HV/LV inter-trip

[DavH]

I am looking for some advice please. I have several recently installed/commissioned 11kV/440V dry transformers. At present the facility to inter-trip the LV ACB when the HV GCB is switched to OFF or trips (using HV breaker status to shunt trip LV breaker) is not used. Question is - are there any IEC requirements for HV/LV inter-trip in this situation? I have attached a schematic of the standard layout.

 

[slavag]

Hi DavH.
Im not sure if it's some IEC requirements.
In the Germany it's rule. In all applications where we work it's rule, instead few utilities.
Please see on this from protection and operation view.

1. Protection reason: HV side protection send trip, reasons:
trafo fault, or ACB fault in this case you feed fault from downstream: motor contribution, generators, parallel operation with second infeed.
2. Operation reason, usually in such application all auto logic on the LV side : ATS, paralleling of two infeeds, sync. of standbay generation. RMU is only switching and protection w/o any voltage devices. You can found your trafo is feeding from downstream/LV side and will close HV CB w/o syncronyzation.
Hope that help.
Best Regards.
Slava

 

[isquaredr]

At present the facility to inter-trip the LV ACB when the HV GCB is switched to OFF *****or trips*****

Are you saying there is no protection intertrip from hv to lv, if so a transformer or HV cable fault would trip its feeding Hv cb but the fault could then draw large currents via the parallel transformer. This assumes the lv bs cb is closed.


















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[RRaghunath]

Refer IEEE242 (Buff book) which is a widely used reference book for protection engineers. It is a requirement that HV trip should trip the LV breaker too.
After all, this is the only way you ensure that the faulty equipment is completely isolated from the power supplies.

There could be exceptions and such times it could be sufficient to comply with the local electricity authority regulations.

 

[DavH]

Thank you for your responses.
isquaredr - there is no requirment for the transformers to operate in parallel.
slava/raghun - This is exactly what I am aiming at. The LV ACB('s) are fitted with undervoltage relays which will trip if the HV GCB opens. This was primarily provided for ATS reasons.
New question - does UV protection comply with requirments for HV/LV inter-trip?

Thanks again for your input

 

[slavag]

Hi DavH.
No, UV (27) dosen't comply with requirments for HV/LV inter-trip.
UV (27) function for the ATS issue only, it's operated in case of upstream HV CB is opened too, for example infeed CB or utility CB.
Next point is timing of UV (27) function, operated time of UV is usually about 1-2sec ( depend on a project).
You have include both function, inter trip and UV (27).
In additional, recommended block UV function from start or trip OC (51, 50, 51N, 50N) functions for avoid maloperation of ATS.
Best Regards.
Slava

 

[DavH]

Thank you. You have confirmed what I thought and I can now confront the installer.