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# Can I use my THS720P to make 3-phase power measurements?

### Question :

Can I use my THS720P to make 3-phase power measurements?

Certainly. Here's how the THS720P can be used to duplicate "Two and Three Wattmeter" power measurements in three phase systems.

In three-phase/three wire systems (i.e. no neutral connection), two True Power readings are taken - one from A to B, the second from B to C. Likewise, two Apparent Power readings are taken - one from A to B, the second from B to C. Connect the scope to the three phase system as follows:

1. Use a properly rated voltage probe on CH1 and a properly rated current probe on CH2.
2. Set the scope to trigger on CH1.
3. To take the first set of readings, connect the voltage probe across AB and the current probe to A.
4. To take the second set of readings reading, connect the voltage probe across BC and the current probe to C.

The two True Power readings must each be multiplied by Cos 30 deg (i.e. 0.866) to accommodate the 30 deg line to neutral shift inherent in three-phase systems, then arithmetically added to arrive at total True Power.

As above, the two Apparent Power readings are each multiplied by COS 30 deg, then added together to arrive at total Apparent Power. The ratio (total True Power/total Apparent Power) is taken to determine Power Factor. This duplicates the traditional "Two Wattmeter" method.

In three-phase/four wire systems (i.e. neutral connected), three separate measurements are taken (Power A/N, Power B/N, Power C/N). Arithmetically add the three True Power readings to arrive at total True Power (no Cos 30 deg correction however).

As above, the three Apparent Power readings are added together to arrive at total Apparent Power (no Cos 30 deg correction). The ratio (total True Power/total Apparent Power) is taken to determine Power Factor. This duplicates the traditional "Three Wattmeter" method.

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Product:

FAQ ID 60466

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