Page 214 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

• Since the system load is assumed to be constant, generator No. 2 will drop some of its load
• thereby weakening its series field which will result in its further dropping off its load.
• This effect is cumulative.

• Generator No. 1 will, therefore, tend to take the entire load and finally drive generator No. 2 as a motor. For
making the parallel operation of over-compound and level-compound generators stable, they are always used
with an equalizer bar connected to the armature ends of the series coils of the generators.

• The equalizer bar is a conductor of low resistance.
• Suppose that generator No. 1 starts taking more than its proper share of load.
• Its series field current is increased.
• But now this increased current passes partly through the series field coil of generator No. 1 and partly it flows
via the equalizer bar through the series field winding of generator No. 2.
• Hence, the generators are affected in a similar manner with the result the generator No. 1 cannot take the
entire load.

Troubleshooting in DC machines

At the end of this exercise you shall be able to
• use the trouble shooting chart to rectify defects in i) DC machines in general ii) DC motors iii) DC generators.

DC machines have Power problems which are not normally found in AC machines. DC motors and generators
have commutators and brushes, which cause special problems. If the commutator is properly maintained, it
will give many years of useful service.
Chart 1 deals with DC motors and Chart 2 is for DC generator.

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CITS : Power - Electrician & Wireman - Lesson 30-37