Reverse Power trip 3

[slavag]

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

 

[collies99]

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 ?

 

[slavag]

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.

 

[odlanor]

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.

 

[odlanor]

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.

 

[collies99]

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.

 

[odlanor]

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

 

[collies99]

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.

 

[odlanor]

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!

 

[odlanor]

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!

 

[collies99]

Ok I understand the time stamp, thanks.

MW oscillation frequency, best guess is about 1.88 hz ?