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 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 118)
EQUATION1986 V1 EN-US (Equation 119)
EQUATION1848 V2 EN-US (Equation 120)
Where:
DA absolute voltage deviation from the set point
D relative voltage deviation in respect to set deadband value
For the last equation, the condition
t1 > tMin
shall also be fulfilled. This practically means that
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
152 are for 30, 60, 90, 120, 150 & 180 seconds
settings for
t1
and 10 seconds for
tMin
.
1MRK 511 358-UEN A Section 13
Control
301
Application manual
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