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Induction Motors-Design, Manufactured and Test based on API 541 Copyright Material IEEE Paper No. PCIC- AM 43

Rajendra Mistry Scott Kreitzer Senior Member, IEEE Member, IEEE Siemens Industry, Inc. Siemens Industry, Inc. 4620 Forest Ave. 4620 Forest Ave. Norwood, OH 45212 Norwood, OH 45212 USA USA rajendra.mistry@siemens.com scott.kreitzer@siemens.com Abstract – Generally there are two types of end users of induction motors, i) Basic design based on IEC, NEMA [2] or some other standards and ii) basic design with the addition of the API 541[1] requirement. The second category is mostly used in refinery, power plant, and oil and gas industries where long term reliability is sought. This paper will discuss the basic design, manufacturing and testing and the additional requirements of API 541. In addition, this paper will help answer the following questions: what are API requirements, what benefits do they provide, and is the extra effort necessary or not? Finally it will conclude with the advantages and disadvantages of non API and API motors.

Index Terms — Induction motor, Standards, API, NEMA, IEC

I. INTRODUCTION Over the years the demand continues to grow for motors

with greater reliability. When done properly, a high degree of reliability can be achieved while keeping economics in mind. This paper will discuss the design, manufacturing and testing per ANSI/API STANDARD 541-2003 4th Edition 2004 for motors 500 horse power (373 kW) and larger. The discussion within this paper is limited to Above NEMA motors.

II. MOTOR DESIGN

A motor is made up of the following components, as

shown in Fig. 1. [9]

A. Frame and Stator B. Rotor C. Bearings and Bearing housings D. Enclosures E. Terminal Box

A. Frame and Stator

The frame is generally made from cast iron or fabricated

from steel. It houses the steel laminated stator together with the winding. Rigid frame and precise machined feet are necessary for low vibration. Good thermal conductivity helps to dissipate the heat generated by losses. The stator is held inside the frame with a good interference fit. Proper air circulation is necessary to keep the winding and insulation temperature low. On higher power motors where the cast frame is not possible, a steel fabricated frame is used. The proper size and type of the steel selection is necessary.

Fig. 1 Motor Components

B. Rotor

The rotor is the second major component after the stator in an induction motor. There are four different types of rotor construction: aluminum die cast (ADC), copper die cast (CuDC), fabricated aluminum bars (AlBar), and fabricated copper or copper alloy bars (CuBar).

We will concentrate only on the widely used aluminum die cast (ADC) and copper alloy bar (CuBar), and their advantages and disadvantages. Fig. 2 shows a copper and ADC rotor.

Fig. 2 Copper (left) and ADC (right) Rotor

Typically, ADC rotors are easier to manufacture and more

economical than CuBar rotors. An aluminum rotor bar is

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approximately 3.3 times lighter than copper bar and has the specific heat capacity of 2.3 times the specific heat of copper. Additionally, the co-efficient of a thermal expansion for a given temperature change is approximately 32% greater for aluminum over copper. Aluminum also has lower yield strength than copper. [7]

As a result of the material density, specific heat and thermal expansion differences, aluminum bars will get much hotter, expand further and generate much higher stresses while accelerating the same load inertia (WK2) compared to a CuBar rotor. Porosity may also be present in the die cast rotors due to trapped gases during the casting process or due to uneven shrinkage during cooling, particularly in a long rotor.

Today most manufacturers maintain good control over these processes, eliminating most of the concern. In conclusion, all types of rotor constructions can be designed and manufactured to ensure low vibration. In general, a copper fabricated rotor should be more robust and can visually be inspected for flaws during manufacturing to ensure a high quality product. Although this type of construction has the ability of being more easily repaired in the field, if impractically designed and manufactured, these advantages would not be guaranteed. Finally, the design must take into account relative movement during motor starting so that the motor still continues to perform after multiple starts. C. Bearings and Bearing housings

Rolling element and fluid film are the two bearing types that are used in commercial induction motors, Fig. 3. The particular type to be used is determined by the load and speed requirements, economics and other factors, as shown in Fig 4. There are advantages and disadvantages of each bearing type and these are weighed against other factors.

Fig. 3 Sleeve (left) and Roller (right) Bearings

Rolling element bearings are simple and yet versatile. For a wide variation of speeds and loads, one can always find a bearing type and size which meet one’s application. The number of bearing bracket parts for a rolling element bearing is less than that of a sleeve bearing, and the design is relatively simple.

Formulas and tables for the calculation of rolling bearing fits, life and power loss are available universally. For example, the ball bearing basic life or L10 life in millions of cycles is given by:

L10 = (C/P) n

C dynamic load rating of the bearing (from

manufacturer’s tables) P weighted sum of the applied axial and radial loads n 3 for ball bearings and n = 3.33 for roller type

Fig. 4 Bearing Selections.

The L10 life of the bearing is defined in ISO and ABMA standards as “the life that 90% of a sufficiently large group of apparently identical bearings can be expected to reach or exceed”. The median or average life is about five times the L10 life.

In the calculations of bearing lives, it is always assumed that bearings are supplied with clean and cool lubricant of appropriate quantity and viscosity. If such lubricant is not available for the bearing then the calculated bearing life is invalid. The opposite is also true. Bearing manufacturers use factors that extend bearings lives if the lubrication and environment are better than normal.

One of the advantages of the rolling element bearing is the unified understanding of the designs of these bearings by manufacturers and service shops. For motor applications the bearings are designed with small interference with the shaft and small clearance with the housing. The bearing is also selected to have larger than normal internal clearance fit or C3. This simplifies the aftermarket supply and repair and avoids unnecessary and costly mistakes.

Generally speaking, larger machines and particularly faster ones use fluid film bearing only. Fluid film bearings in motors depend on the hydrodynamic action for the generation of the load carrying capacity. Shearing the viscous fluid between the journal and bearing surfaces generates a hydrodynamic pressure with typical distribution as shown in Fig. 5. This keeps the journal surface separated from the bearing surface. A big part of the fluid film bearing design is concerned with ensuring sufficient separation between the moving and stationary surfaces.

Like the case with the rolling element bearings, fluid film bearing life depends on proper lubricant type, quantity and cleanliness. Ring lubricated sleeve bearings require that the oil level be monitored and maintained. Perhaps one of the disadvantages of the sleeve bearing, as compared to rolling element bearings is the very short time it will run with no lubricant. The life of a sleeve bearing cannot be calculated

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using readily available formulas such as the case with the rolling element bearings. Perhaps for that reason, some believe that fluid film bearings have infinite life.

Fig. 5 Oil Pressure profile

There are several sleeve bearing designs which satisfy the requirements but finally look different. For example the sleeve bearing may be supported from its axial ends and one central oil ring is employed for oil delivery. This allows extra stiffness. Or the bearing is supported at the center and two side oil rings are used for oil delivery. This allows for some self-aligning capability while the two rings deliver more oil to the bearing area, but not directly at the hot central spot as in the first design. Each design has its own advantages and disadvantages.

The variety in bearing designs and types grow even bigger in vertical motors where the bearing may be required to carry a significant thrust. The thrust may be upward and downward or the shaft may be hollow. The bearing housing is also manufactured from cast or steel material as discussed in the frame design. Rigidity and high stiffness is necessary for lower vibration. Proper tolerances and precision machining is necessary for long term motor reliability

D. Enclosures

The enclosure is critical for the protection of the stator. As a result, it is necessary to select the proper enclosure. Table 1 lists the different type of enclosures typically available. Proper selection of enclosures is necessary for motor long term reliability.

For Zone 1 or Division 1 hazardous locations, totally enclosed enclosures are required while for Zone 2 or Division 2 any enclosures are suitable.

TABLE 1 TYPES OF ENCLOSURES

NEMA (IEC) IEC/NEMA SIZE COST ODP -Open Drip

Proof (IC0A1) IP12 Small Low

WPI -Weather Protected Type

(IC0A1)

IP22 Small Low

WPII -Weather Protected Type II

(IC0A1)

IP24W Small Moderate

TEAAC -Totally Enclosed Air to Air Cooled (IC6A1A1)

IP44-IP54 Large +20% higher

TEFC-Totally Enclosed Fin Cooled

(IC4A1A1)

IP44-IP54 Large +30% higher

TEWAC-Totally Enclosed Water-Air Cooled (IC8A1W7)

IP44-IP54 Large Higher

TEFV-Totally Enclosed Forced

Ventilated (IC3A6or7)

IP44 Small Moderate

E. Terminal Box In regards to large induction machines, NEMA MG 1[2]

provides terminal box guidelines for Type 1 terminal housings with unsupported and insulated terminations, and Type 2 terminal housings with supported terminations. The NEMA table for Type 1 terminal housings provides values for the minimum usable terminal box volume, minimum internal dimension, and the minimum distance from the conduit entrance to the centerline of the machine leads. These values are listed for several voltage ranges between 0 and 13,800 volts and various maximum full load current ranges between 160 and 2000 amps. The NEMA table for type 2 terminal housings lists the minimum values for various internal dimensions within the terminal box including the overall box length, width, and height, the spacing between the standoff insulators, and the distance between the insulators to the terminal box surfaces. These dimensions are tabulated for various machine voltage ratings between 460 and 13,800 volts.

Similarly DIN 42962-1 and -2 standard describes the terminal boxes connection for IEC motors. In IEC 60079-7 the creapage and clearances are mentioned for the different voltage level and thus establishes the minimum volume of the boxes.

III. API REQUIREMENTS

API 541 [1] is considered by many to be the premier

induction motor specification. It has been in existence for approximately 22 years. Each review/revision cycle of the standard has involved feedback from users of the standard (both motor end-users and suppliers), which has led to its continuous improvement.

Although each revision yields changes that promote increased motor reliability, safety and value, the ramifications of each change (from a manufacturer’s, a consultant’s, and a user’s perspective) is not always apparent.

The equipment (including auxiliaries) covered by this standard shall be suitable for specified operating conditions and shall be designed and constructed for a minimum service life of 20+ years and at least 3 years of uninterrupted and continuous operation. It is recognized that this is a design criterion and that uninterrupted operation for this period of time involves factors beyond the vendor's control.

A. Design Considerations [8]

1) Equipment shall be designed to permit rapid and economical maintenance. Major parts, such as

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frame components and bearing housings, shall be designed (shouldered or doweled) and manufactured to ensure accurate alignment on reassembly. Easily removable covers shall be provided for maintenance and inspection of coil end turns. The benefit is time savings during disassembly and reassembly.

2) The enclosure shall be designed to facilitate cleaning and painting of the motor's interior if required.

3) If aluminum is used, it shall have a copper content of < 0.2 percent. The higher content of copper increases the stress corrosion in aluminum alloy by decreasing the corrosion resistance.

4) The impact of potential risks due to possible circulating currents in the enclosure should be considered for motors using multi section enclosures installed in classified locations. This means overheating or sparking due to possible circulating currents shall be avoided where necessary by securing together the conducting components in a sound electrical and mechanical manner, or by providing adequate bonding straps between the motor housing components This reduces the sparking and/or arcing for hazardous location.

5) No frame resonances should exist within the following ranges:

N = nNop ± 0.15Nop, ±0.15 of 1f, ±0.15 of 2f,

0.4 to 0.6 of Nop

where N frequency range (Hz) n 1, 2… Nop Operating speed frequency (Hz) f Line frequency (Hz)

6) Foundation

A massive foundation is recommended. The natural frequencies of the foundation after the machine is erected must differ by at least ± 20% from one and two times the running-speed frequency and by at least 20% from one and two times the electric line frequency.

7) Rotor Shaft A forged shaft is required for the following

conditions; - Finished shafts larger than 8”. - Two-pole machines 1000 HP & larger - Flexible shaft machines - Motors driving reciprocating loads - Motors using tapered hydraulic fit couplings - Allowable combined electrical & mechanical

run-out is to 0.375 mils, to reduce variability on vibration measurement.

8) The rotating element shall be designed and constructed to withstand the starting duties with a fatigue life of at least 5000 full-voltage starts or as specified by the purchaser.

9) When specified, a rotor dynamic analysis with motor half-coupling weight and taking into account the effect of the foundation shall be performed by the motor vendor. The vendor shall identify the

foundation data required from the purchaser to perform.

10) Shaft extension(s) shall conform to API 671, AGMA 9002, ISO R/773, R/774, R/775. [3][4][6] Where tapered shaft extensions are supplied, the fit shall be verified by a purchaser supplied ring gage. This will help verify accuracy and integrity of the fit in case of a hydraulic coupling.

11) End rings without circumferential joints are required on motors intended to operate at synchronous speeds greater than or equal to 1000 RPM.

12) Fans cannot be bolted to end connectors for two, four, and six pole machines. Higher speeds will result in higher stresses in bolting joints and may cause the risk of failure.

13) Rotors operating at speeds in excess of the first actual lateral critical speed shall be balanced in at least three planes. This provides additional flexibility to better balance machine rotors for all vibration modes.

14) Hydrodynamic bearing oil sump temperature limits are reduced. Oil temperature rise for flood lubricated bearings should be 20°C and for ring-lubricated bearings, the oil sump temperature should be limit to 80°C

15) For machines rated higher than 600 volts, accessory leads located in the main terminal box are required to be accessible without removal of the main door or cover.

16) Wire insulation shall be impervious to petroleum-based products. Where synthetic oils are to be used it will be the end-users responsibility to verify compatibility.

17) A minimum of two stator winding RTDs (per phase) are mandatory, and shall be platinum type.

18) Air filters are mandated for all Weather Protected Type II machines. Filter performance criteria: removes 90% of particulates 10 micron and larger.

19) Frequency spectrum sweeps should cover a range from 25% to 4 times the line frequency.

20) Fan systems, blades, and housings shall be designed to prevent sparking as a result of mechanical contact or static discharge. They shall be made of corrosion-resistant, ductile materials to minimize failure from corrosion or fatigue.

21) Adjustable Speed Drives (ASD) or Variable Frequency Drive (VFD) in present day use on large induction motor applications may add extra requirements to a motor. In general additional concerns are related to vibration questions due to the range of speeds, possibly increased temperature rises due to low speed ventilation concerns, and electrical vibration and other questions due to the applied power being non sinusoidal to some extent. Specifically, the main extra requirements listed include:

a) When specified, the sound level shall be measured on the specified drive.

b) The motor shall not generate excessive heat or spark on the specified drive.

c) The voltage and frequency ratings shall be mutually agreed upon by the purchaser and vendor.

d) Temperature rises throughout the specified power and speed range shall be identical to those of a motor on a utility supply.

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e) Motor for use only on a drive may have performance characteristics such as locked rotor currents and torques selected to optimize performance on the drive.

f) The motor insulation shall be selected to withstand any unusual applied voltages.

g) For dynamic analysis, a well damped resonance may be permitted where a 15% separation margin from lateral critical is not practical. Also for torsional analysis, the effects of adjustable speed operation on shaft stresses must be considered.

h) Under special tests, it is pointed out that the efficiency of motors on an ASD or VFD may not be the same as the same motor on utility supply, and also the requirements for some tests that are relevant only to utility supply (locked rotor and accelerating performance) are relaxed for motors that will operate only on an ASD or VFD.

22) Allowable vibration limits per Fig. 6.

Fig. 6 Allowable Shaft Vibration (top) and Housing Vibration

(bottom) per API

B. Manufacturing

1) Equipment shall be manufactured to ensure accurate alignment and within the designed tolerances.

2) Structural welding including weld repair shall be performed by operators using procedures qualified in accordance with AWS D 1.1. [5] Other

welding codes may be used if specifically approved by the purchase.

3) Manufactured per specified primary dimension if dual dimension system is used on the drawings.

4) The shaft machining and finish to meet the slow roll vibration.

5) Follow the bolts/screws tightening torque as specified on the drawings.

6) Use proper sealing compounds to seal the required surfaces for long service operation.

7) When radiographic, ultrasonic, magnetic particle or liquid penetrant inspection of the welds is required, perform and keep the test data.

8) Calibrated equipment should be used to manufacture the motors.

Appendix A Table 2 shows the manufacturing requirement between NEMA MG – 1 [2] and API 541 4th [1] Edition C. Testing

The motor shall perform within the specified acceptance criteria on the test stand and on its permanent foundation. After installation the performance of the combined units shall be the joint responsibility of the purchaser and the vendor who has responsibility for the train. The purchaser reserves the right to observe the testing, dismantling, inspection, and reassembly of equipment, as specified.

1) When specified, before the start of testing, the manufacturer shall demonstrate the accuracy of the test equipment and or automated data acquisition systems. The calibration and minimum deviation, from a recognized standard, at all phase angles and anticipated frequencies and harmonics, shall be demonstrated.

2) Perform routine test or type test as specified by the purchaser.

3) Take data as specified in test schedules. 4) Test and check all auxiliary devices that they are

performing as intended for. 5) Check guaranteed limits of data, such as overall

vibration levels, limits of harmonic vibration components, frequency and amplification factors of critical speeds, motor efficiency and noise levels, and stator temperature rise.

6) Unless otherwise specified, all test results shall verify by the vendor and transmitted to the purchaser in reproducible form.

7) If specified perform special test such as tandem test, unbalance response test, bearing housing natural frequency test, sealed winding conformance test.

IV. ADVANTAGES OF API MOTORS

When designed and manufactured per API standard’s the

requirements ensure low vibration and reliability. To achieve these requirements the following points should be considered. [10]

1) Good, stable shaft material 2) Proper rotor core to shaft fit 3) No loose parts that could change balance or

unbalance during operation and speed change 4) End connector symmetrically brazed (depending on

rotor construction) 5) Low run-out

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a. Bearing journals b. Probe fits c. Shaft extension d. Rotor core outer diameter

6) No resonant frequencies near the operating speed or known forcing frequencies

7) No degradation of the above items due to multiple restarts

8) Proper rotor construction for the application: copper, ADC, etc.

9) Proper bearing selection for the application: sleeve, AFB, etc.

10) Stiff frame construction with proper foot flatness 11) No resonances in frame or bearing housing that

can cause excessive vibration at known forcing frequencies

Appendix A Table 3 shows a comparison of shaft vibration between NEMA MG – 1 [2] and API 541 4th [1] Edition

V. COST VERSUS RETURN

Along with lower vibration levels, there is a motor cost

increase associated with more controlled manufacturing processes, close tolerances and better raw materials. The table below compares the requirements for greater reliability with respect to three motor construction characteristics: rotor construction, bearing type, and shaft construction. Components Requirements for greater reliability Rotor, ADC • Better quality aluminum

• More precise and accurate injection method

• lose tolerance machining Rotor, CuBar • Better quality copper

• Good connecting process to end connectors

• Close tolerance machining Bearing, AFB • High precision, quality bearing

• Better fit and tighter tolerances between bearing, shaft and housing

• Better lubrication Bearing, Sleeve

• Better process for manufacturing • Better circulation of lubrication • Better fit and tighter tolerances

between shaft journal and bearing • Better lubrication and better

temperature control for better viscosity stability

Shaft, solid • Homogeneous material for good slow roll and stability

• Good stress relieved shaft material • Precision machining, tighter

tolerances • Better fit and tighter tolerances

between core and shaft • Better thermal stability

Shaft, spider • Homogeneous material for good slow roll and stability

• Better process for uniform welding between various types of shaft and spider bar materials

• Good stress relieved shaft material • Precision machining • Better fit and tighter tolerances

between core and shaft • Better thermal stability

API 541 will be revised and the 5th edition will be released. Some changes are listed below for reference and knowledge purpose.

• Different data system for the customer to use for English or SI units, and has a selection for US or international market

• Service life of motor is changed from 20 years to 25 years

• IEC references are added at several places • Test of motor insulation procedure and data should

be recorded • Dynamic performance should be checked for

customer supplied half coupling when mounted on the motor shaft.

• Added for TEWAC (IC8A1W7) motor heat exchanger performance test is added

• Added vibration change limit from over speed to rated speed and the over speed capability for the ASD or VFD operation

• Better defined for long term storage at job site. • Better defined the documentation • List of spare parts, cut sheets, catalogue and

ordering numbers • Data retention for at least 5 years

VI. CONCLUSION

The design requirements for API motors will result in

machines with greater reliability, safety, and value. The focus on value is based on life cycle cost, not necessarily initial purchase price.

Along with greater reliability, safety, and value, there is a motor cost increase associated with more controlled manufacturing processes, higher tolerances and better raw materials. It is impossible to predict the cost impact, as different end users are impacted in different ways. However, in some cases it is worth having a higher initial purchase cost than an unpredicted plant shutdown and a loss of much higher revenue.

The API designed motor will cost approximately 20 to 30% more than a basic ANEMA frame 680 or IEC frame 450. The API cost increase on higher frame sizes will be slightly less when compared to the adder on smaller frame sizes.

There are manufacturers in US, Canada, and Europe who manufacture IEC frame size motors per API standards but more so in Europe than IN US or Canada.

VII. REFERENCES

[1] ANSI/API Standard 541, 2003 4th Edition American Petroleum Institute, Washington, D.C.

[2] NEMA MG 1-2006, Motors and Generators, Rosslyn, VA: NEMA.

[3] ANSI/API Standard 671, 20074th Edition American Petroleum Institute, Washington, D.C.

[4] ANSI/AGMA Standard 9002-B04, 2004, American Gear Manufacturers Association, Alexandria, VA

[5] AWS Standard D 1.1/D1.1M 2010, American Welding Society, Miami, FL

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[6] ISO Standards R773/774/775, International Organization for Standardization, Geneva-20, Switzerland

[7] Finley B, Hodowanec M. “Selection of Copper vs. Aluminum Rotors for Induction Motors” In IEEE PCIC Conference Record, 2000, pp 187-197

[8] Hodowanec M, Costello M, Lockley B, Rama J, Griffith T. “Introduction to API standard 541, 4TH edition – Form Wound Squirrel Cage Induction Motors Larger Than 500 Horsepower” In IEEE PCIC Conference Record, 2003 pp 311-319

[9] Rajendra V Mistry, William Finley, Scott Kreitzer, Emam Hashish. “An Induction Motor – Keep It Running.” In IEEE PCIC Conference Record, 2010, pp 1-12.

[10] Rajendra V Mistry, William Finley, Scott Kreitzer. “Induction Motor Vibrations In View of the API 541- 4th EDITION.” In IEEE PCIC Conference Record, 2008, pp 1-10.

VIII. VITA

Rajendra Mistry, PE received his B.E. degree in Mechanical Engineering in India and a Bachelor of Technology in Electrical Engineering in the U.K. He is currently a principal engineer at Siemens Industry, Inc. (Norwood) in the engineering development department responsible for developing Above NEMA induction motors. In addition to his industry role, he has attended several courses in vibrations, design for manufacturing, concurrent engineering, and digital signal processing. He is also responsible for certifying induction motors for Hazardous location and material expert. He is a member of American Society of Mechanical Engineers (ASME) American Material Science International (ASM) and American Foundry Society (AFS). He holds four patents for components in hydraulic elevators and on Induction motors. Scott Kreitzer graduated with a BSME degree from Wright State University in 1993 and received a Master of Science degree in Aerospace Engineering from the University of Cincinnati in 1995. Scott worked for Reuland Electric in 1994 as a Design Engineer developing high-speed AC induction motors. He has been a Mechanical Engineer in the Above NEMA motor development group at Siemens Energy and Automation since 1995. Scott is an associate member of IEEE.

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Appendix

Table 2 Comparison of Manufacturing Requirements

Standard NEMA MG1 2006 API 541 2nd Edition

1987 API 541 3rd Edition API 541 4th Edition

Bearing Journal Runouts Not mentioned Not mentioned To limit the vibration

values To limit the vibration values

Non Contacting Eddy Current Probe Fit Runout

Not mentioned 25% of unfiltered p-p or 0.25 mil total

30% of unfiltered p-p or 0.25 mil total

25% of unfiltered p-p or 0.25 mil total

Forged Shaft Not mentioned Not mentioned

Yes - 2 pole and Operating speed > 1st Lateral critical speed

Yes - Special requirements

Seamless End Connectors Not mentioned Not mentioned Required for speed >

1500 RPM Required for speed > 1000 RPM

Tight Rotor Bars Not mentioned Not mentioned Yes Yes Center Locked Rotor Bars Not mentioned Not mentioned Yes Yes

Induction Brazed End Rings Not mentioned Brazing material must

be phosphorous free Yes allowed and other methods too

Yes allowed and other methods too

End Rings Symmetrically Brazed Not mentioned Not mentioned Yes Yes

Step Balance Not mentioned Not mentioned Yes Yes Balance Spec Not mentioned Not mentioned Unbalance ≤ 4W/N Unbalance ≤ 4W/N Full Speed Balancing Not mentioned Not mentioned No No Air Gap Tolerance Not mentioned Not mentioned ± 10% ± 10%

Foot Flatness Not mentioned

o All feet in the same horizontal plane within 0.005 inch

o Flatness of each foot within 0.0005 inch per foot

o Mounting planes parallel within 0.002 inch per foot

o All feet in the same horizontal plane within 0.005 inch

o Each foot parallel to same horizontal plane within 0.002 inch per foot

o All feet in the same horizontal plane within 0.005 inch

o Flatness of each foot within 0.0005 inch per foot

o Mounting planes parallel within 0.002 inch per foot

Trim Balancing Allowed Not mentioned Same as API 541 if probes required

Yes, but not for thermal compensation

Yes, but not for thermal compensation

Hot Vibration Measurement Not mentioned Same as API 541 if

probes required

No change > 50 % of the allowable limit from hot to cold

No change of 1X > 0.6 mil on shaft and 0.05 ips on housing from hot to cold

Modulation Not mentioned Not Mentioned 15 minutes for 2 pole 15 minutes for 2 pole

Mounted on Massive Foundation

Yes, at machine feet, vibration < 25% of max velocity at bearing housings

Not Mentioned

Yes, at machine feet, vibration < 30% of max velocity at bearing housings

±20% of 1 and 2X and 20% of 1 and 2 LF

Frame Resonance

±10% of 1X RPM, ±5% of 2X RPM and 1X and 2X LF

N= nNop ± 0.25Nop (1) N= nNop ± 0.20Nop (1)

N= nNop ± 0.15Nop (1)

Balance with Key Not mentioned Not mentioned Yes Yes (1) N = frequency range (Hz); Nop = Operating Frequency (Hz); n = 1, 2, 3

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Table 3 Comparison of Shaft Vibration Limits

Assumptions: • Rigid mounting base • Velocity Zero to Peak • Displacement Peak to Peak • Vibration values listed are for 2,4 and 6 pole motors

Standard Unfiltered Filtered 1X Filtered 2X <1X NEMA MG1 – From 1993 Rev 1 to 2006

2.8 mils 2p 3.5 mils 4+p

N/A N/A N/A

IEC 60034 -14 Ed 3.1 2007-03 (2)

2.5 mils 2p 3.5 mils

>4p

N/A N/A N/A

API 541 2nd Edition 1987

2.0 mils 2p 2.5 mils 4p 3.0 mils

6+p (1)

1.5 mils 2p 2.0 mils 4p 2.4mils

6+p (1)

1.0 mils 2p 1.5 mils 4p 2.0 mils

6+p (1)

API 541 3rd Edition 1995 1.5 mils 2,4,6+p 1.2 mils 2,4,6+p (3) 0.5 mil 2,4,6+p 0.1 mil or 20% of

unfiltered API 541 4th Edition 2004 1.5 mils 2,4,6+p 1.2 mils 2,4,6+p (3) 0.5 mils 2,4,6+p 0.1 mil or 20% of

unfiltered (1) Special purpose motor – Driving un-spared equipment in critical service, motor rated over 1000 HP, motors driving high inertia (2) Sleeve bearing vibration limit, Vibration grade – A, includes run out. (3) Run out compensated