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209 Cards in this Set
- Front
- Back
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List four losses that occur in an induction motor |
Iron losses Core losses Friction loss Winding loss |
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Two machines designed to measure the torque of a motor |
Prony brake Dynameter |
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What are the three main parts of a production motor |
Frame Stator Rotor |
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Which rotor design has poor speed regulation but high starting torque |
Design D |
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The rotor bars are skewed to prevent |
Cogging |
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Which type of windings have varying pitch |
Concentric |
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Slip speed can be defined as the difference between____ and ____ |
Synchronous speed and rotor speed |
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Where in the motor is the rotating magnetic field established? |
Stator |
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What term is used to describe the movement of electric charges that create magnetic flux |
magneto-motive force |
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The rotational frequency on the name play always indicates the |
Full load rotor speed |
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The current rating found on the name plate of a motor represents the |
Full load stator current |
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Which type of insulation class would be used in a high ambient temperature |
H |
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What value is the NEMA starting code used to determine |
Inrush current |
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When does breakdown torque (max torque) occur |
Xr=Rr |
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A 100% slip is also known as a |
Blocked motor |
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A rotor with 0% slip is spinning at |
Sync speed |
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Six rotor perameters that are affected by motor speed. What happens to them when speed increases. |
Frequency (decease) Voltage (decease) Current (decease) Active current (decease) Power factor (increase) Impedence (decease) |
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As load is added to a rotor the torque will_____ until______torque is reached. After this any increase in load will cause the rotor to stall. |
Increase Breakdown |
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At what percent of synchronist speed does a NEMA design a or b rotor produce breakdown torque? |
75%-80% |
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Which NEMA rotor design has the highest full low speed |
A |
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What NEMA rotor design produces a breakdown torque of 225% |
C |
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When a wound rotor motor is accelerated, the resistance of the motor is ( Increased/ decreased. |
Decreased |
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What are two disadvantages of a wound rotor motor |
Extra maintenance Higher cost |
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List two reasons why the resistor circuit Is of a wound rotor motor in seldom used for speed control |
More resistance lower speed Efficiency decreases at lower speed |
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The slip rings of a WRM are used to connect the stater to the source of voltage. True/false |
False |
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When an induction motor rotate it creates a |
Rotational motion called torque. |
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An electrical motor is a device that converts______ into mechanical power |
Electrical power |
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Efficiency is the ratio of |
Output energy over input energy Pout ÷ Pin energy Pout ÷ Pin |
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EBr × s= |
Er |
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nr = |
Rotor speed |
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ns = |
Slip speed |
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nsyn = |
Synchronous speed |
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Find ns ÷ nsyn = |
S |
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F x r = |
T |
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In a balanced three phase delta system, the voltage between two lines is the same as |
Phase voltage |
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The voltage between any 2 lines of a Delta connection load should be. |
Equal to the voltage measured across the phase. |
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In a Delta system, the phase voltage equals. |
V Line |
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If the load and a delta connection are unbalanced |
The phase current must be added phasorally to obtain the line current value. |
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The phaser sum of the 3 line currents in any 3 phase Delta system is: |
Zero is all balanced and unbalanced circuit. |
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what is induction |
the interaction of a conductor and a magnetic fields which induces a voltage onto a conductor |
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lensz law states |
A induced voltage will cause a current to flow in a direction that its magnetic effect will oppose the change that produced it |
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Faradays laws of induction states |
Faradays laws of induction states that the magnitude of the voltage induced into the conductor is proportional to the rate that it is cutting lines of flux |
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At a constant speed torque and counter torque are? |
The same |
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Rotational motion in a motor is called |
Torque |
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What is the formula for HP |
HP = T• n \7121 Hp= horse power n= rotational speed in RPM T= torque in Nm |
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what is the power formula (motor) |
P= mechanical power in watts n= rotational speed in RPM T= Torque in Nm |
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The rotor will always spin ____ then the RMF (faster/slower) |
The rotor will always spin slower the the RMF |
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What are the 2 types of motor losses |
1. Electrical (iron losses)+(copper losses) 2.Mechanical (friction)+(windage) |
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What is another word for torque |
The moment of force |
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The stator spins at a constant speed called the ? |
Synchronous Speed |
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What is the formula for Torque |
T=F•r T= Torque in Nm F= force in newtons r= radius in meters |
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What is Lorentz force |
When a current carrying conductor is placed in a magnetic field it is subjected to a force (motion) |
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What is magnetic flux |
Lines of force around a magnet/conductor |
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1Hp= ?w |
746 Watts |
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What does RMF stand for? |
Rotating Magnetic Field |
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Skewed rotor bars are for (SCIM) |
To prevent " motor locking"(no spinning) |
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A drip proof frame is used for indoor or outdoor use? |
Indoor drip proof is also known as DP or ODP (open drip proof) |
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A TE frame is used for a indoor or outdoor use? |
outdoor use (TEFC)+(TENV)+TEPV) |
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What is the formula for synchronous speed |
n syn= 120•f\N 120=constant f= frequency 60Hz N= number of poles |
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Lap winding are consider? |
the same pitch, identical coil in size |
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concentric windings are consider? |
Are wound on top of each other and different in sizes |
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A 2 pole motor has _____ poles per phase |
2 |
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the rotor will always spin slower than the RMF and the difference in speed |
Slip speed |
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RMF always spin at a constant speed called |
Synch speed |
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Rotor current formula |
Ir =Er/Zr |
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Rotor impedance formula |
Zr= Rr+Xr |
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Rotor reactance formula |
Xr=XBr•slip |
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Rotor frequency formula is |
Fr= FBr•Slip |
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Is the resistance of the rotor constant?(true/false) |
True |
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Slip speed definition is |
The difference between rotor and sync speed Slip Speed= sync speed -Rotor speed |
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Slip is |
The ratio of the slip speed to sync speed slip=slipspeed/ syncspeed |
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The current listed on a motor nameplate is |
Full load current (in the stator) |
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The speed listed on the name plate is |
Full load speed |
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How do you you calculate motor over current |
S.F. |
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percent speed regulation is |
Percentage of no load speed to full load speed nREG= nNL-nFL/nFL x 100 |
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NEMA rotor design A |
Produce starting current 600% starting torque 150% Produce a breakdown torque 200% highest efficiency, but massive starting current |
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NEMA rotor design B |
Produce a starting current 500% starting torque 150% Produce a breakdown torque 200% high efficiency, slightly less massive starting current |
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NEMA design C |
Produce starting current 500% starting torque 225% |
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NEMA design D |
Produce starting current 400% Starting torque 275% |
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When does breakdown torque occur |
When reactance=resistance or when of is 0.707/45° |
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Active rotor current formula (in phase) |
I r(R)= Ir x cosΘ |
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Reactive rotor current formula (out of phase) |
I r(X)= Ir x sinΘ |
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Two devices to measure torque |
Prony brake Dynamometer |
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NEMA starting code |
Is used to estimate a motor starting current letter between A and V A is exceptionally low V is exceptionally high |
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Insulation class of motors |
A B F H H is the motor required to run hot |
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The rotor rotates in the ____ direction as the rotating magnetic field of the stator (same/opposite) |
Same |
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If duty is not indicated on the motor's nameplate |
it is a continuous duty motor |
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Duty cycle is |
The amount of the time a motor can run without a cooling period |
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NEMA states that motor voltage and frequency variation can not exceed |
10%± for the name plate voltage 5%± for the name plate frequency 10%± for the combined variation |
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closed-transition starting |
closed-transition starters maintain current to the motor though the auto transformer winding during the transition from reduced voltage to full voltage |
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What is the formula for OC with a Wye-Delta starter |
FLA x S.F. /√3 |
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A tap labelled FCBN would be used for when the voltage is ____ then the transformer rated primary voltage (higher/lower) |
Lower |
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What type of transformer core is considered to produce the least amount of leakage flux |
H-type |
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What does a 2½% RCBN labelled tap mean? |
2½% RCBN lower then rated voltage and reduced kva capacity at tap |
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what is the main propose behind constructing a transformer core from individual laminated sheets? |
To reduce eddy currents |
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What is voltage regulation formula |
VNL-VFL/VFL x 100 |
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What does FBCN stand for |
Full capacity Below Normal |
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3 types of transformer cores are |
Core type(most leakage flux) shell type H type (least leakage flux) |
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The max voltage and current for meter sockets |
200A and/or 600V |
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conducted VA rating formula |
S conducted= Vcommon x Iseries |
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transformed VA rating formula |
S transformed= Vcommon x Icommon |
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Al load is added to a rotor, the torque produced will(increase/decrease) untill(breakdown/full load) torque is reached. After this any increase in load will cause the motor to stall |
Increase Breakdown |
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what are the 4 insulation classes for a motor |
A- rarely used on motors B-common F-common H-high temp (A<-- lowest-highest -->H) |
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what are the tap% that the auto-transformer will offer? |
50% 65% 80% |
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Design B Rotor produces what kind of stats |
Starting FLA Current 500% Starting FL torque 150% breakdown 200% bad high inertia/ hard to start loads |
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Design D rotor produces what kind of stats |
Starting FLC 400% starting FL torque 275% Breakdown 275% Good high inertia/ frequent start/ hard to start |
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Part-winding start terminals? and Wye-Delta start terminals? |
Part winding T1,T2,T3 T7,T8,T9 Wye-Delta T1,T2,T3,T4,T5,T6 |
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Design C Rotor produces what kind of stats |
Staring FLA current 500% starting FL torque 225% breakdown (maximum) torque @ instant start suitable for most loads, not high inertia |
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Design D Rotor produces what kind of stats |
Staring FLA current 400% starting FL torque 275% breakdown (maximum) torque @ instant start suitable for most loads, very high inertia |
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Rotors bars closer to the surface cause? |
Low inductance |
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At what load range does efficiency and power factor fall off? |
2/3 |
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three type of totally enclosed motors? (frame types) |
TENV totally enclosed non vent TEPV totally enclosed pipe vent |
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NEMA rotor A &B produce breakdown at what synchronous speed? (nsyn) |
75-80% |
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Which 3ø induction motor has slip rings? and which one has end rings? |
WRM= sliprings SCIM= end rings |
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Slip speed varies between _____ and ____% |
2-8% |
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Pre-drilled hole placement info on the motor nameplate can be found under? |
The frame code |
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NEMA starting codes A or V mean? |
In rush current A-low staring current V-high starting current |
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What type of transformer lower high line voltage for residential use? |
Distribution transformer |
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What is current that flow under a no-load condition on the primary side (transformer operation) |
Exiting current |
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For current to be induced there must be a difference in ____ and ____. The difference is called? (Rotor operation) |
Rotor speed/synchronous speed And the difference is called slip speed |
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Two different types of stator winding are? |
Lap windings( identical in size and position) Concentric windings (the oppsite) |
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How many watts are in 1 HP? |
746W |
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What are the two types of stator components? |
Winding and the core |
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Another name for Torque |
Moment of force |
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Which phase would have the lowest voltage across is when the neutral opens? |
Lowest impedance |
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How would you find the required overload size with the service factor? |
Less the 1.15= FLA•1.15 1.15 or greater= FLA •1.25 |
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How do we prevent cogging/magnetic locking in a SCIM rotor? |
We have the bars at a slant(skewed) and to create a uniform speed |
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What are two types of induction motors? |
SCIM WRM |
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What is the term that describes the movement of electric change that create flux? |
Magneto-motive force |
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What happens when the part winding motor is started? |
The impedance is high and inrush current is reduce by 60-65%. Motor must have both windings energies within 2 seconds to prevent damage. |
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The most common single phase motor socket are? |
120v 2-wire 1ø (4jaw) 120/240 3-wire 1ø (4jaw) 120/208 3-wire 1ø/2ø network (5jaw) |
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What are the effects of flux with a load compared to a no-load? |
No-load=Exicting current(always) MAX CEMF Load=Exciting current(always) CEMF @ min |
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What is the formula for total copper losses at a different load? |
Square the different load ex. 50%=0.5²x Total copper loss |
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In a WRM when external rotor resistor are completely by passed what will happen |
Rotor resistance will increase starting torque and reduce starting current |
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What are the electrical losses of a 3Ø induction motor? |
Copper losses iron losses |
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What are the mechanical losses of a 3Ø induction motor |
Friction windage |
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What type of motor configuration is need for a part-winding |
Wye connection |
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A magnetic field that rotates at a constant speed and magnitude is called? |
Synchronous speed |
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The current and speed on a nameplate is always? |
FULL LOAD!!! |
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efficiency formula? |
Eff= (Power out÷power in) x 100 |
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The current rating on a name plate represents the ? |
The full load current in the stator |
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what are 4 losses with in a induction motor? |
iron(core) losses copper losses friction losses windage losses |
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What is the speed regulation formula? |
(nNL-nFL)÷nFL x 100 |
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What is reluctance? |
The opposition of a magnetic field |
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Self contained meters don't require instrument transformers and are use on? |
Services with a Max of 200A and 600V |
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What determines transformer impedance? |
The physical construction -the amount/type of core -winding wire size -Number of winding turns -The degree of magnetic coupling |
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If the tickler is removed from a 120/208v system what would the potential on the coil be? |
The highest voltage is divided by 2 ex. 208÷2=104v |
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Metering equipment that has instrument transformer has what amount of Amps and Volts? |
200A or greater 600V or greater |
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Burden for CTs are rated in ___and also rated in _____ |
OhmsΩ Volt-amp VA |
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PTs and CTs have what type of polarity? |
sub-tractive polarity |
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What are 3 auto transformer adv compared to mutual induction |
-better volt regulation -smaller and cheaper -increased Kva using the same core as mutual induction |
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The current transformer used for service rated over _____A are these 3 types |
200A -wound primary -Bar type -Toroidal(doughnut or window) |
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What determines max secondary short-circuit current? |
-Apprent power -voltage -percent impedance voltage |
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What is the formula for finding taps??? |
(Volts have÷ volts needed) x 100= tap% |
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On the truth tables the X and O stand for? |
X for closed O for open |
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What kind of test finds the copper losses? |
short circuit test |
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What is the formula for copper losses |
1) VA÷V=I 2)I²R=W (W= losses) 3) total copper losses= primary losses+ secondary losses |
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What happens to a mutual induction that is connected as a auto-transformer? |
The Kva Capacity will increase |
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Voltage ratio is 1:5 Vprimary÷Vsecondary what would it be if it was current? |
5:1 current ratio |
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What are the 3 names for the truth table? |
Truth table Target table Sequence table |
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PT are what type of transformer configuration? |
Step down transformer |
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Maximum Secondary short-circuit current formula is? |
1)Full-load secondary current(Kva÷V)=I 2)Full-load secondary current÷%IZ 3)Convert %IZ to a decimal 0.00000 |
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What measures core-loss of a transformer |
Open circuit test- using a watt meter connected to the primary side |
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What kind of tap Reduces the Kva capacity |
RCBN- reduce capacity |
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what are 3 disadvantages to auto-transformer compared to a mutual induction |
-They don't isolate secondary current from the primary . -If the common becomes open it will apply source to the load -Lower IZ= Higher short circuit currents |
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Inductance is the property of a circuit that? |
Oppose the change in current |
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What test determines %Impedance? |
Short circuit test |
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Is the core of the transformer made up of a soild core (True/False) |
False the core is cut up into sheets then laminated between each sheets |
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Why are transformer not 100% efficient? |
-Copper losses in the winding -eddy/hysteresis losses in the core |
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Volt meters(PTs) and Amp meters(CTs) have what type of contacts? |
-Volt meters are break before make contacts -Amp meters are make before break contacts |
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The instant more load is added to a transformer the self induced voltage will? |
Decrease |
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CTs is what type of transformer configuration? |
Step up transformer |
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When a secondary current flux oppose the exciting current flux the difference is known as? |
The resultant flux |
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What happens to current when there is more load added to the transformer? |
More load= more current on both the primary and the secondary transformer |
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Time delay is also know as? |
Dual element ( can withstand 500%) |
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Left hand generator rule Thumb= Pointer= Middle= |
Thumb=motion of conductor Pointer=magnetic polarity Middle=induced Active Current |
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Right hand motor rule Thumb= Pointer= Middle= |
Thumb=Developed force Pointer=magnetic polarity(North to south) Middle=Active Rotor Current |
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Standard maximum ambient temperature for motors is ____⁰c |
40⁰c |
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In North America a motor running at 90% of synchronized speed has a frequency of? |
6 Hz |
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What do they mean by a blocked rotor? |
When an induction motor accelerates from standstill |
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For a balanced, three-phase load the total power can always be found by multiplying the phase value by three(true or false) |
True |
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For an unbalanced, Wye or Delta system the power of each phase must be added together to find the three-phase power. (true or false) |
True |
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A three phase purely resistive delta connected load will show the line current in phase with the line voltage.(true or false) |
False=There is a phase displacement of 30 between I phase and I line |
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A three phase purely resistive delta connected load will show the phase current in phase with the phase voltage.(true or false) |
True |
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A crest factor higher than 1.8 indicates no waveform distortion.(PQA)(true or false) |
False -A Crest factor of 1.41 will indicate no waveform distortion |
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The number of leads on a three-phase PQA can vary from 6 to 9.(True or False) |
True |
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A three phase power quality analyzer in a three phase circuit reads |
phase voltages line voltages line currents |
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A three phase balanced delta load with a power factor of 0.766 lag will show the line current lagging phase current by |
30 degrees |
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A three phase purely resistive wye connected load will show the line current in phase with the line voltage.(true or False) |
False |
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What is the inductive load? |
a type of electrical load that stores energy in a magnetic field. (L) |
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What is active load and reactive load? |
The active power is the real power(S)(VA) consumes by the load. Where as, the reactive power(Q)(VARs) is the useless power. |
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PTs are a step up or step down transformation |
Step down |
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What kind of socket connection for a 120/240 1p 3wire |
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What kind of socket connection for a 120/208 2p 3wire network |
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What kind of socket connection for a 120v 1p 2wire |
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What kind of socket connection for a 120/208v 3p 4wire |
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What kind of socket connection for a 120/240 3p 4wire |
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What kind of socket connection for a 240v 3p 3wire |
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Name the 3 basic CT types. |
Wound, primary bar type, toroisal(doughnut |
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A motor with low percent speed regulation is more efficient then one with high percent speed (true/false) |
True |
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As a Squirrel cage motor accelerates from a standstill to normal running speed, active rotor current will |
Increase and then decreases |
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What rotor performs best in terms of producing hight starting torque, low starting current and full-load efficiency is |
Wound rotor |
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Speed regulation is most related to the % of |
Rotational frequency change from no-load to full load speed |
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The property of an electric current that opposes a change in current is called |
Inductance |
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The symbol used to represent the unit of measurement of voltage is. |
V |
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Which of the following is directly affected by a changing supply frequently |
Stator reactance |
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In a VFD application, torque boost would be used for? |
used to prevent a constant torque load from stalling |
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In a VFD what section achieves the modulation of timed dc voltage pulses? |
Inverter section |
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In order to determine the core loss of a transformer is necessary to perform what circuit test |
Open circuit test |
