CONTENT

1. INTRODUCTION

2. DESIGN PRINCIPLE and OPERATION

3. CIRCUIT DESCRIPTION

I. Power supply

II. Led Indicator Section

III. Relay driver

IV. Signal conditioning circuit

V. Comparator

a. Over / Under voltage

VI. Buzzer Driver

4. FUTURE EXPANSION

Introduction

In the present scenario of technological revolution it has been observed that

every application products are impacted with multiple functions. The design is

also moving forward the miniature architecture; all this properties can be

achieved in a product by using programmable device. When ever we are thinking

about any programmable devices then the embedded technology comes into fore

front. The embedded is now a day very much popular and most the product are

developed with Microcontroller based embedded technology. The electrical

engineering and its applications are the oldest streams of engg. In the present

scenario all the electrical protection systems are based on electro mechanical

devices. Though these systems are quit reliable and cheaper. It has certain

disadvantages. The electro mechanical protection relays are too bulky and needs

regular maintenance. The multifunctionality is out of question. Recently, the

technical revolution made embedded technology cheaper, so that it can be

applied to all the fields. The pioneer manufactures of switch gear and protection

system such as SIMENS,LARSON & TUBRO,CUTLER HAMPER

etc.manufacturing protection relays based on embedded technology. The

proction devices may be of any kind but they are very much important,

interconnectivity and networking between different proactive devices are very

much required in the modern age instrumentation and control. Now a days the

protective devices and developed with Rs485 compatible and also multiple

protections are integrated in a small and economical package. This technology is

very fast so controlling of multiple parameters is possible, also the parameters

are field programmable by the user. The ancent electromechanical relays cannot

be adjusted very accurately.

The combined protection relay is one of the relays, which basically

designed to protect the user device from negative phase sequence, single

phasing and also the power distribution line with the help of a differential relay.

The negative phase sequence relay basically protects the devices against the

reverse phase sequence and also against the unbalance phase sequence

generated due to unbalance loading. Single phasing relays protect the device

against the phase failure. The differential relay protect the zone of the

transmission line.

The specialty in this project is the design is made on 89c51 micro

controller, which is faster and controls all the relays. This is static relay so no

much mechanical movement is there. The response time is very fast and can be

programmed fro any value. The great advantage of programmability is available

to the user.

This protection is developed on a 89C51 Microcontroller. If the relay will

be developed with same facility by electro mechanical comnponent, then the cost

and size of the device will be too high. The use of Microcontroller reduces extra

hard wares such as timers and connectors etc. The controller is embedded with

all the components. The controller is the heart of the device and there are other

hardwares used for signal conditions and comparison. In this relay there are four

current setting and it can handed maximum up to 15A current.

Design principle and operation

PRINCIPAL OF OPERATION:

Single Phasing Relay

Principle:

Single-phase relay can be designed on many principles the most popular

methods are voltage sensing and current sensing methods. The voltage sensing

method is quit popular compared to the current sensing method. In current

sensing method the abrupt current change cannot be taken care and the design

is for a specific load only. Where as voltage sensing method is very much

flexible and can be designed for any system.

The basic principle of this relay that senses the three phase voltage and step

down it, which further converted in Square waves. This signal is conditioned to a

CMOS compatible signal pulses and feed to the micro controller and checked

sequentially for its presence.

The phase to neutral voltage is VPN =230volt, with the help of a voltage divider

network a low voltage is sampled and pulses are generated at the zero cross

points.

Differential Relay:

This relay works on the principle of current sensing. There are two special type of

current sensors used to sample current. The output of both the current

transformer are compared and found if both the C.T. s are reading the same

current then the transmission line connected between the C.T.s is found to be

normal and there is no fault. Whenever there is a short circuit in the protected

zone, then the current bleed on the short-circuited path so the reading of both the

C.T. s differs that out put is taken into the micro controller for deciding the fault

condition.

B) CURRENT SIMPLING SECTION: This section consists of a special type of

ferrite core transformer a signal condition circuit. The current transformer

develops a secondary voltage proportional to primary current.

Current transformer

1) Design of current transformer.

This is a special type of current transformer which is having 5 turns of 10SWG

winding in the primary and 350 turns of 38SWG at secondary winding. The cone

is high-density ferrite cone. The cones are made out of E-section and the winding

is made as the central limb.

Signal conditioning`

The output of the current transformer is rectified and the DC output is

smoothened by using a RC filter and that out put is feed to the comparator circuit

through a voltage divider network.

UNDER VOLTAG & OVERVOLTAGE RELAY

The under voltage and over voltage section samples the line voltage through a

step-down transformer and converts it into DC voltage and compare it with a

reference to detect under voltage and over voltage condition. The corresponding

bits are send to the micro controller for action.

CIRCUIT DESCRIPTION

I) POWER SUPPLY:-( +ve)

Circuit connection: - In this we are using Transformer (0-12) VAC, 1A, IC 7805

& 7812, diodes IN 4007, LED & resistors.

Here 230V, 50 Hz ac signal is given as input to the primary of the transformer

and the secondary of the transformer is given to the bridge rectification diode.

The o/p of the diode is given as i/p to the IC regulator (7805 &7812) through

capacitor (1000mf/35v). The o/p of the IC regulator is given to the LED through

resistors.

Circuit Explanations: - When ac signal is given to the primary of the

transformer, due to the magnetic effect of the coil magnetic flux is induced in the

coil(primary) and transfer to the secondary coil of the transformer due to the

transformer action.” Transformer is an electromechanical static device which

transformer electrical energy from one coil to another without changing its

frequency”. Here the diodes are connected in a bridge fashion. The secondary

coil of the transformer is given to the bridge circuit for rectification purposes.

During the +ve cycle of the ac signal the diodes D2 & D4 conduct due to

the forward bias of the diodes and diodes D1 & D3 does not conduct due to the

reversed bias of the diodes. Similarly during the –ve cycle of the ac signal the

diodes D1 & D3 conduct due to the forward bias of the diodes and the diodes D2

& D4 does not conduct due to reversed bias of the diodes. The output of the

bridge rectifier is not a power dc along with rippled ac is also present. To

overcome this effect, a capacitor is connected to the o/p of the diodes (D2 & D3).

Which removes the unwanted ac signal and thus a pure dc is obtained. Here we

need a fixed voltage, that’s for we are using IC regulators (7805 & 7812).”Voltage

regulation is a circuit that supplies a constant voltage regardless of changes in

load current.” This IC’s are designed as fixed voltage regulators and with

adequate heat sinking can deliver output current in excess of 1A. The o/p of the

bridge rectifier is given as input to the IC regulator through capacitor with respect

to GND and thus a fixed o/p is obtained. The o/p of the IC regulator (7805 &

7812) is given to the LED for indication purpose through resistor. Due to the

forward bias of the LED, the LED glows ON state, and the o/p are obtained from

the pin no-3.

Description (78XX regulator)

The L78xx series of three-terminal positive regulators is available in TO-

220, TO-220FP, TO-3, D2PAK and DPAK packages and several fixed output

voltages, making it useful in a wide range of applications. These regulators can

provide local on-card regulation, eliminating the distribution problems associated

with single point regulation. Each type employs internal current limiting, thermal

shut-down and safe area protection, making it essentially indestructible. If

adequate heat sinking is provided, they can deliver over 1 A output current.

Although designed primarily as fixed voltage regulators, these devices can be

used with external components to obtain adjustable voltage and currents.

Features

■ Output current to 1.5 A

■ Output voltages of 5; 6; 8; 8.5; 9; 12; 15; 18; 24 V

■ Thermal overload protection

■ Short circuit protection

■ Output transition SOA protection

1k

0-12/1A

230V

50H

z

POWER SUPPLY

2.2K

L ED

L ED

IN 4007 * 4

1000

uF/3

5V

+5V

7812 +12V

7805

II.LED INDICATOR The indicator section consists of a light emitting diode and its driver circuit is

designed on the basis of current required to glow the light emitting diode. Here

the driver circuit is required for the following functionality.

1) The Microcontroller cannot provide adequate current for glowing the LED.

The LEDs requires a current between 10mA to 20mA of current to glow.

2) The driver circuit provides current to the load from a separate source, so

the load current used not pass through the Microcontroller.

3) The driver circuit activates the load on receipt of a logic signal from the

Microcontroller and of the load in the absence of the signal as he current

requirement Is very less to glow a LED a single stage driver is sufficient to

drive the load. The driver circuit is nothing other than a perfect a transistor

switch. The driver transistor goes in to saturation on receipt of base signal

and drives into cut-off region, in absence of base signal.

The driver designs around a BC548/BC547 transistor and designed for a

working voltage of +5 V dc and 10mA current.

Rc= Vcc-VCEsat = 5-0.2V

IC 10mA

= 4.8K

Ib=Ic/=10mA/200=5x10-5 A=0.5x10-6A

=0.5A

As per the design a 0.5A current is sufficient to trigger the driver circuit. As

this current is very small and to avoid mistriggering a base current of 100A is

assumed

VB-IBRB-VBE=0

IBRB = 5-0.7

RB = 5-0.7V/100A = 4.3/100 M

= 0.043x10-6

= 43K

On approximation 68K is connected by calculating back

IB = 4.3/68K = 60 70A

Which is adequate to avoid mis-triggering level also this amount of current

can be drawn from the Microcontroller without any problem.

The indicator section consists of 8 no of driver with 8 no of LED as indicator

load. The circuit diagram is enclosed.

Whenever there is a fault in any of the condition (parameter) it indicates a

high output at the Microcontroller, which is given to the base of the driver

transistor (BC547/BC548) with a base resistance (68k/56k) & thus transistor

comes to saturation condition i.e. ON condition, thus the emitter current flows

to the collector of the transistor at which the LED is connected through a

current limiting resistor (330E/470E) thus the LED gets forward biased which

turns ON the LED it indicates the channels fault .

LED

RELAY

Normal

68k

68k

LED

LED

Y

LED

LED INDICATOR

68k

BC547

BC547

470E

B

LED

470E

BC547

470E

LED

470E

470E

470E

VCC=+5V

68k

BC547

BC547

68k

68k

68k

LED

BC547

68k

U.V

BC547

470E

BC547

R

470E

O.V

LED

FAULT

330E

LED INDICATOR

68k

BC 547

DATAINPUT

V CC

L ED

III. RELAY DRIVER

The relay driver is design by using a BC547 transistor .The relay used here

having the specification as follows

Coil resistance =400ohm

Coil voltage=12Vdc

Contact capacity=230V, 7A

The above specification indicates that the coil requires 12V dc and 200mA

current dc. The Microcontroller can’t supply more then 10mA current. So driver

section is very much required. BC547 has a typical current gain of 200 and

maximum current capacity of 1A. So a typical base current of 200 A can trigger

to on the relay.

ELECTRO MAGNETIC RELAY

These are vary much reliable devices and widely used on field. The operating

frequency of these devices are minimum 10-20ms.That is 50Hz – 100Hz.The

relay which is used here can care 25mA currents continuously. The

electromagnetic relay operates on the principle magnetism. When the base

voltage appears at the relay driver section, the driver transistor will be driver

transistor will be driven into saturation and allow to flow current in the coil of the

relay, Which in turn create a magnetic field and the magnetic force produced

due to that will act against the spring tension and close the contact coil.

Whenever the base voltage is withdrawn the transistor goes to cutoff .So no

current flow in the coil of the relay. Hence the magnetic field disappears so the

contact point breaks automatically due to spring tension. Those contact points

are isolated from the low voltage supply, so a high voltage switching is possible

by the help of electromagnetic relays.

The electromagnetic relays normally having 2 contact points. Named as normally

closes (NC), normally open (NO). Normally closed points will so a short CKT path

when the relay is off. Normally open points will so a short CKT path when the

relay is energized.

10u F

RELAY DRIVER

1.5K

BC 547

DATAINPUT

IN 4007

REL A Y SPDT

35

412

V CC

IV. SIGNAL CONDITIONING The output form the input signal i.e. comparator or any other external circuit must

be compatible with the -controller, because the -controller can takes 5V as

input voltage and gives a 5V as output voltage. That for we need a signal

conditioning circuit as given in the below figure.

BC5471.5k

10k

(1:0)

VCC= +5vVCC= +5v

(1:1)

INPUT

1.5k

SIGNAL CONDITIONING

OUTPUT

10kOUTPUT

BC547

INPUT

fig..1:1

In the fig1: 1, whenever the base voltage is HIGH the transistor comes to

saturation condition i.e. the collector current flows to the emitter which gives a

high voltage at the output corresponding to Vcc given at the collector. The output

is taken from the emitter junction through a current limiting resistance and the

output signal is given to the - controller or any other circuit which needs a

compatible (5V) voltage. Similarly, whenever the base voltage is LOW the emitter

current flows from the emitter junction of the transistor, which gives a low voltage

at the output corresponding to GND. The output is taken from the emitter junction

through a current limiting resistance and the output signal is given to the -

controller or any other circuit which needs a compatible (5V) voltage.

fig..1:0

In the fig1: 0, whenever the base voltage is HIGH the transistor comes to

saturation condition i.e. the emitter current flows to the collector which gives a

low voltage at the output corresponding to GND. The output is taken from the

collector junction through a current limiting resistance and the output signal is

given to the - controller or any other circuit which needs a compatible (5V/0V)

voltage. Similarly, whenever the base voltage is LOW the collector current flows

from the collector junction of the transistor, which gives a high voltage at the

output corresponding to Vcc. The output is taken from the emitter junction

through a current limiting resistance and the output signal is given to the -

controller or any other circuit which needs a compatible (5V/0V) voltage.

10K

SIGNAL CONDITIONING / NOT GATE

1.5K

BC 547

DATAINPUT

V CC

V. COMPARATOR

a. UNDER / OVER VOLTAGE: In this section our aim is to detect the line varying voltage.

10K100uF

LINE VOLTAGE

IN4007 10k

SIGNALLING CKT

50Hz

TO COMP..

230VAC

0-9V/500mA

The line voltage (230vac) coming from the mains is to be step down that voltage

with the help of a step down transformer. If the line voltage varies, the step down

voltage also varies in accordance with the input voltage. Due to the mutual

induction of the transformer, if the primary winding of the transformer voltage is

more the flux induced is more and the secondary voltage is more. Similarly, if the

primary winding of the transformer voltage is less the flux induced is less and the

secondary voltage is less. In this way under/over voltage occurs.

The above figure shows a half-wave rectifier, in which it will

converts ac to dc voltage. We can vary the voltage with the variable load

resistance (10k) The sample voltage can be calibrated by varying the load

resistance RL The important part of this design to sample the voltage accurately

as an replica of the line voltage. The step down transformer samples the line

voltage at a reduced signal voltage

Vac = (N2/N1)*VL

The DC voltage after the half wave rectifier is approximately Vm due to the

charging of the capacitor, this capacitor voltage represents the line voltage. The

time constant of the circuit is defined by C*RL. The time constant of the circuit

must be more then five times of the time period of the signal. RC>5T. If the RC

value is less the 5T then the sample voltage fluctuates unnecessarily, if the RC

value is too high the sampling response becomes too slow.

Operation: The output of the signal sampling voltage (3v) goes to the input of

both of the comparator. In the first comparator we have set the voltage say

3.5Vto the non-inverting terminal. In this case non-inverting terminal is greater

than the inverting terminal. That means output of the first comparator is LOW. At

present under temperature cant be done because the room temperature will be

always available If we wants to do under temperature, we have to vary or

change the set point which is connected to the inverting terminal of that

comparator. Similarly, for the second comparator we have set the voltage say 4V

to the inverting terminal. In this case inverting terminal is greater than the non-

inverting terminal that means output of the second comparator is HIGH.

If the temperature increases, the corresponding voltage will

increase say 4.5V. That voltage goes to the input of both of the comparator. In

the first comparator we have set the voltage say 3.5Vto the non-inverting

terminal. In this case inverting terminal is greater than the non- inverting terminal.

That means output of the first comparator is HIGH this means that over

temperature has occurred. Similarly, for the second comparator we have set the

voltage say 4V to the inverting terminal. In this case non- inverting terminal is

greater than the inverting terminal that means output of the second comparator is

LOW.

That output signal is not compatible with the -controller because as we

know that the controller takes input signal as 5V and gives output as 5V.

VCC= +5v

1.5k

OUTPUT-2 10k

SIGNAL CONDITIONING

10k

COMP-11.5k

VCC= +5v

BC547

OUTPUT-1

COMP-2

BC547

FIG..-2

For this reason we needs a signal conditioning circuit which is given in the below

figure-2. That output signal is compatible with the controller because the current

will flows from the collector of the transistor whenever the base voltage is high

due to the transistor action. Similarly the output is low in the absence of the input

signal to the signal conditioning circuit from the comparators.

10k

VCC=+5v

BC547

LED

10k

10k

1.5k

P1.7

VCC=+12v

15k

BC547

VCC=+5v

LM393

1

3

2

84

OUT

+

-

+vcc

-vcc

BC547

10k

10k

P1.6

VCC=+12v

LED

15k

470E

UNDER/OVER VOLTAGE

68k

470E

10k

VCC=+5v

10k

68k

VCC=+5v

LM393

7

5

6

84

OUT

+

-

+vcc

-vcc

BC5471.5k

VCC=+12v

Under voltage/over voltage detector

In this section our aim is to detect the line varying voltage.

10K100uF

LINE VOLTAGE

IN4007 10k

SIGNALLING CKT

50Hz

TO COMP..

230VAC

0-9V/500mA

The line voltage (230vac) coming from the mains is to be step down that voltage with the

help of a step down transformer. If the line voltage varies, the step down voltage also

varies in accordance with the input voltage. Due to the mutual induction of the

transformer, if the primary winding of the transformer voltage is more the flux induced is

more and the secondary voltage is more. Similarly, if the primary winding of the

transformer voltage is less the flux induced is less and the secondary voltage is less. In

this way under/over voltage occurs.

The above figure shows a half-wave rectifier, in which it will converts ac

to dc voltage. We can vary the voltage with the variable load resistance (10k) The sample voltage

can be calibrated by varying the load resistance RL The important part of this design to sample

the voltage accurately as an replica of the line voltage. The step down transformer samples the

line voltage at a reduced signal voltage

Vac = (N2/N1)*VL

The DC voltage after the half wave rectifier is approximately Vm due to the charging of the

capacitor, this capacitor voltage represents the line voltage. The time constant of the circuit is

defined by C*RL. The time constant of the circuit must be more then five times of the time period

of the signal. RC>5T. If the RC value is less the 5T then the sample voltage fluctuates

unnecessarily, if the RC value is too high the sampling response becomes too slow.

Operation: The output of the signal sampling voltage (3v) goes to the input of both of the

comparator. In the first comparator we have set the voltage say 3.5Vto the non-inverting

terminal. In this case non-inverting terminal is greater than the inverting terminal. That

means output of the first comparator is LOW. At present under temperature cant be done

because the room temperature will be always available If we wants to do under

temperature, we have to vary or change the set point which is connected to the inverting

terminal of that comparator. Similarly, for the second comparator we have set the voltage

say 4V to the inverting terminal. In this case inverting terminal is greater than the non-

inverting terminal that means output of the second comparator is HIGH.

If the temperature increases, the corresponding voltage will increase say 4.5V. That

voltage goes to the input of both of the comparator. In the first comparator we have set the

voltage say 3.5Vto the non-inverting terminal. In this case inverting terminal is greater than

the non- inverting terminal. That means output of the first comparator is HIGH this means

that over temperature has occurred. Similarly, for the second comparator we have set the

voltage say 4V to the inverting terminal. In this case non- inverting terminal is greater than

the inverting terminal that means output of the second comparator is LOW.

Description (lm393)The LM2903/LM2903I, LM393/LM393A, LM293/ LM293A consist of two independent voltage

comparators designed to operate from a single power supply over a wide voltage range.

Features

• Single Supply Operation: 2V to 36V

• Dual Supply Operation: ｱ 1V to ｱ 18V

• Allow Comparison of Voltages near Ground Potential

• Low Current Drain 800μA Type.

• Compatible with all Forms of Logic

• Low Input Bias Current 25nA Type.

• Low Input Offset Current ｱ 5nA Type.

• Low Offset Voltage ｱ 1mV Type.

470E

VCC=+12V

10K

10K

P1.1

UNDER/OVER VOLTAGE

VCC=+12V

10K15k

VCC=+5V

VCC=+5V

1.5k

BC547

VCC=+5V

10K

VCC=+5V

VCC=+12V

+

-

LM393

2

31

84

68k

P1.0

BC547

470E

68k

-

+

LM393

5

67

84

BC547

15k

10K

BC547

1.5k

10K

10K

FUTURE EXPANSION

This project can be expanded in the following direction,

1. The protective relays like distance relays and over current relays can

be incorporated in this project.

2. This setup can be interfaced to computer network and keep a log on

the faults.

CONCLUSION

This project is working satisfactorily in the laboratory condition and with the

simulated faults. The performance of the relay can be improved by using better

quality current Transformer (CT)