Components of starter motor and their functions pdf
Please forward this error screen to 104. A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. 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 components of starter motor and their functions pdf 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. Motor controllers can be manually, remotely or automatically operated. They may include only the means for starting and stopping the motor or they may include other functions. An electric motor controller can be classified by the type of motor it is to drive such as permanent magnet, servo, series, separately excited, and alternating current. 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. 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. This is the simplest type of motor starter. A DOL motor starter also contains protection devices, and in some cases, condition monitoring. 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.
For example, a utility may require rural customers to use reduced-voltage starters for motors larger than 10 kW. DOL starting is sometimes used to start small water pumps, compressors, fans and conveyor belts. 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. For three phase motors, this is achieved by swapping the wires connecting any two phases. Two or more contactors may be used to provide reduced voltage starting of a motor. 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. 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. 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.
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 second type of thermal overload relay uses a eutectic alloy, like a solder, to retain a spring-loaded contact. When too much current passes through the heating element for too long a time, the alloy melts and the spring releases the contact, opening the control circuit and shutting down the motor.
Electronic digital overload relays containing a microprocessor may also be used, especially for high-value motors. These devices model the heating of the motor windings by monitoring the motor current. They can also include metering and communication functions. Starters using magnetic contactors usually derive the power supply for the contactor coil from the same source as the motor supply. An auxiliary contact from the contactor is used to maintain the contactor coil energized after the start command for the motor has been released.
If a momentary loss of supply voltage occurs, the contactor will open and not close again until a new start command is given. Servo controllers are a wide category of motor control. Servo controllers use position feedback to close the control loop. This is commonly implemented with encoders, resolvers, and Hall effect sensors to directly measure the rotor’s position. These are therefore often called “sensorless” control methods.
Another control method is pulse and direction. A stepper, or stepping, motor is a synchronous, brushless, high pole count, polyphase motor. Control is usually, but not exclusively, done open loop, i. Because of this, precise positioning with steppers is simpler and cheaper than closed loop controls. Modern stepper controllers drive the motor with much higher voltages than the motor nameplate rated voltage, and limit current through chopping. The usual setup is to have a positioning controller, known as an indexer, sending step and direction pulses to a separate higher voltage drive circuit which is responsible for commutation and current limiting. 1 Batterymarch Park, Quincy, MA 02169: NFPA.
Article 430 Motors, Motor Circuits and Controllers”. Archived from the original on January 12, 2013. Links to manufacturers, associations, and other resources. This page was last edited on 6 February 2018, at 12:43.
For other types of motorized vehicles, see Motor vehicle. Most definitions of car say they run primarily on roads, seat one to eight people, have four tires, and mainly transport people rather than goods. Cars have controls for driving, parking, passenger comfort and safety, and controlling a variety of lights. Over the decades, additional features and controls have been added to vehicles, making them progressively more complex. There are costs and benefits to car use. The benefits include on-demand transportation, mobility, independence, and convenience. The first working steam-powered vehicle was designed — and quite possibly built — by Ferdinand Verbiest, a Flemish member of a Jesuit mission in China around 1672.