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What are the Advantages and Disadvantages of Induction type Wattmeter? Advantages: The advantages of induction watt meters are the same as those of induction ammeters  long scale, freedom from effects of stray field, and have effective damping torque. Disadvantages: Following are the disadvantage of the induction type instruments: a) Change in temperature causes variation in the resistance of the moving element, affects the eddy currents therein, and so the operating torque. The error due to this is in part offset by a balancing effect due to change in temperature of the windings. b) Change in frequency from that of the calibration value causes variations in both the reactance of the voltage coil circuit, which is highly inductive, and also in the amount of compensation from the phase  compensating circuit. Within the limits of frequency variation met within practice on the mains, this last error in not important.

Explain the construction of Induction type Wattmeter. A watt-meter has two laminated electromagnet, one of which is excited by load current or definite fraction of it, and is connected in series with the circuit, known as series magnet and the other is excited by the current proportional to the applied voltage or fraction of it and is always connected across the supply, known as shunt magnet. An aluminum disc is so mounted so that it cuts the fluxes produced by both the magnets. As a result of which, two e.m.fs are produced which induces two eddy currents in the disc. C - Magnet is used to provide necessary damping torque to the pointer, to damp out the oscillations.   Deflecting torque is produced due to interaction of these eddy currents and the inducing flux. Copper shading bands are provided either on central limb or on the outer limb of the shunt magnet, and can be so adjusted as to make the resultant flux in the shunt magnet lag behind the applied voltage by 90. Both the watt-

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Document 1: Practical Part 1 (Dated27/08/2019) Document 2: Practical Part 2 (Dated 24/09/2019) Document 3: Practical 01