Ship Generators Problem Running In Parallel - KVAR Unequal

Hello Controls guy 25

Following is submitted:

1. Did you ever try to compare both Load sharing module behaviour..

"May i know how can i do it separately for individual generators. we don't have a testing facility onboard as of now."

By using Load sharing module ( which OEM is it?) make some tests on reactive load bank ..see if KVAr COMPENSATION is done by Generator excitation ( field current )...

Dont know what kind of load is mostly present in your ship...there can be some devices that demanding Kvars..

Can you specificy facility load consumers..

If you have necessary materials you can perform some test separately I mean for 2 generators ( doing same tests ) like factory test ...you surely understood whta i mean..




2. Both AVRs should have same caracteristics/settings as you mentionned.

"Yes sir, as per my knowledge both the settings are same quadrature droop set to 2% and AVR is set for quadrature droop setting not the cross current compensation. (2 AVR's are not communicating to each other)"

Can you ( are you able to check capability curves and carcteristics of both generator )by performing tests as rules and regulations (OEM recommandations, )

3. Does the reactance value or the resistance value of the rotor/ stator can vary overtime which can lead to unequal sharing of KVARs? if yes is there any reference book wherein i can read about the same.

You may check if you can make some transients test and see if caracteristics on both ge,nerators are matching or not its a good idea!


That can be a reason but for me it is relatively minima to give KVAR sharing unbalanced

You right but we still do not know what is gap in KVAR SHARING MODE in this ship...

Sir, i did a small MATLAB simulation in which i came across that, if the Xd, Xd', Xd" and Xq, Xq', Xq" are varied for a similar rating machine then the reactive power sharing is unequal. (although not much but it is unequal) i don't know the how the reactances vary with time- (i am looking for some reference material wherein i can go in-depth on this topic)"

Will check if i can add here a reference for such tests in matlab..

4. I guess that these generator criterias that you mentioned are more subject during transients mode/operations

"but this is happening during steady state as well"

Okay can you give us again Kvar sharing values( both generators )and field excitation values on this topic..

5. Can you tell us how you operate those units in the ships..( isochronous/droop mode used)

"we operate in a droop mode- The no-load voltage of the incoming generator is made equal to the no-load voltage of the running generator using voltage trimmer in switchboard. Post matching the no-load voltages- the units are synchronised' . once both the units are synchronised we see the KVAR sharing- if it is deviating at steady state then we again alter the trimmer to ensure good KVAR sharing. "

How frequency is maintained on this ship?

6. Also did you have a read on cross current compensation /droop KVAR compensation?
"yes- after your suggestion' Good

7. My advice is to get the kvar droop compensation /cross current compensation ok...

"do you intend to say that i need to tune the AVR?" (if yes then why it is required when it is already tuned initially as per OEM recommendation- this is my specific question- i could make out that AVR need tuning but WHY? what factors do change overtime?)
Maybe capability curves registred on AVR (if existing ) is not matching load consumers in this ship needs no more ...
I mean generator capability (mostly recative power capability need to be confirmed for both)


8. Also what is OEM of the Load sharing module ( woordwad ? or other brand)...

"The governor is woodward and the AVR is COSIMAT N8+."okay what about load sharing module (PMS ) brand ?

9. A good thing would be to get some datas capture during the mode that you described ..so we can have better overview on the plant behavior then we will be a better support from here..

"i will get back to you on this but for now i have a grab which shows;
Gen-1 380V 258KW 583Amps 50Hz 0.67PF
Gen-2 380V 275KW 520Amps 50Hz 0.77PF

Both generators are running in parallel mode (with APMS- semi Control mode)"

Thank you sir,

Regards
Hi ALL ,

@Shagun Tandon here some answers( written in red ) on the questions that you posted ( see your last post18)
This is what i can add for the moment, as we still do not know how APMS is operating in KVAR sharing mode ...

Also we need KVAR /field excitation values for both generators during that event..

Thank you
regards,
James
 
Shagun Tandon...
This problem has been on this forum for longer than a year. In my experience I find PF is unusually low ! So, let's start from the beginning:
1) Were generator load-tests ever carried out using a sea-water tank?
2) Have the generators ever worked well together?
3) Did the problem occur after a major change in Load, Wiring, Maintenance, or Accident?
4) Are there Low-Voltage (220V) loads?
5) What are the phase-to-phase Voltages for each generator?
6) What are the phase-to-neutral Voltages for each generator?
7) What is neutral-Amperes for each generator?
8) What is phase-Ampere unbalance for each generator, 1-2% or higher?
9) What are voltage-drops between generator-terminals and closest Load-Panel?
10) What are voltage-drops between generator-terminals and farthest Load-Panel?
11) What are phase-neutral Voltages at each Load-Panel?
12) What is neutral-Amperes at each Load-Panel?
13) What type of cable is used, for example... (Single, 3x1c or 4x1c, Trefoil 1x3c or1x4c?
14) How is bulk-head cable-piercing arranged?
Forgot most important question:
15) Can you furnish an SLD, for Singe-Line-Diagram?
Regards, Phil
 
Hi all!

Here is what i found on Xd/X'd...generators caractheristics/parameters..calculations using Matlab simpowersystem..

See attached file ...

iT IS ABOUT a case study on machine about 6MW at least and one 800MVA..but it can be a good read for all!



Simpowersystems block diagram for generator short circuit test. IV. SOME SYNCHRONOUS GENERATOR LOAD REJECTION TESTS AT RATED VOLTAGE The load rejection tests aims to the determination of the synchronous d and q-axis permanent, transient and subtransient reactances and also the open circuit transient and sub-transient d and q-axis time constants. There are three types of load rejection tests: 1) the "d-axis load rejection test" which permits to determine only x d , x' d , x" d , T' do and T" do , 2) the "q-axis load rejection test" which permits to determine only x q and x" q and 3) the "arbitrary axis load rejection test" which permits to determine only x q , x' q , x" q , T' qo and T" qo. The parameters are determined from the envelope of the armature terminal voltage after de load rejection. To perform the load rejection test the load must be switch off at the same time as the turbine is tripped, the excitation system must be in manual position and the voltage of the field winding must be maintained constant during the load rejection test. The short-circuit time constants can be calculated using the equations shown in the appendix A [13]. To perform the "d-axis load rejection test" it is necessary to have the generator connected to the electrical power system supplying zero active power and supplying or drawing reactive power and the field current must be adjusted. ..
 

Attachments

Gentlepeople...
Thus far, a great deal of theory has been presented, but I have not seen advice given that can fix it!
It is my contention that the problem does not exist because of differences within the machines, but, instead systematic problems outside of them!
The data to prove or disprove it is readily available ! Only it hasn't been revealed yet!
Regards, Phil Corso
 
Shagun Tandon...
One more question...
17) If the engines and AVR's are the same did the problem begin when either or both generator field-excitation sources were worked-on or changed?
Phil
 
Shagon...
Although you addressed James, please advise forum participants if your listed V, kW, A, and PF numbers were provided by instruments or hand calculation? Also, what are excitation Amperes and Volts? Finally, please provide kVAr meter readings and Gen'r Nameplate photo's, if at all possible!
Phil
Hello Phil.

The figures i have provided are the reading of actual instruments.

I dont have the values of excitation amperes and Volts.

As of now i dont have the KVAR meter reading either. but i am sure if we use Pf=P/S we can find out the approx value of KVAr at that time.

Sharing generator name plate is not feasible but i can provide majority of the nameplate data.

Thanks and Regards
 
Hi All!

No problemo @PhilCorso although it is adressed to me anybody is free to add some notes here to support @Shagun Tandon ...


Also i will review the questions and try to reply as best as i can .

How is frequency maintained? I mean by 2 engines on droop mode are you sure that both should be in droop mode ..How about isochronous mode..
Hello ControlsGuy25,

Sir frequency is maintained on the using droop settings. (But what i have studied theoretically, it is always better to have frequency droop control for generators running in parallel rather than isochronous mode.)
 
Shagun Tandon...
This problem has been on this forum for longer than a year. In my experience I find PF is unusually low ! So, let's start from the beginning:
1) Were generator load-tests ever carried out using a sea-water tank?
2) Have the generators ever worked well together?
3) Did the problem occur after a major change in Load, Wiring, Maintenance, or Accident?
4) Are there Low-Voltage (220V) loads?
5) What are the phase-to-phase Voltages for each generator?
6) What are the phase-to-neutral Voltages for each generator?
7) What is neutral-Amperes for each generator?
8) What is phase-Ampere unbalance for each generator, 1-2% or higher?
9) What are voltage-drops between generator-terminals and closest Load-Panel?
10) What are voltage-drops between generator-terminals and farthest Load-Panel?
11) What are phase-neutral Voltages at each Load-Panel?
12) What is neutral-Amperes at each Load-Panel?
13) What type of cable is used, for example... (Single, 3x1c or 4x1c, Trefoil 1x3c or1x4c?
14) How is bulk-head cable-piercing arranged?
Forgot most important question:
15) Can you furnish an SLD, for Singe-Line-Diagram?
Regards, Phil
Hello Phil

Yes your pre-assumption is correct. Engine expert says nothing wrong with engines.

1) Were generator load-tests ever carried out using a sea-water tank?
Yes sir. it was done using sea water tank, and also using the Loadbanks.

2) Have the generators ever worked well together?
Yes sir, they have worked well together but may be in early 20's. (She is a mature lady)

3) Did the problem occur after a major change in Load, Wiring, Maintenance, or Accident?
i have no idea that when did this problem started, but is has definitely degraded overtime. (load changes are there but the core load is unchanged) (maybe post major overhaul when the windings of the generators were redone)

4) Are there Low-Voltage (220V) loads?
Yes sir, there are 230V Loads.

5) What are the phase-to-phase Voltages for each generator?
380 V

6) What are the phase-to-neutral Voltages for each generator?
Star connected- approx 220V

7) What is neutral-Amperes for each generator?
Sir, please correct me, you are asking if there are zero sequence current flowing? (i dont know the values but there are load imbalances.

8) What is phase-Ampere unbalance for each generator, 1-2% or higher?
Sir, it depends on the PF one gen with low PF have the higher current and one with the higher Pf has the lower share of current.

9) What are voltage-drops between generator-terminals and closest Load-Panel?
Not Checked.

10) What are voltage-drops between generator-terminals and farthest Load-Panel?
Not checked.

11) What are phase-neutral Voltages at each Load-Panel?
there is a miniscue voltage drop. we have generally seen 219.(somethings)

12) What is neutral-Amperes at each Load-Panel?
No idea.

13) What type of cable is used, for example... (Single, 3x1c or 4x1c, Trefoil 1x3c or1x4c?
1X3c
14) How is bulk-head cable-piercing arranged?
it depends, we have both horizontal and vertical deck piercings. if you want to know the number of cable in each gland, that will be tough question for me.

Forgot most important question:
15) Can you furnish an SLD, for Singe-Line-Diagram?
Pardon me sir. i cant share that.

16) Generator cap.
Both generators are rated at 1100KVA/380V/50Hz. (same make)

17) If the engines and AVR's are the same did the problem begin when either or both generator field-excitation sources were worked-on or changed?
Engines are same
AVR remains the same for both generators. As per me- it might have changed where is one of the AVR's deflunked and was replaced (i saw a log in some book).


Thanks and regards.

Shagun Tandon
 
Shagun Tandon...
I decided to arrange my response by Question Number:

0) ST: Yes your pre-assumption is correct. Engine expert says nothing wrong with engines.

1) PC: Were generator load-tests ever carried out using a sea-water tank?
ST: Yes sir. it was done using sea water tank, and also using the Load-Banks.
PC: If not too much trouble, can you reveal results?

2) PC: Have the generators ever worked well together?
ST: Yes sir, they have worked well together but may be in early 20's. (She is a mature lady)

3) PC: Did the problem occur after a major change in Load, Wiring, Maintenance, or Accident?
ST: I have no idea that when did this problem started, But is has definitely degraded overtime. (load changes are there but the core load is unchanged. Maybe post major overhaul when the windings of the generators were redone)
PC: So there was major change... Rewinds of both, but the problem didn’t start at that time?

4) PC: Are there Low-Voltage (220 V) loads?
ST: Yes sir, there are 230 V Loads.
PC: Are Load studies available?

5) ST: What are the phase-to-phase Voltages for each generator? 380 V
PC: Assume terminals are labeled Va, Vb, Vc, can you provide ph-ph values meaning Vab, Vbc, Vca? ’

6) PC: What are the phase-to-neutral Voltages for each generator?
ST: Star connected- approx 220 V.
PC: Since the generators are Y or star-connected the “neutral” is the midpoint of the Y or “N”. Then, ph-neutral voltages are Van, Vbn, Vcn ! The neutral is grounded! Brings up Q19) How are midpoints of both generator Y's “grounded” ?

7) PC: What is neutral-Amperes for each generator?
ST: Sir, please correct me, you are asking if there are zero sequence current flowing? I don't know the values but there are load imbalances.
PC: No, this is not Zero Sequence current. You will find a combination of Ia & In, or Ib & In, or Ic & In delivering power to 220 V Load Panels. Knowing these currents will be helpful for determining imbalance ! Also, knowing the 3 line-currents, Ia, Ib, Ic, connecting large 3-phase Loads to 380 V, will be helpful for determining imbalance!

8) PC: What is phase-Ampere unbalance for each generator, 1-2% or higher?
ST: Sir, it depends on the PF one gen with low PF have the higher current and one with the higher Pf has the lower share of current.
PC: It has nothing to do with PF which is computed knowing just kVA and kW.

9) PC: What are voltage-drops between generator-terminals and closest Load-Panel?
ST: Not Checked.

10) PC: What are voltage-drops between generator-terminals and farthest Load-Panel?
ST: Not checked.

11) PC: What are phase-neutral Voltages at each Load-Panel?
ST: There is a minuscule voltage drop. We have generally seen 219 V (somethings)!

12) PC: What is Neutral-Amperes at each 220 V Load-Panel?
ST: No idea.

13) PC: What type of cable is used, for example... Single (3x1c or 4x1c)? or Trefoil (1x3c or 1x4c)?
ST: Trefoil 1x3c!
PC: That means there isn’t a 4th conductor to carry the unbalanced current caused by unbalanced 220 V loads!

14) PC: How is bulk-head cable-piercing arranged?
ST: It depends, we have both horizontal and vertical deck piercings. if you want to know the number of cable in each gland, that will be tough question for me.
PC: Good answer. That means the 3 conductors in a cable are going thru the same bulkhead piercing! State another way... the 3 conductors in a cable don't go through 3 piercings, 1 for each conductor!

15) PC: Can you furnish the SLD, for Single-Line-Diagram?
ST: Pardon me sir, I can't share that.

16) PC: Generator capacity.
ST: Both generators are rated at 1,100 kVA/380V/50Hz. (same make).
PC: Thank you. Are they Cummins Gensets?

17) PC: If the engines and AVR's are the same did the problem begin when either or both generator field-excitation sources were worked-on or changed?
ST: Engines are same. AVR remains the same for both generators. As per me... it might have changed where one of the AVR's deflunked and was replaced. I saw a log in some book.
PC: I may be at fault for this one because I didn’t ask for kWdc, i.e., Vdc and Adc, powering the Generator Rotors.
Finally, I would also be remiss if I didn't give you "The rest of the story": A very long time ago I was involved with an extremely rare Generator problem! Only dealt with it once in my 67-year career! It’s called “Overfluxing” and could be caused by a maverick exciter! In fact, there is an ANSI/IEEE Protective Relay Code Number for it... #24, or the Volts/Hz Relay !

It's been a pleasure working with you!
Regards, Phil Corso
 
Hello Phil

Please find the continuation to your questions:

0) ST: Yes your pre-assumption is correct. Engine expert says nothing wrong with engines.

1) PC: Were generator load-tests ever carried out using a sea-water tank?
ST: Yes sir. it was done using sea water tank, and also using the Load-Banks.
PC: If not too much trouble, can you reveal results?
ST: Pardon me sir. I can not share those details.

2) PC: Have the generators ever worked well together?
ST: Yes sir, they have worked well together but may be in early 20's. (She is a mature lady)

3) PC: Did the problem occur after a major change in Load, Wiring, Maintenance, or Accident?
ST: I have no idea that when did this problem started, But is has definitely degraded overtime. (load changes are there but the core load is unchanged. Maybe post major overhaul when the windings of the generators were redone)
PC: So there was major change... Rewinds of both, but the problem didn’t start at that time?
ST: no sir problem did not start at that time.

4) PC: Are there Low-Voltage (220 V) loads?
ST: Yes sir, there are 230 V Loads.
PC: Are Load studies available?
ST: Pardon me sir. Yes they are but i wont be able to share them.

5) ST: What are the phase-to-phase Voltages for each generator? 380 V
PC: Assume terminals are labeled Va, Vb, Vc, can you provide ph-ph values meaning Vab, Vbc, Vca? ’
ST: Alright sir

6) PC: What are the phase-to-neutral Voltages for each generator?
ST: Star connected- approx 220 V.
PC: Since the generators are Y or star-connected the “neutral” is the midpoint of the Y or “N”. Then, ph-neutral voltages are Van, Vbn, Vcn ! The neutral is grounded! Brings up Q19) How are midpoints of both generator Y's “grounded” ?
ST: Attached to ships hull.

7) PC: What is neutral-Amperes for each generator?
ST: Sir, please correct me, you are asking if there are zero sequence current flowing? I don't know the values but there are load imbalances.
PC: No, this is not Zero Sequence current. You will find a combination of Ia & In, or Ib & In, or Ic & In delivering power to 220 V Load Panels. Knowing these currents will be helpful for determining imbalance ! Also, knowing the 3 line-currents, Ia, Ib, Ic, connecting large 3-phase Loads to 380 V, will be helpful for determining imbalance!

8) PC: What is phase-Ampere unbalance for each generator, 1-2% or higher?
ST: Sir, it depends on the PF one gen with low PF have the higher current and one with the higher Pf has the lower share of current.
PC: It has nothing to do with PF which is computed knowing just kVA and kW.
ST: i wil get back to you.

9) PC: What are voltage-drops between generator-terminals and closest Load-Panel?
ST: Not Checked.

10) PC: What are voltage-drops between generator-terminals and farthest Load-Panel?
ST: Not checked.

11) PC: What are phase-neutral Voltages at each Load-Panel?
ST: There is a minuscule voltage drop. We have generally seen 219 V (somethings)!

12) PC: What is Neutral-Amperes at each 220 V Load-Panel?
ST: No idea.

13) PC: What type of cable is used, for example... Single (3x1c or 4x1c)? or Trefoil (1x3c or 1x4c)?
ST: Trefoil 1x3c!
PC: That means there isn’t a 4th conductor to carry the unbalanced current caused by unbalanced 220 V loads!
ST: Right sir.

14) PC: How is bulk-head cable-piercing arranged?
ST: It depends, we have both horizontal and vertical deck piercings. if you want to know the number of cable in each gland, that will be tough question for me.
PC: Good answer. That means the 3 conductors in a cable are going thru the same bulkhead piercing! State another way... the 3 conductors in a cable don't go through 3 piercings, 1 for each conductor!
ST: Three conductors in the cable are going through same bulkhead piercng.

15) PC: Can you furnish the SLD, for Single-Line-Diagram?
ST: Pardon me sir, I can't share that.

16) PC: Generator capacity.
ST: Both generators are rated at 1,100 kVA/380V/50Hz. (same make).
PC: Thank you. Are they Cummins Gensets?
ST; No sir, A Van Kaick (AVK)

17) PC: If the engines and AVR's are the same did the problem begin when either or both generator field-excitation sources were worked-on or changed?
ST: Engines are same. AVR remains the same for both generators. As per me... it might have changed where one of the AVR's deflunked and was replaced. I saw a log in some book.
PC: I may be at fault for this one because I didn’t ask for kWdc, i.e., Vdc and Adc, powering the Generator Rotors.
Finally, I would also be remiss if I didn't give you "The rest of the story": A very long time ago I was involved with an extremely rare Generator problem! Only dealt with it once in my 67-year career! It’s called “Overfluxing” and could be caused by a maverick exciter! In fact, there is an ANSI/IEEE Protective Relay Code Number for it... #24, or the Volts/Hz Relay !
ST: Yes sir. i have read about the overfluxing in some of the articles. however, the APMS we use, caters for this V/f protection.


LAST BUT NOT THE LEAST:


Thank you sir,

Its been a sheer pleasure for me to have a conversation with someone so experienced.
The questions you asked were really helpful in understanding certain points which go un-noticed during regular working conditions.
Further,
Pardon me sir, i cannot share some of the specific details you asked for. But i will surely look into those facts as well.

Thanks and Kind Regards.

Shagun Tandon
 
Shagun Tandon...

Here are the current (Please excuse the pun) stats! I'm available at Cepsicon.com !

GENSET OPERATING VALUES
Gen #
V
A
kVA
kW
kVAr
PF
Gen 1
380
583
383.7
258.0
284.0
0.67
Gen 2
380
520
342.3
275.0
203.7
0.80
Totals
380
1,103
726.0
533.0
487.8
0.73

Regards, Phil Corso
 
Shagon Tandon...
I.M.H.O, the quickest and simplest test is to measure amps in each generator's star.point-to-hull cable. The presence of current, especially if in both, is indicative of the phenomenon called "Negative-Sequence"! It results in increased generator and engine temperatures!
Q20) What are generator and engine operating temperatures?
Regards, Phil
 
Top