TTL Tekim - Class 07

8/10/2019 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%

Go forward

Not given: Torque


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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.

Go back


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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.

Go back


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Voltage & current rating:

Go back


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Thermal specification:

Time rating is continuous operation.

Insulation class F maximum temperature ofinsulation should not exceed 1550C.

Go back


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NEMA code G:

NEMA code tells the starting-current

requirements.

Code G means 5.60 to 6.29 kVA/hp

Go back


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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.

Go back


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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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Torque vs speed:

17651800

1800202)(

)(

nTT

slopeT

NPNL

mNLNPm

NLmm


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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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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?

Go back


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SINGLE-PHASE INDUCTIONMOTOR


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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

Documents

TTL Tekim - Class 07