15-01-2013, 04:01 PM
AUTOMATIC PHASE CHANGER
AUTOMATIC PHASE CHANGER.pdf (Size: 137.92 KB / Downloads: 70)
The mains power supply phase R
is stepped down by transformer X1 to
deliver 12V, 300 mA, which is rectified
by diode D1 and filtered by capacitor
C1 to produce the operating
voltage for the operational amplifier
(IC1). The voltage at inverting pin 2 of
oprational amplifier IC1 is taken from
the voltage divider circuit of resistor
R1 and preset resistor VR1. VR1 is used
to set the reference voltage according
to the requirement. The reference voltage
at non-inverting pin 3 is fixed to
5.1V through zener diode ZD1.
Till the supply voltage available in
phase R is in the range of 200V-230V,
the voltage at inverting pin 2 of IC1
remains high, i.e., more than reference
voltage of 5.1V, and its output pin 6
also remains high. As a result, transistor
T1 does not conduct, relay RL1 remains
de-energised and phase ‘R’ supplies
power to load L1 via normallyclosed
(N/C) contact of relay RL1.
As soon as phase-R voltage goes
below 200V, the voltage at inverting
pin 2 of IC1 goes below reference voltage
of 5.1V, and its output goes low.
As a result, transistor T1 conducts and
relay RL1 energises and load L1 is
disconnected from phase ‘R’ and
connected to phase ‘Y’ through relay
RL2.