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.