ABSTRACT
This chapter explains the significance of a wattmeter's polarity markings. The importance of wattmeters' polarity marks observes the sense of the quantity measured. The chapter illustrates Blondel's Theorem for using wattmeters to measure the power of a three-phase a.c. load. The wattmeters have two coils, namely voltage coil and current coil. The voltage coil is connected in parallel with the load whereas the current coil is connected in series with the load. Wattmeter uses the three-phase circuits that supplies both balanced and unbalanced loads. The simplest method to measure the total power of a balanced or unbalanced system is to use the three-wattmeter method. The common methods used for measuring the power of a three-phase load are the two-wattmeter method. The two-wattmeter method works well for unbalanced three-wire loads, it is often used to measure the power of balanced loads, such as three-phase induction motors, where it is used to determine the load's power factor.
