This document describes an automatic phase changer system that provides uninterrupted power supply for single phase loads even when one or two phases fail in a three phase system. The system monitors the voltage levels of each phase and connects a phase with low voltage to a healthy phase to continue supplying power to loads. It uses a microcontroller, comparators, and relays to sense phase voltages and switch the connections. The system allows loads to operate normally even during phase failures or low voltages in the supply.

1. AUTOMATIC PHASE CHANGER

2. Aim:
The main aim of this system is to provide
uninterruptable power supply for single phase loads
even in the failure of one or two phases in a three
phase system.

3. Introduction:
If any one or two phases in a 3-phase supply
interrupted/goes low and you want equipment to
work on normal voltages then this circuit will give
solution .
This system is designed to monitor the presence
of supply to the three phases and to display
condition of each phase on an LCD.

4. Hardware Requirements:
Power Supply 5V.
Microcontroller AT89C51.
Step Down Transformers.
Comparators.
Switching Devices.
Other Hardware Components

5. Power supply to all sections
Step
down
T/F
Bridge
Rectifier
Filter
Circuit Regulator
Block Diagram of power supply:
D 1 3
R 1 5
P U S H P A K T E C H N O L O G I E S
D 1 6
C 1 1
D 1 5
V C C
U 5
31
2
V O U TV I N
GND
C 1 2
P O W E R S U P P L Y
< R e v C o d e >
3 P H A S E D R I V E S A F T Y S Y S T E M
C u s t o m
2 2S a t u r d a y , M a r c h 1 3 , 2 0 1 0
T it le
S iz e D o c u m e n t N u m b e r R e v
D a t e : S h e e t o f
P S T V IN
D 1 4 C 1 3
G N D IN
L E D 1

6. Relay Relay Relay
Output Output Output
Transformer1 (R-phase) Transformer2 (Y-phase) Transformer3 (B-phase)
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Comparator Comparator Comparator
Relay Relay Relay
Output Output Output
Transformer1 (R-phase) Transformer2 (Y-phase) Transformer3 (B-phase)
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Comparator Comparator Comparator
Transformer1 (R-phase) Transformer2 (Y-phase) Transformer3 (B-phase)
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Rectifier & Filter
circuit
Comparator Comparator Comparator
Sensing Module:

7. Working:
It monitors the presence of three phases and to
display condition of each phase on an LCD.
It monitors the voltage condition of each phase. If the
voltage level of any phase is under the rated /
specified voltage rating, immediately this phase is
connected to a healthy phase thus, supplies to the
load.
The phase voltage is stepped down 230 V to 12 V,
300 mA.

8. These 12v is rectified through a rectifier circuit
and filtered through a capacitor.
The voltage at inverting terminal of Op-Amp is
taken from voltage divider circuit of resistor R1
and preset resistor VR1, at non inverting terminal
5.1 V will be set through zener diode.
When the line voltage is below 200 V, the voltage
at the inverting terminal is less than the voltage at
the non-inverting terminal. Thus the output of the
operational amplifier now goes low.

9. As a result transistor conducts and output is fed
to microcontroller and output microcontroller is
fed to electromagnetic relay through a transistor.
Consequently, the AC supply is shifted to absence
phase and electrical appliances turn ON.
Thus the appliances are protected against under-
voltage.

10. Circuit Diagram:
R 8
R 5
G N D I N
P H A S E I N 2
R 1 8
L 3
-
+ U 23
2
6
7
1
4
5
D 6
R 9
Q 4
S W 3 1 2
R 1
V C C
R 2
R L 3
C 7
D 1 1
R 1 7
R 1 2
-
+ U 33
2
6
7
1
4
5
D 7
C 2
R 1 1
R 7
S W 1 1 2
R 6
V C C
V C C
S W 4 1 2
P H A S E I N 1
R 1 0
Q 1
L S 1
3
5
4
1
2
C 1
Q 2
R L 1
Q 5
P H 1
P H A S E I N 3
P S T V I N
R 4
P H 2
D 8
V C C
R 3
T 2
15
6
48
C 6
D 9
L S 2
3
5
4
1
2
P U S H P A K T E C H N O L O G I E S
C 4
Q 6
Q 3
D 3
D 2
V C C
D 1
L 2
V C C
V C C
D 1 0
D 4
L S 3
3
5
4
1
2
C 3
-
+ U 13
2
6
7
1
4
5
C 5
D 1 2
L 1
D 5
V C C
S E N S IN G M O D U L E < R e v C o d e >
3 P H A S E D R I V E S A F T Y S Y S T E M
A 4
1 2S a t u r d a y , M a r c h 1 3 , 2 0 1 0
T it le
S iz e D o c u m e n t N u m b e r R e v
D a t e : S h e e t o f
V C C
R L 2
S W 2
1 2
N E U T R A L
R 1 6
T 3
15
6
48
P H 3
T 1
15
6
48
Sensing Module

11. D 2 1
L E D 2
D 2 0
R L 3
D 1 9
S W 5 O K
D 1 7
C O N T R O L M O D U L E < R e v C o d e >
3 P H A S E D R IV E S A F T Y S Y S T E M
C u s t o m
2 2T u e s d a y , J u ly 1 9 , 2 0 1 1
T it le
S iz e D o c u m e n t N u m b e r R e v
D a t e : S h e e t o f
R L 1
B Z 1
P O T
R 1 3
3
1
2
V C C
A P P L I A N C E
P U S H P A K T E C H N O L O G I E S
Y 1
U 4
A T 8 9 S 5 2
29
3 0
40
20
31
191 8
9
3 9
3 8
3 7
3 6
3 5
3 4
3 3
3 2
1
2
3
4
5
6
7
8
2 1
2 2
2 3
2 4
2 5
2 6
2 7
2 8
1 0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
PSEN
A L E
VCC
GND
EA
X1X 2
R S T
P 0 . 0 / A D 0
P 0 . 1 / A D 1
P 0 . 2 / A D 2
P 0 . 3 / A D 3
P 0 . 4 / A D 4
P 0 . 5 / A D 5
P 0 . 6 / A D 6
P 0 . 7 / A D 7
P 1 . 0 / T 2
P 1 . 1 / T 2 E X
P 1 . 2
P 1 . 3
P 1 . 4
P 1 . 5 / M O S I
P 1 . 6 / M I S O
P 1 . 7 / S C K
P 2 . 0 / A 8
P 2 . 1 / A 9
P 2 . 2 / A 1 0
P 2 . 3 / A 1 1
P 2 . 4 / A 1 2
P 2 . 5 / A 1 3
P 2 . 6 / A 1 4
P 2 . 7 / A 1 5
P 3 . 0 / R X D
P 3 . 1 / T X D
P 3 . 2 / I N T 0
P 3 . 3 / I N T 1
P 3 . 4 / T 0
P 3 . 5 / T 1
P 3 . 6 / W R
P 3 . 7 / R D
C 8
L E D 1
P H 3
D 1 8
P H 2
R 2 2
C 1 0
L E D 3
R 2 1
V C C
O K
R 1 9
V C C
J 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
P H 1
R 2 0V C C
L E D 3
B U Z Z E R
R 2 3
A P P L I A N C E
B U Z Z E R
R 1 4
V C C
R L 2
L E D 2
C 9
L E D 1
Control Module

12. Programming modules:
LCD module.
Phase sensing Module.
Control Module.

13. Advantages:
Revenue Collection Efficiency
Transparency in distribution
Better customer Service
Zero man-made errors
Continuous running of single phase loads

14. Applications:
Small and Medium Scale Industries
Residential Apartments.
Offices.
ATM.

15. REFERENCES
1. Electron Devices and Circuits by P. Ramesh Babu,
T.R. Ganesh Babu,Scitech Publications(INDIA) Pvt.
Ltd. Chennai.
2.http://www.circuitstoday.com/wpcontent/uploads/
2009/09/741ic-inverting- comparator-circuit.jpg
3.IEEE Standard , Standard Inverse-Time
Characteristic Equations for Overcurrent Relays.
4. http://www.en.wikipedia.org/wiki/tansformer#mw-
head.