We liven our new UG transmission cable last nite 33kV. This is a backup transmission line to the parallel OH line.
OverHead (OH) trans already on service.
Underground (UG) energise last nite and causing Generator MVARs to drop down.

Soon after we liven this UG cable the Generator MVAR drops down to 500kVAR (Machine Rating 5770kW @ 0.8pf, 11kV).
On the UG cable relay info
Apms per phase: 20A
MWatts: 0
MVARs: -1.2MVARS.

Need to know if this UG cable inject pure capacitive load to the system.

The generators running on low MVARs with High KV.

Thanks

 

Victor... several questions:

1) Is Generator neutral NGR earthed?

2) Is 33kV system solidly-earthed?

3) Is UG cable 3 or 4-conductor?

4) Is UG cable metal-shielded?

4) What is MVA capacity of step-up Xfmr?

5) Did Generator trip?

6) If tripped, which protective device was activated?

7) What were pre-fault and post-faut parameters, i.e., V, A, MVA, MW, MVAr, and PF?

Regards, Phil Corso

 

>Victor... several questions:
>
>1) Is Generator neutral NGR earthed?
No, Generator connected to 11kV BUS which earthed using a earthing transformer.

>2) Is 33kV system solidly-earthed?
No

>3) Is UG cable 3 or 4-conductor?
3 conductor

>4) Is UG cable metal-shielded?
No, XPLE type

>4) What is MVA capacity of step-up
>Xfmr?
15/20MVA

>5) Did Generator trip?
No, only one generator was online. Other Generator could not synch due to high voltage on the 11kV BUS (went up to 12kV)

>6) If tripped, which protective device
>was activated?
NA

>7) What were pre-fault and post-faut
>parameters, i.e., V, A, MVA, MW, MVAr,
>and PF?
>
>Regards, Phil Corso

 

Victor, without pre-fault and post-fault parameters, I can only address your original question:

Yes! Upon switching it on the UG cable behaves like a shunt-capacitor! And, although the steady-state current (20A) is relatively small, the transient inrush and more importantly, its duration, probably caused the AVR to respond!

Regards, Phil Corso