ETAP generator modeling - swing & voltage control

[antigfk]

I will have 12 480V generators in parallel with KW and KVAR load sharing connected to a 4160V bus through a bunch of 2500kVA transformers. I am attempting to run a Dynamic motor start study with one 5000HP motor running and one 5000HP motor starting on the 4160V bus. The 5000HP motors are started on a 250% to 350% current ramp soft starter.

Here is my issue:
Upon hitting the start button, the voltage will initially drop. In reality, then generators' AVR's will excite the generator into providing more VAR than the motor requires to start, which will pick the voltage back up to 480V (on the generator terminals) even while the motor is accelerating. I don't know how to simulate this using ETAP.

All the generators are identical - there is no "swing" generator or a "voltage control" generator. They all provide the KW and KVAR required by the load, plus KVAR to raise the voltage to near nominal volts. In ETAP, when I put the generators on "swing", they do not react to correct voltage. When I select "voltage control", the KW output does not change with the load requirements.

I know that there must be one "swing" generator on the system for ETAP to operate correctly. Is there any way I can get the generators to have both properties - swing and voltage control at the same time?

Here's a graph of the voltage vs time during the motor acceleration. The green line is ETAP's calculation (I would expect the curve to look like this if the power source was utility power with no voltage regulation). The red (which I drew in using mspaint) is what I would expect the actual voltage to look like in my scenario.

http://files.engineering.com/getfil...b1-9894-e9932fa220bd&file=voltage_vs_time.bmp

What do you guys think?

 

[Eleceng01]

antigfk, in response to your statement about "In reality, then generators' AVR's will excite the generator into providing more VAR than the motor requires to start, which will pick the voltage back up to 480V (on the generator terminals) even while the motor is accelerating."

In your figure, it appears that the AVRs do respond to the transient in around 1-second. Attached is a good reference that shows the transient responses to an event for different devices. At approximately 1 second the AVRs do correct the voltage to pre-start values so the model seems correct.

 

[timm333]

You cannot have both swing and voltage control properties at the same time. I typically put all the generators in the swing mode.

As far as I think, the current ramp starter will not help in the motor starting. Because even though it will improve the voltage at the generator bus, it will drop the voltage at the motor terminals. Because by principal, the soft starter decreases both the current and voltage across the motor terminals.

 

[waross]

I am not an ETAP user but I know a little about generators. What is a swing generator?


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

 

[davidbeach]

In the power system modeling software, all of them as far as I know, there has to be a swing source. The swing source is where the program goes to get the Watts and VArs necessary to make the system solution close. Some sources can be set to operate in a fix or narrow band or voltages, power, or reactive power. If they all max out in one direction or the other there has to be a source that can make up any shortfall. Doesn't exactly match anything in real life but is a necessary fiction for the system modeling programs.

 

[waross]

Thank you for the information, David.
Bill

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

 

[matt111111]

antigfk's how expirenced are you with ETAP I just began using it and have a few questions any help would be great!

 

[trosepe]

antigfg,
You should contact Hamid at ETAP in Irvine,CA. He is the generator modeling expert and one of the key ETAP developers.

 

[ePOWEReng]

In the dynamic motor start study in ETAP the exciters/governs aren't model (ref page 16-24 in manual). If you want to include the dynamic characteristics of your generators you have to run the motor start as a transient stability study.

 

[ePOWEReng]

If you run the model in the transient stability mode, you can choose to run a load flow to set the initial conditions. When the transient simulation begins all generators are modeled dynamically from time = 0+