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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
2. 120 V
3. 230 V
There is no electrical connection between the coil and the contacts.
True or False
True
What are contacts rated for?
1. Voltage
2. Amperage
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.
True or False
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
2. LRA
3. Resistive
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
2. Current actuated
3. Combination of current and temperature
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 or False
True
All
overload relays may be field adjusted for manual or auto reset function.
True or False
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 or False
True
What is harmonic current distortion?
Low frequency noise generated through wires.
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