FAULT DETECTION AND PROTECTION

OF INDUCTION MOTOR USING PLC

ABSTRACT

Protection of an induction motor (IM) against possible problems, such as

overvoltage, over current, overload, and under voltage, occurring in the course of

its operation is very important, because it is used intensively in industry as an

actuator. IMs can be protected using some components, such as timers, contactors,

voltage, and current relays. This method is known as the classical method that is

very basic and involves mechanical dynamic parts. Computer and programmable

logic controller (PIC) based protection methods have eliminated most of the

mechanical components.

Now we are using the PLC , in this method, all contactors, timers, relays, and the

conversion card are eliminated. Experimental results show that the PLC-based

protection method developed costs less, provides higher accuracy as well as safe

and visual environment compared with the classical, the computer, and the PLC-

based protection systems.,

This system uses the PLC for detecting the fault in induction motor and according

to the fault , it provides protection to the IMs.

CHAPTER-1

INTRODUCTION

Protection of an induction motor (IM) against possible faults, such as

overvoltage, over current, overload, and under voltage, occurring in the course of

its operation is very important, because it is used intensively in industry as an

actuator. IMs can be protected using some components, such as timers, contactors,

voltage, and current relays. This method is known as the classical method that is

very basic and involves mechanical dynamic parts. Computer and programmable

logic controller (PIC) based protection methods have eliminated most of the

mechanical components.

Now we are using the PLC , in this method, all contactors, timers, relays, and the

conversion card are eliminated. Experimental results show that the PLC-based

protection method developed costs less, provides higher accuracy as well as safe

and visual environment compared with the classical, the computer, and the PLC-

based protection systems.,

The proposed system is PLC for detecting the fault in induction motor and

according to the fault, it provides protection to the IMs.

1.1BLOCK DIAGRAM:

1.2: PLC:

Programmable Logic Controllers (PLCs), also referred to as programmable controllers, are in the computer family. They are used in commercial and industrial applications.

PLC consists of input modules or points, a central processing

unit(CPU) and output points.

Parts of PLC:

The CPU monitors the inputs and makes decisions based on

instructions held in the program memory PLC consists of input

3 Phase Supply

Potential Transform

er

Rectifier Filter

Current Transform

er

I/V Convert

er

Rectifier & Filter

PLC

Control Unit

Load

modules or points, a central processing unit(CPU) and output

points.

1.3 CURRENT TRANSFORMER:

CHAPTER-2

LITERATURE REVIEW

The general consciousness of over voltage and under voltage in the industry and international disputes over the environment, global safety, and the quality of life, have created an opportunity for new efficient less wasting of power and industry with advance technologies of control robustness, and modularity.This project on induction motor is one such effort to improve the protection by controlling the voltage, current , and temperature.

Ramazan Bayindir , member of IEEE, Department of Electrical Education,

He received the B.Sc., M.Sc., and Ph.D.degrees in electrical education from Gazi University,Ankara, Turkey, in 1992, 1998, and 2002,respectively.He present paper of power factor correction, microcontroller,programmable logic controller (PLC) programming,and automation systems. The proposed PLC consist of battery , cpu input \ output section , and programming section where user can program the PLC according to the output.

IBRAHIM SEFA, Member of IEEE ,Department of Electrical Education. He received the B.Sc. degree from the Department of Electrical Education Gazi University, Ankara ,Turkey , in 1985, and the M.Sc. and Ph.D. degreesfrom the Department of Electrical Engineering, Erciyes University , Kayseri, Turkey, in 1993 and 1997,respectively. He present paper of machine control , power electronics, uninterruptible power supplies, control systems, and alternating energy sources. The spectral performance of the rectifier is investigated. Analysis of conversion of 3 phase ac supply into +5 volt dc supply . PLC works on +5 dc.˙Ilhami Colak , Member of IEEE, Department of Electrical Education.He received the B.Sc. and M.Sc. degrees from the Department of Electrical Education, Gazi University , Ankara, Turkey, in 1985 and 1988, respectively ,the M. Phil. degree in electrical and electronics engineering from Birmingham University, Birmingham ,U.K., in 1991, and the Ph.D. degree from the Department of Electrical Engineering, Aston University Birmingham, in 1994.He presents the paper on machine control, power electronics, control systems , computer

programming, system modeling, and alternating energy sources. To produce high quality output it synthesizes a relay for controlling the induction motor.Askin Bektas , Member of IEEE. He presents the paper on Remote control And Programmable logic controller (PLC) control systems and he stated that we can program the PLC by Ladder logic. By giving the +5 v dc voltage to PLC , it protect the 3 phase induction motor by over voltage ang under voltage.

CHAPTER-3 INDUCTION MOTOR

3.1 INTRODUCTION:

Operating Principles:

It has been pointed out previously that one: of the advantages of a polyphase system (3<1>in particular) is that it can produce a rotating magnetic field. This rotating field provides the basis of operation for all a.c. machines. It is obtained by distributing a set of three phase windings about the periphery of the motor core. When three phase currents flow in these windings, the time and space phase shifts resulting in an mmf wave which has the appearance of rotating at a constant angular velocity in the air gap between the rotor and stator. Having obtained this, there are two basic means of using this rotating wave to produce rotational motion. One method is to have the rotor travelling at the same speed as the rotating field. This results in a "synchronous" motor where the rotor is locked into step, or synchronized, with the field. Since the speed of the rotating field is determined solely by the input frequency and the geometry of the machine (i.e. number of poles), this produces a constant speed motor. The other method is to allow the rotor speed to be less than the speed of the rotating field to produce a flux cutting, or transformer action. This results in an "asynchronous" (or induction) motor where the rotor operates at a "slip" speed. Slip ~defined as the difference between rotor and field speeds divided by the field speed (the field speed is called the synchronous speed). The induction motor is an asynchronousmotor which has a speed which decreases slightly as more load is applied.

3.2 THREE PHASE INDUCTION MOTOR

Construction Details for Induction Motors:The induction motor comes in two forms:1)the wound rotor version and2)the cast, squirrel cage rotorThe wound rotor version has 3<1c>opper windings embedded in the rotor with the samepole structure as the stator. The winding terminals are accessible through sliding contactson one end of the rotor (called slip rings). Wound rotor motors are primarily used for speed control applications where the rotor resistance is externally controlled, thus controlling the speed vs. torque characteristic. Squirrel cage motors are by far the most common induction motor because of their ruggedness and constructional simplicity. A ring of short circuited bars parallel to the rotor axis is made out of cast aluminum. (These bars look very much like the exercise wheel used for small pet squirrels, hamsters, etc.; hence its name). This cage will take on whatever pole structure the stator windings present. Most squirrel cage motors have a single fixed speed and operate under full load at approximately 95% of synchronous speed.

3.3PROCEDURE:

3.3.1Machine Under Test:

The Lab Volt Wound Rotor Induction Motor may be started direct-on-line from a 200 V,60 Hz supply provided that you short-circuit the ammeter and current coil of the wattmeter to protect them against the very high starting current. Open-Circuit Test:

With the rotor winding open-circuited, connect the stator to a 200 V, 60 Hz, 3-phase supply as shown in Figure I. Take readings of the stator input current and input power, and the stand-still rotor e.m.f / phase E2.

Locked-Rotor Test:

Use the locking device on the Induction Motor to lock the rotor. Short circuit the rotor windings and increase VI very slowly until II=1.3A, record VI, II' and input power(WI x 3)

CHAPTER 4 DELTA PLC

4.1.1 INTRODUCTION TO PLC

Programmable Logic Controllers (PLCs), also referred to as

programmable controllers, are in the computer family. They are used

in commercial and industrial applications. It was called “Sequence

Controller” beforeIt was named “Programmable Logic Controller

(PLC)” by NEMA (National Electrical Manufacture Association) in

1978 and defined as electronic equipment. The operation of PLC is

in the following:

Step 1. Read the external input signal, such as the status of

keypad, sensor, switch and pulse.

Step 2. Using microprocessor to execute the calculations of logic,

sequence, timer, counter and formula according to the status and

the value of the input signal read in the step 1 and pre-write

programs saved inner to get the Corresponding output signal, such

as open or close of relay, operation of controlled machine or

procedure to control automatic machine or procedure of

manufacture. PLC also can be used to maintain and adjust of

production program by editing or modifying the peripheral

equipments (personal Computer/handheld programming panel). The

common program language of PLC is ladder diagram. There are

stronger functions in PLC with the development and application

requirements of electronic technology, such as position control,

network and etc. Output/Input signals are DI (Digital Input), AI

(Analog Input), PI (Pulse Input), DO (Digital Output), AO (Analog

Output) and PO (Pulse Output). Thus PLC plays an important role in

the feature industry.

4.1.2 BASIC PLC OPERATION

PLC consists of input modules or points, a central processing unit

(CPU) and output points

Fig 1.BASIC COMPONENTS OF PLC

4.1.3 PARTS OF PLC

4.1.3.1. CPU

The central processing unit (CPU) is a microprocessor system which

contains the system memory and is the PLC’s decision making unit.

The CPU monitors the inputs and makes decisions based on

instructions held in the program memory. The CPU performs relay,

counting, timing, data comparison, and sequential operations

Figure 2. CENTRAL PROCESSING UNIT

4.1.3.2. ANALOG INPUTS

An analog input is an input signal that has a continuous signal.

Typical analog inputs may vary from 0 to 20 milliamps, 4 to 20

milliamps, or 0 to 10 volts. In the following example, a level

transmitter monitors the level of liquid in a tank. Depending on the

level transmitter, the signal to the PLC can either increase or

decrease as the level increases or decreases.

FIG.3ANALOG INPUT

4.1.3.3. DIGITAL INPUTS

A discrete input, also referred to as a digital input, is an input that is

either in an

ON or OFF condition.

Fig 4 DIGITAL INPUT

4.1.3.4. DISCRETE OUTPUTS

A discrete output is an output that is either in an ON or OFF

condition. Solenoids, contactor coils, and lamps are examples of

actuator devices connected to discrete outputs. Discrete outputs

may also be referred to as digital outputs. In the following example,

a lamp can be turned on or off by the PLC output it is connected to.

Fig 5. DISCRETE OUTPUTS

4.1.3.5. ANALOG OUTPUTS

An analog output is an output signal that has a continuous signal.

The output may be as simple as a 0-10 VDC level that drives an

analog meter. Examples of analog meter outputs are speed, weight,

and temperature. The output signal may also be used on more

complex applications such as a current-to pneumatic transducer that

controls an air-operated flow-control valve.

Fig 6. ANALOG OUTPUT

4.1.2 BASIC INNER EQUIPMENTS OF THE PLC

TABLE 1:- BASIC INNER EQUIPMENTS OF THE PLC

Input

relay

Input relay is the basic storage unit of internal memory that corresponds to external input point (it is the terminal that used to connect to external input switch and receive external input signal). Input signal from external will decide it to display 0 or 1. You couldn’t change the state of input relay by program design or forced ON/OFF via HPP. The contacts (contact a, b) can be used unlimitedly. If there is no input signal, the corresponding input relay could be empty and can’t beused with other functions. Equipment indication method: X0, X1,…X7, X10, X11,…. The symbol of equipment is X and the number uses octal. There are numeric indications of input point on MPU and expansion unit.

Output Output relay is the basic storage unit of

relay internal memory that corresponds to external output point (it is used to connect to external load). It can be driven by input relay contact, the contact of other internal equipment and itself contact. It uses a normally open contact to connect to external load and other contacts can be used unlimitedly as input contacts. It doesn’t have the corresponding output relay, if need, it can be used as internal relay. Equipment indication: Y0, Y1,…Y7, Y10, Y11,…. . The symbol of equipment is Y and the number uses octal. There are numeric indications of output point on MPU and expansion unit.

Internal

relay

The internal relay doesn’t connect directly to outside. It is an auxiliary relay in PLC. Its function is the same as the auxiliary relay in electric control circuit. Each auxiliary relay has the corresponding basic unit. It can be driven by the contact of input relay, output relay or other internal equipment. Its contacts can be used unlimitedly. Internal auxiliary relay can’t output directly, it should output with output point. Equipment indication: M0, M1,…, M4, M5. The symbol of equipment is M and the number uses decimal number system.

STEP DVP PLC provides input method for controlling program of step actions. It is very easy to write control program by using the conversion of control step S of command STL. If there is no step program in the program, step point S could be used as internal relay M or alarm point. Equipment indication: S0, S1,…S1023. The symbol of equipment is S and the number uses decimal.

Timer Timer is used to control time. There are coil, contact and timer storage. When coil is ON, its contact will act (contact a is close, contact b is open) when attaining desired time. The time value of timer is set by settings and each timer has its regular period. User sets the timer value and each

timer has its timing period. Once the coil is OFF, the contact won’t act (contact a is open and contact b is close) and the timer will be set to zero. Equipment indication: T0, T1,…,T255. The symbol of equipment is T and the number uses decimal system. The different number range corresponds with the different timing period.

Counter Counter is used to count. It needs to set counter before using counter (i.e. the pulse of counter). There are coil, contacts and storage unit of counter in counter. When coil is form OFF to ON, that means input a pulse in counter and the counter should add 1. There are 16-bit, 32-bit and high-speed counter for user to use. Equipment indication: C0, C1,…,C255. The symbol of equipment is C and the number uses decimal.

Data

register

PLC needs to handle data and operation when controlling each order, timer value and counter value. The data register is used to store data or parameters. It stores 16-bit binary number, i.e. a word, in each register. It uses two continuous number of data register to store double words Equipment indication: D0, D1,…,D9,999. The symbol of equipment is D and the number uses decimal..

File

register

The file register can be used to store data or parameter when the register that PLC needs is not enough during handling data and parameter. It can store 16-bit binary number, i.e. a word, in each file register. It uses two continuous number of file register to handle double word. There are 1600 file registers for SA/SX/SC series and 10000 file registers for EH series. There is not the real equipment number for file register, thus it needs to execute READ/WRITE of file Register via commands API148 MEMR, API149 MEMW or the peripheral equipment HPP and WPLSoft. Equipment indication: K0~K9,999. There is no equipment symbol and uses decimal

number for number.Index

register

Index register E and F are 16-bit data register just the same as general data register. It can be wrote and read freely and has the function of index indication to use for character device, bit device and constants. Equipment indication: E0~E7, F0~F7. The symbols of equipment are E, F and the number uses decimal.

4.1.5 PLC SCAN

Fig7. PLC SCAN CYCLE

4.1.5.1 READING INPUT – Reads input and updates process input. The input can be either in analog or digital form

4.1.5.2. EXECUTE PROGRAM – executes user program once. The program is in the form of ladder logic diagram

4.1.5.3. CHECKS COMMUNICATION – Takes care of the system processes (such as communication with other PLC’s)

4.1.5.4. UPDATES OUTPUT – The PLC updates the output according to the execution of the program

CHAPTER-5

3.1.6 THE WORKING PRINCIPLE OF LADDER DIAGRAM

Ladder diagram is an automatic control diagram language

that developed during World War II. At first, it just has basic

components, such as A contact (normally open), B contact (normally

close), output coil, timer, counter and etc. (The power panel is made

up of these basic components) It has more functions, differential

contact, latched coil and the application commands, add, minus,

multiply and divide calculation, that traditional power panel can’t

make since PLC is developed. The working principles of the

traditional Ladder Diagram and the PLC Ladder Diagram are similar

to each other; the only difference is that the symbols for the

traditional ladder diagram are expressed in the format that are close

to its original substance, while those for the PLC ladder diagram

employ the symbols that are more explicit when being used in

computers or data sheets. In the Ladder Diagram Logics, it could be

divided into the Combination Logics and the Sequential Logics, and

is described as follows:

3.1.6.1. Combination Logics:

The following example is the combination logics that show in

traditional diagram and PLC ladder diagram separately.

Fig9.PLC ladder diagram

3.1.6.2. Sequential logics:

The sequential logics are a type of circuit that possesses the “Draw-

Back” structure, which is to draw back the circuit’s output result and

has it serve as the input condition. Thus, under the same input

condition, different output results will be generated in accordance

with previous conditions and motions with different orders.

The following example is the sequential logics that show in traditional diagram and PLC ladder diagram separately

Table 1: BASIC INSTRUCTIONS OF DELTA PLC

.

CHAPTER-6

FAULT DETECTION IN INDUCTION MOTOR

SINGLE PHASE FAULT

• 3HP induction motor.

• At fault conditions, Y phase cutoff from the supply,this is achieved by

using ideal switch.

• Input current=20-30A.

• Losses nearly 500 W.

• Output power=1.75KW.

UNDER VOLTAGE FAULT

• 3HP induction motor.

• Input voltage=115V.

• Torque is continuosly varied.

• Motor not tends to rotate.

• This type of motor destroy the drive application.

UNBALANCED FAULT

• 3HP induction motor.

• Input voltage is varied continuously.

• Torque & speed is also varied continuously.

• This type of faults totally destroys the drive application at all.

BLOCKED ROTOR FAULT

• In blocked rotor conditions, the speed of the induction motor is zero.

• It simply acts as a secondary short-circuited transformer.

• The whole power is utilised to produce the losses.

• Here, the output power is wattles (useless).

OVER VOLTAGE FAULT

• Input voltage>230V.

• Input current is high.

• Both the stator & rotor losses is high.

• Torque is plenty, due to high starting torque , there is an advantage in

starting, but there is always high amount of losses.

• Output power is so much reduced.

POWER SUPPLY UNIT

5v Power Supply

+5v

C10

100u

F/16V

D2

LED

C9

470uF/25V

U1

LM78051 3

2

IN OUT

GND

C110.1uF

CON1

AC Input

121

2R1

330E

- +

D1

DB106

1

2

3

4

Almost all the electronic devices and circuits require a

D.C, source for all the operation. One form of D.C. source is batteries. But they are

costly and require frequent replacement. The easily available and most economical

source is A.C. into a suitable D.C. such a device is called power supply. The power

supply consists of the following the three sub divisions

1. Rectifier

2. Filter

3. Voltage regulator

CHAPTER 7

RECTIFIER

A rectifier is a device which offers a low resistance to the current in one direction

and a high resistance in the opposite direction. Such a device is

capable of converting A.C. voltage into a pulsating D.C. voltage. The rectifier

employs one or more diodes. It may be either a vacuum diode or a semiconductor

diode.

There are two types 1. Half wave rectifier

2. Full wave rectifier

3. Bridge rectifier

BRIDGE RECTIFIER

Bridge rectifier is a full wave rectifier. It consists of four

diodes , arranged in the form of a bridge . it utilizes the advantages of the full

wave rectifier and at the same time it eliminates the need for a centre tapped

transformer. The supply input and the rectified output are the two diagonally

opposite terminals of the bridge.

During the positive half cycle, the secondary terminal A is

positive w.r.t. terminal B. now the diodes D1 and D3 are forward biased and hence

do not conduct. The current flows from terminal A to terminal B through D1, load

resistance RL and the diode D3 and then through the secondary of the transformer.

During the negative half cycle, terminal B is positive

w.r.t point A. now diodes D2 and D4 are forward biased and hence conduct.

Diode D1 and D3 are reversed biased and hence do not conduct. The current flows

from terminal B to terminal A through diode D2, the load resistance RL and diode

D4 and then through the secondary of the transformer.

On both positive and negative half cycles of the A.C.

input, the current flows through the load resistance RL in the same direction. The

polarity of the voltage developed across RL is such that the end connected to the

junction of the diodes D1 and D2 will be positive.

ADVANTAGES

1. Centre tapped transformer is not necessary.

2. D.C. saturation of the transformer does not take place since the two

currents flow in the opposite direction through transformer secondary.

3. Transformer utilization factor is increased.

4. PIV rating across each diode is Vm.

DISADVANTAGES

1. The circuit requires a four diodes and hence additional voltage drop that

reduce the output voltage through the transformer secondary.

2. It’s rarely used with thermionic diode value because of heater supply

problem.

FILTER

Output from the rectifier unit having harmonic contents , so we

can provided the filter circuit, filter circuit is used to reduce the harmonics. Here

we can use the pi filter .pi filter consists of capacitance and inductance (i.e. two

capacitance in parallel and one inductance in series). These eliminates the

harmonics from both voltage and current signals.

VOLTAGE REGULATOR

Voltage regulator is used to maintain the constant voltage with

the variation of the supply voltage and the load current, mainly we can use the two

types of voltage regulator they are

1. series voltage regulator

2. zener diode voltage regulator

RELAY INTRODUCTION

The first relay was invented by Joseph Henry in 1835. The name relay derives from the  french noun relais that indicates the horse exchange place of the

postman. Generally a relay is an electrical hardware device having an input and output gate. The output gate consists in a one or more electrical contacts that switch when the input gate is electrically excited. It can implement a decoupler, a router or braker for the electrical power, a negation, and, on the base of the wiring, complicated logical functions containing and, or, and flip-flop. In the past relays had a wide use, for instance the telephone switching or the railway routing and crossing systems. In spite of electronic progresses (as programmable devices), relays are still used in applications where ruggedness, simplicity, long life and high reliability are important factors (for instance in safety applications)

RELAY DRIVER CIRCUIT

+12V

MC Port Pin Q12N2222

1K

D1

1N40

07

NC

AC LOADNO

Relays are components which allow a low-power

circuit to switch a relatively high current on and off, or to control signals

that must be electrically isolated from the controlling circuit itself.

Newcomers to electronics

CHAPTER-8 Current transformer & Voltage transformer

3.4.1General Description

A current transformer is a type of "instrument transformer" that is designed to provide a current in its secondary which is accurately proportional to the current flowing in its primary.

Current transformers are designed to produce either an alternating current or alternating voltage proportional to the current being measured. The current transformers used with the Watt node transducers produce a 333 mV alternating voltage when the rated current is measured (either 30A, or 50A). The OSI power transducers employ CT's that produce 5V output at rated value.

Current transformers measure power flow and provide electrical inputs to power transformers and instruments. Current transformers produce either an alternating current or alternating voltage that is proportional to the measured current. There are two basic types of current transformers: wound and toroidal. Wound current transformers consist of an integral primary winding that is inserted in series with the conductor that carries the measured current. Toroidal or donut-shaped current transformers do not contain a primary winding. Instead, the wire that carries the current is threaded through a window in the toroidal transformer.

Current transformers have many performance specifications, including primary current, secondary current, insulation voltage, accuracy, and burden. Primary current, the load of the current transformer, is the measured current. Secondary current is the range of current outputs. Insulation voltage represents the maximum insulation that current transformers provide when connected to a power source. Accuracy is the degree of certainty with which the measured current agrees with the ideal

value. Burden is the maximum load that devices can support while operating within their accuracy ratings. Typically, burden is expressed in volt-amperes (VA), the product of the voltage applied to a circuit and the current.

3.4.1.1.Accuracy:

he accuracy of a CT is directly related to a number of factors including:

Burden Burden class/saturation class Rating factor Load External electromagnetic fields Temperature and Physical configuration. The selected tap, for multi-ratio CT's

3.4Voltage Transformer:

Voltage transformers (VT) or potential transformers (PT) are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 V or 120 V at rated primary voltage, to match the input ratings of protection relays.

The transformer winding high-voltage connection points are typically labeled as H1, H2 (sometimes H0 if it is internally grounded) and X1, X2 and sometimes an X3 tap may be present. Sometimes a second isolated winding (Y1, Y2, Y3) may also be available on the same voltage transformer. The high side (primary) may be connected phase to ground or phase to phase. The low side (secondary) is usually phase to ground.

The terminal identifications (H1, X1, Y1, etc.) are often referred to as polarity. This applies to current transformers as well. At any instant terminals with the same suffix numeral have the same polarity and phase. Correct identification of terminals and wiring

is essential for proper operation of metering and protection relays.

While VTs were formerly used for all voltages greater than 240 V primary, modern meters eliminate the need VTs for most secondary service voltages. VTs are typically used in circuits where the system voltage level is above 600 V. Modern meters eliminate the need of VT's since the voltage remains constant and it is measured in the incoming supply. This is mostly used in H.V.

RMS TO DC CONVERSION (AD536A):

The AD536A is a complete monolithic integrated circuit that performs true rms-to-dc conversion. It offers

performance comparable or superior to that of hybrid or modular units costing much more. The AD536A directly computes the true rms value of any complex input waveform containing ac and dc components. A crest factor compensation scheme allows measurements with 1% error at crest factors up to 7. The wide bandwidth of the device extends the measurement capability to 300 kHz with less than 3 dB errors for signal levels greater than 100 mV. An important feature of the AD536A, not previously available in rms converters, is an auxiliary dB output pin. The logarithm of the rms output signal is brought out to a separate pin to allow the dB conversion, with a useful dynamic range of 60 dB. Using an externally supplied reference current, the 0 dB level can be conveniently set to correspond to any input level from 0.1 V to 2 V rms. The AD536A is laser trimmed to minimize input and output offset voltage, to optimize positive and negative waveform symmetry (dc reversal error), and to provide full-scale accuracy at 7 V rms. As a result, no external trims are required to achieve the rated unit accuracy. The input and output pins are fully protected. The input circuitry can take overload voltages well beyond the supply levels. Loss of supply voltage with the input connected to external circuitry does not cause the device.

The AD536A is available in two accuracy grades (J and K) for commercial temperature range (0°C to 70°C) applications, and one grade (S) rated for the −55°C to +125°C extended range. The AD536AK offers a maximum total error of ±2 mV ± 0.2% of reading, while the AD536AJ and AD536AS have maximum errors of ±5 mV ± 0.5% of reading. All three versions are available in a hermetically sealed 14-lead DIP or a 10-pin TO-100 metal header package. The AD536AS is also available in a 20-terminal leadless hermetically sealed ceramic chip carrier.

The AD536A computes the true root-mean-square level of a complex ac (or ac plus dc) input signal and provides an eluvia-lent dc output level. The true rms value of a waveform is a more useful quantity than the average rectified value because it relates directly to the power of the signal. The rms value of a statistical signal also relates to its standard deviation.An external capacitor is required to perform measurements to the fully specified accuracy. The value of this capacitor deter-mines the low frequency ac accuracy, ripple amplitude, and settling time. The AD536A operates equally well from split supplies or a single supply with total supply levels from 5 V to 36 V. With 1 mA quiescent supply current, the device is well suited for a wide variety of remote controllers and battery-powered instruments.

sometimes want to use a relay for this type of application, but are unsure about the

details of doing so. Here’s a quick rundown. To make a relay operate, you have to

pass a suitable .pull-in. and .holding current (DC) through its energizing coil.

3.8 RS-232 DETAILS

3.8.1 SERIAL COMMUNICATION

3.8.1.1. INTRODUCTION:

In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time (contrast parallel port). Throughout most of the history of personal computers, data transfer through serial ports connected the computer to devices such as terminals or modems. Mice, keyboards, and other peripheral devices also connected in this way.

While such interfaces as Ethernet, FireWire, and USB all send data as a serial stream, the term "serial port" usually identifies hardware more or less compliant to the RS-232 standard, intended to interface with a modem or with a similar communication device.

(Fig18 RS 232 PORT)

3.8.2 HOW RS232 WORKS

This section describes how RS232 works in general without describing complex handshake methods - only the simplest system is described - this it the most useful and the most likely to work

Data is transmitted serially in one direction over a pair of wires. Data going out is labeled TX (indicating transmission) while data coming in is labeled Rx (indicating reception). To create a two way communication system a minimum of three wires are needed TX, RX and GND (ground). Crossing over TX & RX between the two systems lets each unit talk to the opposite one.

Each byte can be transmitted at any time (as long as the previous byte has been transmitted). The transmitted byte is not synchronized to the receiver - it is an asynchronous protocol i.e. there is no clock signal. For this reason software at each end of the communication link must be set up exactly the same so that each serial decoder chip can decode the serial data stream.

CHAPTER-9

PROTECTION OF INDUCTION MOTOR

INTRODUCTION:

AC INDUCTION MOTORS (IMs) are used as actuators in many industrial processes [1]. Although IMs are reliable, they are subjected to some undesirable stresses, causing faults resulting in failure. Monitoring of an IM is a fast emerging

technology for the detection of initial faults. It avoids unexpected failure of an industrial process. Monitoring techniques can be classified as the conventional and the digital techniques.

It is well known that IM monitoring has been studied by many researchers and reviewed in a number of works. Reviews about various stator faults and their causes, and detection techniques, latest trends, and diagnosis methods supportedby the artificial intelligence, the microprocessor, the computer, and other techniques in monitoring and protection technologies have been presented. In other works, ball bearing failures, speed ripple effect, air gap eccentricity, broken rotor bars, shaft speed oscillation, damaged bearings, unbalanced voltage , inter turn faults .

Nowadays, the most widely used area of programmable logic controller (PLC) is the control circuits of industrial automation systems. The PLC systems are equipped with special I/O units appropriate for direct usage in industrial automation systems . The input components, such as the pressure, the level, and the temperature sensors, can be directly connected to the input. The driver components of the control circuit such as contactors and solenoid valves can directly be connected to the output. Many factories use PLC in automation processes to diminish production cost and to increase quality and reliability [16]. There are a few papers published about the control of IMs with PLC.One of them is about power factor controller for a three-phase IM that utilizes a PLC to improve the power factor and to keep its voltage-to-frequency ratio constant over the entire control range. The other paper deals with monitoring control system of the induction motor driven by an inverter and controlled by aPLC providing its high accuracy in speed regulation at constantspeed– variable-load operation [16].Despite the simplicity of the speed control method used, this system presents constant speed for changes in load torque, full torque available over a wider speed range, a very good accuracy in closed-loop speed controlscheme.

CHAPTER-11

CONCLUSION

In this project, a novel protection system for three phase IMs designed and implemented. A 1500RPM 0.5HP three-phase IM has been connected to the protection system through the measuring components.

The induction motor is connected to the kit and by using PLC we protected the motor from several faults like voltage variation. If any fault is observed during online operation of the motor, a warning message appears on computer and then the motor is stopped.

REFERENCE[1] M. Peltola, “Slip of ac induction motors and how to minimize it,” ABBDrives Press Releases Techical Paper, ABB, New Berlin, 2003, pp. 1–7.

[2] ˙I. Colak, H. Celik, ˙I. Sefa, and S. Demirbas, “On line protection system forinduction motors,” Energy Convers. Manage., vol. 46, no. 17, pp. 2773–2786, 2005.

[3] A. Siddique, G. S. Yadava, and B. Singh, “A review of stator fault monitoringtechniques of induction motors,” IEEE Trans. Energy Convers.,vol. 20, no. 1, pp. 106–114, Mar. 2005.

[4] Y. Zhongming and W. Bin, “A review on induction motor online faultdiagnosis,” in 3rd Int. Power Electron. Motion Control Conf. (PIEMC2000), vol. 3, pp. 1353–1358.

[5] M. E. H. Benbouzid, “Bibliography on induction motors faults detectionand diagnosis,” IEEE Trans. Energy Convers., vol. 14, no. 4, pp. 1065–1074, Dec. 1999.

[6] N. Tandon, G. S. Yadava, and K. M. Ramakrishna, “A comparison of somecondition monitoring techniques for the detection of defect in inductionmotor ball bearings,” Mech. Syst. Signal Process., vol. 21, no. 1, pp. 244–256, Jan. 2007.

[7] F. Filippetti, G. Franceschini, C. Tassoni, and P. Vas, “AI techniques ininduction machines diagnosis including the speed ripple effect,” IEEETrans. Ind. Appl., vol. 34, no. 1, pp. 98–108, Jan./Feb. 1998.

[8] W. T. Thomson, D. Rankin, andD.G.Dorrell, “On-line current monitoringto diagnose airgap eccentricity in large three-phase induction motors—

In this project, the fault can be described and found by the operator. The test has been found successful in detecting the faults and in recovering them.