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2.7 Overexcitation Protection
Overexcitation protection is applied to protect transformers from overvoltage and overfluxing
conditions.
Any single phase-to-phase connected voltage is used to detect overexcitation. Trip and alarm
characteristics, which are based on a measurement of the voltage/frequency ratio, are provided.
Figure 2.7.1 shows the scheme logic of overexcitation protection. Overexcitation element V/F
responds to voltage/frequency and outputs three signals. Signal T has an inverse time
characteristic. Signals H and A have high-set and low-set definite time characteristics
respectively. Signal T and signal H with a delayed pick-up timer TVFH are used for tripping.
Signal A is used for alarm with a delayed pick-up timer TVFA.
The V/F element has a reset feature with definite time reset. The reset time RT is set to match the
cooling characteristic that is the time for the protected transformer to reach a normal temperature
after releasing the overexitation condition.
363
362
&
&
≥1
V/F
A
H
T
82
80
81
TVFH
1 - 600s
0
t
TV/F-H
V/F-T
V/F-H TRIP
350
≥1
V/F TP
V/F-L TRIP
+
+
+
+
+
+
[V/F1]
[V/FA]
[V/F2]
[V/F3]
[V/F4]
[V/F5]
V/F-2
V/F-A
242
&
&
&
&
&
&
TV/F-H
V/F-T
TVFA
1 - 600s
0
t
V/F-1
V/F-3
V/F-4
V/F-5
Note: Models 203 and 204 are not provided with V/F-4 and V/F-5.
Figure 2.7.1 Scheme Logic of Overexcitation Protection
Overexcitation protection can trip up to five breakers. Any of the breaker tripping signals V/F-1 to
V/F-5 can be blocked by the scheme switch [V/F1] to [V/F5] settings.
Note: Models 203 and 204 are not provided with V/F-4 and V/F-5.
Alarm signal V/F-A can be blocked by the scheme switch [V/FA] setting.