ABB Relion REC670 Applications Manual page 306

Section 13
Control
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.
Automatic voltage control for a single transformer
Automatic voltage control for tap changer, single control TR1ATCC measures the magnitude of
the busbar voltage U
compensation), this voltage is further used for voltage regulation.
TR1ATCC then compares this voltage with the set voltage,
should be taken. To avoid unnecessary switching around the setpoint, a deadband (degree of
insensitivity) is introduced. The deadband is symmetrical around
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
value near to the power transformer's tap changer voltage step (typically 75–125% of the tap
changer step).
*)
0
IEC06000489 V2 EN-US
Figure 151: Control actions on a voltage scale
During normal operating conditions the busbar voltage U
(interval between U1 and U2 in figure 151). In that case no actions will be taken by TR1ATCC.
However, if U
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
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
A situation where U
When U
Ublock , or rises above Umax , actions will be taken in accordance with settings for blocking
conditions (refer to table 33).
300
The LV-busbar voltage is designated U
voltage U .
L
. If no other additional features are enabled (line voltage drop
B
*)
Raise Cmd
Ublock Umin U
1
*) Action in accordance with setting
becomes smaller than U1, or greater than U2, an appropriate raise or lower
B
Umin and Umax .
falls outside this range will be regarded as an abnormal situation.
B
Ublock , or alternatively, falls below setting Umin but still above
falls below setting
B
B
Security Range
D U D
U
Lower Cmd
DU DU
in in
U
Uset Umax
2
. The inner deadband ΔU
in
, the load current I and load point
L
USet and decides which action
USet , see figure 151, and it is
Udeadband should be set to a
*)
Voltage Magnitude
IEC06000489_2_en.vsd
, stays within the outer deadband
B
UDeadbandInner should
, setting
in
1MRK 511 358-UEN A
SEMOD159053-73 v6
Application manual