Ship Generator uneven load

Hi,
Hope you’re well. Currently an electrical cadet on a product tanker.
We are having an issue onboard with one of our generators. The generator will take load, delivering the same power (KW) as the other generators in parallel, but the current tends to be roughly half of that as the other generators.
When the other generators go offline and the faulty one is running on its own we get a low voltage alarm followed by a blackout.
We have swapped the governor from one of the working generators onto the faulty one but did not solve the issue. While it was swapped we tested both generators under load and the governor of the faulty generator worked fine on the other generator.
I Believe it to be the AVR but the technician onboard seems to disagree. We have swapped the AVR with one from the spare parts bin ( used ) and still getting the same issue.
The generator first blacked out approx one month ago, during rough sea conditions.

Marine based system using Aconis-2000 PMS.
Both generators have set output of 450V 60hz

Trips approx 10 seconds after other generator goes offline.

Volt low trip - 95% - 10 seconds
Volt low low trip - 85% - 1 second
Any help or guidance greatly appreciated.
Thanks
 
Hi

Would you plz tell us :

Number of operating Genset(s)?

Prime mover controller ( Governor /speed controller Manufacturer OEM)

Is there a Single line diagram available ?

AVR OEM

Nature of load consumers ?

So it seems that Load sharing philosophy is not well respected on this utilty as per your notes..

We will try to give a remote support as soon as you can provide the mentioned informations...

Regards,

@ControlsGuy25
 
Hmmmm....

Welcome to Control.com.

Power (watts; kW; MW) = Vt * Ia * 3^0.5 * pf

Vt = Generator Terminal Voltage
Ia = Generator Stator Phase Current
3^0.5 = Square Root of 3
pf = Power Factor

If you look at the formula and take into consideration how (synchronous) generators work, they produce a relatively constant terminal voltage and a variable stator current, and the square root of 3 is a constant (1.723, I think) and for the most part the power factor should be relatively constant (unless there's a lot of motors starting and stopping all the time). So, if the power is to change, one changes the Ia value, the generator stator current. (More on that below.)

You said: "... The generator will take load, delivering the same power (KW) as the other generators in parallel, but the current tends to be roughly half of that as the other generators." [Emphasis is mine.]

This does not compute. Something is amiss with the instrumentation, or you are reading the wrong current meter (perhaps you are looking at field current and not stator phase current?).

When it comes to producing real power (Watts, kW, MW) the generator does so at a relatively constant terminal voltage (a function of the AVR) and the biggest variable is Ia (generator stator phase current). The generator converts torque (from its prime mover) into amperes (just as electric motors convert amperes into torque--electricity is just the medium by which torque is transmitted from one place to another (otherwise every "motor" need to have its own prime mover (steam turbine; hydro turbine; reciprocating engine; etc.)). Torque is the output of the generator's prime mover and the input to the generator; the generator's output is amperes (and voltage--but that's more a function of excitation (the AVR) than the prime mover (although to produce a constant voltage the generator needs to spin at a constant speed and that's the prime mover's governor responsibility).

I presume all of the generators feed a common "bus" and there's some kind of power meter on the bus. That would be the sum of the power outputs of all the generators feeding the bus. So, if there is such a configuration on the ship, what does the bus power metering/instrumentation say?

An AVR (usually) runs in "Automatic" mode--that is, it adjusts the excitation being applied to the generator field (ultimately) in order to maintain a generator terminal voltage setpoint. That means it needs to get a good generator terminal voltage signal--or it can't do it's thing properly. You've swapped the governors and that didn't change anything. And you've swapped the AVR (for a "used" one--so condition is really unkown) and that didn't change anything. Actually, it kind of tells you that the AVR you installed is doing the same thing with its inputs (generator terminal voltage; excitation current and/or voltage).

There's yet another possibility here--often when multiple synchronous generators are synchronized to a common bus there is some kind of 'power management system' or 'load control' system that adjusts the governors of the generator prime movers to maintain frequency and (usually) power factor (by adjusting the AVR setpoints). It's entirely possible that the inputs to the AVR of this particular generator from the power management/load control system aren't working properly (cause that's likely another input to the AVR that has work properly and could be complicating matters).

Finally, you didn't mention anything about the power factor of the problem generator when it's on the bus with other generators. If it's excessively leading that could mean that the AVR isn't doing it's thing properly for whatever reason.

So, that's a lot to digest, and the only thing I ask is that you provide feedback to this thread as you troubleshoot and resolve the issue. The presence of feedback to most of the threads on Control.com is what really sets it apart from many other (wannabe) similar forums. When feedback is provided it lets others who read this thread--now and in the future (because all the threads are archived and searchable!)--know what worked and what didn't and what solved the problem. BUT, only if feedback is provided. And, thankfully, most of the posters here (the ones who request help) do provide feedback--and, again, that's what makes this forum better than many others.

Welcome to Control.com, and welcome to the merchant marine industry/profession. I've worked with some very good merchant mariners over decades, and always learned a lot from them and was impresses with their knowledge and abilities. Seems to be a good training ground for lots of different careers.

Looking forward to hearing back from you soon!
 
Can you tell us more on the ACB status did they tripped I mean standby ACB or normal ACB According to the manual of OEM for this Aconis PMS there should be blackout restore bus procedure Ith the standv generator and ACB
 
Hi,
Hope you’re well. Currently an electrical cadet on a product tanker.
We are having an issue onboard with one of our generators. The generator will take load, delivering the same power (KW) as the other generators in parallel, but the current tends to be roughly half of that as the other generators.
When the other generators go offline and the faulty one is running on its own we get a low voltage alarm followed by a blackout.
We have swapped the governor from one of the working generators onto the faulty one but did not solve the issue. While it was swapped we tested both generators under load and the governor of the faulty generator worked fine on the other generator.
I Believe it to be the AVR but the technician onboard seems to disagree. We have swapped the AVR with one from the spare parts bin ( used ) and still getting the same issue.
The generator first blacked out approx one month ago, during rough sea conditions.

Marine based system using Aconis-2000 PMS.
Both generators have set output of 450V 60hz

Trips approx 10 seconds after other generator goes offline.

Volt low trip - 95% - 10 seconds
Volt low low trip - 85% - 1 second
Any help or guidance greatly appreciated.
Thanks
Did you investigate the CT?? Are current on all the three phase showing less value?
 
Hi

Would you plz tell us :

Number of operating Genset(s)?

Prime mover controller ( Governor /speed controller Manufacturer OEM)

Is there a Single line diagram available ?

AVR OEM

Nature of load consumers ?

So it seems that Load sharing philosophy is not well respected on this utilty as per your notes..

We will try to give a remote support as soon as you can provide the mentioned informations...

Regards,

@ControlsGuy25
Hi @ControlsGuy25

Hope you are keeping well.

We’ve 3 generators onboard. 450V, 3PH, 60hz , 1000KVA(800KW) , 1283A.
They all work and in Parallel, No.1 and No.2 can work on their own.
We recently had had No.3 working in parallel with No.2.

No.2 was supplying – 649A, 443V, 288kW
No.3 was supplying – 445A, 443V, 296kW
(Taken from Acconis GDP)

But with a hevier load in running in parrellel with No.1 we were seeing circa 300kW from No.3 and circa 600kW from No.1


Governor – Woodward UG dial governor UG-8

AVR model : Hyundai 6GA2–491-1A

Load Consumers : Pumps, Motors , Accommodation lighting, Laundry and galley equipment.

Thanks very much for the help :)
 

Attachments

Hmmmm....

Welcome to Control.com.

Power (watts; kW; MW) = Vt * Ia * 3^0.5 * pf

Vt = Generator Terminal Voltage
Ia = Generator Stator Phase Current
3^0.5 = Square Root of 3
pf = Power Factor

If you look at the formula and take into consideration how (synchronous) generators work, they produce a relatively constant terminal voltage and a variable stator current, and the square root of 3 is a constant (1.723, I think) and for the most part the power factor should be relatively constant (unless there's a lot of motors starting and stopping all the time). So, if the power is to change, one changes the Ia value, the generator stator current. (More on that below.)

You said: "... The generator will take load, delivering the same power (KW) as the other generators in parallel, but the current tends to be roughly half of that as the other generators." [Emphasis is mine.]

This does not compute. Something is amiss with the instrumentation, or you are reading the wrong current meter (perhaps you are looking at field current and not stator phase current?).

When it comes to producing real power (Watts, kW, MW) the generator does so at a relatively constant terminal voltage (a function of the AVR) and the biggest variable is Ia (generator stator phase current). The generator converts torque (from its prime mover) into amperes (just as electric motors convert amperes into torque--electricity is just the medium by which torque is transmitted from one place to another (otherwise every "motor" need to have its own prime mover (steam turbine; hydro turbine; reciprocating engine; etc.)). Torque is the output of the generator's prime mover and the input to the generator; the generator's output is amperes (and voltage--but that's more a function of excitation (the AVR) than the prime mover (although to produce a constant voltage the generator needs to spin at a constant speed and that's the prime mover's governor responsibility).

I presume all of the generators feed a common "bus" and there's some kind of power meter on the bus. That would be the sum of the power outputs of all the generators feeding the bus. So, if there is such a configuration on the ship, what does the bus power metering/instrumentation say?

An AVR (usually) runs in "Automatic" mode--that is, it adjusts the excitation being applied to the generator field (ultimately) in order to maintain a generator terminal voltage setpoint. That means it needs to get a good generator terminal voltage signal--or it can't do it's thing properly. You've swapped the governors and that didn't change anything. And you've swapped the AVR (for a "used" one--so condition is really unkown) and that didn't change anything. Actually, it kind of tells you that the AVR you installed is doing the same thing with its inputs (generator terminal voltage; excitation current and/or voltage).

There's yet another possibility here--often when multiple synchronous generators are synchronized to a common bus there is some kind of 'power management system' or 'load control' system that adjusts the governors of the generator prime movers to maintain frequency and (usually) power factor (by adjusting the AVR setpoints). It's entirely possible that the inputs to the AVR of this particular generator from the power management/load control system aren't working properly (cause that's likely another input to the AVR that has work properly and could be complicating matters).

Finally, you didn't mention anything about the power factor of the problem generator when it's on the bus with other generators. If it's excessively leading that could mean that the AVR isn't doing it's thing properly for whatever reason.

So, that's a lot to digest, and the only thing I ask is that you provide feedback to this thread as you troubleshoot and resolve the issue. The presence of feedback to most of the threads on Control.com is what really sets it apart from many other (wannabe) similar forums. When feedback is provided it lets others who read this thread--now and in the future (because all the threads are archived and searchable!)--know what worked and what didn't and what solved the problem. BUT, only if feedback is provided. And, thankfully, most of the posters here (the ones who request help) do provide feedback--and, again, that's what makes this forum better than many others.

Welcome to Control.com, and welcome to the merchant marine industry/profession. I've worked with some very good merchant mariners over decades, and always learned a lot from them and was impresses with their knowledge and abilities. Seems to be a good training ground for lots of different careers.

Looking forward to hearing back from you soon!
Hi ‘’ WTF? ‘’
Hope you’re well. Thanks for the warm welcome.

Apologies in advance if I say anything drastically wrong... new as new can be to the industry !

* The faulty Generator will be referred to as Gen.3 *


I was thinking that the uneven sharing did not make sense but then wondered of the possibility of Gen No.3 AVR ( or AVR related ) being faulty. If for some reason this does not produce a strong enough excitation field would the other Generator running in parallel compensate to keep the busbar voltage ,causing unequal sharing of the kVAR so unequal reactive current ?

Correct in saying all generators feeding a common bus, but unfortunately we do not have a power meter! Only have Current meter and voltmeters on the generator control panels,
Earth fault meter on distribution panels, frequency meter and kW meters on the synchronous panel.
With regards to the AVR could possibly be the reason why it was swapped in the past and someone never took note… We have a box full of them but not labelled. May be worth while trying one or two of the others ones to see if the generators produces more current ?

From the generator running in parallel today I got these readings off the PMS GDP;
Gen.2 : 649A, 443V, 288kW = 288Kw / (( 649A x 443V x 1.732 ) / 1000 ) = 0.578 P.F
Gen.3 : 445A, 443V, 296kW = 296K /(( 445A x 443V x 1.732 ) / 1000 ) = 0.866 P.F

‘’ It's entirely possible that the inputs to the AVR of this particular generator from the power management/load control system aren't working properly ‘’ – Defiantly something I will be looking into in the morning… not sure where to start but ill try!

Will defiantly be keeping the forum updated. Totally agree with feedback being needed to help resolve future similar problems.

Thanks again for the welcome to both the forums and merchant marine industry
 
Can you tell us more on the ACB status did they tripped I mean standby ACB or normal ACB According to the manual of OEM for this Aconis PMS there should be blackout restore bus procedure Ith the standv generator and ACB
Only Gen.3 ACB tripped. The standby generator came online within 30 seconds allowing Gen.2 to start shorlty after.
 
Also can you give us Gdp panel and Gdp alarms ans status leds
I have gotten all paramters 1-124 from the 3 systems. I will make it into a list tomorow and post it here. We are using Aconis-2000 GCE onboard.

Have also been inconact with them and they have requested a recording of the voltage and current from GDP while also getting voltage readings from the generator locally while blackout occurs.

Thanks again for the help its greatly appreicated.
 
I think you are on right track with suspecting the input signal to the regulator. I thought I saw an external pot on the wire diagram. I had a system once that would take a step change about 4 pm every afternoon and then step back about 11 pm. One of the wires going to a preset pot had several broken strands within the jacket so you really couldnt see it. In the heat of the afternoon the wire expanded and connected more of the strands changing the pot value. As you said the problem started during rough seas I was thinking a bad connection on the input wiring somewhere.

Good luck
 
Hi @ControlsGuy25

Hope you are keeping well.

We’ve 3 generators onboard. 450V, 3PH, 60hz , 1000KVA(800KW) , 1283A.
They all work and in Parallel, No.1 and No.2 can work on their own.
We recently had had No.3 working in parallel with No.2.

No.2 was supplying – 649A, 443V, 288kW
No.3 was supplying – 445A, 443V, 296kW
(Taken from Acconis GDP)

But with a hevier load in running in parrellel with No.1 we were seeing circa 300kW from No.3 and circa 600kW from No.1


Governor – Woodward UG dial governor UG-8

AVR model : Hyundai 6GA2–491-1A

Load Consumers : Pumps, Motors , Accommodation lighting, Laundry and galley equipment.

Thanks very much for the help :)
Hi

Thank you for replying here and sharing such datas

It would be great if you can share a kind of load balance list for better view of load consumers like galley equipment ...
 
Hi

What I am tryin to do is to get a better approach and understanding of the utility behaviour regarding laod nature..

You mentionned that system wen to undervoltage it can be possible lile Reactive power is not shared equally between DG..
 
Blake James...
The numbers you provided in Msg 8 indicate two problems to me:
1) The Genset kW outputs are less then 40% of their rated capacity ! Thus, being operated underload, a condition which can severely damage the Diesel-Engine, and shorten it's life service.
2) Amperes are not proportional to kW. This is indicative of circulating-current between the 2 generators! This is typically an AVR-setting mismatch!
Regards, Phil Corso
 
Thanks for all your feedback and information.

Your calculations are off; you multiply every variable in the formula--including the power factor. The formula calculates watts, not power factor. In a three phase AC power system, the real power output of the generator (watts, kW, MW) is affected by the power factor of the load and the system.

I want to caution you VERY STRONGLY that if you or anyone lifts a wire off a CT or of a CT circuit while current is flowing in the primary of the CT there will be arcs and sparks, and whomever is holding the wire is probably going to . CT secondary circuits (the output circuit) DO NOT like to be open-circuited when current is flowing in the primary (through the main opening of the CT, such as when the generator is running and the generator output circuit breaker is closed and the generator is providing power (real power).

The best way to check the CTs when the generator is running is to use a clamp-on ammeter on the CT wires connected to the generator control panel. There may be one or more CT circuits providing power to the AVR. Since the generators are three-phase, and there would be one or more CTs on each phase, it would be best to compare the outputs of the same three CTs to make sure that they are at least close to each other in magnitude. (Differences in the loads on the three phases will cause some differences in the readings, but on a well-designed system they should be pretty minimal differences).

Most CTs are devices that measure current flow in the primary and produce a highly accurate output on the secondary. Most CT circuits operate on 5A being equal to the rated current flow through the primary. So, for example, the CTs might be rated at 5A in the output (the secondary circuit) for 1000A flowing through the primary circuit. That doesn't seem like a lot--but IF the secondary circuit is opened the voltage on the secondary circuit wiring rises up to the voltage of the primary circuit (in that case it would be 440 VAC, nominal). It's just not a good thing to do.

If there is some kind of power management system it likely has mA (milli-amp) inputs at a minimum for both real power and reactive current. It's entirely possible that one or more of the mA transducers providing the signals to the power management system is not working correctly. If you can see the inputs on some kind of monitor/screen that might help troubleshoot the problem.

I have another question to ask. Was there any kind of work done to the generator control panel(s) and/or bus and/or switchgear just prior to this problem arising? Was there any damage that was repaired or preventive maintenance work done shortly before this problem started?

I want to stress this: Troubleshooting is very often a process of elimination, especially when the system has so many possibilities and components. In this case I'm talking about generator governors, AVRs, many different types of sensors. So, a good idea is to try to think about the situation and decider what is the best likely root cause of the problem and check it out. And if that doesn't turn out to be the problem, then make note of what was done and what the results were, and move to the next likely cause, and continue until the cause is determined and can be resolved. But, it's best to try to "divide and conquer" by working to understand what may be the most likely cause and start there.

I hope you're shoreside somewhere, and can get this resolved before you get underway.

Be safe, and I hope you're getting good support from the equipment manufacturers and your company's technical support staff.
 
WTF?...
My opinion is... the Diesel-engine is at fault. Your opinion is... Generator electrics are at fault.
Only one person can resolve it... Blake James.
So, Blake... you are up !
Regards, Phil Corso
 
WTF?….


Blake’s calculations look good. If you re-read his post he is giving the voltage, amps and Kwatts read off of the meter. He merely divided both sides of your equation by the voltage, current and square root of 3 to solve for the Pf. I redid his calculation and also added one for the generator VAR and VA output. Here is a table of results:

Gen # Amps Volts Kwatts Kva Kvar Pf
2 649 443 288 498 406 0.578
3 445 443 296 341 170 0.867

If the Regulators were sharing the reactive load evenly, each would be putting out about 288Kvars this would result in the table being:

Gen # Amps Volts Kwatts Kva Kvar Pf
2 531 443 288 407 288 0.707
3 538 443 296 413 288 0.716

With the mismatch, as PhilCorso said in message #16 item 2, you set up a circulating current between the two generators. If Generator #3 is trying to put out lower voltage, this would account for the readings. Generator #2 would be holding the bus voltage up. When it is shutdown, the voltage being held low by Generator #3 would trip the breaker on low voltage.
==============================
Blake,

I’ve looked over the prints you have supplied and the only inputs I see to the AVR is the voltage feedback and an external pot on the G31 dwg. I also don’t see any current input to the voltage regulator. Is there any other load or var sharing control that I’m not seeing?

If generator # 3 is putting out low voltage(masked by the voltage of the other generator) it means either:

1. Its mistakenly being asked to be low due to low signal of the set point. (Bad pot signal ??)
2. Its mistakenly being told it is doing a good job by receiving to high of a voltage feedback. (Not sure of a failure mode for this).
3. It’s trying but the power electronics portion of the regulator has failed and not giving you the full. field current. (I assume this was eliminated when the regulator was replaced. I assume this meant the power module also.

Looks like #1 to me as a likely suspect. I think you can disable the external pot by closing a dip switch #3 and just using the board pot.

I have to put a disclaimer that I have no experience on these regulators and this is just what it looks like reading online manuals and looking at the prints you provided…..Good Luck.
 
MWO,

Okay; so I see what he did with the formulas....

This is from the IMG_4799(1).png:

1672996011716.png

I looked and looked and looked and finally found this.
 
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