Anybody modeling in PSS-Adept?

[pajce]

There are 3 different ways we can model generators in PSS software.
1. PV Machine
2. Constant Power
3. Induction machine with negative active power

When are we supposed to use which model and why???

1. I noticed that when I use PV machine model machine (generator) pumps out as many +/- VAR’s as needed to keep generator terminal voltage at preset value. I don’t have problem with this, since all generators are exactly working this way in reality. Problem I have with this is that I noticed Reactive Power Flow is going in different direction that I would expect. It is going from source of lower voltage to the source of higher voltage. (Generator was set at 1.0 pu, and source at TS was set at 1.0 pu too) I expect that reactive power flow should always be going from higher to lower voltage bus in the system. In all fairness this is happening with models only when I have utility source and generator source on the same model Generator source far downstream of the utility bus). Please explain how am I suppose to interpret these results? I noticed that by playing with the generator scheduled voltage in p/u. I can swing this reactive energy flow in the opposite direction, and then it is in the correct direction (relative to the voltage magnitude). Which p.u. setting I should chose if setting in the field is not known?

2. Constant Model, same issues when I have generators and utility on the same feeder. Reactive power flow wrong. Additional problem is High Voltage that shows in proximity to the generators.

3. Induction machine with negative active power model? When are we supposed to use this? This is motor NEMA or IEC, but there is option for entering negative WATTS, so it is working as a generator??? This is so little information for accurate model in my mind. What is this option for??

From all above mentioned, summarized question is - when are we supposed to use what model and how do we interpret VAR flow results on the model???

 

[dpc]

I'm not familiar with this particular program, but in general for power flow modeling:

If it's an induction generator, then model as induction. This is a separate type of generator. It is either induction or synchronous and you need to select the proper type.

If you model a synchronous generator as PV, it will produce vars are required to maintain the specified voltage at the specified bus. It doesn't care what direction the vars are flowing to do this. Obviously, a real generator can operate only over a limited range of power factor, so your results need to be checked against the reality of your equipment. You will still need to specify a kW output.

The Constant Power model generally produces a fixed kW and kVAR output regardless of system conditions.

 

[pajce]

Thank you dpc. I guess my question is when should I model sync generator as a PV and when as a Constant Power machine?
Confusion about reactive power flow is that on my model reactive power is flowing from node with lower voltage magnitude to the node of higher voltage magnitude. This is not right, is it?
Forgive me for my generator ignorance, but what is the difference between induction generator and standars synchronous machine? I think motor can be generator if it runs with speed higher then synchronous for the machine.

 

[dpc]

It depends on what you are trying to determine and how the generators are normally operated. If this is a 100 kVA generator connected to a big power grid, there is no point in bothering with PV mode, since it can't really operate in this mode.

Real world machines can be set up to operate either way. It depends on the situation. You may want to try both configurations to see if the results match the real world data you have and if the generator stays within its operating limits.

Regarding induction generator - just Google it, or try Wikipedia.