basics of 3-phase induction motor (part 3)

7/28/2019 Basics of 3-Phase Induction Motor (Part 3)

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Toshiba three-phase induction motor nameplate

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phase-induction-motor-3

Basics of 3-phase Induction Motor (part 3)

Continued fro second part Basics of 3-phase Induction Motor (part 2)

Technical data to be specified by purchaser before purchasing a 3 phase induction

motor:

Site Conditions

No. Technical data to be specified Data

1. General data about ambient temperature and altitude:

2. Area Classification:

3. Temperature Class:

4. Gas Group:


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5. Type of Protection:

Basic Data


1. Supply System: 415V 3 Ph 50

Hz

2. Neutral:

3. Cooling method (Any one of the below):

TENV Totally Enclosed, Non-Ventilated/ TEFC Totally Enclosed, Fan

Cooled/TETC Totally Enclosed, Tube Cooled/ TEAAC Totally enclosed, Air

to Air cooled /CACA Totally Enclosed, Air circuit machine with air

cooler/CACW Totally Enclosed, Air circuit machine, water cooled air cooler.

4. Degree of Enclosure Protection:

5. Continuous Rating:

6. Service Factor:

7. Synchronous Speed:

8. Insulation Class:

9. Max. Permitted Temp Rise: Class 77

Deg Celsius

10. Direction of Rotation (Any one of the below):CW/CCW/Bi-Dir.

11. Method of Starting:

12. Winding Connection:


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13. Neutral Terminals req.:

14. Shaft Orientation (Any one of the below):

Horizontal/Vertical

15. Mounting: Foot/Flange

16. Slide Rails Required:

17. Heater Required:

18. Heater Voltage: (Motors rated

below 37 kWshall employ

24V AC direct

winding)

19. Drain Required:

20. Breather Required:

21. Maximum Noise Level: 85dB (A) at

1m

22. GD2 (Pump + Coupling) =

23. Winding temperature monitoring:

1. RTDs Required:

2. Thermocouples Req.:

3. No. per Winding:

24. Bearing temp monitoring:

1. RTDs Required:

2. Thermocouples Req.:

3. No. per bearing:


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Differential CT's

25. Differential CTs:

If yes then:

1.

Required CT Ratio:

2. Accuracy Class:

3. CT Arrangement:

26. Cable Type:

1. Motor:

2. Heater:

3. Winding RTD:

4. Bearing Sensor:

5. CT:

27. Heater Terminal Box Entry:

28. RTD/Thermocouple Terminal Box Entry:

29. CT Terminal Box Entry:

30. Motor Starter Protective System (Any one of the

below):Fuses+Contactor+OLR/ Circuit Breaker with

overload, earth fault, undercurrent, Phase Unbalance,

under voltage, Stall, Limit No. of Starts, over current

31. Prospective System Fault Current: 50 kA (RMS

SYM.)

32. Surge Protection Required:


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Motor view

Technical data to be specified by manufacturer beforeselling a 3 phase induction motor


1. Standard:

2. Full Load Current (FLC):

3. Starting Current:

4. Efficiency (100/75/50%):

5. Power Factor (100/75/50%):

6. Power Factor (Starting):

7. Full Load Torque (FLT):

8. Starting Torque: % FLT

9. Minimum Accelerating Torque (Motor & Load) @

80%Volts:

% FLT


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10. Pull-Out Torque: % FLT at

%SLIP

11. Locked Rotor Withstand Time:

100% Volts: Hot: sec Cold: sec


12. Run-Up Time (Motor & Load):



13. Insulation Class & Temp Rise above Design Ambient:

14. Maximum No. of Successive Starts:

15. Max. No. of Starts in 1 Hour:

16. Rotor Resistance (ac) @ 20C pu Motor VA(Locked Rotor / Rated Load)

17. Rotor Reactance @ 20C pu Motor VA(Locked Rotor / Rated Load)

18. StatorResistance (ac) @ 20C pu Motor VA(Locked Rotor / Rated Load)

19. Stator Reactance @ 20C pu Motor VA(Locked Rotor / Rated Load)

20. Stator Leakage Reactance @ 20C pu Motor VA(Locked Rotor / Rated Load)

21. Magnetizing Resistance @ 20C pu Motor VA

22. Magnetizing Reactance @ 20C pu Motor VA


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23. Torque / Speed Characteristic

24. Current / Speed Characteristic

25. Heating Time Constant:

26. Cooling Time Constant:

27. Bearing Type: Ball/Roller/Sleeve/Antifriction

28. Lubrication: Oil/Grease

29. Oil/Grease

30. Cooling System:

31. Rotor End float: +mm -mm

32. Rotor End-Play: +mm -mm

33. Rotor Air Gap: mm

34. Moment of Inertia GD (Motor & Load):

kgm Referred to motor (including gearbox where

applicable)

35. Weight of Motor: kg

Noise Level: dB @ m

What precautions are to be taken while designing offoundation of rotating machines (Here 3 Phase inductionmotor)?

General

1. Description of driving and driven machinery,


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2. Operating speed or speed ranges,

3. Number and arrangement of cylinders,

4. Distance between axis of main shaft of the machine and the top face of foundation,

5. Maximum rated output,

6. Gear box ratio where applicable, and

7. Maximum operating temperature in the bases of the machine.

For Static Design

1. A detailed loading diagram comprising plan, elevation and section showing details

of communication and point of all loads on foundation.

2. A detailed drawing showing the position and size of mounting feet and details ofholding down bolts.

For Dynamic Design

1. Details of out of balance forces and couples shall be given, together with

associated frequencies for all possible modes ofvibration for driving and driven

machinery. These include the following:

a) External forces,b) External primary couples,

c) External secondary couples, and

d) Harmonic torques.

2. Mass moments of inertia of driving and driven machine about three principal axes

shall be indicated.

3. Additional information relating to specific machines, as given below, shall be

provided where necessary:

a) Loads due to dynamic short circuit conditions, andb) Loads due to an abnormal sudden stoppage.

4. Where it is found necessary to use anti-vibration mountings, the type and positions

be indicated.

Data on Ground and Site Conditions

The following soil data shall be known:

1. Soil profile and soil characteristics up to a depth at least three times the expectedmean plan dimension of the foundation which can be taken as the square root of

the expected area, or hard strata.

2. Soil investigation to the extent necessary in accordance with IS: 1892-1979 and for


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the determination of dynamic properties of soil in accordance with IS: 5249-1977.

3. The relative position of the water table below ground at different times of the year.

Frequency ratio

Wherever possible the natural frequency of the foundation soil-system shall be higher

than the highest disturbing frequency and the frequency ratios shall not be normally lessthan 0.4.Where this is not possible, the natural frequency of the foundation-soil system

shall be kept lower than the lowest disturbing frequency. The frequency ratios in such

cases shall not be lower than 1.50.

While the above criteria shall be applied to all possible modes of vibration, it may be

permitted to operate machines closer to the resonance in certain modes of vibration

provided the resulting amplitudes do not exceed the permissible limit.

Even though machine may be balanced, minor disturbing forces can occur due to

manufacturing tolerances and other causes, for sensitive installations, the frequenciesarising from these may have to be considered.

Permisible Amplitudes

Limitations of Vibration Amplitude to Avoid Damage to Machinery

This shall be specified by the manufacturer and shall in no cases be exceeded. Where

no specific limit has been stated by the manufacturer, it may be taken that foundation

satisfying the following amplitude criteria shall provide a satisfactory base for machinery.

Limitations of Vibration Amplitude to Avoid Damage to Machinery

the damage in neighboring buildings due to resonance will be negligible if the amplitude

vibration of the foundation is less than 200 microns at frequencies below 20 Hz, where

the disturbing frequency exceed 20 Hz, a lower amplitude may be necessary for certain

installations.

Limitation of Vibration Amplitude to Avoid Discomfort of Persons

for low speed machines, it is unlikely that foundations which satisfy the previous point will

produce vibrations of sufficient amplitude to be disturbing to persons. In special cases

where there are particular reasons to avoid discomfort to personnel

Limitations of Amplitude to Avoid Settlement

for most soil types, foundations for low speed machines designed to limiting amplitude of

200 microns will not suffer undue settlement due to dynamic loads. In case of some soils

like loose sands and silts in conjunction with high water table, there is a possibility of

significant settlement to occur. In all such cases, it shall be preferable to consolidate the

soil underneath the foundation.

Anti-Vibration MountingsWhere it is found to be impracticable to design a foundation consisting of a simple

concrete block resting on the natural soils to give satisfactory dynamic characteristics, it

may be possible to reduce the transmitted vibrations to acceptable levels by means of


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anti-vibration mounting. Depending upon the nature of the machinery and the installation,

the anti-vibration mounting may be used:

a) Between machinery and foundation, and

b) Between a foundation block and a supporting system.

Free vibration analysis

Free vibration analysis shall be carried out to calculate the natural frequencies and mode

shapes of the foundation. The highest natural frequency calculated should be at least 10

percent higher than the operating frequency of the machine. Damping may be neglected

for the purpose of free vibration analysis.

Frequency criteria

The following frequency criteria shall be checked:

The fundamental natural frequency shall be at least 20perccnt away from the machine

operating speed.

That is, fn < 0.8 fm orfn > 1.2 fm

Where

fn = fundamental natural frequency of the foundation, and

fm = operating speed of the machine.

However, it is preferable to maintain a frequency separation of 50 percent.

Conclusion

The foundation of any rotating electrical machine operating at 50 Hz should be such thatthe natural frequency of vibration is either less than 40 Hz or greater than 60 Hz.

References:

1. NEMA MG-1.

2. Industrial Power Engineering and Application Hand Book by K C Agarwaal.

3. Industrial Power System Hand Book by Shoaib Khan.

4. Theory and Calculation of Alternating Current Phenomena by Charles Proteus

Steinmetz

5. Motor protection relay (MM30) manual from L&T

basics of 3-phase induction motor (part 3)

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