ABB RELION RET670 Applications Manual page 766

Section 15
Control
760
When V falls below setting Vblock, or alternatively, falls below setting Vmin but still
B
above Vblock, or rises above Vmax, actions will be taken in accordance with settings
for blocking conditions (refer to table 60).
If the busbar voltage rises above Vmax, TR1ATCC (90) can initiate one or more fast
step down commands (VLOWER commands) in order to bring the voltage back into
the security range (settings Vmin, and Vmax). 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 VLOWER command, in fast step down mode, is issued with
the settable time delay tFSD.
The measured RMS magnitude of the busbar voltage V
value BUSVOLT under Main menu/Test/Function status/Control/
TransformerVoltageControl(ATCC,90)/TR1ATCC:x/TR8ATCC:x.
Time characteristic
The time characteristic defines the time that elapses between the moment when
measured voltage exceeds the deadband interval until the appropriate VRAISE or
VLOWER 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 VSet 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:
= -
DA VB VSet
ANSIEQUATION2294 V1 EN-US
DA
=
D
D
V
EQUATION1846-ANSI V1 EN-US
1MRK 504 163-UUS A
is shown on the local HMI as
B
(Equation 504)
(Equation 505)
Transformer protection RET670 2.2 ANSI
Application manual
SEMOD159053-82 v5