Editing Motor controller (section)

== Types of motor controller ==
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.<ref name="Siskind">{{Cite book|title=Electrical Control Systems in Industry|last=Siskind|first=Charles S.|publisher=McGraw-Hill, Inc.|year=1963|isbn=0-07-057746-3|location=New York|url-access=registration|url=https://archive.org/details/electricalcontro0000unse}}</ref><ref name=NEC430>{{Cite book | author=National Fire Protection Association | title= NFPA 70 National Electrical Code | access-date=2008-01-15 | year=2008 | publisher=NFPA | location=1 Batterymarch Park, Quincy, Massachusetts 02169 | pages=298 | chapter= Article 430 Motors, Motor Circuits and Controllers | chapter-url=http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70&cookie%5Ftest=1}}</ref><ref name=Campbell>{{Cite book | first=Sylvester J. | last=Campbell | year=1987 | title=Solid-State AC Motor Controls | publisher=Marcel Dekker, Inc. | location=New York | isbn=0-8247-7728-X}}</ref>

An electric motor controller can be classified by the type of motor it is to drive, such as permanent [[magnet]], [[servomechanism|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.

=== Motor starters ===
{{See also| Motor soft starter}}
A small motor can be started by simply connecting it to power. 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. This is the simplest type of motor starter. A DOL motor starter often contains protection devices (see below), and in some cases, condition monitoring. Smaller sizes of direct on-line starters are manually operated; larger sizes use an electromechanical contactor 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. For example, a utility may require rural customers to use reduced-voltage starters for motors larger than 10&nbsp;kW.<ref name=Summers87>[[Terrell Croft]] and Wilford Summers (ed), ''American Electricans' Handbook, Eleventh Edition'', McGraw Hill, New York (1987) {{ISBN|0-07-013932-6}} pages 78-150 through 7-159</ref>

DOL starting is sometimes used to start small [[Pump|water pumps]], [[compressor]]s, [[Fan (machine)|fans]] and [[conveyor belt]]s. In the case of an asynchronous motor, such as the [[AC motor#Squirrel Cage rotors|3-phase squirrel-cage motor]], the motor will draw a high starting current until it has run up to full speed. This starting current is typically 6-7 times greater than the full load current. To reduce the inrush current, larger motors will have reduced-voltage starters or [[adjustable-speed drive]]s 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&nbsp;— one for clockwise operation and the other for counter-clockwise operation, with mechanical and electrical interlocks to prevent simultaneous closure.<ref name=Summers87 /> For three phase motors, this is achieved by swapping the wires connecting any two phases. Single phase AC motors and direct-current motors often can be reversed by swapping two wires but this is not always the case.

Motor starters other than 'DOL' connect the motor through a resistance to reduce the voltage the motor coils get on start up. The resistance for this needs to be sized to the motor - and a quick source for a good resistance to use is another coil in the motor - i.e. series/parallel. In series gives a gentler start then switched to parallel for full power running. When this is done with three phase motors, it is commonly called a star-delta (US: Y-delta) starter. Old star-delta starters were manually operated and often incorporated an ammeter so the person operating the starter could see when the motor was up to speed by the fact the current it was drawing had stopped decreasing. More modern starters have built-in timers to switch from star to delta and are set by the electrical installer of the machine. The machin's operator simply presses a green button once and the rest of the start procedure is automated.

A typical starter includes protection against overload, both electrical and mechanical, and protection against 'random' starting - if, for instance, the power has been off and has just come back on. An acronym for this type of protection is TONVR - Thermal Overload, No Volt Release. It insists that the green button is pressed to start the motor. The green button switches on a solenoid which closes a contactor (i.e. switch) to primarily power the motor. It also powers the solenoid to keep the power turned on when the green button is released. In a power failure, the contactor opens turning itself and the motor off. The only way the motor can then be started is by pressing the green button. The contactor can be quickly tripped by the starter passing a very high current due to an electrical fault downstream of it in either the wiring to the motor or within the motor. The thermal overload protection consists of a heating element on each power wire which heats a bimetallic strip. The hotter the strip, the more it deflects to the point it pushes a trip bar which disconnects power to the contactor solenoid, turning everything off. Thermal overloads come in different range ratings and this should be chosen to match the motor. Within the range, they are adjustable enabling the installer to set it correctly for the given motor.

Which type for specific applications? DOL gives a quick start so is used more commonly with generally smaller motors. It is also used on machines with an uneven load such as piston type compressors where the full power of the motor is needed to get the piston past the compression stage - the actual working stage. Star-delta is generally used with larger motors or where either the motor is under no load at starting, very little load or a consistent load. It is particularly suited to motors driving machinery with heavy flywheels - to get the flywheels up to speed before the machine is engaged and driven by the flywheel.

=== Reduced voltage starters ===
Reduced-voltage or soft starters connect the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps.<ref name=Siskind /><ref name=NEC430 /><ref name=Campbell /> 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. 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 [[Korndörfer autotransformer starter|autotransformer starter]] was patented in 1908.

Larger 3 phase induction motors can have their power reduced within the motor ! The motor is started 'DOL' with full voltage supplied to the field coils of the motor outer part ('stator'). The inner part ('rotor') has a current induced into it to once again react with the magnetic field generated by the stator. By breaking the rotor into parts and electrically connecting these parts to external resistances via slip rings and brushes as well as control contactors, the magnetic power of the rotor can be varied - i.e. reduced, for starting or low power running. Although a much more complex process, it means the currents (electrical loads) being switched are significantly lower than if reducing the power to the main feed of the motor.

A third way to achieve a very smooth progressive start is to dip resistance rods into a conductive liquid (e.g. mercury) which has a layer of insulative oil on the top. As the rods are lowered the resistance is gradually reduced.

A star delta starter is another type of Reduced-voltage starter in induction motor. A star delta starter will start a motor with a star connected stator winding. When motor reaches about 80% of its full load speed, it will begin to run in a delta connected stator winding. Star Delta Starter are two types. (1) Manual Operated Star Delta Starter, (2) Automatic Star Delta.

The manual operated star delta starter mainly consists of a TPDP switch which stands for Triple Pole Double Throw switch. This switch changes stator winding from star to delta. During starting condition stator winding is connected in the form of a star. Now we shall see how a star delta starter reduces the starting current of a three-phase induction motor.<ref>{{Cite web|last=Electrical4U|title=Star Delta Starter: What is it? (Working Principle & Circuit Diagram) {{!}} Electrical4U|url=https://www.electrical4u.com/star-delta-starter/|access-date=2021-10-26|website=www.electrical4u.com/|language=en-US}}</ref>

The above function achieved by using a power contactor and timer in automatic star delta starter. The automatic star delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a direct on line starter as they are controlling winding currents only. The currents through the winding are 1/root 3 (58%) of the current in the line. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor. These are AC3 rated at 58% of the current rating of the motor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third (33%) of the motor rating.<ref>{{Cite web|last=Portal|first=EEP-Electrical Engineering|date=2012-04-10|title=Star-delta motor starter explained in details - EEP|url=https://electrical-engineering-portal.com/star-delta-motor-starter|access-date=2021-10-26|website=EEP - Electrical Engineering Portal|language=en}}</ref>

The transition from star to delta can be an open transition or a closed transition. During open transition, the motor starter momentarily disconnects from the motor and reconnects in a delta configuration. In closed transition, the transition from the star to delta configuration is achieved without disconnecting the motor. In order to achieve that, an additional three-pole contactor and three resistors are required.<ref>{{Cite web |date=2020-12-25 |title=Star-delta starter (Wye-Delta Starters) - Circuit, working |url=https://www.electricalclassroom.com/star-delta-starter/ |access-date=2022-06-12 |website=www.electricalclassroom.com |language=en-US}}</ref>

=== Adjustable-speed drives ===
{{Main| 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. In common usage, the term "drive" is often applied to just the controller.<ref name=NEC430 /><ref name=Campbell /> Most modern ASDs and VSDs can also implement soft motor starting.<ref>{{Cite web |url=http://machinedesign.com/engineering-essentials/soft-starters|title= Soft Starting |date= 16 July 2014 |publisher=machinedesign.com}}</ref>
{{Further|FAM control of induction motor}}

=== Intelligent controllers ===
An ''Intelligent Motor Controller'' (IMC) uses a [[microprocessor]] to control power electronic devices used for motor control. 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 [[volt-ampere reactive|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.