ABB RET650 Applications Manual page 229

1MRK 504 169-UEN A
Transformer protection RET650 2.2 IEC
Application manual
In figure 81, it can be noted that the fixed extension (c) 4 sec. of tPulseDur, is
made to prevent a situation with TCINPROG set high without the simultaneous
presence of an URAISE or ULOWER command. If this would happen, TCMYLTC
or TCLYLTC would see this as a spontaneous TCINPROG signal without an
accompanying URAISE or ULOWER command, and this would then lead to the
output signal TCERRAL being set high and TR1ATCC or TR8ATCC function
being blocked. Effectively this is then also a supervision of a run-away tap
situation.
Hunting detection
Hunting detection is provided in order to generate an alarm when the voltage
control gives an abnormal number of commands or abnormal sequence of
commands within a pre-defined period of time.
There are three hunting functions:
1. The Automatic voltage control for tap changer function, TR1ATCC for single
control and TR8ATCC for parallel control will activate the output signal
DAYHUNT when the number of tap changer operations exceed the number
given by the setting DayHuntDetect during the last 24 hours (sliding window).
Active as well in manual as in automatic mode.
2. TR1ATCC or TR8ATCC function will activate the output signal HOURHUNT
when the number of tap changer operations exceed the number given by the
setting HourHuntDetect during the last hour (sliding window). Active as well
in manual as in automatic mode.
3. TR1ATCC or TR8ATCC function will activate the output signal HUNTING
when the total number of contradictory tap changer operations (RAISE,
LOWER, RAISE, LOWER, and so on) exceeds the pre-set value given by the
setting NoOpWindow within the time sliding window specified via the setting
parameter tWindowHunt. Only active in automatic mode.
Hunting can be the result of a narrow deadband setting or some other abnormalities
in the control system.
Wearing of the tap changer contacts
Two counters, ContactLife and NoOfOperations are available within the Tap
changer control and supervision function, 6 binary inputs TCMYLTC or 32 binary
inputs TCLYLTC. They can be used as a guide for maintenance of the tap changer
mechanism. The ContactLife counter represents the remaining number of
operations (decremental counter) at rated load.
=
ContactLife ContactLife
n+1
EQUATION1873 V2 EN-US
where n is the number of operations and α is an adjustable setting parameter,
CLFactor, with default value is set to 2. With this default setting an operation at
a
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I
load
- ç
÷
ç ÷
n
I
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rated
Section 11
Control
SEMOD159053-361 v4
SEMOD159053-376 v4
(Equation 54)
223