Cyndi Nyberg
Former EASA Technical Support Specialist 

There are a number of different types of wind­ing protection devices used with motors. However, they all basically do the same thing; they sense a change from the normal operating temperature and either sound an alarm or take the motor off line when the specified temperature limit has been met or exceeded. 

Temperature protection is not limited to just large motors. A smaller motor that is critical to op­eration would be a good candidate for winding temperature protection if a failure would cause significant costs due to downtime. 

DESCRIPTION
Filled with practical information, this 118-page handbook (3.5" x 6", 9cm x 15cm) makes a great “give-away” item for your customers and potential customers! Buy this great resource as is OR custom brand your company logo and information on the cover to turn it into a great marketing piece for your salespeople!

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TABLE OF CONTENTS

MOTOR DATA–ELECTRICAL
Standard Terminal Markings and Connections
DC Motors and Generators (NEMA & IEC Nomenclature)
Field Polarities of DC Machines
General Speed-Torque Characteristics
Full-Load Efficiencies of Energy Efficient Motors
Full-Load Efficiencies of NEMA Premium™ Efficient Motors
Effect of Voltage Variation on Motor Characteristics
Power Supply and Motor Voltages
Effect of Voltage Unbalance on Motor Performance
Starting Characteristics of Squirrel Cage Induction Motors
Allowable Starts and Starting Intervals

MOTOR DATA–MECHANICAL
Suffixes to NEMA Frames
NEMA Frame Assignments–Three-Phase Motors
NEMA Frame Dimensions–AC Machines
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines
IEC Shaft Extension, Key And Keyseat Dimensions–Continuous Duty AC Motors (Inches)
NEMA Shaft Extension And Keyseat
Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–Foot-Mounted DC Machines (Inches)
NEMA Frame Dimensions–AC Machines (mm)
IEC Mounting Dimensions–Foot-Mounted AC and DC Machines (mm)
IEC Shaft Extension, Key and Keyseat Dimensions–Continuous Duty AC Motors (mm)
NEMA Shaft Extension and Keyseat Dimensions–Foot-Mounted DC Machines (mm)
NEMA Frame Dimensions–Foot-Mounted DC Machines (mm)

MOTOR CONTROLS
Power Factor Improvement of Induction Motor Loads
Capacitor kVAR Rating for Power-Factor Improvement
Full-Load Currents–Motors
Maximum Locked-Rotor Currents–Three-Phase Motors
NEMA Code Letters for AC Motors
Starter Enclosures
NEMA Size Starters for Three-Phase Motors
NEMA Size Starters for Single-Phase Motors
Derating Factors for Conductors in a Conduit
Allowable Ampacities of Insulated Conductors
Motor Protection Devices–Maximum Rating or Setting

TRANSFORMERS
Full-Load Currents for Three-Phase Transformers
Full-Load Currents for Single-Phase Transformers
Transformer Connections

MISCELLANEOUS
Temperature Classification of Insulation Systems
Resistance Temperature Detectors.
Thermocouple Junction Types
Dimensions, Weight and Resistance: Solid Round Copper Wire (AWG and Metric)
Square Bare Copper Wire (AWG)
Insulation Resistance and Polarization Index Tests
Properties of Metals and Alloys

USEFUL FORMULAS AND CONVERSIONS
Temperature Correction of Winding Resistance
Temperature Correction of Insulation Resistance.
Formulas for Electric Motors and Electrical Circuits.
Motor Application Formulas
Centrifugal Application Formulas
Temperature Conversion Chart
Conversion Factors
Fractions of an Inch–Decimal and Metric Equivalents

Winding RTDs are resistance-based temperature monitoring devices. Aside from just reporting winding temperature, here are some tips for maximizing the benefit of RTDs. Place six RTDs, spacing them uniformly around the core so there are two per phase. Provide a location map, numbering the RTDs, starting with the number 1 RTD in the 12:00 position. Number the RTDs clockwise facing the connection end.

Knowing where each RTD is located (which phase, as well as the physical location in the stator) provides some powerful diagnostic ability. Possible causes for deviation in temperature are:

• Two RTDs reading high, and both in the same phase: Check for voltage / current unbalance; higher current in one phase causes higher temperature in that phase.
• If the number of circuits is half the number of poles, circulating currents can occur. This situation can be exacerbated by uneven airgap which cause a further temperature increase. The corrective action, in this case, is to use the appropriate extra-long jumpers when connecting the winding.
• Higher temperature indicated in adjacent RTDs may indicate obstructed ventilation. Some possible causes are clogged filters, missing soundproofing, displaced weather-stripping, poorly positioned air baffles, or a missing J-box cover.
• Some manufacturers place all six RTDs across the 10:00 to 2:00 portion of the winding, to report more uniform temperatures. By distributing the RTDs symmetrically around the stator -- instead of just on the top -- the reported apparent temperatures often look alarming. Before returning the motor, let the end-user know where they were originally, and explain that the symmetrical placement will yield more realistic results.

When installing winding Resistance Temperature Detectors (RTDs), divide the number of stator slots by the number of RTDs to install (usually six) and mark the slots accordingly. For example, a 72-slot stator with six RTDs would position an RTD in every 12th slot. That results in two RTDs per phase. Be sure to number the RTDs and provide a map of their locations to aid the customer in interpreting temperature differences. For example, unbalanced voltage might result in higher temperature in two RTDs in the same phase, while obstructed ventilation is likely to cause higher temperature in two or three adjacent RTDs.

One anomaly is WPI or WPII (weather protected) enclosures, where the top hood is integral to airflow. Some manufacturers place all six RTDs across the top of the windings (from the 10:00 - 2:00 positions) so that all RTDs are within the area receiving better cooling. This is not deceptive; it’s just meant to avoid a customer asking questions about temperature differences. For repairers, it’s a talking point with your customer when rewinding such a motor. Do they want the RTDs evenly spaced, recognizing that they will see the differences in actual operating temperature? Or do they want them placed as the manufacturer did? Better to have that conversation first, rather than raise doubts after the motor returns to service.

Note that, depending on the coils/ group and pitch, an RTD might be between top and bottom coils of the same phase, or of different phases.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

It’s a striking fact that operating a three-phase induction motor at just 10°C above its rated temperature can shorten its life by half. Whether your facility has thousands of motors or just a few, regularly checking the operating temperature of critical motors will help extend their life and prevent costly, unexpected shutdowns. This article will show you how to go about it.

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Richard Hughes (deceased)
Pump & Motor Works, Inc.

This series of four articles covers many schemes of motor protection and control.

Topics covered include:

• Time delay fuses
  • Fuse selection
  • Over-current protection
  • Avoiding fuse overloads
• Circuit breakers
  • Inputs to electronic protection relays
  • Feeding, protecting a motor starter
  • Common features
• Motor starters
  • How motor starters operate
  • Light, medium or heavy duty
  • Momentary start button
  • Wye series start, parralel run
  • Variety of controls
• IEEE and ANSI power system device numbers
• Dashpot type overload relay
• Thermal overload relay
• Current transformer
• Compact relays
• Restoring balanced voltage
• Transient voltages
• Surge capacitor, surge arrestor

By Jim Bryan
EASA Technical Support Specialist (retired)

The Institute of Electrical and Electronics Engineers (IEEE) has published a new standard: IEEE Std. 3004.8-2016, “Recommended Practice for Motor Protection in Industrial and Commercial Power Systems.” If you’re an electrical professional who deals with a broad spectrum of motor protection schemes, including low- and medium-voltage AC and DC motors, then you need to become familiar with this standard.

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This version of Principles of Medium & Large AC Motors manual is now available to address applicable IEC standards and practices. This 360-page manual was developed by industry experts in Europe along with EASA's engineering team. (The "original" version of this book based on NEMA standards remains available as a separate document.)

This manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, information on enclosures, construction on components and applications. Many of the principles included apply to all AC motors, especially those with accessories that are associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters and vibration sensors).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 37 to 3,700 kW (300 to 5,000 hp) range, low- and medium-voltage, most of the principles covered apply to other sizes as well. 

This valuable instructional/resource manual is available in printed and downloadable versions, and focuses primarily on IEC motors.

Sections in the manual include:
(Download the PDF below for the complete Tables of Contents)

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

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PRINTED BOOK DOWNLOADABLE PDF

This book is also available focusing on NEMA Standards — in both English and Español.

NEMA - English NEMA - Español

Por Gene Vogel
Especialista de Bombas & Vibraciones de EASA

Las bombas sumergibles pueden tener diferentes tipos de sensores o dispositivos de protección internos, los cuales pueden ser sensores de temperatura, transductores de vibración o sensores de humedad. Los sensores de temperatura y de vibración son idénticos a los utilizados en los motores no sumergibles, por lo que solo los sensores de humedad guardan especial relación con las bombas sumergibles. Es importante que los técnicos involucrados en la reparación de las bombas sumergibles sean conscientes de su presencia en cualquier bomba en los que se puedan encontrar y que comprendan como trabajan para asegurarse que funcionan correctamente después de terminar los trabajos de reparación.

Gene Vogel
EASA Pump & Vibration Specialist

Submersible pumps may have any of several types of internal sensors or protective devices. These may include temperature sensors, vibration transducers or moisture sensors. The type of temperature and vibration devices are identical to those used in non-submersible style motors, so only the moisture sensors are of special interest regarding submersible pumps. It is important for technicians involved in the repair of submersible pumps to be aware of their presence in any specific pump they may encounter, and understand the manner in which they function to ensure they work properly after repairs are completed.