Form-wound Squirrel Cage Induction Motors—375 kW (500 Horsepower) and Larger

API STANDARD 541

FIFTH EDITION, DECEMBER 2014

REAFFIRMED, MAY 2021

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Copyright © 2014 American Petroleum Institute

Foreword

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iii

1. General 1

   1. Scope 1

   2. Alternative Designs 1

   3. Dimensions and Standards 1

   4. Conflicting Requirements 2

2. Normative References 2

3. Terms and Definitions 6

4. Basic Design 8

   1. General 8

   2. Electrical Design 10

   3. Winding and Insulation Systems 14

   4. Mechanical Design 16

5. Accessories 40

   1. Terminal Boxes 40

   2. Winding Temperature Detectors 42

   3. Bearing Temperature Detectors 42

   4. Space Heaters 42

   5. Screens and Filters 43

   6. Alarms and Control Devices for Motor Protection 43

   7. Ground Connectors 44

   8. Vibration Detectors 44

6. Inspection, Testing, and Preparation for Shipment 45

   1. General 45

   2. Inspection 46

   3. Final Testing 47

   4. Preparation for Shipment 61

7. Guarantee and Warranty 62

8. Vendor’s Data 63

   1. Proposals 63

8.3 Contract Data 65

1. Drawings 66

2. Final Data 68

3. Instruction Manuals 68

Annex A Datasheets 70

Annex B Vendor Drawing and Data Requirements 97

Annex C Datasheet Guide 101

Annex D Procedure for Determination of Residual Unbalance 144

Annex E Procedure and Guidance for Determining the Allowable Resultant Vector Change During

a Heat Run Test 152

Annex F Alternate Criteria for Defining a Well Damped Resonance 155

Annex G AC Stator Form Coil Data 157

Bibliography 160

Figures

1. Typical Rotor Mode Shapes 27

2. Shaft Vibration Limits (Metric Units, Relative to Bearing Housing Using Noncontact Vibration Probes) for All Hydrodynamic Sleeve Bearing Machines with the Machine Securely Fastened

   to a Massive Foundation 49

3. Shaft Vibration Limits (U.S. Customary Units, Relative to Bearing Housing Using Noncontact Vibration Probes) for All Hydrodynamic Sleeve Bearing Machines with the Machine Securely

   Fastened to a Massive Foundation 49

4. Bearing Housing Radial and Axial Vibration Limits (Metric Units) for Sleeve and Antifriction

   Bearing Machines with the Machine Securely Fastened to a Massive Foundation 50

5. Bearing Housing Radial and Axial Vibration Limits (U.S. Customary Units) for Sleeve and

   Antifriction Bearing Machines with the Machine Securely Fastened to a Massive Foundation 50

6. Adjacent Core 57

1. (Blank) Residual Unbalance Worksheet 146

2. (Blank) Residual Unbalance Polar Plot Worksheet 147

3. Sample Residual Unbalance Worksheet for Left Plane 148

4. Sample Residual Unbalance Polar Plot Worksheet for Left Plane 149

5. Sample Residual Unbalance Worksheet for Right Plane 150

6. Sample Residual Unbalance Polar Plot Worksheet for Right Plan 151

1. Example of a Polar Plot Complying with 6.3.3.13 153

2. Example of a Polar Plot Not Complying with 6.3.3.13 153

3. Example of a Polar Plot Not Complying with 6.3.3.12 154

4. Possible Option if a Motor Fails Basic Specification Criteria 154

F.1 Evaluation of Amplification Factor (AF) from Speed Amplitude Plots 156

Tables

1. Voltage Ratings for Three Phase 60 Hz Systems 11

2. Voltage Ratings for Three Phase 50 Hz Systems (British Standards) 11

3. Voltage Ratings for Three Phase 50 Hz Systems (General) 11

4. Starting Capabilities 13

5. Machine Enclosures and Corresponding NEMA or IEC Specifications 17

6. Maximum Severity of Defects in Castings 47

7. DC Test Voltages for Insulation Resistance and Determination of Polarization Index 52

8. DC High-Potential Test Voltage Levels 59

   
   

   Form-wound Squirrel Cage Induction Motors— 375 kW (500 Horsepower) and Larger

   
   

   1. General

      1. Scope

         
         

         1. This standard covers the minimum requirements for special purpose form-wound squirrel cage induction motors 375 kW (500 hp) and larger for use in petroleum, chemical, and other industry applications. This standard can also be used for induction generators by substituting “generator” for “motor” where applicable.

            
            

            Notes following a paragraph in Sections 1 through 8 are informational only and are not enforceable as part of this standard.

            
            

            NOTE A special purpose machine typically has one or more of the following characteristics:

            
            

            1. is in an application for which the equipment is designed for uninterrupted, continuous operation in critical service, and for which there is usually no installed spare equipment;

               
               

            2. is larger than 2250 kW (3000 hp) for speeds 1800 rpm and below;

               
               

            3. is rated 600 kW (800 hp) or greater for two pole (3000 rpm or 3600 rpm) machines of totally enclosed construction, or rated 930 kW (1250 hp) or greater for two pole machines of open or guarded construction (including machines with WP-I or WP-II type enclosures);

               
               

            4. drives a high-inertia load (in excess of the load Wk2 listed in NEMA MG 1, Part 20);

               
               

            5. uses an adjustable speed drive (ASD) as a source of power;

               
               

            6. is an induction generator;

               
               

            7. is a vertical machine rated 375 kW (500 hp) or greater; or

               
               

            8. operates in abnormally hostile environments.

               
               

               A round bullet (●) at the beginning of a paragraph indicates that either a decision is required or further information is to be provided by the purchaser. This information shall be indicated on the datasheets (see Annex A); otherwise, it shall be stated in the quotation request or in the order.

               
               

               A diamond bullet () at the start of a paragraph indicates additional requirements for motors applied with ASDs.

               
               

         2. This standard requires the purchaser to specify details and features. The purchaser shall complete the datasheets in Annex A.

NOTE Guidance for completion of the datasheets is provided in Annex C.

1. Alternative Designs

   
   

   The vendor may offer alternative designs (see 8.1.9).

   
   

2. Dimensions and Standards

• 1.3.1 Both the metric (SI) and U.S. customary (USC) system of units and dimensions are used in this standard. Data, drawings, and hardware (including fasteners) related to equipment supplied to this standard shall use the

1