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148 Cards in this Set
- Front
- Back
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electrical motor converts |
electrical power into mechanical power |
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an induction motor get energy from the |
mutual induction |
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torque is also called |
moment of force |
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what is the load called in a motor |
counter torque |
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if a conveyor runs at a constant speed the torque and counter torque are |
balanced |
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if the load increases what will happen ie more weight |
the counter torque increases the motor will slow the current will increase increases the torque to match the counter torque but at the lower speed |
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if counter torque goes down |
the opposite happens ie torque reduced and increased speed |
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what devices measure torque? |
a prony brake and dynamometer the dynamometer is an electric generator |
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what does the belt do on a prony brake |
increase or decrease counter torque |
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equation for torque |
T=F•r |
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F means? |
force |
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T means what and what unit of measurement? |
torque and Newton meters Nm |
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r means? and the unit of measurement |
radius meters m |
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how to get power equation |
P=(Txn)÷9.55 |
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why 9.55 |
it's a constant like pie |
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what is n |
rotational speed or frequency in RPM |
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horse power or hp is calculated by |
hp= (Txn)÷7121 |
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7121 is? |
9.55 • 746 W/hp |
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1hp is how many watts |
746w=1hp |
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40nm motor at half load would be |
20nm |
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efficiency is calculated by |
output energy over input energy |
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how to calculate efficiency |
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electrical losses in a motor are |
iron losses and copper losses |
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iron losses happen in the |
rotor |
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mechanical losses happen from |
friction and windage |
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windage is |
air movement from the rotor |
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why multiply efficiency by 100 |
to make it a percentage |
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counter torque is measured by what 2 mechanical qualities |
force and radius |
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3 main parts of a induction motor |
frame stator rotor |
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the frame is also called a |
stator frame or enclosure |
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the frame is made up of |
forged steel frame end brackets or end bells the bearings the juction box |
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the frame helps prevent dmg like |
abrasion from grit |
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nema |
national electrical manufacturers association |
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nema defines more than ----- types of enclosure |
20 |
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open frame motors are rare most motors have a special process to make them ----- |
drip proof |
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DP and ODP |
drip proof and open drip proof |
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TE |
totally enclosed |
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3 types of TE |
fan cooled non vented pipe vented |
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pipe vented TE would be for? |
to replace explosion proof motors |
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the stationary portion of a motor is |
a stator |
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a stator includes |
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a stator is a |
iron core cut with slots to fit wire windings |
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the laminations look like this |
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what's the 2 ways to stator winding |
lap winding concentric winding |
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what is the diff |
lap has identical pitch concentric varys pitch concentric has coils for each phase for each pole and the coils become progressively bigger |
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delta is usually for wye is usually for |
delta for large motors wye for small |
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the speed and magnitude of a 3 phase induction motor is constant is constant the speed is called? |
synchronous speed |
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2 kinds of rotors are |
squirrel cage and wound rotors |
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rotors include |
laminated iron conductors shaft |
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squirrel cage rotors consist of aluminum or copper _______? |
rotor conductors or rotor bars |
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the iron core is laminated and varnished before bars are in place memorize this pic |
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current will not be induced if |
rotor speed n and synchronous speed n^syn are the same |
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the diff in speed between rotor and stator is called |
slip speed n^s |
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graph of squirrel cage induction |
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the two end rings let the rotor bars |
have paths to share current |
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rotor bars are skewed so that? |
torque is uniform magnetic locking is prevented motor runs smooth and quiet |
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review this paragraph |
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WRM |
wound rotor motor |
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WRM stator currents are |
150% for full load currents |
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wrm is good for |
conveyors large grinders crushers fans pumps elevator Bridge cranes and most industrial applications |
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memorize components of the wound rotor motor |
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describe the operation of a 3 phase induction motor |
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in a 2 pole motor one cycle produces one mech rotation of the stator magnetic field except for |
0° and 180° points in the cycle when current is zero |
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each pair of windings has how many poles |
2 opposite in variety |
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just as electrical phases are shifted 120° so are |
windings in a stator |
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a 4 pole motor has |
12 windings or 6 pairs and 4 magnetic rotating poles |
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a four pole rotates faster or slower than a 2 pole? |
it rotates at half the speed |
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magnetomotive force is proportional with |
current or magnitude of flux |
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ingress protection |
IP protection rating |
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magnetic Flux is zero when |
current is zero |
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current and magnetic Flux will work together in what ways |
magnitude and polarity when current is negative the polarity flips |
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open frame motors are usually found in |
appliances |
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open drip proof looks like? |
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totally enclosed motors are eather |
fan cooled or non ventilated |
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silica steel reduces |
hysteresis |
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motors frames are usually made from |
cast iron |
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retentivity is how |
much the metal retains magnetic fields |
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dielectric strength is somthings |
resistance |
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the varnish between laminations is |
baked on so the stator windings stay still won't move |
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review pg 21 figure 14 |
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what helps create low vibration/noise and high efficiency |
the combined magnetomotive force produces a single Flux that is constant in magnitude and rotates at a consistent speed |
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to find directions of electron flow and magnetic lines of force use the |
left hand conductor rule |
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left handed generator rule |
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review pg 22 23 24 figures |
they cover left hand rules |
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sence Flux does not cross they just? |
distort around the conductor Flux becomes stronger behind the conductor and weak ahead |
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Lorentz force is |
the direction of rotation from force by the magnetic field on the conductor |
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a short circuit will be made for the |
rotor |
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secondary current is determined by |
slip speed |
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slip speed is the difference between |
synchronous speed and rotor speed |
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slip speed Increases when |
voltage and current induced increases |
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the powerfactor of the secondary rotor is reflected by the |
primary current |
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the information on a motor nameplate is for |
selection of overcurrent device type and size starter type and size overload device or setting wiring means and conductor type and for troubleshooting |
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what is this? |
wound rotor |
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wound rotors need maintenance because |
the winding comes undone when centrifugal force pulls it out |
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important notes on kW and HP on a motor label |
they will commonly round the conversion the rating indicates the mechanical power output |
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2 categories of frames are |
fractional horsepower frame integral horsepower frame |
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what are standard fractional frames and will the frame tell you the motor type? |
42 48 56 and no not necessarily |
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the frame code will let you know |
most info on mounting and dimensions when searched in a catalog |
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3 types of mounting strategies are |
base plates face mounted flange mounted |
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amps on a nameplate are |
under full load conditions |
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rotation of magnetic fields |
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line of Flux cannot |
cross |
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when you start a motor you'll be at |
maximum slip |
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when a rotor is speed to a constant that slip speed is called |
synchronous speed |
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more load means |
more slip and more slip means more current more load more current |
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generated force is for left or right |
left hand rule |
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mechanical force is for left or right |
right hand rule |
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when a current carrying conductor in placed in a magnetic field |
magnetic force pushes because of polarity |
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is there a difference between North American system voltage and the nema motor voltage? |
yeah |
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can you put a 230v motor on 208v circuit |
no you could burn it out |
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nema standards allow variations what are they |
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if there is less voltage on the motor what happens to the current P=EI active |
it increases because it need to supply the electric power for mechanical power |
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north American frequency is |
60hz |
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what is a VFD |
a variable frequency drive |
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motor slips speeds are usually |
2% to 8% of synchronous speed |
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open shafted means |
not mechanically connected |
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a low percent speed regulation is |
desirable |
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low speed motors require differ than high speed in which ways |
larger because more iron is needed for the torque lower pf and because of that higher currents and lower efficiencies |
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how can you reduce the speed to the driven load |
using a gearbox or belt drive |
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describe insulation classes |
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more insulation can cause |
heat and less wearing and tearing |
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standard ambient temperature what and can be different under what situations |
40 °C is standard and can change with certain insulation classes written on the nameplate |
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if continuous duty is not labeled the motor is |
continuous |
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and continuous motor has certain traits |
if can run without a cool down period the size of conductors and their insulation |
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formulas for inrush VA and max. Unruh current |
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squirrel cage induction motors are a.b.c.d designs their characteristics are |
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it is poor practice to |
specify motors of excessively large horse power size and less the two thirds of full load efficiency and power factor fall off dramatically pg 34 |
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the service factor can provide power beyond the nameplate HP rating under what conditions |
rated V and hz are applied to the motor line voltages are balanced the ambient temperature is less than or equal to 40°C |
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motor with a maxed service factor for too long can cause |
reduced speed overheating decreased efficiency decreased power factor shorten the lifespan |
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CEC 28-306 |
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a non stated service factor is |
1.00 |
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nema says the front end of a motor is the |
side without a shaft |
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motor rotation from the front of a motor is spinning |
counter clockwise |
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IEC terminology for front and back |
drive end and non drive end |
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do exercise questions on obj 5 |
2 4 6 8 9 10 13 14 15 20 |
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memorize I guess? |
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a stators conductors are always |
insulated |
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how to get rpm or n |
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wound rotor motor has a |
2%-5% slip |
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lowest and highest temp ratings |
A is lowest H is highest |
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no time rating means |
continuous load |
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inrush VA and max inrush VA formulas |
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highest nema starting currents code is |
V |
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A is the highest or lowest nema starting code |
A is the lowest starting current |
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motors with a service factor of 1.15 or greater shall have an overload of |
less than or equal to 125% |
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overload settings of less than or equal to 115% of full load current are for service factors of |
or greater 1.15 |
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the current on a nameplate represents |
full load stator current |
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poles x phases gives |
nunber of windings |
