Voltage Vector Shift

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StormRiderRit

a. What situations cause Voltage Vector Shift practically?

b. In our plant we installed a Grid Interconnection Protection relay on our 132 kV line. Its VVS setting is at 2 deg. I somewhere read depending on the voltage level this angle varies. Is this setting fine or how do i determine VVS Setting?

c. In case we are not operating in parallel is VVS required?
 
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> a. What situations cause Voltage Vector Shift practically?

The Vector Shift protection algorithm is based on voltage angle measurements performed on all three phase voltages. A measurement is taken from each of the 3 phase voltages after every half-cycle and the decision is made after a full cycle. In general, a VS relay measures the same values as the under/over frequency relays, however the operating principles are different. The angle difference is calculated from the zero-crossing times between the present and the previous cycle. This gives six results at the end of each power system cycle (2 half-cycles x 3 phase voltages). If 5 of those 6 results are above the setting threshold, a trip signal is initiated. Since the VS relay compares only two consecutive results it provides fast decision making and tripping in approximately 30ms. The use of the three phases makes the algorithm less exposed to harmonic distortion, interference and imbalanced faults. This improves protection stability and decreases the probability of spurious tripping during non-symmetrical faults.

>b. In our plant we installed a Grid Interconnection
>Protection relay on our 132 kV line. Its VVS setting is at 2
>deg. I somewhere read depending on the voltage level this
>angle varies. Is this setting fine or how do i determine VVS
>Setting?

this setting is basically an advanced protection of your generator against sudden jerk. This jerk will generate if you made On the breaker (grid) without synced condition. The allowable degree of protection will depend on your generator characteristic. And this protection value is to be provided by the generator supplier.

>c. In case we are not operating in parallel is VVS required?

If your generator is operating on is-landing mode i.e. only one side has generator then this protection may be withdrawn.
 
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