Design And Construction A Motor Soft Starter For A Three Phase Motor Using Arduino

INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Our industries use various kinds of machines. The induction machine is one of the most used three phase AC machine which is almost 70% of the motors used in industries. Their robust construction and high efficiency makes it the best choice for every industrial sector. But they do require protection devices and equipment used for their safe operation so it can operate safely and prevents any potential damage to the motor and also increase their life span. The most essential equipment used for three phase induction motor is a motor starter.
The soft starter is a type of motor starter that uses the voltage reduction technique to reduce the voltage during the starting of the motor.
The soft starter offers a gradual increase in the voltage during the motor startup. This will allow the motor to slowly accelerate & gain speed in a smooth fashion. It prevents any mechanical tear and jerking due to sudden supplying of full voltage.
The torque of an induction motor is directly proportional to the square of current. & the current depends on the supply voltage. So the supply voltage can be used to control the starting torque. In a normal motor starter, applying full voltage to the motor generates maximum starting torque which possess mechanical hazard to the motor.
Therefore we can say that a soft starter is a device that reduces the starting torque & gradually increase it in a safely manner until it reaches it rated speed. One the motor attains its rated speed, the soft starter resumes the full voltage supply through it.
During motor stopping, the supply voltage is gradually reduced to smoothly decelerate the motor. Once the speed reaches zero, it breaks the input voltage supply to the motor.
The main component used for the regulation of voltage in a soft starter is a semiconductor switch such as a Thyristor (SCR). Adjusting the firing angel of the thyristor regulates the voltage supplying through it. Other components such as OLR (overload relay) used for overcurrent protection is also used.

1.2 PROBLEM STATEMENT
Connecting the motor to power supply draws a huge amount of current in the stator winding due to this low impedance called inrush current. The alternating current in the stator generates a rotational magnetic field (RMF) that induces current in the rotor windings.
The electromagnetic torque pulsations also causes long term effects on various mechanical system components if the strength of materials is exceeded which might lead to fatigue also.
The reduced voltage starting by soft starters eliminates stress from the electrical supply and it also reduces the possibility of voltage dip and brown out conditions. Soft and smooth starters provide smooth acceleration of rotor of three phase induction motor. Reduced voltage starting reduces high amount of starting torque applied on the shaft and therefore eliminates the shock on the driven load. An instantaneous high amount of starting torque can cause a jolt on the conveyor which can damage products, pump cavitations and water hammer in pipes. Therefore, a soft starter ramps up the voltage applied to the motor from the initial voltage to the full voltage. The voltage is initially kept low to avoid sudden jerks during the start. The voltage and torque increases gradually so that the induction motor starts to accelerate. This ramp up voltage provides sufficient torque for the load to accelerate gradually and hence mechanical and electrical shocks are minimised from the system, The voltage supplied to stator windings are adjustable and it has ramp characteristics.

1.3 AIM AND OBJECTIVES OF THE STUDY
The main aim of this work is to build a motor soft starter for a three phase electric motor using arduino. The objectives of this work are:
i. To help you reduce mechanical wear and tear on startup.
ii. To reduce energy costs.
iii. To minimize loss of production hours from equipment breakdown.

1.4 ADVANTAGES OF SOFT STARTER
Advantages of Soft Starter are as follows:
Smooth Startup: Unlike conventional motor starter, it provides very gradual increase of voltage thus speed that results in a very smooth startup. There is no mechanical stress whatsoever or jerks that can damage the motor.
Acceleration & Deceleration Control: It offers a fully adjustable acceleration & deceleration of the motor. Varying the firing angle slowly or quickly can control the acceleration during startup & deceleration during stopping of motor. This is used in application where startup acceleration needs to be adjusted.
No Power Surges: Since the conventional motor starter allows full voltage across the motor, a huge inrush current start flowing into the motor that cause a power surge in the circuit. the soft starter limits such current thus preventing the power surges.
Multiple Startups: Some applications require the motor to start & stop multiple times in small period of time. such motor if used with a conventional starter will experience overheating due to high starting current. However, soft starters drastically increases the number of startups for a motor in a specific duration.
Reduction of Overheating: The motor overheating is a very serious problem. It occurs due to the high winding current during its startup. The soft starter allows a very small amount of starting current which prevents the overheating of motor.
Increased Life Span: The soft starter as compared to a conventional starter improves the life time of the motor. it is due to the smooth operation & absence of electrical & mechanical stress on the motor.
Less Maintenance: Due to its smooth operation, the induction motor is less likely to have any mechanical faults, which is why it require less maintenance as opposed to conventional motor starter.
Efficiency: A conventional motor starter supply full voltage (very high inrush current) to the motor that consumes too much energy. A soft starter significantly reduces it & allows a gradual increase in energy consumption. Also the power switches are controlled using very low voltage level. It improves the overall efficiency of the motor.
Compact & Small Size: The soft starter has a very compact design that takes up very small space. Unlike other motor starters, it has very small size.
Low Cost: compared to other starters such as VFD, this sure does cost cheaper.

1.5 DISADVANTAGES OF SOFT MOTOR STARTER
No Speed regulation: The soft starter only allows the control of input voltage supply i.e. from 0 volts to line voltage with a fixed line frequency. Since the frequency is constant the motor speed is constant & only regulates by the load connected with it. The speed of induction motor is regulated by varying the supply frequency below or above the line frequency according to the need. Such feature is only available in VFD (variable frequency drive).
Heat dissipation: The semiconductor switches inside the soft starter dissipates some energy in the form of heat. Therefore, it also requires heat sinks for cooling the power switches.
Reduced starting Torque: Since it reduces the input voltage that corresponds to the input current which is directly proportional to the starting torque of the induction motor, it significantly reduces the starting torque.

1.6 APPLICATIONS OF SOFT STARTER
The soft starter is used in industries & is more appropriate to be used for motors that run on a constant speed.
Fans: The huge fans used in industries runs at a constant speed. However, they do require the startup protection. A soft starter is a best option for such fans.
Conveyer belts: The conveyer belts in industries are used for moving objects & it needs extra care. The sudden jerks during starting or stopping using conventional starter may misalign the belts, damages the belt due to mechanical stress & damage the objects placed on it. It requires a smooth starting & stopping offered by a soft starter
Motors using belt & pulleys: The motor that drives load through belts & pulleys cannot tolerate the sudden jerks. It wears the belt that couples it to the load. A soft starter offers a smooth starting for such motor applications.
Water or liquid Pump: Any type of pump connected with a motor requires a smooth starting & stopping due to the sudden pressure building inside the pipes. A conventional starter may generate enough pressure at startup to break the line. A soft starter offer gradual increase in the pressure to such liquid pumps. However, there is no speed control of the pump during normal operation. A VFD is a better choice for variable pump speed.

1.7 LIMITATION OF THE STUDY
Electrical motor starters are usually used for heavy power rated motors. Small motors below 1Hp does not require motor starter due to their high impedance. However, they do need overcurrent protection that is available in DOL starter.

1.8 SCOPE OF THE STUDY
The scope of this work covers building a motor soft starter to safely start and stop an electric motor using arduino as the heart of the circuit.