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MOTOR CONTROL PDF

Thursday, May 9, 2019


Once the proper motor is selected, understanding the many various control devices There are four major motor control topics or categories to consider. Each of. wire a simple control circuit from a control ladder diagram. • discuss protection of motor control circuits. • name the NEMA enclosure types and give an example. MOTOR. 3CT. TO V. SEPARATE. CONTROL. * OT is a switch that opens when an overtemperature condition exists (Type MFO and MGO only). T1. T3.


Motor Control Pdf

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Interpret this AC motor control circuit diagram, explaining the meaning of each Examine this three-phase motor control circuit, where fuses protect against. 1 Basic Principles of UNIT Motor Controls Unit 1—Introduction This unit discusses the basic concepts of motor control, including “motor control language” and. Motor control circuits are an effective way to reduce cost by using smaller wire and reduced-amperage devices to control a motor. Imagine trying to wire a.

A larger motor requires a specialized switching unit called a motor starter or motor contactor. When energized, a direct on line DOL starter immediately connects the motor terminals directly to the power supply. In smaller sizes a motor starter is a manually operated switch; larger motors, or those requiring remote or automatic control, use magnetic contactors.

Very large motors running on medium voltage power supplies thousands of volts may use power circuit breakers as switching elements. A direct on line DOL or across the line starter applies the full line voltage to the motor terminals, the starters or cubicle locations, can usually be found on an ELO drawing.

This is the simplest type of motor starter. A DOL motor starter also contains protection devices, and in some cases, condition monitoring. Smaller sizes of direct on-line starters are manually operated; larger sizes use an electromechanical contactor relay to switch the motor circuit.

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Solid-state direct on line starters also exist. A direct on line starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit.

The maximum size of a motor allowed on a direct on line starter may be limited by the supply utility for this reason. In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor , the motor will draw a high starting current until it has run up to full speed.

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This starting current is typically times greater than the full load current. To reduce the inrush current, larger motors will have reduced-voltage starters or variable speed drives in order to minimise voltage dips to the power supply.

A reversing starter can connect the motor for rotation in either direction.

Such a starter contains two DOL circuits—one for clockwise operation and the other for counter-clockwise operation, with mechanical and electrical interlocks to prevent simultaneous closure.

Single phase AC motors and direct-current motors require additional devices for reversing rotation. Reduced voltage starters[ edit ] Reduced-voltage, star-delta or soft starters connect the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps. By using an autotransformer or a series inductance , a lower voltage is present at the motor terminals, reducing starting torque and inrush current.

Once the motor has come up to some fraction of its full-load speed, the starter switches to full voltage at the motor terminals. Since the autotransformer or series reactor only carries the heavy motor starting current for a few seconds, the devices can be much smaller compared to continuously rated equipment.

The transition between reduced and full voltage may be based on elapsed time, or triggered when a current sensor shows the motor current has begun to reduce.

An autotransformer starter was patented in Main article: Adjustable-speed drive An adjustable-speed drive ASD or variable-speed drive VSD is an interconnected combination of equipment that provides a means of driving and adjusting the operating speed of a mechanical load.

An electrical adjustable-speed drive consists of an electric motor and a speed controller or power converter plus auxiliary devices and equipment. IMCs monitor the load on a motor and accordingly match motor torque to motor load. This is accomplished by reducing the voltage to the AC terminals and at the same time lowering current and kvar. This can provide a measure of energy efficiency improvement for motors that run under light load for a large part of the time, resulting in less heat, noise, and vibrations generated by the motor.

Overload relays[ edit ] A starter will contain protective devices for the motor. At a minimum this would include a thermal overload relay.

The thermal overload is designed to open the starting circuit and thus cut the power to the motor in the event of the motor drawing too much current from the supply for an extended time. The overload relay has a normally closed contact which opens due to heat generated by excessive current flowing through the circuit. Thermal overloads have a small heating device that increases in temperature as the motor running current increases.

There are two types of thermal overload relay. In one type, a bi-metallic strip located close to a heater deflects as the heater temperature rises until it mechanically causes the device to trip and open the circuit, cutting power to the motor should it become overloaded. A thermal overload will accommodate the brief high starting current of a motor while accurately protecting it from a running current overload.

The heater coil and the action of the bi-metallic strip introduce a time delay that affords the motor time to start and settle into normal running current without the thermal overload tripping. Applications[ edit ] Every electric motor has to have some sort of controller.

The motor controller will have differing features and complexity depending on the task that the motor will be performing. The simplest case is a switch to connect a motor to a power source, such as in small appliances or power tools. The switch may be manually operated or may be a relay or contactor connected to some form of sensor to automatically start and stop the motor.

The switch may have several positions to select different connections of the motor. This may allow reduced-voltage starting of the motor, reversing control or selection of multiple speeds.

Motor Control and Learning

Overload and over current protection may be omitted in very small motor controllers, which rely on the supplying circuit to have over current protection. Small motors may have built-in overload devices to automatically open the circuit on overload. Larger motors have a protective overload relay or temperature sensing relay included in the controller and fuses or circuit breakers for over current protection.

An automatic motor controller may also include limit switches or other devices to protect the driven machinery. More complex motor controllers may be used to accurately control the speed and torque of the connected motor or motors and may be part of closed loop control systems for precise positioning of a driven machine. For example, a numerically controlled lathe will accurately position the cutting tool according to a preprogrammed profile and compensate for varying load conditions and perturbing forces to maintain tool position.

Types of motor controller[ edit ] Motor controllers can be manually, remotely or automatically operated.

The influence of previous experience on predictive motor control.

They may include only the means for starting and stopping the motor or they may include other functions. A motor controller is connected to a power source such as a battery pack or power supply, and control circuitry in the form of analog or digital input signals.

See also: Motor soft starter A small motor can be started by simply plugging it into an electrical receptacle or by using a switch or circuit breaker. A larger motor requires a specialized switching unit called a motor starter or motor contactor. When energized, a direct on line DOL starter immediately connects the motor terminals directly to the power supply.

In smaller sizes a motor starter is a manually operated switch; larger motors, or those requiring remote or automatic control, use magnetic contactors. Very large motors running on medium voltage power supplies thousands of volts may use power circuit breakers as switching elements.

A direct on line DOL or across the line starter applies the full line voltage to the motor terminals, the starters or cubicle locations, can usually be found on an ELO drawing.

This is the simplest type of motor starter.

A DOL motor starter also contains protection devices, and in some cases, condition monitoring. Smaller sizes of direct on-line starters are manually operated; larger sizes use an electromechanical contactor relay to switch the motor circuit.

Solid-state direct on line starters also exist. A direct on line starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit. The maximum size of a motor allowed on a direct on line starter may be limited by the supply utility for this reason.

In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor , the motor will draw a high starting current until it has run up to full speed.

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This starting current is typically times greater than the full load current. To reduce the inrush current, larger motors will have reduced-voltage starters or variable speed drives in order to minimise voltage dips to the power supply.

A reversing starter can connect the motor for rotation in either direction. Such a starter contains two DOL circuits—one for clockwise operation and the other for counter-clockwise operation, with mechanical and electrical interlocks to prevent simultaneous closure. Single phase AC motors and direct-current motors require additional devices for reversing rotation.

Reduced voltage starters[ edit ] Reduced-voltage, star-delta or soft starters connect the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps.

By using an autotransformer or a series inductance , a lower voltage is present at the motor terminals, reducing starting torque and inrush current. Once the motor has come up to some fraction of its full-load speed, the starter switches to full voltage at the motor terminals.

Since the autotransformer or series reactor only carries the heavy motor starting current for a few seconds, the devices can be much smaller compared to continuously rated equipment.Motor Control Circuits Motor control circuits are an effective way to reduce cost by using smaller wire and reduced-amperage devices to control a motor.

At a minimum this would include a thermal overload relay.

This is accomplished by reducing the voltage to the AC terminals and at the same time lowering current and kvar. Loss of voltage protection[ edit ] Starters using magnetic contactors usually derive the power supply for the contactor coil from the same source as the motor supply.

Main article: Adjustable-speed drive An adjustable-speed drive ASD or variable-speed drive VSD is an interconnected combination of equipment that provides a means of driving and adjusting the operating speed of a mechanical load.