ttl tekim - class 07
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Class 7
Introduction to Electric Motors
Firmansyah Nur Budiman
Lab. Transmisi & Distribusi
Jurusan Teknik Elektro & Teknologi Informasi FT UGM
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Introduction
Electric motors are everywhere:
90% are induction motors
Electric
Motors
At home:
-Air conditioner
-Hair dryer
-Blender
In the shop:
-Tool
-Fan
In the office:
-Printer
-Cooling fan for
electronic devices
In the factory
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Terminology
Armature & field
Types:
(i) single-phase motor (ii) three-phase motor
Armature circuit Field circuit
(1) Carries current Produce magnetic flux
(2) Has few turns of larger wire
carrying relatively large currents
Has many turns of wire carrying
relatively small currents
(3) For induction motor: on the
rotor
For induction motor: on the
stator
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Motor Characterization in Steady-State
Operation
1 motor 3 motor
Input electrical
power
Output
mechanical
power
Efficiency
PFIVP LNin PFIVP LLin 3
55.9
nTTPout
inout PP /
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Motor Characterization in Steady-State
Operation
Example:
Consider a 50-Hz, single-phase induction motor
with the following nameplate information:
1 hp, 1725 rpm, 220 V, 14.4 A, efficiency = 68%
Find the output torque, the power factor, and
the cost of operating the motor per day ifelectric power costs 1000 IDR/kWh!
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The Motor with a Load
Typical motor and load characteristics:
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The Motor with a Load
Motor-load interaction:
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INDUCTION MOTOR
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Induction Motor Principle
(1) The field windings are on the stator
(2) The current in the field windings set up a
rotating magnetic flux, which in turn induces
voltage in the rotor
(3) The voltage in the rotor drives currents that
interact with the flux to produce torque
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THREE-PHASE INDUCTIONMOTOR
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Nameplate Information
Information contained on nameplate of 3f
induction motor:
50 horsepower
Three phases
1765 rpm
NEMA 326T frame
208-230/460 V
140-122/61 ATime rating: continuous
Insulation class: F
1.15 service factor
Maximum ambient temperature: 400C
NEMA code: G
NEMA design: B
NEMA nominal efficiency: 92.4%
NEMA minimum efficiency: 91.0%
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Not given: Torque
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Nameplate Information
Power rating:
Power rating of this motor is 50 hp.
It doesnt mean that the motor will put out 50 hp
on all occasions.Maximum power = service factor x nominal
rating.
If the motor is supplied with 460 V and if load
demands exactly 50 hp, then the motor speedwill be 1765 rpm and the input current will be 61A.
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Nameplate Information
NEMA frame 326T
NEMA: National Electrical Manufacturers
Association.
326T frame the motor output shaft diameter:
2 inches and is centered 8 inches above the
base of all motors.
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Nameplate Information
Voltage & current rating:
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Nameplate Information
Thermal specification:
Time rating is continuous operation.
Insulation class F maximum temperature ofinsulation should not exceed 1550C.
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Nameplate Information
NEMA code G:
NEMA code tells the starting-current
requirements.
Code G means 5.60 to 6.29 kVA/hp
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Nameplate Information
NEMA design B:
Design A: high run efficiency, high breakover torque,moderate starting torque and high starting current.
Design B: moderate run efficiency, moderate breakovertorque, moderate starting torque and low startingcurrent.
Design C: similar to design B but has higher startingtorque and is more expensive.
Design D: relatively low run efficiency, extremely highstarting torque which is also breakover torque, and lowstarting current.
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Nameplate Information
Motor output torque:
Nameplate torque is not given but may be
deduced from output power and speed:
Nm
PT
m
outNP 202
60/21765
74650
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Nameplate Information
Torque vs speed:
17651800
1800202)(
)(
nTT
slopeT
NPNL
mNLNPm
NLmm
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Nameplate Information
Example (pump load):
The 50-hp motor with the torque given by
drives a pump with a torque requirement of
Find the speed at which the motor-pump operatesand the power required by the pump!
Nmn
TL
2
18001002.1
17651800
1800202)(
nTT
NPNL
mNLNPm
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Nameplate Information
Example (long extension cord):
A saws-all electric saw is rated at 120 V, 8 A
single-phase. The saw is used with 100 ft of 16/3
extension cord. How much do the motor losses
increase as a result of the extension cord?
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SINGLE-PHASE INDUCTIONMOTOR
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Nameplate Information
Example of nameplate:
Phase 1
Frame L56
Hz 60
Volts 115
400C
SF 1.35
Type CS
HP 1/3
RPM 1725
Amps 5.8
Insulation class A
Types:
CS capacitor-start/induction-run motor has high starting torque and moderate
run efficiency
SP split-phase motor has low starting torque and moderate run efficiency
CR capacitor-start/capacitor-run motor has high starting torque and high run
efficiency, and is more expensive