why we avoid parallel operation of diesl generator?

Answer Posted / johnson m.c.

1) Potential of both alternators must be equal. Both must
have same output voltage.
2) Phase sequences of both the alternators must be same.
The RYB phases of one alternator must
be connected the RYB phases of the other alternator.
3) Frequency of both the alternators must be equal. If one
alternator is operating at a frequency of 49
Hz and the other one is delivering voltage at 51 Hz, then
load on the second alternator would be
more. We have to increase the speed of the prime mover of
the first alternator in order to effect a
match in frequencies.
4) Phase angle of voltages of the two alternators must not
be more than 10 degrees.
5) During manual operation of synchronization, the load
could witness kick (which is a peak of
current). This kick could burn the alternators on the load.
The only solution is the use of automatic
synchronisation equipment. However, expert engineers could
close the CB of the second
alternator when the difference of phase angle between the
two voltages is 2 degrees.
6) The alternators must share loads with respect to their
ratings.
7) The alternators must have similar voltage drooping
characteristics.
8) The engines of the alternators must have similar
governor characteristics;

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