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50 Cards in this Set
- Front
- Back
Calculate the counter torque produced by a prony-brake producing a force of 3 N on a scale that is 2 m from the centre of the prony-brake drum |
3 |
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Speed regulation of a SCIM is most related to the percentage of: |
Rotational frequency change from no load to full load speeds |
|
Rotational frequency is measured in revolutions per minute |
True |
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Calculate the percent efficiency of a 10hp motor that has total losses of 1017 watts at full load |
88% |
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The stators rotating magnetic field of a squirrel cage induction motor rotates: |
At a continuous and uniform speed |
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The formula to determine the mechanical power of a rotating machine is: |
P= n*T 9.55 |
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A difference between a WRIM and a SCIM is: |
A WRIM has insulated rotor conductors and a SCIM has uninsulated rotor conductors |
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What type of motor enclosure allows outside air to cool the rotor directly |
DP |
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The following information is taken from the nameplate of a motor Volts: 208 - 230/460 V FLC: 2.4 - 2.2/1.1 A What is expected FLC at nominal voltage of 208v |
2.4 A |
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When not used with a variable frequency drive, squirrel cage induction motors: |
Are to be constant speed motors |
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Information that can be derived from an induction motors nameplate but that is not explicitly stated on the nameplate is the: |
Number of poles |
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The rotor of a SCIM will turn if all rotor conductors are open circuit |
False |
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When using Fleming’s left hand rule for generators: |
Forefinger = flux, Thumb = motion, Centre finger = current |
|
Service factor indicates the degree to which a motor can be loaded above the stamped horsepower or kilowatt power output under specific conditions |
True |
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Rotor conductors in a squirrel cage induction motors are left uninsulated because: |
Rotor voltages are small and the resistance of the varnished laminations are high |
|
Two advantages of a wound rotor motor compared to the SCIM are (higher/lower) starting torque and (Higher/lower) starting current |
Higher Lower |
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Calculate the output of an induction motor producing a torque 55.73 Nm at a speed of 1,150 r/min. The output power in horsepower is Hp. |
9 |
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A 4 pole, 50 Hz, SCIM has a no load speed of 1498r/min and a full load speed of 1452r/min what is the percent speed regulation? |
3.168% |
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T is ________ Measured in ________ |
Torque Newton meters (Nm) |
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F is __________ Measured in _______ |
Force Newtons (N) |
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R is _________ Measured in _________ |
Radius Meters (m) |
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P is _______ Measured in ________ |
Mechanical power Watts (w) |
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n is _______ Measured in _________ |
Rotational speed r/min |
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1 hp = _______w |
746 |
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1 hp =_________Kw |
.75 |
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Pf is (Inversely/proportion) to slip |
Inversely Pf goes up as slip goes down |
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Prony brake and dynamometer measure: |
A motors torque |
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Losses in a induction motor are ______ and ________ |
Electrical and mechanical |
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Electrical losses are: |
Iron losses and copper losses |
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Mechanical losses are: |
Friction and windage |
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Induction motor is made of 3 main parts |
The frame The stator The rotor |
|
Frame consists of |
End brackets, bearings in the end brackets and the jb |
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Stator produces a |
Rotating magnetic field |
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The stator core provides |
A high permeability path for magnetism |
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Pitch is: |
Span from one side of a coil to the other |
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The stator windings of a 3 phase induction motor are connected to a 3 phase source to produce a rotating magnetic field. This rotating magnetic field has a_____________________ |
Constant magnitude and rotated at a constant speed called synchronous speed |
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For a current to be induced there must be a difference between: |
Rotor speed and synchronous speed of a stators magnetic field. This difference is called slip speed |
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End rings provide current to flow from |
1 rotor bar to another |
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Insulation class is the temperature tolerance of the motor windings They have a designation of: |
H- withstand highest temperature, A- rarely used on modern motors B and F- are common |
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Duty is: |
Amount of time that a motor can run without a cooling period The duty affects the size of conductors and insulation of conductors |
|
Rotor designs are |
Design A- normal starting torque, high starting current, handle brief periods of overload Design B- most common, normal starting torque, low starting current Design C- high starting torque, low starting current, starting heavy loads, Design D- high starting torque, low starting current, high inertia starts, poor speed regulation |
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Slip speed is typically _____ to _____% of synchronous speed |
2-8% |
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Magnetomotive force is: |
Movement of electric charges that creates magnetic flux |
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Induction motor uses transformer action to: |
Transfer energy from stator to rotor |
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Induction motor as transformer the secondary current is controlled by the_________ |
Slip speed |
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Nameplate includes the: |
Manufacturer, catalog #, specifications, serial # of motor |
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Nameplate helps select: |
The overcurrent device type and size, The starter type and size, The overload device or setting, Wiring means and conductor type and troubleshoot the motor |
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Frame two categories: |
Fractional horsepower and integral horsepower |
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The current displayed on the nameplate is what the motor can draw under___________ conditions |
Full load |
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Regarding variations, the NEMA standard states: |
Voltage variations may not exceed 10% Frequency variations may not exceed 5% The combined variation may not exceed 10% |