Page 161 - Power Electronics Handbook

Onloff control
Optical? +
Slow ~ I coupler I To
control
1 coupler terminal
crossing control source of power
L Optical I devices
I
Fault +
(a) detect coupler
Onloff control
To
control
Zero oscillator os c i I I t o r terminal
a
crossing of power
Fault devices
(b) detect 1 transformer
Isolating
To Forwardl
control
terminals semiconductor reverse
of power +
devices protection

Onloff

Figure 7.4Thrce-phase a.c. contactor control: (a) optical couplers; (b) isolating transformers; (c) forwardreverse control