Previous in Forum: Where's the Noise Coming From?   Next in Forum: Hysteresis Current Controller
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
7 comments
Rate Comments: Nested
Wust53
Participant

Join Date: Apr 2011
Posts: 4

Load Sharing - Again

04/06/2011 1:53 PM

Hello,

This topic has been discussed few times, however that didn't help so far.

System:

3 generators Cat 3512 B

Controls IDM, generic Ross Hill with AC Module, copy or supplied by NOV to IDM for particular job

Situation:

Generator #3 is picking up all the load, while other two generators are going reverse power until certain load is reached (roughly 400 KW on #3 when #1 or #2 are kicking in) and then is distribution something like 80% #3 20% other generator. Same condition is when #1 and #2 are in parallel, where # 2 is picking up around 65-70% and #1 rest. Regardless whether is #3 on line or is brought on line it always picking up the load. PWM (actuator) in 3512 has been swapped between #3 and #2 same situation, all modules has been swapped around always same situation. So, components in AC Module of #1 went in #3, but #3 is always picking up the load, so it is not module (AVR) issue, CT's are giving normal reading, master/slave reading OK, voltage regulator output is bit high on idle (about 250% instead of 10VDC is some 28VDC) while in run mode is a bit on the lower side, 45-50VDC instead of approx 70VDC, but as no input from IDM, don't know whether I can apply all readings normally used for Ross Hill systems. Any thoughts? Ideas? Will appreciate it, thanks.
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
kwcharlie
Power-User
Engineering Fields - Petroleum Engineering - Rig Electrician United States - Member - the Oil Patch Engineering Fields - Power Engineering - Drives & Gen's Engineering Fields - Instrumentation Engineering - Drive Control Popular Science - Cosmology -

Join Date: Jan 2010
Location: Houston off/on-shore @ Oil Patch
Posts: 223
Good Answers: 2
#1

Re: Load Sharing - Again

04/06/2011 6:03 PM

What rig are you on?

Check the load sharing signal between the AC Mods, wires broken if RH, and the fuel system. Maybe you don't have a Ross Hill AC Module and if it's what i think and a IDM Speed regulator it's load sharing signal is adjustable, Ross Hill not so. I'm looking for my IDM book now.

Could be two bad Governors. What kind do you have and have you measured the ma's to them from the speed control?

A true Ross Hill does speed control after idle with the freq from the gen voltage BUT other systems use the Mag pickup for all speed control, check that for dirt and gap and bad wire/conections on the Cats, that goes for the wire to the Governors.

__________________
 Why do they make manhole covers round? so they won't fall in [before asking "Who is John Galt?"]
Register to Reply
Wust53
Participant

Join Date: Apr 2011
Posts: 4
#3
In reply to #1

Re: Load Sharing - Again

04/06/2011 10:23 PM

Cheers kwcharle,

It is RH module all right, however IDM added some things, but no IDM book here, when I took it over thought "piece of cake" I can handle that with both eyes shut. As for governors it is electronically controlled by cat ECM trough the PWM which is getting signal from the AC module. Didn't took mA to PWM, simple reason, 2 gens in use, third one under repair today will be ready then can play with them. No scope available in the range of 400 miles .

Thanks & Cheers
Register to Reply
2
RAMConsult
Guru
Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 3230
Good Answers: 444
#2

Re: Load Sharing - Again

04/06/2011 9:22 PM

Everything is working as it should (but not as you expect) given what you have described. In general paralleling two generators in an isolated system takes more than just synchronizing them, applying load and expecting them to share it equally.

Here's what happens: Assume that Generator 1 is accepting all the load so its governor is supplying just enough fuel to keep the generator frequency at 60Hz. When Generator 2 is synchronized to the same load its governor senses that the frequency is just about right, and its the "just about" part that gets you in trouble. Assuming that both DG sets are identical, both of the governors will attempt to keep the speed/frequency constant until a slight change in load occurs, the problem is that as one increases the fuel slightly the other one will sense the increase in speed and start reducing its fuel supply towards zero which ultimately leads to the condition where the other generator is driving this one as a motor. Things only get more complicated if there are three or more DG sets involved.

'In order to further understand what is happening please supply the following information:

Given that the diesels are all the same model number, do they have the same fuel control system?

Is there any type of interconnection between all three governors?

Are the droop settings correct?

Are all the generators the same with identical electrical characteristics?

Is there any type of interconnection between the Automatic Voltage Regulators?

My guess is that these diesels were not set for load sharing and/or the droop settings are incorrect. You just can't have three controllers trying to control a single control variable; i.e., the speed/frequency of the bus, without some form of setpoint modification to account for this. That's what droop does.

__________________
 “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
Register to Reply Good Answer (Score 2)
No more Good Answers. Go to first "Almost" Good Answer
Wust53
Participant

Join Date: Apr 2011
Posts: 4
#4
In reply to #2

Re: Load Sharing - Again

04/07/2011 2:05 PM

Cheers RAM,

All checked over and over, nailed it this evening, wire by wire, had cold soldering spot on volt adj pot in gen #2, wrongly wired volt adjust pot on gen #1 and as final touch and trouble generator #3 volt adjustment pot neutral wire (grounded) had 140 Ohms to the ground, so it was sending a bit different signal to AVR than it is supposed to be. It actually increased AVR KW share control resistor (R92) of 180 Ohms for additional 140 Ohms so all load went there.

Thanks for guidance to you and to KW.
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
kwcharlie
Power-User
Engineering Fields - Petroleum Engineering - Rig Electrician United States - Member - the Oil Patch Engineering Fields - Power Engineering - Drives & Gen's Engineering Fields - Instrumentation Engineering - Drive Control Popular Science - Cosmology -

Join Date: Jan 2010
Location: Houston off/on-shore @ Oil Patch
Posts: 223
Good Answers: 2
#5
In reply to #4

Re: Load Sharing - Again

04/07/2011 2:45 PM

That's thinking out of the box Wust53; GA to the OP from me, I might have been still been telling you to look in the Speed Controller wiring, with RH doing Master/Slave control for speed should have thought of the AVR sooner

__________________
 Why do they make manhole covers round? so they won't fall in [before asking "Who is John Galt?"]
Register to Reply
Wust53
Participant

Join Date: Apr 2011
Posts: 4
#6
In reply to #5

Re: Load Sharing - Again

04/08/2011 12:18 PM

cheers charlie,

M/S, that was first thing I went when started looking at it

Cheers & Thanks
Register to Reply
ramvinod
Guru

Join Date: Jun 2007
Location: chennai,India
Posts: 592
Good Answers: 19
#7
In reply to #6

Re: Load Sharing - Again

04/12/2011 2:24 AM

Dear sir

Very interesting experience!

Can you inform us how long this problem was going on ?

When the sets were commissioned? is this problem cropped up now or is it there right from commissioning?

I am requesting this information out of curiosity and also such problems come up regularly for advise.

ramvinod

__________________
 Ramesh,Freelance Electrical/automation Consultant
Register to Reply
Register to Reply
Have a Different Question?
7 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

kwcharlie (2); RAMConsult (1); ramvinod (1); Wust53 (3)

Previous in Forum: Where's the Noise Coming From?   Next in Forum: Hysteresis Current Controller

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (81 right now)
Show Members
Advertisement