January 2015

WHAT IS POWER FACTOR Power factor (PF) is simply the relationship between the active and reactive power on an electricity distribution network and a measure of whether the system’s voltage and current are ‘in phase’. Take, for example, a frothy latte. The coffee body is the ‘active power’ that you can use to do work.

The stator winding of a synchronous motor is similar to that of a 3 phase induction motor. The rotor consists of salient poles excited by dc field windings like that of inward-projecting poles of a dc motor. The rotor field windings are energized by direct current passed through slip rings from an external source or

Single phase motors are manufactured in fractional kilowatt range to be operated on single phase supply and for use in numerous applications like ceiling fans, refrigerators, food mixers, hair driers, portable drills, vacuum cleaners, washing machines, sewing machines, electric shavers, office machinery etc. Single phase motors are manufactured in different types to meet the requirements

The direction of rotation of a universal motor can be changed by either: (i) Reversing the field connection with respect to those of armature; or (ii) By using two field windings wound on the core in opposite directions so that the one connected in series with armature gives clockwise rotation, while the other in series with the

The stator of a standard split phase motor has two windings viz., a main winding and an auxiliary winding. These two windings have different ratios of resistance to inductive reactance. The windings are connected in parallel across the single phase ac supply. The line current is thus split into two parts; one part flowing through

Capacitor type split phase motors are generally similar to the standard split phase construction except for the addition of capacitor and a slightly modified switching arrangement for the two value capacitor type motors. The three types of capacitor split phase motors have been shown in Figure. Figure: Three types of capacitor type split phase motors

We know that direction of a split phase motor can be reversed if the connection of one of the windings is reversed with respect to the other. In an automatic starter this can be achieved by using two contactors i.e., one for forward direction of rotation and the other for reverse direction of rotation. The

This type of split phase motors have two capacitors of different values in the auxiliary winding. The motors develop a high starting torque with one capacitor of a higher value and gives a quite running performance with the other capacitor of comparatively lower value. The circuit for forward / reverse operation of a two value

This type of starter uses a current relay in series with the main winding and an auto-transformer in the auxiliary winding to increase the effective value of the capacitors in the auxiliary winding circuit. The circuit has been shown in Figure. In this circuit, when contactor M is energized, a high inrush current flows through