ABB ret650 - Page 201

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
27).
If the busbar voltage rises above Umax, TR1ATCC can initiate one or more fast
step down commands (ULOWER commands) in order to bring the voltage back
into the security range (settings Umin, and Umax). The fast step down function
operation can be set in one of the following three ways: off /auto/auto and manual,
according to the setting FSDMode. The ULOWER command, in fast step down
mode, is issued with the settable time delay tFSD.
The measured RMS magnitude of the busbar voltage U
B
is shown on the local HMI
as value BUSVOLT under .
Time characteristic
SEMOD159053-82 v5
The time characteristic defines the time that elapses between the moment when
measured voltage exceeds the deadband interval until the appropriate URAISE or
ULOWER command is initiated.
The purpose of the time delay is to prevent unnecessary load tap changer
operations caused by temporary voltage fluctuations and to coordinate load tap
changer operations in radial networks in order to limit the number of load tap
changer operations. This can be done by setting a longer time delay closer to the
consumer and shorter time delays higher up in the system.
The first time delay, t1, is used as a time delay (usually long delay) for the first
command in one direction. It can have a definite or inverse time characteristic,
according to the setting t1Use (Constant/Inverse). For inverse time characteristics
larger voltage deviations from the USet value will result in shorter time delays,
limited by the shortest time delay equal to the tMin setting. This setting should be
coordinated with the tap changer mechanism operation time.
Constant (definite) time delay is independent of the voltage deviation.
The inverse time characteristic for the first time delay follows the formulas:
1MRK 504 169-UEN A Section 11
Control
Transformer protection RET650 2.2 IEC 195
Application manual