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2.16.9 Voltage and Synchronism Check Elements OVL, UVL, OVB, UVB and SYN
The voltage check and synchronism check elements are used for autoreclose.
The output of the voltage check element is used to check whether the line and busbar are dead or
live. The voltage check element has undervoltage detectors UVL and UVB, and overvoltage
detectors OVL and OVB for the line voltage and busbar voltage check. The undervoltage detector
checks that the line or busbar is dead while the overvoltage detector checks that it is live.
Figure 2.16.9.1 shows the characteristics of the synchronism check element used for the
autoreclose if the line and busbar are live.
The synchronism check element operates if both the voltage difference and phase angle difference
are within their setting values.
The voltage difference is checked by the following equations:
SY1OV ≤ V B ≤ SY1UV
SY1OV ≤ V L ≤ SY1UV
where,
V B = busbar voltage
V L = line voltage
SY1OV = lower voltage setting
SY1UV = upper voltage setting
The phase difference is checked by the following equations:
V B ⋅ V L cos θ ≥ 0
V B ⋅ V L sin(SY1θ ) ≥ V B ⋅ V L sin θ
where,
θ = phase difference between V B and V L
SY1θ = phase difference setting
Note: When the phase difference setting and the synchronism check time setting are given, a
SY1 θ
θ
SY1OV
Figure 2.16.9.1 Synchronism Check Element
146
6 F 2 S 0 8 5 0
V L
V B
SY1UV
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