Paralleling of distribution transformers

1. Turn off Caps Lock.
2. Make sure the phase rotation of both is the same.
3. Make sure the overcurrent protection on each winding is sufficient.
4. Make sure the voltage output of each phase is the same.....
5. Etc.

If you need to ask, then answers given in a forum such as this wont help.

The risk of something loud and bright happening is too great, you'll need to pay for the services of an expert.

Is there any vector group DYn11? I think what the guy meant is Dyn11

Theoretically, the ideal conditions for paralleling transformers are as follows:

1. Identical turn ratios and voltage ratios otherwise a circulating current will flow, even at no-load

2. Equal % impedances

3. Equal ratios of resistance to reactance. If different, although there will be no circulating current at no-load, the applied load will not be shared proportional to their KVA ratings

4. Same polarity

5. Same phase angle shift

6. Same phase rotation

For the single-phase transformers, only the first four conditions apply as there's no phase rotation or phase angle shift

Practically I will advise you cosult professionals as someone has rightly advised.

Dear

I am assuming that secondary voltage of your Distribution Transformers are LT.

You have to check following things :

1 Vector group of both the transformers should be same.

2. Both the Transformers shaould have same voltage ratio at all the taps & when you run transformers in parallel, it should operate as same tap position.

3 If you have OLTC with RTCC panel, one RTCC should work as master & other should work as follower to maintain same tap positions of Transformer.

4. YOu must do synchronising check of both the supply voltages. This you can chech directly with multimeter between L1 phase of Trafo 1 & L1 phase of Trafo 2. Then L2 Phase of Trafo 1 & L2 Phase of Trafo 2. & then L3 Phase of Trafo 1 & L3 Phase of Trafo 2. In all the cases Multimeter should show 0 voltage theoritically. These checks you must do at synchromising breakers only. YOu have to also check that breaker out going terminals are connected in such a way that L1 Termianls of both the Breakers comes to same Main Busbar of panel. Same for L2 & L3.

5. YOu can install check synchronising relay & synchro scope also.

6. Best way to check syncronisation on LT is charge complete panel with 1 sourse up to out going terminals of another incoming breaker terminals. Then just measure Voltage difference on Incoming & out going termianals of Incoming Breaker. It should be near to 0.

7. To check circulating current Sunchronize both the trafos without out going load. Then check current. It will give you circulating current.

8. If Secondary of Trafo is not Lt then you must use check synchronising realay. & Commission the system properly. In brief, after connecting relay. remay must be charges with only 1 supply & check that realy is functioning poperly. They you can trust on wiring between relay & PT.

Hi there,

You are asking for a big bang if you want to parallel transformers are not sure what to look for!

Get hold of the electrical engineers handbook as well as the Network, Protection and Automation guide from Alsthom.

This will explain in great detail and more what you are looking for, and if you read it correctly - you will shy away from transformer paralleling.

Regards,

Craig

Do not forget that you will also double the available fault current. I have seen this as the limiting factor when transformers are to be operated in parallel.

HI GUYS!

ALL IS FINE, BUT YOU ALL HAVE NOT REPLIED

1. WETHER WE CAN PARALLEL NEUTRAL WIRES ALSO ?

2. WHAT PRECAUTION DO WE NEED TO TAKE ? ONLY REVERSE POWER RELAY WILL BE SUFFICE ? OR YOU NEED DIRECTIONAL OVER CURRENT & E/F RELAY ALSO ?

Hi there,

I thought I did reply? GET HOLD OF THE ELECTRICAL ENGINEERS HANDBOOK as well as the NETWORK PROTECTION AND AUTOMATION GUIDE from Alsthrom. IT WILL EXPLAIN EVERYTHING YOU NEED TO KNOW ABOUT PARALLELING TRANSFORMERS AS WELL AS THE PRECAUTIONS AND PROTECTION ASSOCIATED THEREWITH!

Regards,

Craig

what is equal ratio of resistance to reactance? Do you mean series reactance and resistance in the equivalent circuit? if so how the currents on transformers change if % u are same? does it matter that they have different R/X ratio? Can you open this condition?