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Motor Controller Contents Motor Controller Contents 1 Motor controller 1 1.1 Applications .............................................. 1 1.2 Types of motor CONTROLLER ................................... 1 1.2.1 Motor starters ......................................... 1 1.2.2 Reduced voltage starters ................................... 2 1.2.3 Adjustable-speed drives .................................... 2 1.2.4 Intelligent controllers ..................................... 2 1.3 Overload relays ............................................ 2 1.4 Loss of voltage protection ....................................... 3 1.5 Servo controllers ............................................ 3 1.6 Stepper motor controllers ....................................... 3 1.7 World record ............................................. 3 1.8 References ............................................... 3 1.9 See also ................................................ 4 2 Contactor 5 2.1 Construction .............................................. 5 2.2 Operating principle .......................................... 6 2.3 Arc suppression ............................................ 6 2.4 Ratings ................................................ 7 2.4.1 IEC utilization categories ................................... 7 2.4.2 NEMA ............................................ 7 2.5 Applications .............................................. 7 2.5.1 Lighting control ........................................ 7 2.5.2 Magnetic starter ........................................ 7 2.5.3 Vacuum contactor ....................................... 8 2.6 References ............................................... 8 3 Circuit breaker 9 3.1 Origins ................................................. 9 3.2 Operation ............................................... 10 3.3 Arc interruption ............................................ 11 3.4 Short-circuit current .......................................... 11 i ii CONTENTS 3.5 Standard current ratings ........................................ 11 3.6 Types of circuit breakers ....................................... 12 3.6.1 Low-voltage circuit breakers ................................. 12 3.6.2 Magnetic circuit breakers ................................... 13 3.6.3 Thermal magnetic circuit breakers .............................. 13 3.6.4 Common trip breakers .................................... 13 3.6.5 Medium-voltage circuit breakers ............................... 14 3.6.6 High-voltage circuit breakers ................................. 14 3.6.7 Sulfur hexafluoride (SF6) high-voltage circuit breakers .................... 15 3.6.8 Disconnecting circuit breaker (DCB) ............................. 15 3.6.9 Carbon dioxide (CO2) high-voltage circuit breakers ..................... 16 3.7 Other breakers ............................................. 16 3.8 See also ................................................ 16 3.9 References ............................................... 17 3.10 External links ............................................. 17 4 Motor soft starter 18 4.1 Applications .............................................. 18 4.2 See also ................................................ 19 4.3 References ............................................... 19 5 Autotransformer 20 5.1 Operation ............................................... 20 5.2 Limitations .............................................. 21 5.3 Applications .............................................. 21 5.3.1 Power transmission and distribution ............................. 21 5.3.2 Audio system ......................................... 22 5.3.3 Railways ............................................ 22 5.4 Variable autotransformers ....................................... 22 5.4.1 Variac Trademark ....................................... 22 5.5 See also ................................................ 22 5.6 Notes ................................................. 23 5.7 References ............................................... 23 5.8 Text and image sources, contributors, and licenses .......................... 24 5.8.1 Text .............................................. 24 5.8.2 Images ............................................ 25 5.8.3 Content license ........................................ 25 Chapter 1 Motor controller A motor controller is a device or group of devices 1.2 Types of motor CON- that serves to govern in some predetermined manner the TROLLER performance of an electric motor.[1] A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse ro- Motor controllers can be manually, remotely or automat- tation, selecting and regulating the speed, regulating or ically operated. They may include only the means for limiting the torque, and protecting against overloads and starting and stopping the motor or they may include other faults.[2] functions.[2][3][4] 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. 1.1 Applications 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. 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 1.2.1 Motor starters performing. The simplest case is a switch to connect a motor to a See also: Motor soft starter power source, such as in small appliances or power tools. The switch may be manually operated or may be a relay A small motor can be started by simply plugging it into or contactor connected to some form of sensor to auto- an electrical receptacle or by using a switch or circuit matically start and stop the motor. The switch may have breaker. A larger motor requires a specialized switching several positions to select different connections of the unit called a motor starter or motor contactor. When en- motor. This may allow reduced-voltage starting of the ergized, a direct on line (DOL) starter immediately con- motor, reversing control or selection of multiple speeds. nects the motor terminals directly to the power supply. Overload and over current protection may be omitted in Reduced-voltage, star-delta or soft starters connect the very small motor controllers, which rely on the supplying motor to the power supply through a voltage reduction circuit to have over current protection. Small motors may device and increases the applied voltage gradually or in have built-in overload devices to automatically open the steps.[2][3][4] In smaller sizes a motor starter is a manually circuit on overload. Larger motors have a protective over- operated switch; larger motors, or those requiring remote load relay or temperature sensing relay included in the or automatic control, use magnetic contactors. Very large controller and fuses or circuit breakers for over current motors running on medium voltage power supplies (thou- protection. An automatic motor controller may also in- sands of volts) may use power circuit breakers as switch- clude limit switches or other devices to protect the driven ing elements. machinery. A direct on line (DOL) or across the line starter applies the More complex motor controllers may be used to accu- full line voltage to the motor terminals, the starters or cu- rately control the speed and torque of the connected mo- bicle locations, can usually be found on an ELO drawing. tor (or motors) and may be part of closed loop control This is the simplest type of motor starter. A DOL mo- systems for precise positioning of a driven machine. For tor starter also contains protection devices, and in some example, a numerically controlled lathe will accurately cases, condition monitoring. Smaller sizes of direct on- position the cutting tool according to a preprogrammed line starters are manually operated; larger sizes use an profile and compensate for varying load conditions and electromechanical contactor (relay) to switch the motor perturbing forces to maintain tool position. circuit. Solid-state direct on line starters also exist. 1 2 CHAPTER 1. MOTOR CONTROLLER A direct on line starter can be used if the high inrush cur- and VSDs can also implement soft motor starting. [6] rent of the motor does not cause excessive voltage drop in the supply circuit. The maximum size of a motor al- lowed on a direct on line starter may be limited by the 1.2.4 Intelligent controllers supply utility for this reason. For example, a utility may require rural customers to use reduced-voltage starters for An Intelligent Motor Controller (IMC) uses a [5] motors larger than 10 kW. microprocessor to control power electronic devices DOL starting is sometimes used to start small water used for motor control. IMCs monitor the load on a pumps, compressors, fans and conveyor belts. In the case motor and accordingly match motor torque to motor of an asynchronous motor, such as the 3-phase squirrel- load. This is accomplished by reducing the voltage to the cage motor, the motor will draw a high starting current AC terminals and at the same time lowering current and until it has run up to full speed. This starting current kvar. This can provide a measure of energy efficiency is typically 6-7 times greater than the full load current. improvement for motors that run under light load for a To reduce the inrush current, larger motors will have large part of the time, resulting in less
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