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Terms in this set (35)What is a relay? Electrically operated switch, designed for normally open switches or normally closes switches. What are common voltages for relay coils? 1. 24 V There is no electrical connection between the coil and the contacts. True What are contacts rated for? 1. Voltage How much amperage are relays generally designed for? Less than 20 amps What's another name for light duty relays? Pilot duty relays Light duty relays switch motors on and off. False, they do NOT switch motors on and off. Heavy duty relays turn motors on and off. What do light duty relays do? Switch large contactors or staters that in turn start and stop motors. What are heavy duty relays? Do not switch motor contactors and starters on and off but instead are used to directly start motors. What do heavy duty relay need to withstand? Inrush of current as the motor starts. What are heavy duty relay contacts often made up of? Silver cadmium oxide to reduce pitting from the arcs created by the high inrush starting current. What does a large motor require to be able to start? Motor starter or motor contactor What does a direct online starter do? Immediately connects the motor terminals directly to the power supply. What is a reduced voltage starter? Connect the motor to the power supply by increasing the voltage gradually or in steps. May use two or more contactors. What is generally relay contracts rated? 15 amps or less What are the 3 contact ratings? 1.
FLA What are the surface in relays and contactors coated with? Special alloy of very conductive material. Prevents contacts from becoming quickly damaged. With what are motor starters often used with? 3 phase motors. What are 3 types of protective devices that are used to protect the motor against excessive heat? 1. Temperature actuated How do line duty overloads protect the device? Break the power How do pilot duty overloads protect? They're like relays, they sense current overload or temp. And opens contactor circuit. What is a line duty device? Senses current and/or temperature in the motor winding. Will disconnect power by directly opening the motors winding. Overload relays are used in conjunction with contactors. True All
overload relays may be field adjusted for manual or auto reset function. False, only some relays What is a magnetic overload relay? Current sensitive type of pilot duty overload. What's an advantage of an magnetic overload relay? That is only slightly affected by ambient temperatures, thereby avoiding nuisance trips. What is a heater element current overload? A device for pilot duty uses a numeral element that responds to heat generated by a heater element. What is a thermal overload relay? Current sensitive with automatic reset and is connected in series with motor winding. What is an external bimetal overload? Current passing through the heater will cause the bimetal to warp. what is a variable frequency drive? System for controlling the frequency of the electrical power supplied to it. What is a drive controller? Solid state power conversions devices. Where are IPMs used? Output sections for many VFDs and include gate circuitry, thermal sensors, self protection devices and network of insulated gate bipolar transistors. What is an IGBT? Electronically actuated semiconductor material with 3 terminals that work as a switch
IGBT can handle high voltage and switch so quickly that their speed is measured in the nanosecond range. True What is harmonic current distortion? Low frequency noise generated through wires. Sets found in the same folderUnit 3622 terms ldgragg AIRC 1040, Test 2, Unit 35 and 3750 terms Patrick_Michaels HVACR ELECTRICAL-CMS, 11 of 14, Motor/Compressorss132 terms dddpopePLUS Unit One40 terms collette_mia Other sets by this creatorUnit 4534 terms HugoAlex4 Unit 4445 terms HugoAlex4 Unit 4345 terms HugoAlex4 Unit 4326 terms HugoAlex4 Verified questions
ENGINEERING When the variation of spectral radiation quantity with wavelength is known, how is the corresponding total quantity determined? Verified answer
ENGINEERING A baseball is thrown horizontally from the pitcher’s mound with a speed of 90 mph. Neglect air resistance, and determine how far the ball will drop by the time it crosses home plate 60 ft away. Verified answer
ENGINEERING In a parallel-flow, water-to-water heat exchanger, the hot water enters at $75^\circ C$ at a rate of 1.2 kg/s and cold water enters at $20^\circ C$ at a rate of 0 9 kg/s. The overall heat transfer coefficicnt and the surface area for this heat exchanger are $750 W/m^2 \cdot K$ and $6.4 m^2,$ respectively. The specific heat for both the hot and cold fluid may be taken to be $4.18 kJ/kg \cdot K.$ For the same overall heat transfer coefficient and the surface area, the increase in the effectiveness of this heat exchanger if counter-flow arrangement is used is (a) 0.09 (b) 0.11 (c) 0.14 (d) 0.17 (e) 0.19 Verified answer
ENGINEERING Estimate the remaining life in revolutions of an 02-30 mm angular-contact ball bearing already subjected to 200 000 revolutions with a radial load of 18 kN, if it is now to be subjected to a change in load to 30 kN. Verified answer Recommended textbook solutionsFundamentals of Engineering Economic Analysis1st EditionDavid Besanko, Mark Shanley, Scott Schaefer 215 solutions
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What are the two basic elements of a motor starter?Contactor Construction and Operation. A magnetic motor starter has two basic parts: the magnetic contactor and an overload relay .
How does a magnetic overload work?The Magnetic Overload relay has a movable magnetic core inside a coil which carries the motor current. The flux set up inside the coil pulls the core upwards. When the core rises far enough (determined by the current and the position of the core), it trips a set of contacts on the top of the relay.
What is a motor overload protector?Overload relays protect the motor, motor branch circuit, and motor branch circuit components from excessive heat from the overload condition. Overload relays are part of the motor starter (assembly of contactor plus overload relay). They protect the motor by monitoring the current flowing in the circuit.
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The motor starter is switched on and off by the quizlet
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