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# An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

## An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

(OP)
That's pretty much my question.

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

None.

The way I understand it, power systems are modelled and studies are performed on a 100 MVA base in order to properly scale the behaviour of all the electrical devices in that system to one another. As such, if you change the scaling for each and every device on that system to a 10 MVA base, the end results of any study you perform should be identical.

If I'm wrong, let the rain of tomatoes begin...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

Crshears is right. The MVA base is selected arbitrarily to any convenient value
If the system has a 50 MVA transformer, the following pu values apply:
1. 100 MVA base: 50 MVA/100 MVA= 0.5 pu
2. 10 MVA base: 50 MVA/10 MVA = 5.0 pu

Although the p.u. values above are different, the actual transformer power rating is unchanged to 50 MVA as well as other system parameters.
For convenience and simplification, the MVA base is usually selected close to the larger unit connected in the network.

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

Unless you care about the per unit values, there is no impact. Selection of base MVA is arbitrary. The software converts to pu to perform the calculations, but then converts back to actual quantities in the reports. If you are trying to compare per unit data, then the bases need to be the same.

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

(OP)
All these answers look right - no impact. And that’s true when I change the value in the software and run a report: same results, different bases.

A Company we work for came out with a defined standard and the 10MVA base is a requirement, - with the caveat: get this right at the beginning, but the existing models are all 100 MVA.

I just wondered if this would change anything or why they cared. Occasionally we do look at the pu values. Perhaps they want to compare data.

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

It has something to do with O/F problems before when computing power was still in its infancy! The choice of MVA base is to allow dealing with numbers that are "scaled" or smaller for faster and more accurate computing! When the numbers the computer was handling are too much, the computer will truncate/ drop off some digits, a situation called "O/F" or overflow.Hence, your results will be far out.

### RE: An existing power study has an 100MVA base what are the ramifications to changing to a 10 MVA base?

Most transmission companies use 100 MVA base like that used by other people they share information with, and the numbers are easy to work with.

Many distribution companies use 10 MVA because the numbers are easy to work with.

It's that simple. Which gives you the easy numbers to work with.

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