Electric Motor Control Final Exam Questions and Answers 2023

motor connections factors - Answer- horsepower, service factor,marked temperature rise, voltage, full load current rating and nema code letter Synchronous motor advantage - Answer- they can provide power factor correction for themselves Squirrel cage induction motors are used - Answer- to power most of the machines throughout industry motor starters can be divided into two classes - Answer- IEC and NEMA NEMA starters range - Answer- 00-8 NEMA size 00 - Answer- is rated to control a 2-horsepower motor connected to a 460 volt, three phase power supply NEMA size 8 - Answer- Will control a 900 horsepower motor connected to a 460 volt, three phase power supply semiautomatic controls - Answer- characterized by the use of push buttons, limit switches, pressure switches and other sensing devices to control manual controls - Answer- simple devices that are hooked onto the line of a motor Automatic controls - Answer- similar to semiautomatic controls but operator does not have to initiate control across the line starting - Answer- accomplished by connecting the motors directly to the power line ramping - Answer- requires a motor to start at a low speed and accelerates to full speed over time Simplest method of stopping - Answer- disconnect power line Normally open push button - Answer- Normally closed push button - Answer- When components are shown connected by a dashed line in a schematic diagram - Answer- it indicates that the components are mechanically connected together Normally open liquid flow switch - Answer- float switch - Answer- temperature switch - Answer- disconnect switch - Answer- circuit breaker - Answer- on delay timer - Answer- Current transformer - Answer- air core transformer - Answer- Dual voltage transformer - Answer- Auto transformer - Answer- First step of trouble shooting - Answer- determine whether the motor is overloaded Shorted windings in the motor - Answer- can cause the motor to draw excessive current Current flow in a 3 phase motor should - Answer- all be the same manual starters that are installed in a switch box - Answer- more susceptible to ambient temperature problems Motors have a current draw of - Answer- 300-800% more than the full load current Locked rotor current - Answer- Motor current starting Overload relays are generally set to trip at - Answer- 115% Solder melting overload relay - Answer- activates from the melting of solder Bimetal strip - Answer- constructed by bonding to different types of metal together dashpot overload relays - Answer- basically a container, a piston and a shaft if the motor is overloaded - Answer- the magnetic field will be strong enough to continue drawing current from the shaft bridge type relay - Answer- operates by drawing a piece of metal or plunger inside a coil eddy currents - Answer- small electric currents that are induced on or near the surface of the material Power source - Answer- the most important considerations for a motor machines the employ gears - Answer- generally require a motor that can start at reduced speed Squirrel cage motors are controlled by - Answer- variable frequencies The type of controller can vary - Answer- depending on the requirements of the motor MOV is connected - Answer- across a coil intended to operate on 120 volts Double acting pushbuttons - Answer- contain both normally open and normally closed contacts Schematics are always drawn to show - Answer- components in their de-energized state limit switch normally open held closed - Answer- limit switch normally closed help open - Answer- Jogging and inching - Answer- are methods employed to m