Dynamometer Type Three-Phase Wattmeter

β€’    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.

β€’    The arrangement is shown in Fig.

β€’    There are two current coils and two pressure coils.

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

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

β€’    The torque on each element is proportional to the power being measured by it.

β€’    The total torque deflecting the moving system is the sum of the deflecting torque of the two elements.

β€’    Hence the total deflecting torque on the moving system is proportional to the total Power.

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

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

Fig. Three-Phase Wattmeter

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