ABB Relion REC670 Applications Manual page 307

1MRK 511 358-UEN A
If the busbar voltage rises above
commands (ULOWER commands) in order to bring the voltage back into the security range
(settings
following three ways: off /auto/auto and manual, according to the setting
ULOWER command, in fast step down mode, is issued with the settable time delay
The measured RMS magnitude of the busbar voltage U
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 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,
direction. It can have a definite or inverse time characteristic, according to the setting
(Constant/Inverse). For inverse time characteristics larger voltage deviations from the
value will result in shorter time delays, limited by the shortest time delay equal to the
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
DA
=
D
D
EQUATION1986 V1 EN-US
=
tMin
EQUATION1848 V2 EN-US
Where:
DA
D
For the last equation, the condition
tMin will be equal to the set t1 value when absolute voltage deviation DA is equal to ΔU
( relative voltage deviation D is equal to 1). For other values see figure 152. It should be noted
that operating times, shown in the figure
settings for
Application manual
Umin , and Umax ). The fast step down function operation can be set in one of the
t1 , is used as a time delay (usually long delay) for the first command in one
U
t
1
D
absolute voltage deviation from the set point
relative voltage deviation in respect to set deadband value
t1 and 10 seconds for tMin .
Umax , TR1ATCC can initiate one or more fast step down
is shown on the local HMI as value
B
t1 > tMin shall also be fulfilled. This practically means that
152 are for 30, 60, 90, 120, 150 & 180 seconds
Section 13
Control
FSDMode . The
tFSD .
SEMOD159053-82 v5
t1Use
USet
tMin
(Equation 118)
(Equation 119)
(Equation 120)
301