# Dynamometer Type Three-Phase Wattmeter

•    A dynamometer-type three-phase wattmeter consists of two separate wattmeter movements mounted together in one case with the two moving coils mounted on the same spindle.

•    The arrangement is shown in Fig.

•    There are two current coils and two pressure coils.

•    A current coil together with its pressure coil is known as an element. Therefore, a three-phase wattmeter has two elements.

•    The connections of two elements of a 3-phase wattmeter are the same as that for two wattmeter method using two single-phase wattmeters.

•    The torque on each element is proportional to the power being measured by it.

•    The total torque deflecting the moving system is the sum of the deflecting torque of the two elements.

•    Hence the total deflecting torque on the moving system is proportional to the total Power.

•    In order that a 3-phase wattmeter read correctly, there should not be any mutual interference between the two elements.

•    A laminated iron shield may be placed between the two elements to eliminate the mutual effects.