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Permissible Loading of Generators and Large Motors

Bijan Ghayour, P.E.


Course Outline

This 2-hour course is intended to fill the need for practical information concerning the temperature and mechanical and electrical overload limits of rotating electric equipment such as generators and large motors. Rotating electrical equipment cannot be overloaded on the same basis as transformers and is not as able to stand short-time overloads. This is largely because equipment cooled by air does not have the heat transfer ability which the higher thermal conductivity of insulating oil gives to transformers; also, the windings in rotating equipment are confined in slots in the steel and are subject to temperature expansion problems. For any abnormal loading of generators, the electrical, mechanical, and thermal characteristics must be evaluated to determine the machines limitations.

Machines should not be loaded beyond the manufacturer's defined overload capability unless a complete study of the unit has been made to define safe limits. Additional tests might have to be conducted to substantiate the possibilities for higher-than-rated loadings.

The course materials are based entirely on the Unified States Department of the Interior, Facilities Instructions, Standards, and Techniques Volume 1-4.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.


Learning Objective

The purpose of this course is to provide guidance in determining the amount of overload that rotating electrical equipment can carry under various operating conditions.

At the conclusion of the course the student will be familiar with the:


Intended Audience

This course is intended for design and operating engineers involved in the design, operation, and maintenance of generators and large motors.


Benefit to Attendees

The student will become familiar with the concept of operating rotating equipment under overload conditions. Topics discussed include types of insulation, short-time and emergency overloads, mechanical limitations, temperature rise, limiting temperature rise, cooling water and regulation of cooling water, and the effects of voltage control on temperature rise.

This course also includes easy to use generator capability curves in determining the permissible kW loadings for rotating equipment under various voltage and power factor operating conditions.


Course Introduction

In general loads in excess of normal ratings may be carried under certain conditions when necessary. Rotating electrical equipment cannot be overloaded on the same basis as transformers and is not as able to stand short-time overloads. This is largely because equipment cooled by air does not have the heat transfer ability which the higher thermal conductivity of insulating oil gives to transformers; also, the windings in rotating equipment are confined in slots in the steel and are subject to temperature expansion problems. For any abnormal loading of generators, the electrical, mechanical, and thermal characteristics must be evaluated to determine the machines limitations.

Machines should not be loaded beyond the manufacturer's defined overload capability unless a complete study of the unit has been made to define safe limits. Additional tests might have to be conducted to substantiate the possibilities for higher-than-rated loadings.


Course Content

This course contains specific examples, table and graphs for estimating the amount of overload for different generators and large motors under various operating conditions.

You are required to study volume 1-4, Permissible Loading of Generators and Large Motors, published by the Unites States Department of the Interior, Bureau of Reclamation.

Permissible Loading of Generators and Large Motors (PDF 470KB)

(For an electronic copy of FIST 1-4 go to http://www.usbr.gov/power/data/fist_pub.html and then click on volume 1-4)

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

The following contains the outline of Volume 1-4 of Permissible Loading of Generators and Large Motors, published by the Unites States Department of the Interior, Bureau of Reclamation:

Permissible Loading of Generators and Large Motors (PDF 470KB)

Table of Contents

1- Types of insulation used on rotating machines, their insulation life, and deterioration causes
2- Mechanical Limitations
3- Damage caused by expansion of copper
4- Limiting temperatures for insulation
5- Hottest spot allowance
6- Limiting temperature rise
7- Operation of machines under warranty
8- Operation up to rated capacity
9- Short-time and emergency overloads
10- Load limitations of associated equipment
11- Cooling water
12- Cooling water regulation
13- Supplemental cooling
14- Keeping machines clean
15- Temperature of old machines
16- Changing voltage to reduce temperature
17- Load temperature tests
18- Measuring stator temperature
19- Measuring field temperature
20- Computing stator winding temperature rise
21- Generator capability curves
22- References


Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

 


DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.