Two Wattmeter Method

The phase voltages are balanced but the phase currents do not have the same phase angles in this metering configuration..

The procedure is correct and so are the answers.

Check if phases sequence are correct.

The total power delivered to the load is the algebraic sum of the two wattmeter readings and they will have the same readings only when the loads are totally resistive (power factor = 1) or totally reactive (power factor = 0). For a totally resistive load, the polarity of the reading on both wattmeters will be the same but if the load is totally reactive the polarity of the reading will be + on one meter and - on the other.

The transition from a negative to positive ratio occurs when the power factor of the load is 0.5. At this power factor one wattmeter will read 0 while the other will read the total power delivered to the load.

Hi Omhar 991;

In-support of Snakers and Bluestones replies, heres a wiring diagram of two wattmeters (single phase wattmeters) for measuring power in a three-wire three phase circuit.

As Bluestone mentioned, for either balanced or unbalanced loads or voltages, the algebraic sum of the reading of the two watt meters will be the total three phase power of the circuit. For balanced loads at unity power factor (p.f=1.0), readings on the two watt meters will be zero. When the load power factor is 50% (p.f=0.50), W2 will read zero and W2 will read the total three phase power. At power factors between 50% and 100%, W1 will read higher than W2. AT power factors lower than 50%, W2 will be negative and the total three phase power will be W1-W2. At zero power factor W1 and W2 will have identical readings, but of opposite signs, indicating zero power factor.

In balanced 3-phase 3-wire systems where Ø is the angle of phase difference between the phase current and the phase voltage, it is proved that

tan Ø = √3 (W1-W2/W1+W2).

To further understand the change in power factors as stated above, read on the resistive, capacitive, and inductive loads which have effect on power factor and with regards to phase angle.

in two watt meter method ,wattmeter have two coil upper one is small winding and lower one is large compare to upper one.,which one is moving and which one is fixed coil(upper one or lower one)????????

Hi;

From the circuitry shown;

1. Moveable coil is connected in parallel with the load. It has a series resistor to it

which forms the potential element.

2. Stationary Coil is connected in series with the load. It is the current element

whic carries the load current

The measurement technique works on the Electrodynamometer mechanism.