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From: RAGAVENDAR on 29 Jul 2010 06:37
Hi All

I am Doing Simulation of Grid so i am just Connecting Different voltage source and Load so that the power flow can be analysed But using of Transformer imposes Problem How the Values of R & L of Primary and Secondary of Transformer Needs to be Determined and also how to fix Mutual Reactance and Resistance.

Please Suggest Me Some Ideas...
From: Frank W. on 30 Jul 2010 04:31
> Hi All
>
> I am Doing Simulation of Grid so i am just Connecting Different voltage source and Load so that the power flow can be analysed But using of Transformer imposes Problem How the Values of R & L of Primary and Secondary of Transformer Needs to be Determined and also how to fix Mutual Reactance and Resistance.
>
If you have to use the real model for the transformer and there are datasheets of the transformer available I suggest using a transformer pu model (use the presets). The relations between primary, secondary and magnetizing resistance are rather indepedent of the transformers nominal power. The leakage inductances depend on the transformer design and mainly determine the bahaviour in a simulation (range 0.05...0.15pu).
It is also possible to replace the transformer with a RL series Reactance (Rt, Lt). If you are interested in the system bahaviour when energizing the transmission line this will yield wrong results. For simulating the motor start-up or so this is a suitable solution. Then
Rt = Ps * (Unom_sec/Snom)^2
with Ps=short circuit power (measured in the testfield), Unom_sec=secondary side(!!!) nominal voltage (motor voltage in your case) and Snom= nominal transformer power. Rt might also be ignored if you don't know Ps (L is much bigger than R see preset values of pu transformer block).
Lt = sqrt(Zs^2 - Rt^2) with Zs = uk*Unom_sec^2/Snom
uk from the datasheet or 0.05...0.15 (mainly around 0.12...0.15). If Rt cannot be calculated simply use Zs as the value for Lt.
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