synchronising of Diesel generator sets

Yes, two dissimilar rated DG sets can be synchronised.The load sharing will be in the ratio of ratings.For example supposing you are synchronising the two sets namely 250 kVA and 125 kVA and the load is 300 kVA .the load will be shared as 200 kVA and 100 kVA respectively.

But there should be load balancing relay provided for each of the set.Droop characters should be set properly.The Alternators should have AVR for proper reactive power sharing.

Mr Ramvinod,

Please dont mind to elaborate on what are droop characters and AVR for proper reactive power sharing?

I am working on a Auto-Synchronizing panel. I have purchase GAC Auto-Synchronizer SYC6714 and Load Sharing Module LSM672. But I am unable to decide what model of Interfacing Module to purchase as the owner has yet to decide what (brand) gensets to use as it is a co-gen plant where the gensets are for future provision.

What are the types of signalling exist for the controller to communicate with genset in order to fine tuning the speed during synchronizing process?

sir,

Our genset 250 kva is of cummins engine and generator of stamford we have AVR of SX440 we have woodword GCP in synchronising panel,at present we are synchrinising with same capacity of gen of 250 kva. If we want to synchronise with 125 Kva of cummins engine and kirloskar generator AVR of normal Kumar make. what are the alterations to be done.

kindly give me the guidence

M.yogendranath

Afcons Infrastructure ltd.,

1) Each set should have one woodward GCP

2) Please check with Kirloskar by giving details of both alternators about the suitablity.You have to give the specifics to Kirloskar-like model no type of AVR is provided etc., details of quadrature current compensation CT etc.

They can only advise you properly.There is no general theory.

I have seen a power diesel power station Cummins made of 5 gensets of 1250 kva controlled with powercontrol devices. It works fantastically well;

I have very good experience on these GAC relays and commissioned more than 6 such sytems.These GAC relays will not do any adjustment of voltage and will not do anything for reactive power sharing.

You may have to go in for EAM interfacing modules.model depends on make of engine and Governor type.

If it is Indian Cummins engine you may have to go in for one more pcb card for reference voltage.

You may have to set the engine governor for analog setting instead of digital setting.

The wiring is little bit complicated take care for proper circuitry especially on DC reference voltages otherwise you have problems in load sharing.

I am only cautioning you to take care of certain aspects.

Sir, from where can I learn more about GAC relays? any web site? I have lot of work experience but first time I got an answer for the basic question. 250KVA syn with 125 KVA. Any loss in efficiency? (in Rupees or Dollars per unit - KWH)

yes, look on the net,it is unique and goes from Spain to Russia probably

The conditions for synchronizing are

same voltage within admitted tolerances

same frequency within admitted tolerances

same phases , if not you destroy your equipment and provoque a short circuit

phase angle within the tolerances between the actual net and the genset to connect

the load sharing must be done automatically playing with the first two factors

We saw a guy burn up two small generators when he tried to synchonize them to share a load. The phases were not the same and both generators were totally ruined $$$. BE CAREFUL on the exact same phases , if its not locked in , in such a way as to never be changed you will be in trouble in the future. Its alot easier to simply make one gen drive one load system and the other gen drive other separate loads. One way that "might" work is to connect the drive shafts together when they are both in same phase, this mechanical method 'might' be the most effective to prevent accidental phase changes.

ramvinod is right in his specific solution which is one of the several possible.

I would like to warn you about initial approach to setting and maybe calibration:

Well designed control system should have so called AUTO-MAN (manual or HAND)switch. It is also for initial tests and settings. Sharing S, P and Q powers can be done (in worse case scenario when Controller failed) via generator exciting (DC winding) current adjustment. Remember to have all (2 sets per generator x 3 = 6) meters: kVA, kW, kVAr so your adjustments will be monitored and an operator will know what is going on in the system.