Overexcitation Protection - Toshiba GRT100 Series Instruction Manual

2.8 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 2.8.1 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.
T
V/F
H
A
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.
Alarm signal V/F-A can be blocked by the scheme switch [V/FA] setting.
TVFH
t 0
1 - 600s
TVFA
t 0
1 - 600s
Figure 2.8.1 Scheme Logic of Overexcitation Protection
 34 
1
[V/F1]

"ON"
[V/F2]

"ON"
[V/F3]

"ON"
[V/F4]

"ON"
[V/F5]

"ON"
[V/FA]

"ON"
6 F 2 S 0 7 8 9
V/F-1
&
&
V/F-2
&
V/F-3
&
V/F-4
&
V/F-5
&
V/F-A