PLC BASED INDUCTION MOTOR STARTING AND PROTECTION

PLC BASED INDUCTION MOTOR STARTING AND PROTECTION

ABSTRACT

The intent of the paper is starting, speed control and protection of induction motor. There by limiting the starting current and increase the starting torque and so as to protect the induction motor. There are different methods for starting of the Slip Ring induction Motor. But we have opted the Rotor Resistance Control method for Starting the Induction Motor. Programming is done by using Programmable Logic Controller; control panel is designed and programmed according to requirements. The motor will start with high rotor resistance and the rotor resistance is cut off with respective time delay and the motor will run at rated speed. The contactor is used for the switching of three phase supply to the stator winding. This is how the starting, speed control and protection of induction motor is achieved and the operation is very reliable, sufficiently high efficient. Induction motors are widely used in many operating areas and industrial applications as they are simple, robust, reliable and have low production costs. The reliability of an induction motor is of great Importance in applications such as commercial, aerospace and military and many industrial applications. In this paper different problems of IM are dealt with as over current, overvoltage, over temperature, over speed, inrush current, vibration monitoring during it’s time of operation. There are various proposed methods for fault diagnosis and protection of IM. Some of them are Stator fault monitoring techniques, protection system using On-line fault detection, Programmable Logic Controller (PLC) based protection system. In this study, the method which is applied is PLC based protection system of an IM.

Keywords— Induction Motor, Rotor resistance, Protection, Speed control, PLC, Ladder logic, Fault diagnosis

INTRODUCTION

The starting, speed control and protection of Induction motor can achieved easily by using PLC. Three-phase induction motors are widely used in industrial drives because they are rugged, reliable and economical. High Starting torque is a desired feature in some special industrial applications which use 3-Ph Slip Ring Induction motor. An induction motor or asynchronous motor is a 3phase 4pole induction motor. This is a type of alternating current motor where power is supplied to the rotor by means of electromagnetic induction. The 3 phase 4pole induction motor electric motor turns because of magnetic force is exert between the stationary electromagnet called the stator and a rotating. The three-phase induction motors are the most widely used electric motors in industry.

They run at essentially constant speed from no-load to full-load. However, the speed is frequency dependent and consequently these motors are not easily adapted to speed control .We usually prefer d.c. motors when large speed variations are required. Nevertheless, the 3-phase induction motors are simple, rugged, low-priced, easy to maintain and can be manufactured with characteristics to suit most industrial requirements.This3phase 4pole inductions electric motor turns because of magnetic force exert between emotion less electromagnet called the stator and a rotating electromagnet called the rotor. If the slip ring induction motor is started with all the slip rings or the rotor terminals shorted, like a normal induction motor, then it suffers extremely high locked rotor current, ranging upto1400%, accompanied with very low locked rotor torque as low as 60%.So,it is not advised to start a slip ring induction motor with its

OVERVIEW OF BLOCK DIAGRAM

 

FIG.1 BLOCK DIAGRAM

PROGRAMMABLELOGIC CONTROLLER

A PLC or a programmable controller is a small computer used for automation of real-world processes, such as control of ma- chinery on factory assembly lines. A PLC can be programmed to sense, activate, and control industrial equipment. Therefore, a PLC incorporates a number of I/O points, which allow electrical signals to be interfaced. Input and output components of the processes are connected to the PLC; and the control program is loaded on the PLC memory. The basic structure of the PLC is illustrated in Fig. 2.

 

FIG2. PROGRAMMABLE LOGIC CONTROLLER

In this study, the PLC measures the current, the voltage, the temperature, and the speed of an induction motor through analog inputs. In addition, it continuously monitors the inputs and activates the outputs according to the program. Siemens PLC S7-200 module with 14 digital input/10 digital output addresses with CPU 224 sample (14∗DI 24 V dc/10∗DO 24 V dc) is preferred due to its easy usefulness in experimental application. The PLC programming memory used is composed of 4096 words. STEP 7—Micro/Win 32 programmer was used as the software. Statement list editor (STL) and ladder diagram (LAD) were used as programming languages. Software of the PLC was prepared on the computer and loaded on the PLC by RS 232-RS 485 PC/planposition indicator (PPI) cable. While the program prepared is being loaded on the PLC from the computer, the most important point is the baud rate between the PLC and the computer. The baud rate must be appropriate to switch setup on the bound cable in manual.

PROTECTION SYSTEM

 

FIG.3.SCHEMATIC DIAGRAM OF THE PROTECTION SYSTEM.

Motor Electrical Protection

• Thermal Overload

• Process Caused (Excessive load)

• High Ambient Conditions (Hot, Blocked Ventilation)

• Power Supply Issues (Voltage/Current Unbalance, Harmonics)

• Phase Fault

• Ground Fault

• Abnormal Operating Conditions

• Over & Under Voltage

• Underfrequency

• Voltage and Current Unbalance

• Load Loss

• Jamming

• Jogging

Overvoltage Protection

The overall result of an overvoltage condition is a decrease in load current and poor power factor. Al though old motors had robust design, new motors are designed close to saturation point for better utilization of core materials and increasing the V/Hz ratio cause saturation of air gap flux leading to motor heating.

The overvoltage element should be set to 110% of the motors nameplate unless otherwise started in the data sheets.

Undervoltage Protection

The overall result of an undervoltage condition is an increase in current and motor heating and a reduction in overall motor performance. The undervoltage protection element can be thought of as backup protection for the thermal overload element. In some cases, if an undervoltage condition exists it may be desirable to trip the motor faster than thermal overload element. The undervoltage rip should be set to 80-90% of nameplate unless otherwise stated on the motor data sheets. Motors that are connected to the same source/bus may experience a temporary undervoltage, when one of motors starts. To override this temporary voltage sags, a time delay set point should be set greater than the motor starting time.

Short Circuit Protection

The short circuit element provides protection for excessively high overcurrent faults Phase-to-phase and phase-to-ground faults are  common types of short circuits When a motor starts, the starting current (which is typically 6 times the Full Load Current) has asymmetrical components . These asymmetrical currents may cause one phase to see as much as 1.7 times the RMS starting current. To avoid nuisance tripping during starting, set the the short circuit protection pick up to a value at least 1.7 times the maximum expected symmetrical starting current of motor. The breaker or contactor must have an interrupting capacity equal to or greater than the maximum available fault current or let an upstream protective device interrupt fault current.

LADDER LOGIC FOR STARTING OF MOTOR DIFFERENT PROGRAMMING LANGUAGES

1. LADDER DIAGRAM

2. FUNCTIONAL BLOCK DIAGRAM LANGUAGE

3. SEQUENTIAL FUNCTION CHART LANGUAGE

4. INSTRUCTION LIST LANGUAGE

HERE WE ARE USED LADDER LOGIC FOR STARTING AND PROTECTION PURPOSE

 

fig.4.ladder logic for starting of motor

CONCLUSION

Speed control and protection of induction motor is achieved and the operation is very reliable, sufficiently high efficient. Without changing in any hardware connection just by simply changing the program in the PLC; the motor can be made to run in for any duration of time. This system also used for one of the starting method of three phase slip ring Induction motor this system not only reduces the starting current to a limit, but also develops High starting torque which is required in many of the induction motor applications. This can be applicable to run the lift, by changing the logic in a program and it can also be used for any industrial applications. This PLC based system requires less hardware compared to any microcontroller or microprocessor based system. Programmable Logic Controllers (PLC) are widely used in industrial control because they are inexpensive, easy to install and very flexible in applications. A PLC interacts with the external world through its inputs and outputs.

REFERENCES:

1. Maria G. Ioannides, “Design And Implementation Of Plc-Based Monitoring Control System For Induction Motor,” Ieee Transactions On Energy Conversion, Vol. 19, No. 3, September 2004.

2. Ravi Masand, DeepikaJadwani, Prof. S.P Shukla, ―Fault Diagnosis Of Induction Motor Using Plc,‖ International Journal Of Advanced Research In Electrical, Electronics And Instrumentation Engineering, Vol. 2, Issue 12, December 2013.

3. Mrs.JigneshaAhir, ―Design And Development Of Plc And Scada Based Control Panel For Continuous Monitoring Of 3- Phase Induction Motor ,‖ National Conference On Recent Trends In Engineering & Technology, May 2011.

4. Colak, H.Celik, ˙i.Sefa, ―On Line Protection System For Induction Motors,‖ Energy Convers. Manage.Vol. 46, No. 17, Pp. 2773–2786, 2005.

5. PROGRAMMABLE LOGIC CONTROLLER, ―AN AUTOMATION TECHNIQUE FOR PROTECTION OF INDUCTION

MOTOR‖ PUBLISH BY INTERNATIONAL RESEARCH JOURNAL OF SUSTAINABLE SCIENCE &ENGG.

6. PLC AND SCADA BASED FAULT DIAGNOSIS OF INDUCTION MOTOR, INTERNATIONAL JOURNAL OF DIGITAL APPLICATION & CONTEMPORARY research (VOLUME 2, ISSUE 6, JANUARY 2014)

7. FAULT DETECTION AND PROTECTION OF INDUCTION MOTORS USING SENSORS-RAMAZANBAYINDIR, MEMBER, IEEE, ˙IBRAHIM SEFA, MEMBER, IEEE, ˙ILHAMICOLAK, MEMBER, IEEE, AND ASKINBEKTAS

8. Y. ZHONGMING AND W. BIN, ―A REVIEW ON INDUCTION MOTOR ONLINE FAULT DIAGNOSIS, IN 3RD INT. POWER ELECTRON. MOTION CONTROL CONF. (PIEMC 2000), VOL. 3, PP. 1353–1358.

9. M. E. H. BENBOUZID, ―BIBLIOGRAPHY ON INDUCTION MOTORS FAULTS DETECTION AND DIAGNOSIS, IEEE TRANS. ENERGY CONVERS., VOL. 14, NO. 4, PP. 1065– 1074, Dec. 1999

10. SIEMENS, S7-200 PROGRAMMABLE CONTROLLER SYSTEM MANUEL, 1999.

11. OKOLI F.I, ONUBOGU J.O, OKEZIE C.C, OKOROGU V.N, ‖THE SIMULATION OF THE CONTROL OF AN INDUSTRIAL MIXER USING PLC’’ INTERNATIONAL JOURNAL OF INVENTIVE ENGINEERING AND SCIENCES (IJIES) ISSN: 2319–9598, VOLUME-1, ISSUE-2, JANUARY 2013, 25.

12. W. T. THOMSON AND M. FENGER, ―CURRENT SIGNATURE ANALYSIS TO DETECT INDUCTION MOTOR FAULTS,‖ IEEE IND. APPL. MAG., VOL. 7, NO. 4, PP. 26–34, JUL./AUG. 2001

DESIGN, IMPLEMENTATION AND PERFORMANCE STUDY OF PROGRAMMABLE AUTOMATIC VOLTAGE REGULATOR

DESIGN, IMPLEMENTATION AND PERFORMANCE STUDY OF PROGRAMMABLE AUTOMATIC VOLTAGE REGULATOR

ABSTRACT

This paper proposes the design and implementation of a Programmable Automatic Voltage Regulator (PAVR) with higher precision, appropriate hysteresis and defense of anomaly. Current systems available locally lack precision and suffer the problem of oscillating between two output voltage and hence creating surge at the output which can damage valuable electronics. To avoid these, the stabilization of power voltage, minimization of output wave rate and unchangeable power-voltage to the instruments are needed while the load changes. That requires the maintenance of stable voltage and rapid reaction against the sudden change of input voltage and load. This paper defines the shortcomings and introduces a new system in the tolerable and substantial stable of 220V with '4.5% output accuracy for any deviation of input supply voltage within 100V-340V. To control the whole system automatically a microcontroller is used with some protection devices where to detect fault and the circuit implementation in this system are simple and flexible than conventional analog control circuitry. A simulation for both circuit and program has been accomplished for establishing better performance.

Keywords: Programmable Automatic Voltage Regulator (PAVR), Hysteresis, Microcontroller, Protection, Simulation.

INTRODUCTION

AC power supply by Power Development Board (PDB) in Bangladesh is subjected to variation from time to time. Moreover in rural areas supply voltage remains lower than specified most of the times. This poses a considerable threat to the sophisticated electronic devices. For that reason, many important electric machine or electric equipments may destroy. Power quality related problems, in particular voltage sags, surge and brownouts have a major negative impact on industrial productivity. This appears to be true for both industrialized as well as developing nations. So ensuring the input voltage to remain in a tolerable pre-specified limit has become a necessity in rural as well as some urban areas. In order to save these we need to use the Automatic Voltage Regulator.

An AVR is an electronic device that automatically regulates a variation of input voltage at a certain desired level to load. The voltage of main power supply may be affected by various troubling physical factors, so that special regulating equipment is required to keep the voltage steady. In replace of AVR, Programmable AVR is more flexible, easy to modify and the best for good precision and hysteresis. The existing systems like servo-stabilizers, CVTs, Ferro resonant regulators, thyristor ac regulators, tap changers and the electronic regulators are the available means for voltage regulator. Here the performances of existing commercially available technologies are compared by this system regarding response, faults handling, precision, efficiency and other important parameters. It is essential that the supply ac voltage is needed to operate automatically due to the interconnections among the systems in modern age. The electronic control circuit may be utilized to get the desired output which is very simple, flexible, reliable and cost effective.

AVR mainly functions to measure and regulate the input voltage for producing the stable output and to provide the Protection against sag, surge, spike, impulse, notch, brown out, over voltage, under voltage, over current and hysteresis to the sophisticated equipments and machineries. In this system, the whole operations are implemented by a microcontroller. Microcontroller here performs all actions in accordance with the program maintaining proper precision and hysteresis as we desire and the undesired input transitions are handled by the AC protection devices. The whole proposed design is illustrated in the following block diagram (Figure-1).

 

Figure-1: Block diagram of PAVR

A multi-tapped transformer with input supply and switches connected in primary and in secondary respectively to obtain regulated and stabilized output voltage at the load side is used. Here microcontroller plays the important role to decide and hence to control the switches through which secondary tap carries the power from input to load with a steady voltage. This system also provides the protection against surge, spike, lightning, overvoltage and excess current by adding AC breaker (MCB), Automatic Voltage Switcher (AVS) [25] in the Input line. In the upcoming sections the designing procedure with simulations, programming, the control operation of microcontroller and performance analysis will be discussed.

DESIGNING PROCEDURE AND DISCUSSION

Description of Circuit Design

As the designing commitment which is to stabilize automatically a large range (100V- 340V) variation of input voltage at a normal prescribed level output voltage (Table-1) with a great precision. For this the voltage regulation of input supply is designed which is regulated automatically in such a way that when the input voltage varies, the output voltage will remain stable at a constant value. To achieve this, a microcontroller has been programmed is such a way that when the dc input to microcontroller varies in accordance with the variation of input voltage, microcontroller will operate the suitable switch to get a regulated output from desired transformer tap. Table-1 represents the designing configuration of the multi-tapped transformer.

Firstly, the microcontroller compares a converted variable DC voltage which is found by stepped down the ac supply voltage with the range, which is shown in Table-2 and is set in the memory of the microcontroller. The voltage range for the program has been chosen in such different manner for letting switches functioned to select the different taps for getting desired output of around 220V AC (Table-2). Thus the stable output voltage occurs at the output of this designed regulation system for any short of variation of input voltage automatically. The whole schematic of the PAVR is shown in Figure-2 and Figure-3.

 

Figure-2: Schematic diagram of PAVR (Part-1)

 

Figure-3: Schematic diagram of PAVR (Part-2)

Simulation Procedure

To determine the accurate level of voltage for designing of switching and making the microcontroller program this circuit has been simulated using PSPICE Simulator. The operation of switching of PAVR at different level of input voltage is observed as well. Here, for input supply voltage of 130V, the switching operation is shown graphically in

Figure-4 where the switch under PB0 and Q0 is “ON”. At any input voltage within 100V- 340V, one and only one switch is activated at a time as defined in the program.

 

Figure-4: Simulation for 130V Input

Flowchart description

The microcontroller program of the PAVR is designed and functioned, as the following flowchart (Figure-5), to measure the received DC voltage and then to compare with the prescribed range stored in the microcontroller memory and finally to obtain a decision for the output. In the flowchart, it is also shown that when the received DC input is out of the range (i.e. above 5V and below 1V), microcontroller will operate “No Operation (NOP)”. That means, the PAVR will remain “OFF” during excess high and low voltage AC supply to protect the devices and equipments from damaging. Here the increasing and decreasing of DC input voltage are given orderly to maintain the hysteresis properly.

 

Figure-5: Flowchart for the program of microcontroller operation

Description of Program Operation

The program that was designed for the PAVR has been simulated using PIC Simulator IDE software [28]. PIC Simulator IDE is a basic complier, assembler, disassembler and debugger for microchip family PICmicro. Firstly, the microcontroller has to be selected to load the program. Then the simulation has to be run. The sequences of operation have to be executed as follows.

Option>Select Microcontroller

Tools>Assembler

File>open/PAVR.asm

Tools>Assemble & Load

Simulation>Start

Tools>Microcontroller View

Tools>8×LED Board

The overview of simulation is presented by Figure-6 with PIC Simulator IDE interface. In this figure, the PORTB0 is displayed as ON when the input voltage is in the range of 1.0V-1.5V (2Ch-0Fh).

 

Figure-6: The simulation interface of PIC Simulator IDE with output Display

Description of Microcontroller Operation

A PIC16F876A CMOS FLASH-based 8-bit microcontroller (Figure-7) is used to control the whole system which is more reliable, simple and flexible than conventional analog control circuitry. It features especially Self-reprogrammable under software control, 2 I/O pins & 3 I/O ports, 256 bytes of EEPROM data memory, 2 Comparators, 5 channels of 10-bit Analog-to-Digital (A/D) converter, Programmable code protection, Power-saving Sleep mode, Selectable oscillator options and In-Circuit Debug via two pins.

 

Figure-7: Pin diagram of PIC16F876A Microcontroller with program placing.

An assembly language program is loaded in the microcontroller memory (Figure-7) that configures the A/D module, comparator module and I/O ports, and sets different registers of the memory with the different range of digital code (Table-3). In the program the registers are assigned by any arbitrary names to make the program more readable.

Here port-A is used as input port and port-B as output port. Firstly, microcontroller receives the DC input corresponding to supply AC input from stepped-down transformer at RA1 of PORTA. And then it is compared with the ranges that are set in the memory of microcontroller in the form of code via an A/D converter and a comparator. After that it makes anyone of the output pins (RB0-RB7) of PORTB HIGH corresponding to the range, as mentioned in Table-2, which in turn activates a respective switch to get the regulated output from the transformer. Here a constant voltage level is maintained although the input voltage level goes high than the constant desired level (Table-4). To sense this change, the microcontroller periodically checks terminal voltage and compares this with defined reference voltage levels. For designing purpose the reference voltage and code as a range has been calculated to corresponding pins of PORTB. This is shown in Table-2 and Table-3.

Table-1: (For the Design of Multi-tapped Transformer) Output Voltage Range corresponding to Input Range and Transformation Ratio at different Taps at Normal Input Voltage of 220V

Table-2: Selection of output pins, Switches and Transformer Taps for the prescribed input DC voltage range corresponding to input AC supply voltage range.

Table-3: Hexadecimal Value of digital code equivalent to prescribed DC voltage range corresponding to AC input and PAVR output voltage.

Table-4: Experimented Analog DC input for ADC of Microcontroller and Regulated AC Output Voltage for typical AC Input Supply

PERFORMANCE ANALYSIS

This system has been experimented practically after designing. Here for some typical AC input voltage supply, the regulated output approximate to desired level is found that is shown in Table-4. From this table, it is clearly revealed that this PAVR is able to regulate any variation of input voltage of a system within 100V-340V at a stable range of 210V- 230V and also to defend the system from damage due to extreme decrease and increase in AC supply voltage which is out of the range of 100V-340V. In Figures below present some performance curves of PAVR. Figure-8 shows the desired response curve of PAVR which is produced from the desired output voltage (210V-230V) for any input supply voltage within range of 100V-340V. In Figure-9, a typical input-output voltage characteristics curve of PAVR is put on view of the regulated output voltage that is near about 220V AC (Data in Table-4).

The Figure-10 exhibits a practical input-output voltage characteristics of PAVR for random supply. In this response curve, it confirms the design requisition of a stable output in range of 210V-230V as the regulation of any change in AC supply voltage within 100V- 340V, and the protection any system from spoiling due to low voltage i.e. below 100V and high voltage i.e. above 340V. A hysteresis curve, given in Figure-11, shows the hysteresis behavior of PAVR during the operation of switches at the transition of different ranges of input supply voltage. It is needed to maintain properly to prevent the frequent vacillation of switching between “ON” and “OFF”.

 

Figure-8: Desired Response Curve of PAVR

 

Figure-9: Typical Input-Output Voltage Charactesistics of PAVR

 

Figure-10: Practical Input-Output Voltage Characteristics of PAVR for Random Supply

 

 Figure-11: Hyteresis Curve

CONCLUSION

It is clear that, from above design and discussion, and the comparison shown in Table-5 with some other common existing AVR systems, my proposed proprietary PAVR performs better than any other existing systems. Because it is mainly programmable that can be programmed as the demand maintaining proper precision and sufficient hysteresis over a wide range of input variation. Here the protection against the excessive high and low voltage and current is confirmed which is crucial for the sophisticated electrical and electronic equipments. It is mentionable that the PAVR is very much cheap than other systems because of having microcontroller in place of discrete electronic components and simple protection units. Therefore, the circuit design and implementation are very much easy, flexible and the efficiency of this system is good enough as well. According to market comparison study, the commercially available AVR has a three to four step stabilization of the input variable voltage where the output becomes a big changing stable value within a prescribed range that is not an absolute design to get an output precised. For this reason in my research the way has been adopt to make the system for getting the precision output within in a large variation of input is the design of the main transformer having a many number of taps in the secondary winding side of the transformer maintaining a small turn difference between two adjacent taps. PAVR is applied to all electrical and electronics equipments especially in communications and precision instruments of manufactories.

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