is this problem with the AVR?

hi

are both of the DG woring paralle ? if no, have u found similar problem with DG 1 that u r facing with DC 2 ?

first u check is there any undervoltage relay provided for 25 hp motor because this problem is not with DG, as u start 75 hp motor on DG 2, have checked the instant when u switch ON 75 hp motor, what load DG is already delivering ? this problem is not seems to be associated with AVR setting of DG panel, u try to keep all parameter of DG 2 similar to DG 1, i.e. exicitation, frequency, voltage and then once try,

regards

divyesh patel

Could you be a bit more specific, is there any protection which trips : overcurrent , undervoltage. How the motor shut downs slowing down , contactor opens?

The problem is probably with the controls of the motor.

if u found the problem with the control supply of the motor, than measure voltage of the control supply continuously during switching ON the motor of 75 hp. if any dips obseved than make some arrangemen to make it continuous.

regards

divyesh patel

Is the both 25 and 75 hp motors connected with same feeder, if yes then ensure the frequency of both DG is same while u operate independently one DG. May be problem is with voltage response time or speed response time in your one DG.

Rerards

Vishvnath

I understand as follows.

1) There are two sets suitable for parallel operation but you are operating sets in stand alone mode.

2) when put on load like 75 hp motor on machine no 1 everything is working fine

3) But when put on the same load on the machine no 2 , the 25 hp motor trips.

My inference is the 25 hp motor trips on under voltage.

Under voltage occurs since the DG set 2 is sluggish its recovery time is very slow.

this should not happen as the load put on the DG set is < 10% of the rated capacity.

Please check the following

1) Frequency dip (speed dip) when you put on 75 hp load

2) voltage dip when you put on load.

3) what was the pre load on the machine when 75 hp motor put on.

4) Please try to start the 75 hp motor without prel oad find out the voltage and frequency dip

if the frequency dip is predominant then check the engine fuel system,governor etc.

if the voltage dip is predominant check the AVR.

Please give us feed back even if your problem is sorted out or not.

Connect 3 nos of 1ph Analog voltmeter across each Phase - Neutral at the input of Starter of 25hp motor and try starting the 75hp motor first on DG No.1 and then on DG No.2. Record and compare the voltmeters reading on each DGs at the point of shut down. Send me the feedback regarding the same.

Dear members, Thankyou very much for your response and suggestions.

Before I make some checks as suggested I want to clarify some doubts as under:

1. DG Set No. 1 & 2 are not connected in parallel and operate independently.

2. As I mentioned earlier, the problem is with the DG NO. 2 only.

3. If there will be some problem with the under voltage relay of 25 hp motor, then the problem should be on DG No. 1 also. This means there is more voltage drop on DG set NO. 2 when 75 hp motor is switched ON.

4. The DG is Delivering around 400A at full load connected.

5. Frequency and voltage I can adjust from the panel, but from where I can adjust the field excitation.

6. There are no trips anywhere in the system. The 25 hp motor which shuts down while starting 75 hp motor can be started normally without any problem after starting 75 hp motor. As mentioned by Mr. Vishvnath, "May be problem is with voltage response time or speed response time in your one DG". How can I check this and what is the remedy?

7. How can I improve the recovery time, if this is the problem?

More suggestions are welcome till I check the previous suggestions.

Thanks and regards.

You have not answered my questions

1) Is there any preloading.while starting 75 hp motor.

2) Is there any frequecny or voltage dip during the starting of 75 hp mototr.

As i informed you you have to check DG2 for voltage and speed recovery time.Even if the fuel system faulty or governor system is faulty these problems may occur.

What is the rated full load current of the set?

Problem solved…..

Dear members, I made some checks on the Telmech. RM4TA02 relay and adjusted the asym% settings from minimum to maximum but no result. Then I was sure that the problem is with the generator. But I decided to change the relay first to make it sure that the relay is working well. It was strange to notice that the new relay worked well and we don't have any shut down of the 25hp motor and the problem solved.

Still one question is in my mind that why the old relay worked well on DG No. 1 and not on DG No. 2 even I adjusted the asym% setting???????

Thanks to all members for their valuable suggestions from where I got some clues to troubleshoot this problem.

I am a Marine Engineer and have worked with all sizes of generators, I believe you may have a govenor issue with DG # 2 , a large load dropping out other motors is usually a tell tale sign that the Droop seeting may be to low, I would definitley check this out if you have not already done so.