earth voltage can increase with as much as a factor √3 in case of earth faults in a non-solidly
earthed system.
The analog input signals are normally common with other functions in the IED for example,
protection functions.
The LV-busbar voltage is designated U
B
, the load current I
L
and load point
voltage U
L
.
Automatic voltage control for a single transformer
SEMOD159053-73 v6
Automatic voltage control for tap changer, single control TR1ATCC measures the magnitude of
the busbar voltage U
B
. If no other additional features are enabled (line voltage drop
compensation), this voltage is further used for voltage regulation.
TR1ATCC then compares this voltage with the set voltage,
USet
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
USet
, see figure 151, 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 ΔU. The setting of ΔU, setting
Udeadband
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
Umax
U
2
UsetU
1
UminUblock0
Raise Cmd
*) Action in accordance with setting
Security Range
Lower Cmd
IEC06000489_2_en.vsd
DD U U
DU
in
DU
in
*) *) *)
IEC06000489 V2 EN-US
Figure 151: Control actions on a voltage scale
During normal operating conditions the busbar voltage U
B
, stays within the outer deadband
(interval between U1 and U2 in figure 151). In that case no actions will be taken by TR1ATCC.
However, if U
B
becomes smaller than U1, or greater than U2, an appropriate raise or lower
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 will initiate
that the appropriate ULOWER or URAISE command will be sent from TCMYLTC or TCLYLTC
function block to the transformer 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 ΔU
in
. The inner deadband ΔU
in
, setting
UDeadbandInner
should
be set to a value smaller than ΔU. It is recommended to set the inner deadband to 25-70% of
the ΔU value.
This way of working is used by TR1ATCC while the busbar voltage is within the security range
defined by settings
Umin
and
Umax
.
A situation where U
B
falls outside this range will be regarded as an abnormal situation.
When U
B
falls below setting
Ublock
, or alternatively, falls below setting
Umin
but still above
Ublock
, or rises above
Umax
, actions will be taken in accordance with settings for blocking
conditions (refer to table
33).
Section 13 1MRK 511 358-UEN A
Control
300
Application manual
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