Converting Amperes to kVA

The main reason for wishing to make such a conversion is likely to be that, whilst Regulation 311-01-01 of BS 7671 requires the assessed maximum demand of an installation to be expressed in amperes, electricity distributors usually require to be advised of the maximum demand in kVA when dealing with applications for new supplies.

Alternatively, in the case of a house or flat, a distributor may request the maximum demand of the installation in kW (kilowatts), rather than kVA. This is dealt with at the end of this article.

Single-Phase Loads

Converting amperes to kVA

For a single-phase load expressed in amperes, the load in kVA may be calculated using equation (1): eg. supposing the designer of a single-phase 230 V electrical installation has assessed the maximum demand to be 65 A, the load is then equal to 15 kVA (given by 230 V x 65 A ÷ 1,000).

Converting kVA to amperes For a single-phase load expressed in kVA, the load in amperes may be calculated using equation (2): eg. supposing an item equipment of rated voltage 230 V has a nameplate rating of 10 kVA, the rated current of the equipment is then equal to 43.5 A (given by 10 kVA x 1,000 ÷ 230 V).

Balanced Three-Phase Loads

Converting amperes to kVA

For a balanced three-phase load expressed in amperes, the load in kVA may be calculated using either equation (3), which uses the nominal phase (to neutral) voltage (U0), or equation (4), which uses the nominal line (phase-to-phase) voltage (U):

As an example of the use of equation (3), suppose that a threephase installation having nominal phase voltage (U0) of 230 V has a balanced three-phase maximum demand current of 120 A, as shown in Figure 1. The maximum demand in kVA is then equal to 82.8 kVA (given by 3 x 230 V x 120 A ÷ 1,000).

To read full article, please see attachment below...