How will you measure a three phase electric supply?

Answer 1

It really depends on what you mean by 'measure' -that is, what quantity you wish to measure: voltage, current, power, or energy. It also depends on whether the load being supplied is balanced (i.e. having identical phases) or unbalanced. It also depends on whether you wish (in the case of voltage and current) whether you wish to measure line quantities or phase quantities. So, as you can see, you really require quite a complex answer!

The three energised ('hot') conductors that connect a three-phase supply to its load are called 'lines' and the fourth conductor (if present) is called a 'neutral'. 'Phases' are connected either between lines, or between individual lines and the neutral, depending on whether the loads are connected in delta (three-wire systems) or star(four-wire systems).

(Beware that some writers confuse 'lines' and 'phases', calling line conductors 'phase' conductors; you must always use the correct terminology!)

As the line voltages (voltage between lines) are determined by the supply, they are always equal -so to measure the line voltage, only one voltmeter is needed, and it can be connected between any two lines. For a balanced load, all three line currents are equal, so only one ammeter is needed, and it can be connected in series with any one of the individual lines. For an unbalanced load, the line currents are different, so you need to connect three, separate, ammeters, each in series with a line.

To measure power for a balanced, or unbalanced, load, you can use one less wattmeter than there are conductors supplying the load. So for a three-wire system, you can use two wattmeters but, for a four-wire system, you must use three wattmeters. You will need to check out the internet to find a schematic diagram for these connections: search for 'three-wattmeter method', and 'two-wattmeter method'.

Energy meters follow the same connections as the wattmeter methods, but usually comprise a single instrument, rather than individual instruments so, again, you'll need to do an internet search for their wiring diagrams.

Answer 2

To measure a three-phase electric supply, you would typically use a three-phase energy meter which can accurately measure the total energy consumption across all three phases. This meter will record the total power consumed by adding up the power usage across each phase. Additionally, you can use a power analyzer to measure voltage, current, power factor, and other electrical parameters in each phase.