Richard W. Fruge, P.E. (Inactive)

Course Outline

Motor acceleration time at various terminal voltage levels must often be determined to evaluate protective device performance or for power system studies. This module will present a well-documented methodology that is often used by engineers and requires only published motor and load data. The methodology presented calculates a current exponent ratio and a torque exponent ratio that more accurately describes motor performance at reduced voltage levels. In order to enhance the utility of this methodology, a "real world" example that includes a belt driven fan load is used. A template that can be readily used in other motor acceleration time calculations will be developed.

Equations describing motor performance are presented to demonstrate the relationship between the various motor parameters used to calculate motor acceleration time. Equations describing fan performance are presented to demonstrate the relationship between the various fan parameters and the impact of load performance on the motor driving that load. An exercise using the motor and load equations will then be presented to demonstrate the motor starting time calculation methodology.

Evaluation of the acceleration time at a different motor terminal voltage requires re-calculation of the motor torque and accelerating torque. "Automating" the calculation can minimize the impact of this requirement. A toolbox automating the motor starting time calculation is presented in this module to demonstrate the time saving and error reduction potential. A general discussion of a calculation "automation" process is also presented to detail the resource requirements for implementing such a process. A working copy of the toolbox is available at no additional cost to the engineer using this module.

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

Learning Objective

At the conclusion of this 2-hour course, the student will:

• Have reviewed motor acceleration time equations
• Have reviewed belt driven load torque and inertia translation to the motor shaft
• Have reviewed motor voltage, power factor, slip, and torque characteristics
• Have reviewed motor ratings based on IEEE 112 methods
• Have reviewed the "Fan Laws"
• Have reviewed example motor accelerating time calculation exercises
• Recognize the effect of motor RPM on fan performance characteristics
• Recognize the benefits of calculation "automation"
  
  

Intended Audience

The material presented in this module is intended for engineers responsible for evaluating the impact of reduced motor terminal voltage during starting. This course will also benefit engineers desiring a general refresher course for motor starting parameters.

Benefit to the Audience

Users of this course will be presented with situations that may require calculation of approximate motor starting time at reduced power system voltage levels. A discussion of motor voltage/torque characteristics and some widely used assumptions is provided. A method for "automating" motor acceleration time calculations is also provided.

Course Content

Table of Content

I. Motor Equations
II. Fan Equations
III. Exercise for Motor Acceleration Time Calculation
IV. Automation
V. Summary

Quiz

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