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Reverse Power trip
3

Reverse Power trip

Reverse Power trip

(OP)
Dear All.
Attached disturbance recorder of reverse power trip, Comtrade format,
protective terminal Micom P345.
Diesel generator 17MW.
Du-fuel, in trip time was operated on gas with about 13-14MW load.
Setting P1< 3% 10sec with 3sec reset time
P2< 8% 1sec with 0.1sec reset time.
Trip was after 10sec, but P2< with 8% was started too ( I was changed setting now on the 0.3sec of reset delay ).
AVR Excitation is Basler DECS200.
Grid is very very weak and unstable.
According to grid data,on this time, tripped some other generation unit with 10MW production, tripped by some electrical protection.

I think it was out of step situation ( pole slip, 78 ), Im not believe in some real reverse power: diesel fault.

What is your opinion
Thank in advance
Slava

RE: Reverse Power trip

First file actually showed reverse power condition. Current phase shift is greater than 90 degrees which would put the power into the reverse power quadrant.

Relay oprerated correctly. Pole slip unlikely, power swing possibly, field forcing possibly non existent, prime power issue possible.

RE: Reverse Power trip

About your graph:
1 -It was not included digital channels 32R-P1 and32R-P2.
2 - Right vertical cursor indicates triggering of the DPR. What event recorder start this one?
3 - Records of 0.4seg is insufficient for analysis. There should be a oscilogram up to 10sec.
4 - The phasor curve do not depicts the capability of the generator; does not indicate reverse power.

Attached is DR files analysed by a program that I am familiar(DPR Reason brand)
I did not calculate the three-hase power either. I'm assuming CT ratio: 1000/5 A and PT ratio: 13800/115V. Is that correct?

RE: Reverse Power trip

(OP)
Hello:
CT 1000/1A, VT 13.8/sqrt3/ 0.11/sqrt3 kV

Setting Recorder 1sec, 50/50%
Trigger is Power P1 trip.
10sec was start on/off, reset time 3sec is latch function in operation

RE: Reverse Power trip

I stand corrected, looking at your png file on a cycle by cycle basis, current phase shifted the complete range from 0 to 180 degree, pole slip very likely.

RE: Reverse Power trip


oscillograms attached the power phase of the data records.
Cursor left by measuring the direct power and reverse power (-10MW). The oscillations have a period of time <0.3seg prevents the reset cycle when it goes positive. With that P1 was operated after 10sec.

The setting P1 = 3 * 17/100 = 0.5MW and P2 = 8 * 17/100 = 1.36MW are easily achieved, however only P1 gives trip .. Why?

The regularity of the oscillograms Vn and absence of voltage dip, indicating that there was no failure in the AVR or fault.
There was a disturbance starting 10 sec ago (not registered) on which the system tried to take the entire load of the generator.
In my opinion this oscillation does not define an out of step trip.

RE: Reverse Power trip

I think the original png file blow-up was easier to see.

Cycle by cycle analysis shows a propagating current shift from in phase to 180 degrees out of phase and you can only get that from a pole slip.

Easier to view the scenario as a large salient pole unit with an internal impedance of a pure inductor and connected into an infinite bus. Moving the rotor 1 complete pole pitch and you get 180 degrees.

Trace indicates current from pure power to reactive to reverse power to reactive power back to pure power. It would be hard to imagine that it is just rotor swing without going unstable or the oscillations would decay back to normal power generation without tripping.

RE: Reverse Power trip

Studies of stability are associated with delta = power angle.
For simplicity assume deltaR = mechanical angle between the rotor and stator.
In transient stability maximum deltaR is assumed 180degree for avoiding Motoring of synchronous machines.
OST is a loss of estability seen by admitance relays

Motoring the generator that is under the control of the automatic voltage regulator does not threaten the power system. Of course, this assumes the que system can withstand the loss of the failed unit's generating capacity. Because the field circuit is unaffected by the loss of the prime mover, generator Var loading and terminal voltage remains unchanged immediately Following the power reversal.

Engine-driven generators have mechanical protection systems que shut down the drive in the event of mechanical failures such as bearing overheating. On these units, motoring may be the result of a mechanical protective trip. In this situation, motoring can cause severe damage, because the initiating mechanical fault has not been cleared. Also Motoring these units poses a danger of explosion and fire because of unburned fuel. Gas turbines and other gear-driven generator units are subject to damage under motoring conditions When gearing is designed to be unidirectional. In such designs, only one side of the gear tooth is machined to act as a drive surface. Motoring reverses the input to the drive and the wrong tooth acts face the face the drive-Resulting in excess wear and heating.


Motoring is a problem of prime mover. Although not a practical reasoning, I always wonder what would happen if no protection operate: After short time of motoring, diesel prime mover burst and the electrical system would be stable with the generator keeps running as unload induction generator.

Slavag should worry to inspect damage in diesel engine instead of OST, and triggering DPR by pickup relay instead of trip relay.

RE: Reverse Power trip

ERRATA
......................................................................................................
...................................................................................................
....................After short time of motoring, diesel prime mover burst and the electrical system would be stable with the generator keeps running as synchronous condenser.

...........................................

RE: Reverse Power trip

Diesel connected generators are not designed for the function on a sync condense unit.

Trying to drive the prime mover, burst or not will possibly redult in generator damage, likely bearings first the stator overheating, cooked insulation due to lsrge load current from a siezed engine.

Sync condense unit are typically large unloaded synchronous motor or designed such as to operate as a sync condense unit. Other types could be decoupled horizontal machine with starting motor running gear and a decoupling plate, vertical machine duch as pelton ot francis turbine with pressurized scroll case to drive the water below the turbine.

Anyways, that us what we have in our system in with the exception of unloaded sync motors, customers such as paper mills and mining mills have them.

RE: Reverse Power trip

Large diesels have an annoying tendency to pump lube oil when under light load, no load or when motored. Often motoring is the worst case for oil pumping. The lube oil "slobbered" into the exhaust system is liable to ignite or explode. Burning oil may be ejected from the exhaust stack.
The power required to motor a diesel engine is well within the capability of the generator end to drive. There are other possible issues;
If the engine lost power due to fuel shortage, some injectors and some injector pumps may be damaged by running without fuel.
If the engine tried to shut down because of low oil pressure, the engine may be damaged by running with low oil. Low oil pressure may lubricate the bearings but be insufficient to spray oil onto the cylinder walls resulting in piston, piston ring and cylinder liner damage.
A complete loss of lube oil will, of course, also damage the bearings.
Damage to the camshaft, cam followers and tappets may also result.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Reverse Power trip

Merci !

RE: Reverse Power trip

summarizing my point of view:
Motoring is a problem of prime mover not eletrical generator!
That's all!

RE: Reverse Power trip

(OP)
Ok, thanks a lot guys for your opinion.
Engines in tests now, from yesterday in full operation. Will see.
I try now receive new DR, yesterday was again reverse power trip.
My problem, station is very far from me and we have from time to time problem with Ethernet.

RE: Reverse Power trip

In regards to diesel generators as synchronous condensers;
I know of an installation where this is done.
A city was supplied be a diesel generating plant.
A transmission line was built to supply the city from a new hydro installation and the DG plant was mothballed.
The city load grew and the transmission line voltage drop became an issue.
The DG plant was put back in service. The generators are run at low KW output and high KVAR output to offset the transmission line voltage drop.
I don't know if there are oil pumping issues.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Reverse Power trip

(OP)
In any case, I see this as OUT OF STEP and Im worry, becouse Im not have on this moment out of step protection of generators.

RE: Reverse Power trip

slavag,
-1st thread: I think it was out of step situation ( pole slip, 78 ), Im not believe in some real reverse power: diesel fault.
-4rth thread:I try now receive new DR, yesterday was again reverse power trip.

1- You should fix 32R-P1 and P2 because of maloperation if indeed there is no motoring.
2- about tnudot.JPG:I believe this oscillogram is not enough to make a judgment.
if were a comtrade file maybe I could give an opinion.

RE: Reverse Power trip

With do many trips could it be possible that you have inter-plant oscillation.

Perhaps what is occuring is governors are fighting one another when there is large block switching. Increasing speed droop may helo. Have this been ecplored ?

RE: Reverse Power trip

(OP)
Im sure, it's inter-plant oscillation.
It's small utility, very small and very weak.
Utility only study stability issue.
We start as island power plant and after urgently was connected to grid on the HV.

RE: Reverse Power trip

slavag,
1- what relay trip? (32R-P1 / P2 )
2- Is 17MW base for setting 32R relays?
3- Thank you for DR files. I will analyse later.
I am very interested in motoring. Last year at the hydroeletric powerplant of submersible propellers,
during motoring tests the bubble-76MW turbine / generator unit was leading to absorb 128MW.

RE: Reverse Power trip

slavag,
attached my oscilograms of DR2 files.
1- there is no reverse ative power(EfPG1,EfPG2)
2- there is no triggering of DPR. I did not understand!
I only conclude there is an oscilation without damping , and something trip CB.

You should install eletromagnetic brake to improve dynamic stability of this weak system.
This requires an advanced study of system.

RE: Reverse Power trip

If I read this correctly trace 3 and trace 5 are opposite each other. Is that the MW trace (red line ) ?

If G1 and G2 are fighting each other could also be governor issue. Can you put one one on isochronous and base load the other one, or increase droop on both ? or at least one.

Dynamic instability could also be attributed to fast gain exciter, though we normally would not see this on small machines, but we are predominantly hydro with larger rotating mass and much slower in rotational speed.

De-tunning the exciter may help but your response curve from a step input test may not have the best critically damped result. Reducing gain first, then work on the ID loop.

RE: Reverse Power trip

Yes. red is 3-phase MW instantaneous
Blue is 3-phase MW root mean square all above 0 MW.

RE: Reverse Power trip

Odlander:

Interesting comment that you made "and something trip CB" !

What in your breaker control circuit schematic trips the breaker without targetting ? Trying to narrow it down, perhaps remote transfer trip, relay trip without target, operator trip ?

Is the blue number in cycles (50 hz system) ? The blue RMS would then have a frequency of about .1 HZ oscillation about 9.28 seconds period.

For power oscillation between power system we install Power System Stabilizer (PSS) on all units above 20MVA, smaller units are maxed out (based loaded). If governor and exciters are at optimum critical damping/response then the PSS would introduce a counter field forcing signal to make the rotor stable. It is tuned so that by field current have maximum effect to fight the rotor oscillation based on time constant of the field LR circuit and based on the Delta MW oscillation (.1 - 1.5 HZ). Perhaps that could be a solution here. PSS also applicable for inter-pant oscillations.

On you trace 3 and 5 after the vertical cursor, I do not see MW osscillation for both units being of concern. Trace 3 oscillation went from blue to red, I think that is continuous and the same instantaneous MW for unit 1.

Trace 5 have both blue and red before the vertical line, Is that both Unit 1 and Unit 2 MW instantaneous and post the line Unit 2 only ? If that is the case then Last comments on on governors fighting against each other is in effect and governor response is the issue compensating for small deviation in frequency and being out of sync with each other but typical if they do not have a load sharing module to control governor action. Wood wards make such a device do not know if they make PSS for large fast acting diesel unit but they are available to contrao machine around 18 MVA. Our diesels are much much smaller.

RE: Reverse Power trip

collies99
These oscilograms are reproduction of Comtrade data furnished by Slavag.
By data information, record time is same as triggering time at 01/01/1997 00:00:01:000
I guess there was an operator trip with direct transfer trip.

I did not understand how you calculated 9.28sec.


attached is my oscilogram of DR2 files revisited.
-Trace 5
Ef_P_G2= 1MW RMS Active 3-phase power G2
Fr_Ef_P_G2 = Not determined
-Trace 6
P-G2 = 0MW Mean Active 3-phase power G2
-Trace 7
Fr_P_G2 = left vertical bar =not determined right vertical bar = 2Hz

You all right. There is no reverse power neither oscilation!.
Your point of view is more convincing than mine.
Good Job!





RE: Reverse Power trip

collies99
These oscilograms are reproduction of Comtrade data furnished by Slavag.
By data information, record time is same as triggering time at 01/01/1997 00:00:01:000
I guess there was an operator trip with direct transfer trip.

I did not understand how you calculated 9.28sec.


attached is my oscilogram of DR2 files revisited.
-Trace 5
Ef_P_G2= 1MW RMS Active 3-phase power G2
Fr_Ef_P_G2 = Not determined Frequency
-Trace 6
P-G2 = 0MW Mean Active 3-phase power G2
-Trace 7
Fr_P_G2 = left vertical bar =not determined right vertical bar = 2Hz

You all right. There is no reverse power neither oscilation!.
Your point of view is more convincing than mine.
Good Job!

RE: Reverse Power trip

Ok I understand the time stamp, thanks.

MW oscillation frequency, best guess is about 1.88 hz ?

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