# how to convert synchronous generator field voltage from per unit to voltge

I've been working in PSCAD and in this time I'm struggling with synchronous generator in PSCAD. As you know synchronous generator in PSCAD, working in per unite so I have to change its amount to Voltage and Ampere. Therefore it's been for a long that I'm exploring on the internet how to convert synchronous generator field voltage from per unite scale to voltage scale, but unfortunately i couldn't find. If there is someone who had worked on such an issue before, could you please give me some introduction or any other help?

In the per unit system, the values are represented as fractions of a defined base value. So, in order to convert the p.u quantity to a "real" one, (volts, amps etc) you multiply it with the base value.

As explained by @user19955, all per-unit quantities are expressed in terms of a 'base value'. Usually the 'base value' will be the rated value of the parameter in question. So for a generator,

• The base power Sbase is the rated output power of the alternator.
• The base line voltage Vbase is the rated line-line output voltage at the alternator's line terminals.
• and so on...

In your case, the base quantities for the field current and field voltage are the rated field current and the rated field voltage. You may find these values on your alternator's data sheet. These may also be called the rated exciter current and rated exciter voltage. In the example shown below, the exciter is rated 97 volts, 11 amps.

Note that these quantities only make sense if the generator in question has an electric exciter. In the case of a permanent-magnet excited generator (small alternators), there is no such thing as a 'field current' or 'field voltage'.

Finally, for practical purposes it is not usually required to know the physical values of voltage and current inside a alternator's excitation circuit. Per unit is good enough. Unless you work for a power station or a alternator manufacturer, you can treat the excitation system as a black-box and forget about it. 