Page 849 - Basic Electrical Engineering

The constructional details of an induction-type kWh meter has been shown
in Fig. 11.27.
The pressure coil is made of a large number of turns and is connected

across the supply. The pressure coil is highly inductive as is surround by iron.
The core is made of laminated steel sheets. The current coil is shown in two

parts wound around a laminated core and is made of thick wire of a few
turns. The current coil is connected in series with the load.

Working principle: Let V be the supply voltage and I be the load current. The

current flowing through the pressure coil is I . Since the pressure coil is
sh
highly inductive, I will lag voltage V by 90°. Let load power factor be cosϕ.
sh
The load current I will lag the supply voltage by an angle ϕ. Current flowing

through the series coil is I. The flux produced by the series coil will be in
phase with I. The flux produced by the shunt or pressure coil ϕ will be in
sh
phase with current I as shown in Fig. 11.28.
sh

Figure 11.27 Induction-type single-phase energy meter