Additional Switchgear

Dear sms 149,

Better to look into the Electrical Inspectorate guide lines of the state

where you use the power. In Tamilnadu CEIG recommends 75 meters for fixing an

intermediate control to the best of my knowledge.

Manroop.Chennai.

I remember that you had earlier also quoted "Tamilnadu Electrical Inspectorate Guidelines" on another query. As I had responded then, I repeat the same answer:

Tamilnadu Electrical Inspectorate - any other State Electrical Inspectorate for that matter - CANNOT have their own codes of practice or guidelines. Every State, I repeat - every state, MUST follow only the Indian Electricity Rules, 1956, as amended up to date.

Can you trace back your answer of 75 meters for an intermediate control to any IE Rule? Or any published documentation to authentiate your answer? Please don't misguide.

As I have told earlier too, I am a "C" License holder issued by Tamilnadu Electrical Licensing Board. And, I am a "C" license holder in its true sense - that I had applied for & got my License after 22 years of experience in the field - after I fully became confident that I can quote any IE Rule at any time. After all, that is what is expected of a "C" Licednce Holder. Isn't it?

And, with the above qualification, I can vouch that there is no IE Rule that I can recall which calls for any such intermediate switchgear, leave alone a certain distance for such a requirement.

There is no requirement for an interposing outdoor 11 KV CB.

Rather than 200M, the transformer could have been at the city supply grid station some KM's away from your HT room.

At 200meter 132kV switchyard is coming up, through which power is exported to the grid which is inside the plant premises . what is the safe distance up to which I can have cable connection between the swgr and transformer.

What is the minimum bending radius of the cable?

There is no rule here. There is good engineering practice, there are local engineering standards and there is a thing called a risk assessment. To do the last one answer these questions:

1. What is between the supply end and the transformer that will protect the cable from being damaged?

2. What would happen to the transformer if the cable was to fail?

3. If I open the switchgear CB how can I be sure that the transformer is completely isolated to work on it?

4. What protection relays do I have in place to protect the transformer, cable & switchgear?

I can think of many more questions but you need to start looking at what you have, assess those risks & decide if it is worth buting a CB or taking the risk.

Good luck.

In my opinion,you should provide an indoor type 11 kV VCB switchgear within the 132kV Switchyard for facilitating local isolation for maintenance of the Transformer as well as for housing 11 kV side CTs for metering and protection including the vital differential protection of the transformer.You may appreciate that,long control cables between primary and secondary side CTs for differential protection of the equipment is not advisable.The said switchboard can be provided with necessary cable termination panel.The incoming panel of this switchboard and the 11kV terminals of the transformer can be connected through a suitable Busduct.

This arrangement will also help in getting Equipment of higher short circuit withstand ratings as compared to 11 kV Outdoor type equipments.By the way what is the MVA rating of your 11kV/138 kV transformer and what is the value of it's percentage impedence?

Hope this may help.

S PRADHAN

transformer rating is of 12.5MVA with %Z of 10%

With the above parameters of your Transformer you need not go for expensive indoor type 11 kV switchgear in the vicinity of the transformer.Outdoor type 11 kV VCB kiosk complete with necessary CTs & PTs for metering and protection alongwith suitable cable termination facility would be OK.

SPRADHAN Can you please elaborate what exactly is the difference between the indoor type 11kV VCB switchgear and outdoor 11kV VCB kiosk. If both type consist of VCB as a switchgear how outtype VCB kiosk is cheaper. thanks for the help

Indoor type 11kV switchgear board having IP-42 class of enclosure need to be housed inside a switchgear building,where as 11 kV kiosk with VCB & having IP-55 class enclosure can be installed outdoors near the transformer..The Indoor type switchgears are available with short time rating of he order of 40 kA for 3 sec whereas the outdoor type of the order of 21 kA for 3 sec.

You may visit web site of ABB & other manufacturers for further details.

Spradhan thanks for the prompt reply then how outdoor type VCB is cheaper than indoor type

Dear sms149,

If you are in India,you have to follow I.E. Rules, 1956. As per clause no. 50 of I.E. Rules, a circuit breaker of requisite capacity is to be installed as near as possible to the transformer. No specific distanced is mentioned; the distance is depended on the requirements, viz; if differential protection is required for transformer(dpending on transformer rating, sanctioned cost of project),operational and maintenace facilities,safety of human and equipment,etc.

Regards,

Manindra