A Method of Determining the Correctness of Polyphase Wattmeter Connections

The object of this paper is to describe a method of checking the correctness of the connections of a polyphase watt-hour meter on a three-phase circuit; and to show that the methods most commonly used for this purpose are unreliable. Polyphase wattmeters are classified according to the number of their voltage terminals and expressions giving the amount of energy theoretically registered by the meter are derived for all possible arrangements of the connections for each class. The correctness of these expressions was checked experimentally. The expressions are given in the form of tables. A study of these tables reveals the fact that the methods of checking the connections in most common use are unreliable. A method is developed which may be relied upon to check the correctness of the meter connections on a balanced three-phase circuit at any power factor. Rules are worked out from this method, that make the rectification of incorrect connections simple. In addition to this, another method is described which may be used on balanced or unbalanced three-phase circuits at any powe1 factor, provided the opening of one phase at a time is permissible.