Generator Step Up Transformer Scheme

Consult a qualified Electrical Engineer locally, for it would appear that none is available to help with this design activity.

I seconded PWSlack.

1) Adequate system protection can be facilitated on a DELTA or WYE system. The reason for having a WYE distribution system is usually to allow lower voltage-to-neutral circuit capability to meet attached equipment requirements.

2) Avoiding differential protection in my opinion is a suicidal decision. What you need to be considering is what the cost will be for replacing a generator or multiple generators should conditions arise that require differential protection. (The cost of differential protection compared to cost of replacement.)

The earth fault relay protection should be considered as a separate component.

3) The physical location of the CT(s) and their connection(s) determine the protection zone.

I strongly suggest you hire an outside, competent electrical protection specialty company to look at your system and provide guidance before proceeding.

Thanks, mostly differential protn. Provides for high voltage systems only. I don't know y no any genset manufacturers r not providing it as in built provision in their relay.

The obvious people to ask about this are the people you're hiring the equipment from.

They may just have a vested interest in protecting "their equipment" from incorrect installation by you the customer.

Dear Gentleman,

In reference to your first point, regarding design of Transformers and keeping its LV side as Delta and HV side as Star, the important reason is to optimise engineering and cost of the raw materials.

In case of LV side, current is more. due to delta configuration Phase Current gets reduces by root 3 times, i.e. Ph I = Line I/root3. hence less copper in the LV winding.

Similarly, in case of HV side, due to star configuration Phase Voltage gets reduces by root 3 times, i.e. Ph V = Line V/root3. hence less insulation in the HV winding.

the above concept plays major role while designing a transformer.

Thanks, your reply is very clear

"...your reply is very clear...", while true, is totally irrelevant/unrelated to your questions about protective relaying.

sir, i was awaiting you, he mentioned about transformer design concept only, ie why the transformer low voltage side is delta and high voltage side is star. of course its not related with protective relaying. but im sure there is something since you remarked it. request your valuable recommendations.

1. The low voltage delta is there to provide a path for certain harmonics and/or zero sequence currents so that they don't crossover into the high voltage side. "Hope" plays no role in serious engineering design.

2. "...need to avoid since it is not economical...", really? In actuality these small generators usually don't have the individual neutral leads brought out for the requisite differential CTs, instead a single CT is located in the neutral lead after the star point.

3. It is not intended to operate on faults outside the protection zone, but it depends upon being properly set up.

4. One thing that won't be sensed is a fault in the last 20% of the winding closest to the neutral.

5. So you believe that 50 meters of cable laying unprotected in a cable tray is a "...fault free zone..."? Cables do fail, and the zone between a generator and its transformer is in the an area with the highest potential available short circuit current.

If you value your client's installation you should immediately step aside and seek competent engineering assistance.

dear sir,

its job in hand and under negotiation for cost reduction, its true that normally for low voltage gensets there wil b no space to provide diffntl cts in the neutral side, if v need to put they have to go for non standard design which is cost impact. so v r thinking to put 1no. nuetral ct in the star to earth point of genset. my question is as you said if it will not operate for a fault in the transformer secondary (external). the percentage of protection can be changed no? instead of 20% we can set it to 10%. for cable protection the relay in the genset will take care. For transformer secondary wil provide ref. relay. how ever as u advised we may ask assistance from a protection co-ordinator.

thanks

Dear sir, please refer the attached scheme and would you advice about the protection provided, regarding..

Genset having its own protection relay, will this operate on any over current even in the transformer secondary also? so it will protect the cable. e/f relay provided will protect the winding, 85%. differential protn. is not considered. scheme is typical for 10nos gensets

thanks