Figure 1. Block Diagram of PLC
The intent of the paper is to control the speed and give protection to Induction Motor (IM). Thereby it limits the starting current and protects the induction motor under load/ overload conditions. The control panel is designed to control the speed and protection of 3 phase IM and required control is done by PLC (Programmable Logic Controller). The motor is run at no load condition and load condition, for manual mode and PLC mode. At manual mode, if frequency is changed, the motor speed changes by keeping v/f ratio constant but, regulation in speed is high. At PLC mode, if frequency is changed, the motor speed remains constant, by keeping v/f ratio constant and speed regulation zero. The speed control of the induction motor in manual and PLC mode is accessed by using the selector switch [1]. SCADA (Supervisory Control and Data Aquisition) is used for monitoring and controlling of induction motor performance and it also collects performance data of the induction motor. This is how the starting, control the speed and protection of IM is achieved by using PLC and SCADA, and the operation is sufficiently high efficient and reliable [1], [2] .
The three-phase induction motors are widely used in the industry as electric motors. They run at essentially constant speed from no-load to full-load. However, the speed is depending on the frequency and the speed control of these motor is not easily done. We usually prefer DC motors when large speed variations are required. But, the 3-phase induction motors are simple, rugged, low cost, less maintain enhance and its characteristics are suit for industrial applications [3], [6] .
An electric motor converts electrical energy into a mechanical energy which is then supplied to different types of loads. AC motors operate on an AC supply, and they are classified into 1 phase and 3 phase induction, synchronous and special purpose motors. A starting device is used to start the 3 phase IM, it is used for industrial application mainly.
Protection of Induction Motor (IM) against possible problem such as overvoltage, overcurrent, overload, over temperature, 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 relay. This method is known as classical method that is very basic and involves mechanical dynamic parts [3] .
The implementation and monitoring a control system for the induction motor based on Programmable Logic Controller (PLC) technology is described in this paper. Also, the implementation of the hardware and software for speed control and protection with the results obtained from tests on induction motor performance is provided [10] . The PLC correlates the operational parameters to the speed requested by the user and monitors the system during normal operation and under trip conditions and speed regulation is very less. SCADA provides management with real data collection, operation and control the system which improves plant efficiency and safety; and the production cost reduces [6], [7] .
A PLC or a Programmable Logic Controller (PLC) is a specialized computer used to control machines and process [4]. It uses a programmable memory to store instructions and specific functions include on/off control, timing, counting, sequencing, arithmetic and data handling [5]. The basic block diagram of the PLC is illustrated in Figure 1.
Figure 1. Block Diagram of PLC
The PLC measures the current, voltage, the temperature and in addition it activates the output as per the input from the feedback according to the program [12], [13].
SCADA provides management with real data collection, operation and controls the system, which improves plant efficiency and safety; and reduces production cost . Block diagram of SCADA is shown in Figure 2.
Figure 2. Block Diagram of SCADA
Through the human operator controlled process data is given to the input-output devices, including the maintenance scheduled, detailed schematics, logistic information for a specific machine. HMI (Human Machine Interface) systems give the facility to the operator to see the information graphically. The communication between the equipment of the SCADA system is done by the supervisory system such as PLCs, sensors, RTUs (Remote Telemetry Units), etc. RTUs are used to transfer data to the server and receive the messages from the MTU (Maximum Transmission Unit) for controlling the external devices. Hence, these are also called as Remote Telemetry Units (RTU). PLC is connected to the sensors. PLC collects the signal from the sensors and converts them into digital form. For communication purpose in SCADA system; wired, wireless, radio frequency, satellite, etc. are used. For SCADA programming, various softwares are available like Vander wall, Winlog lite, etc[8]
A-B 1400 series is used for the system. Ladder Diagram (LAD) is used in programming languages. Software of the PLC was developed on the computer and loaded on the PLC by Ethernet.
The speed control software flowchart is shown in Figure 3.
Figure 3. Speed Control Software Flowchart
The system is operated in two modes, first is the manual mode and second is the PLC mode as well as SCADA mode. For selection of the mode, the one Two-way switch is used on the panel.
The switch position on manual mode i.e, any controller is used and the system is an open loop system. One main switch mounted on panel for ON/OFF, the panel supply. By rotating the Variable frequency pot, frequency is increased, and so voltage and speed of the motor increases with respect to the frequency. At rated 50Hz frequency, the three phase rated voltage of system is 220V and motor speed is 1500 rpm.
The load applied on Motor, decreases the speed of the motor, frequency and also voltage i.e. V/f ratio is constant. If the load increases linearly, speed also decreases, but current of the motor is increased. The motor might be damaged.
In industry, the motor is used without any controller, it is less efficient. The load on motor increases, the motor current increases or motor will be shut down without any warning. This is totally affects the production of the industry. The efficiency of the plant is decreased.
The switch is switched to the PLC mode. Run the program on PC in Ladder Diagram. By rotating variable frequency pot, frequency is increased, so voltage and speed of the motor increases with respect to the frequency. At rated 50Hz frequency, the three phase rated voltage of the system is 220V and the motor speed is 1500 rpm. This frequency variable switch is used to set the speed via frequency.
When the load is applied on the motor, the speed of the motor initially decreases, but after some time, it reaches to set speed of the motor settled by frequency variable pot. The current also increases but the magnitude of current is less than manual mode operation. Because speed tends to reach a set speed, so current decreases in small amount at same load for both conditions.
If the load on motor linearly increases, at that moment, the load current also increases. After crossing the rated value of motor current, the red bulb indicator on panel will glow and indicates that overcurrent is flowing through the motor. If the condition remains the same, the tripping circuit trips the motor for safety purpose.
In industry, the motor uses PLC as a controller, which is more efficient. When the load on motor increases, the motor current increases, and then the controller gives warning about the increasing current and the motor will be trip. The plant efficiency is high.
The speed control induction motor controlled through PLC is very efficient. PLC should maintain constant speed at any load. The response of PLC is very fast.
The SCADA is executing the program with PLC program, from SCADA screen, SET SCADA through SCADA Set Switch. After clicking on this switch, the SCADA is set. Total operation of the system is done through only SCADA. The frequency variable pot on panel is useless. There is no effect on that pot if rotating for a speed controlling purpose. The set point of the system is given from SCADA screen by scrolling the switch. The actual motor speed and set speed is monitored on the SCADA, also speed vs time graph plotted on SCADA screen on real time basis. If load on motor is increases, the decreasing speed is also monitored, on the graph. At the time when load increases, the speed of that particular time is also recorded. SCADA collect, analyze, and store every parameter of system and control the system. If the load on the motor is linearly increased, that time load current is also increased. After crossing the rated value of the motor current, the red bulb on the SCADA screen will glow and indicates the overcurrent flowing through the motor. The graph speed fluctuations are also observed. If emergency switch is on in the SCADA screen, the motor will be off at any critical condition.
SCADA is the system to monitor every parameter from the remote side. Also, control the parameter and collect all data of the system. SCADA is a real-time monitoring system. In Industry, SCADA plays an important role combined with PLC. Figure 4 shows the flowchart of the proposed system and Figure 5 shows the experimental setup.
Figure 4. Flowchart of Working System
Figure 5. Experimental Setup
The measurements and testing of speed control method used in hardware circuit. The selected results are presented for the comparison between the manual mode, and PLC mode. The speed control on the Transient state response is also observed under various load conditions. The results are analyzed to figure out the most efficient and stable response.
The V/f ratio of system is constant. At the load condition, speed of 3 phase induction motor decreases and the current increases gradually as load increases. The regulation of such system is very high i.e, efficiency is low.
The V/f ratio of the system is constant. At various loading conditions, the speed of 3 phase induction motor remains same. The regulation of such system is Zero.
The motor is started from the rest condition in PLC mode, the frequency of the system increases through frequency variable pot, and then the speed motor is increases linearly up to the set point (1000 rpm). Time required for reaching the set speed is measured and all the parameters of transient response are measured at different loading condition.
The transient response at no load condition is shown in Figure 6, and the obtained results are tabulated in Table 1. When the load values are changed i.e, variable loads are used, the rise time is not available (Figure 7). The observed values are tabulated in Table 2. Figure 8 shows the transient response at large load and the values are tabulated in Table 3.
Figure 6. Transient Response at No Load Condition
Figure 7. Transient Response at Variable Load
Figure 8. Transient Response at Large Load
Table 1. Transient Response at No Load
Table 2. Transient Response a Small but Variable Load
Table 3. Transient Response at Large Load
Hardware model for Controlling of 3 phase induction motor is developed. The PLC and SCADA based circuit is used in this system with a minimum number of components to develop monitor and control a speed of three phase Induction Motor, and protect motor from over current protection using PLC.
V/f control method is one of the speed control method, where V/f remains constant. When suddenly the load changes, speed of induction motor remains constant by using PLC. In the software of Allen Bradley Ladder, logic programming in RS Linx is developed, analysed and implemented in this paper.
SCADA software is used in real data calculation. By using real time system SCADA, motor is control effectively. Transient response is also observed using SCADA. Overshoot is Zero even through there is sudden change in load.