Motor Control 1 Flashcards
____ such as wind and moving water, have been used to mill grain.
Natural Energy Sources.
The source of energy that is used to drive a machine is called the ____.
Prime Mover.
Who invented the first practical AC motor?
Nikola Tesla
A ____ is a device that governs the performance of an electric motor in a predefined manner.
Motor Controller.
Define “Motor Controller”
Governs electric motors in a predefined manner.
What percentage of all electricity used in the U.S. is used to drive electric motors? (according to a ‘98 DE survey)
63%
What two organizations are the standard-setting for MC devices?
NEMA and IEC
What does ‘NEMA’ stand for?
National Electrical Manufacturer’s Association
What does ‘IEC’ stand for?
International Electrotechnical Commission
Marking and Rating are two things usually found in a ___ standard.
NEMA
T/F: NEMA only produces publications for installation professionals.
False
Which standard organization helped the development of the SI standard?
IEC
Devices built according to the ____ standard have four times longer life expectancy.
NEMA
NEMA AC motors are designed for what frequency?
60Hz
Which standard organization’s devices are application specific?
IEC
Which standard organization’s motors are rated in HP?
NEMA
T/F: It is possible for devices to meet the standards of both NEMA and the IEC.
True.
Who operates manually-activated devices?
A human operator.
Double-Break contacts have a ____ current rating of a single break of the same size.
Double.
A contact that changes state when actuated, but returns as soon as actuation is removed is called a ____.
Momentary Operator.
The two parts of a push-button are the ____ and ____.
Operator and Contact Block.
What type of push-button is used when quick actuation by the operator is needed?
Mushroom-Type push-button.
What is the most common type of selector switch?
A two-position selector switch with maintained contacts.
What type of contact is a simple toggle lightswitch?
A maintained contact.
A typical Hand-Off-Auto control operation usually has a ____ position switch and ____ contacts.
3, 2
A ____ is a three-position switch that can be used manually to change the direction of rotation of a three-phase motor.
Drum Switch.
Which of theses four types of lamps is NOT used in visual signaling devices?
I. Fluorescent
II. Incandescent
III. LED (light emitting diode)
IV. Xenon (strobe tube)
I. Fluorescent
What is a ‘cluster’ pilot light?
A single lamp-head with up to four separate lights for signaling.
What two types of visual indication are associated with ‘HAZARD’ or ‘Proceed with Caution’?
Flashing and Rotating Beacons.
Multiple indicators and signaling devices assembled in a column are called a ____.
‘Tower Indicator’ or a ‘Stack Light’
A general purpose horn audible signaling device has a maximum sound output of ____ Db.
108 Db.
Switch failures are grouped into two categories: ____ problems and ____ problems.
Operator and Contact.
____ operated devices are opened and closed by physical contact between a moving part and the actuator of the device.
Mechanically.
How does a limit switch work?
Physical contact with the moving part being sensed activates mechanical contacts within the device.
What is the most important things to consider when installing a limit switch? (Assuming the switch is chosen correctly.)
The rigidity and physical location of the device. It must be accessible for maintenance and replacement.
A correctly installed limit switch should do what two things?
- ) Permit allowed-travel
2. ) Prevent over-travel
A sub-class of switches that are identical, but smaller are called ____.
Micro-switches.
____ are typically used in equipment doors and panel covers to detect if doors are open or shut.
Miniature Switches.
The force applied to the actuator required to operate the switch contacts is called the ____.
Operating Force (OF)
Automatically operated input devices are switches triggered by a change in a ____ parameter.
Process Parameter
What are some examples of process Parameters?
Liquid Level, Pressure, Fluid Flow, Temperature
What type of switch might be used around equipment like boilers, cooling lines, air compressors, and fluid pumps?
Flow Switches
What type of switch is sometimes called a ‘float switch’ and is used to control the level in a tank or bin.
A Level Switch.
____ switches are actuated when additional gas or liquid is added to the system.
Positive Pressure
What type of switch is actuated when a gas or liquid is removed from the system?
Negative Pressure or ‘Vacuum’ Switch.
What type of pressure switch measures two places and actuates based on discrepancies between the two locations?
A Differential Pressure Switch.
____ is the signal range where no action occurs.
Dead Band or Neutral Zone
What two types of devices utilize Neutral Zone the most?
Temperature and Pressure.
Why is a Dead Band or Neutral Zone important?
If your pressure/temperature is right at the operating limit and is hovering there, you might have erratic operation and rapid signals. With Dead Band, there must be a significant change to actuate the device.
Bimetallic strip, capillary tube, and direct immersion probes are examples of mechanical ____ sensing devices.
Temperature.
What material is most commonly used to coat the surface of contacts?
Silver + Cadmium.
What is the maximum number of contacts on a magnetic contact per NEMA?
8 Sets.
What is the most common example of a definite purpose contactor?
A lighting contactor.
What AC coil voltages are typical for IEC contactors?
24-600v
What is the greatest disadvantage of a thermal overload relay?
High ambient temperatures causing issues or weakening the sensing element.
Where in the NEC can NEMA ratings be found?
Chapter 1
What configuration does “OR” logic utilize?
Two NO (Normally Open) Contacts
Motor Control Drawings show all components in what state?
De-energized or ‘shelf state’
Motor motion is described in what terms?
Clockwise/Counter-clockwise.
What causes positive pressure switches to actuate?
When a gas or liquid is added to the system it monitors.
What is an Electromechanical device?
A device that makes/breaks electrical connections because of physical movements/contact.
How are control transformers rated?
In VA (Volt-Amperes)
Who invented the steam engine?
Thomas Savery, in 1698
When was NEMA formed, and where is its headquarters?
September 1, 1926. Washington D.C.
When was the IEC formed, and where is its headquarters?
- Geneva, Switzerland.
What is the most commonly used contactor in motor control?
The Push-button.
What are the four push-button styles?
- ) Flush
- ) Guarded
- ) Extended
- ) Mushroom
____ convert electrical energy into linear mechanical motion.
Solenoids
A ____ is simply an electromagnetically controlled switch.
Relay.
A device that switches a high power circuit using a low powered control circuit is called a(n) ____ relay.
Interposing.
How many contacts can machine tool relays have?
8-12
What are configurable/changeable contacts correctly called?
Convertible Contacts.
A ____ is a device that keeps AC solenoids and relays from ‘chattering’.
Shading coil
What control voltages do CT’s typically step down to?
24v or 120v
What is inrush current?
A overcurrent condition when power is first applied to a magnetic/electric device.
NEMA specifies that AC motor starters must function at voltages as low as ____ of coil voltage.
85%
Where can requirements be found for when CT’s must be fuse protected?
In the NEC
Per the NEC, AC circuits of what voltage and higher must be grounded?
50V
Under what two conditions should voltage measurements be taken when troubleshooting XFMR’s?
At full load and with no load.
What are the three basic parts of a solenoid?
- ) Body
- ) Actuator
- ) Coil
If clips are lost and you are wiring a CT yourself, what should you do?
Use the wire and methods recommended in the manufacturer’s instructions.
What are the three things to consider when sizing a CT?
- ) Inrush Current
- ) Steady-State Current
- ) Power Factor
____ devices initiate a change in the state of contacts.
Pilot Devices.
Define ‘Across-the-Line’ starting.
Starting without any sort of reduced voltage; at full line voltage.
Generally, ____ are used for smaller motors and smaller loads.
Contactors.
Safety Contactors are installed for the safety of ____.
The personnel working with MC systems.
Arc chutes are intended to do what three things?
To confine, divide, and quench arcs.
Definite purpose contactors ____ latch.
CAN.
A motor starter is what two things combined?
A contactor and overload protection.
When it comes to motor control;
____ protects the motor, and ____ protect the control equipment.
Overload and Fuses
What are the three types of motor overloads?
- ) Thermal
- ) Electronic
- ) Magnetic
Contacts that ‘latch’, or mechanically secure in place are called ____ contacts.
Seal-in
____ relays have great flexibility to choose ranges and settings, but are costly.
Electronic
What does DOE stand for?
Delay on Energize
What does DODE stand for?
Delay on De-energize
