation (LDC) can be selected by a setting parameter,
and it works such that the voltage drop from the transformer location to the load point is
calculated based on the measured load current and the known line impedance.
In order to prevent unnecessary load tap changer operations caused by temporary voltage
fluctuations and to coordinate load tap changer operations in radial networks, a time delay is used
for the tapping command to the load tap changer. The time delay can be either definite time or
inverse time and two time settings are used, the first (
t1) for the initial delay of a tap command,
and the second (
t2) for consecutive tap commands.
Section 14 1MRK 502 066-UUS B
Control
870
Technical manual