Electrical Power Systems Technology

Alternating Current Power Systems 141

3. Point your forefinger in the direction of the magnetic lines of force
   (from north to south).


4. Your middle finger will now point in the direction of induced current
   flow (negative to positive).

Voltage Development in a Generator

It is known that when a conductor moves across a certain number of

magnetic lines of force in one second, an induced electromotive force (emf) of

one volt is developed across the conductor. Thus, the induced voltage val-

ue can be changed by modifying either the strength of the magnetic field,

or the speed of conductor movement through the magnetic field. If the

magnetic field is made stronger, more voltage will be induced. If the con-

ductor is moved at a faster speed, more voltage will be induced. Likewise,

if more conductors are concentrated within the magnetic field, a greater

voltage will develop. These rules of electromagnetic induction are very

important for the operation of mechanical generators that produce electri-

cal power.

Sample Problem: Voltage Induced into A Conductor

In electrical generators, the coils move with respect to a magnetic

field or flux. Electromagnetic induction occurs in accordance with Faraday’s

Law, which was formulated in 1831. This law states: 1) If a magnetic flux

that links a conductor loop has relative motion, a voltage is induced, and

2) the value of the induced voltage is proportional to the rate of change of

flux.

The voltage induced in a conductor of a generator is defined by

Faraday’s Law as follows:

Vi = B × L × v

where:

Vi = induced voltage in volts,

B = magnetic flux in teslas,

L = length of conductor within the magnetic flux in meters, and

v = relative speed of the conductor in meters per second.

Given: the conductors of the stator of a generator have a length of 0.5

M. The conductors move through a magnetic field of 0.8 teslas at a rate of

68 m/s.