EPC 8 - AC Generation & Phase Relationships

Question 1

What condition is necessary for a voltage to be induced in a conductor by a magnetic field?

Answer 1

There must be relative movement between them. The relative movement must be such that the conductor CROSSES the associated flux lines.

Question 2

How much voltage is induced in a conductor when it is moved parallel to the flux lines in a magnetic field?

Answer 2

Zero.

A voltage is only induced when a conductor cuts a magnetic field or vice versa.

Question 3

A conductor loop is rotated uniformly within a two pole magnetic field system. At what point(s) is the induced voltage maximum?

Answer 3

When the conductor is cutting the flux lines at right angles (twice per complete revolution in a two pole field).

Question 4

List FOUR ‘values’ of alternating current?

Answer 4

The peak value, 
The root mean square (rms) or effective value, 
The average (avg) value, 
The instantaneous value, 
The peak to peak value.

Question 5

What value of d.c. voltage would be required to produce the same heating effect as 100 V peak a.c.?

Answer 5

70.7 V d.c. approximately. (Vac = Vpeak X 0.707)

Question 6

What value of a.c. does most standard measuring instruments indicate?

Answer 6

Most measuring instruments are calibrated to indicate rms values.

Question 7

What type of a.c. waveform is produced by a typical single phase alternator?

Answer 7

A sinusoidal waveform.

Question 8

What is the phase displacement between the voltages in a three phase distribution system?

Answer 8

120 degrees electrical.