Power Plant Tripping Due to Load Fluctuations

Separate the generators and use the 15MW unit for the sugar plant and the 12MW for the steel plant.

Since yesterday we have separated the generators. Frequent tripping still coming. Failure become when power sudden come 0 from 06MW when steel plant heat drop. When this happen exhaust steam going to the process stop and ultimately makeup steam valve open on auto mode to meet the process demand. This is again loss of superheated steam. Is there any solution other than load banks at the moment?

Separate further the auxiliary load from the 6MW, and put it on the other generator. Then, when the steel plant generator trips on low load, it won't affect the auxiliary load.

Could it not be set up (the two gensets) to have 1/2 share of the total load of 18.8MW? Each running at 9.4MW at least when load reduces abruptly in magnitude of 6.3MW both generator would have approximately, 6.25MW each almost half their rated capacities.

It is to inform you that I am not supplier nor consultant. Professionally I am Engineer and just want to get better idea. Although enquiries for load banks has been floated yet in between if any CR4 member can guide me to get the plant smooth, I shall be thankful to him.

Thanks

What does "Professionally I am Engineer" mean in your country, are you an Artisan called an Engineer or do you have University Degree and Registration as a Professional Engineer that will be acnowledged also in other countries? I doubt but you can explain it to us. We are Professionaly bound to ensure that the knowledge that we give here will be used by a sufficiently qualified person. No nasty intent towards you.

Sorry JohnDG, I place Professionally and morally bound in the same hat. You can not advice someone on this forum on working in a 11kVA instalation if you can derive from his knowledge that he is not Qualified to work on 120 Volt. You are welcome to disagree and I will not be drawn into an argument about it. This guy refer to an installation where he can kill homself or worse kill the parent of someone elses child, I'm will not be party to that.

My Dear,This is the forum where every one can consult. Questions should always be encouraged.The more you give knowledge,the more you have.Pl.always cool mind and give response in a good manner. As a human being this is our prime responsibility. However thank you for your discouraging reply.

I'm sorry if you feel offended but my responsibility towards you and your company is to protect you from unnecessary damage and injury. My advice and many on the forum was to get a qualified consultant to advice you and to do the right thing having done the relevant tests and processing the results. This is one of the most basic principals in Engineering and in itself education. I personaly think that you are out of your depth and can cause damage to yourself or somebody else if you get flooded with information that you can not understand and apply correctly. Get somebody to advice you and learn while they help you, that is my advice, should be uplifting and much better than making a mistake and look like a fool to your boss. Good luck if you carry on gambling, just do it with your own life.

I must agree with Oomborrie!

Giving advice about lethal power supply to those who are not qualified to work/be around it is like giving a loaded gun to a blind man and encouraging him to pull the trigger.

You have no idea of the outcome!

Get qualified help. The life you save may be your own.

<...him...>

Are women not supposed to reply, or something?

His word " Him" is multi racial, multi gender, multi cultural, multi lingual, has nothing to do with meaning of an english word, has to do with his good manners and accepepting that this forum use English as medium of comunication. Thanks to him for trying and all the other posting here in 2 nd, 3 rd and 4 th language.

You need professional, competent help, still.

Why not hire an expert instead of stumbling in the dark.

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The company has budget for consultation for sure, I prefer him to consult not on line, it is a risky decision to make.

May be, he would let suppliers find solutions at least they have the legal right to do that in their local.

You say they have a budget. Maybe, maybe not.

The OP is a regular here, with questions better given to a paid consultant.

Typical of some, OP is trying to save money by soliciting free consultation, again.

That's pennywise and pound foolish say I!

I guess trying to learn the lesson the hard way (destructive testing).

I've just wasted a bit of the time I have left to me looking through his previous posts.

The guy is a parasite.

Hire a consultant that can investigate and recommend improvements. There must be plenty of capable people locally; all one has to do is recruit one.

You could study either or both main processes to find ways for staged shut-downs rather than sudden shut-downs.

If you're tripping on overspeed, then it's probably when the end of the billet leaves the roll stand (And the mill goes from full load to no load instantly).

Some suggestions come to mind:

:- Reducing the billet thickness reduction on each pass might reduce the differential to no-load.

:- Increasing the heat temperature of the billet (making it softer) to reduce the differential to no-load.

:- Increasing the roll stand flywheel mass might absorb the excess energy when the billet exits, so that delta speed is acceptable.

:- Increase the shaft mass of the generator so that delta speed is acceptable.

I'm really not a fan of load banks. They are just a waste of energy.

Thank you my Dear. Let me discuss with my team. Regards

Your issue is no different than sudden event load shedding caused by lightning or other unexpected catastrophic system disturbance.

The generator protection system is functioning correctly by protecting the generator and associated equipment.

The correct way to address this issue is by adopting a load shedding program.

1) Steel plant operations personnel choose load reduction/shedding option prior to shutting down equipment/plant and notify generation station.

2) Steel plant operations personnel initiate planned load shedding sequence program.

3) When load shedding has reduced power supply system demand to an acceptable value that will not disrupt or pose risk to online generators, remaining load can then be disconnected from distribution system.

Installing a load bank will require high speed generator load transfer switching which is required to be automatically initiated by the steel plant operations personnel.

Inherent control reaction time delays associated with the execution of logic, load status feedback signals, and the time required for switch mechanical operation will most likely not allow stopping the generator overspeed trip from occurring and will add the risk of overloading the generators.

I see no way the existing generator excitation can react fast enough to prevent overspeed tripping from occurring when the load suddenly goes from 6.5MW to zero (0) or from 6.5MW to 13MW.

Load anticipation capability might help but will not solve the issue.

It is in your best interest to contact the generator controls manufacturer and solicit their evaluation and input on the existing generator controls capability and ask to what degree the controls can be upgraded.

If the generator is owned by the same company that owns the steel plant; The politics are simple and the owner must decide which is more important: Protect the generators by adopting timed load reduction, or suffer the consequences of losing a generator or generators.

If the steel plant is being supplied by a separately owned utility company; The utility company should adopt time-based load shedding standards to protect their generators that force the steel plant to comply with an acceptable time lapse based load shedding program or pay large penalties for non-compliance.

If the load shedding penalties are higher than the minimal power savings realized from sudden disconnection of the steel plant equipment, the issue will stop.

Thank you very much for giving nice tips.

Best Regards

You are most welcome!

You have not made the circumstances of "cause to trip 12MW turbine" clear.

Is another 12MW or 15MW turbine in parallel at trip? Do they trip?

What is the load before trip?

Was this 6MW step change specified to the generator system designer/ builder?

Does this happen every time - or is it operator "make it good" on one shift and operator "make it quick" on another?

Is 53Hz relay one per site or one per generator? Is there a time delay setting unit following or integral with frequency relay which could be faulty.

Have the actual settings of relays been checked by injection from test set?

Have the speed governors, steam valves etc been checked and set up lately?

Some "wheeze and dodge" things come to mind...

The 15MW unit may have higher inertia (15+12 better than 12+12).

Reduce the system frequency to minimum before the load rejection (48 Hz to 53Hz is 2Hz more speed increase than 50 to 53 Hz) if the steel works give you notice of the step.

67model

My Dear Friend,

Thanks for your response. Reply to your queries is as follows:-

1. Both the turbines were isolated since tripping problem.
2. Load at the trip is 7.5 MW (12 MW TG set).
3. 06 MW step change not specified to the generator system designer/builder.
4. Some time this happen once in a shift & some time twice in a shift.
5. Frequency relay is fitted on generator, set at 53 HZ with time delay of 2 seconds. The frequency relay is healthy because there are 2 frequency meters parallel on same line and these meters also giving same readings at the time of over frequency trip we observe 53 HZ also on back up frequency meter.
6. Yes relay tested through injection tester.
7. Turbine control governor is 505. Its actuator need to calibrate (precautionary).
8. Yes 15 MW have higher inertia but run single 15 not 15+12 synchronized.
9. It is not possible to reduce frequency of system because load rejection is so fast and unexpected.

Regards

Thank you for answering the questions. I think all wise immediate steps have been taken or initiated.

One thing, you describe the step load change as 06 MW - this I have understood as 6000 kW. Note it is not usual to write "leading zeros", except, say, for a kWh meter log reading, where there is a leading "0" on the register.

Many generating units are able to reject full load with no more than 5Hz frequency rise. Maybe, now that the full circumstances are given, other CR4 members with relevant experience may comment.

My feeling is that, given that a trip occurs only once or twice in a shift, there must be many plant cycles in a shift which do not cause a trip. This suggests that questions about when in a "steel" cycle trips occur, with a view to reducing the speed of load reduction, may be fruitful.

The "steel" operation should give thought to :-

1. Cost of the supply interruption in spoilt material and lost production time.
2. Consequences of loss of a turbine, due to stress of repeated tripping, to their operation and maybe damage payments to the turbine operator. A lack of reasonable response to minimise tripping increases their liability risk.
3. Effect on other users of electricity.
4. Whether operation at 49.0 or 49.5 Hz, which may avoid trips, would have any significant effect upon operations. N.B. generators and large motors are usually rated for continuous operation at 49 to 51Hz while smaller items are OK at 48 to 52 Hz.

67model

At last, someone get to the financial implications. In SA the Utility provider will issue a warning if your opperation interupt or cause serious production problems to the opperations of another client. If no steps are taken from your side they will issue a disconnection instruction. This can be devestating to the finances of an production facility. Your advice is higly appreciated, covering a full spectrum of steps.

Oomborrie,

Agreed, having understood the technical situation from Muhammad's last post, I think it needs serious company level artillery, carefully worded in writing, hand-delivered by a person armed to discuss the problem. The object of this would be get cooperation to mitigate or eliminate sudden load cuts or tripping - by better management from all - to minimise the cost to all parties of the problem.

I was formerly involved in gas turbine-generator supplier's quotations. If I had to assess a job requiring a 12 MW unit, running alone, to be repeatedly stepped down from 7.5 MW to 6MW (without tripping or other bad effect) I would have advised that taking the job would be like "putting your head into the mouth of a yawning hippopotamus".

67model

prior to giving you advice for the case, i want you to do something..first is, know the electrical system you are currently working with. know every inch and nook of it (details), develop you one-line diagram, and develop the correct impedance diagram. perform load flow analysis and simulate cases: i.e. normal scenario, and the scenario at which the tripping happens. from your load flow analysis you can now have an idea on what is happening every time you perform load shedding. analyze and then simulate ideas on how you would address your problem. hope this helps. :)