ABB RER670 - Page 299

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 Main menu/Test/Function status/Control/
TransformerVoltageControl(ATCC,90)/TR1ATCC:x/TR8ATCC:x.
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:
IECEQUATION2294 V2 EN-US (Equation 67)
DA
D
U
=
D
EQUATION1986 V1 EN-US (Equation 68)
t
1
tMin
D
=
EQUATION1848 V2 EN-US (Equation 69)
Where:
DA absolute voltage deviation from the set point
D relative voltage deviation in respect to set deadband value
1MRK 506 375-UEN A Section 12
Control
Railway application RER670 2.2 IEC 293
Application manual