Gene Vogel
EASA Pump & Vibration Specialist

This technical paper was presented at the 2014 EASA Convention.

The impeller is generally the most difficult pump component to repair and the most expensive to replace. This paper looks at case histories of failed pumps and the steps to determine the cause of failure.

• Erosion, corrosion, cavitation or wear. What happened to this impeller?
• How to spot the tell-tale signs
• What operational conditions led to impeller damage

Vicki Warren — Iris Power - Toronto, Ontario
Brian F. Moore – Georgia Power - Atlanta, Georgia
Jim Williams – Bradley’s Motors - Corpus Christi, Texas 
Special thanks to Gary Castle at Bradley’s Motors

Traditional tests of insulation resistance, polarization index (IEEE 43) and the controlled DC high voltage test (IEEE 95) have been effective in evaluating certain aspects of global vacuum pressure impregnation (GVPI) stator windings; however, they have not proven adequate for determining whether or not the insulation system is well-consolidated. Recently there has been the development of an IEC standard (IEC 60034-27) that defines the test procedures for performing off-line partial discharge testing as part of quality assurance testing. In addition, globally there has been a move towards using a dielectrics characteristic test, either power factor or dissipation factor, as part of the QA testing for GVPI systems. Partial discharge tests have proven to be effective in locating isolated problems that could lead to failure; whereas, the dielectrics characteristic tests provide a more general condition assessment. Based on experience to date, both are needed to fully evaluate how well the winding is consolidated. 

This paper, presented at the 2014 EASA Convention, describes research done by EASA service shops on the effectiveness and practicality of using offline partial discharge combined with a dielectrics characteristic test to evaluate the consolidation of stator windings in medium voltage machines manufactured by GVPI. Advantages and disadvantages of each test and industrial standards will be described as appropriate.

Neville Sachs, P.E.
Applied Technical Services, Inc.,
Syracuse, NY

This technical paper, presented at the 2014 EASA Convention, will help you understand how and why shafts and fasteners fail. This paper covers:

• Discussion of material properties typically found in motor shafts, machine shafts and common fasteners
• Differentiating between overload and fatigue failures
• Understanding and identifying the difference between ductile and brittle materials, and how their fracture appearances differ
• A detailed explanation of how to identify fatigue failures, including the rate and direction of force application and the effect of stress concentrations
• Examples of several failure analyses

Rick Hoadley
ABB, Inc.
New Berlin, WI

Whenever an application engineer is planning on installing adjustable speed drives for AC motors, line current harmonics and reflected waves are two factors that need to be addressed. Four basic questions should be answered in order to successfully commission the drive system:

1. What is my power system like today
2. What impact will the additional drive(s) have on the power quality for the other equipment
3. If needed, what harmonics mitigation method should be used
4. How long and what type of cable is used between the drive and motor

This paper, originally presented at the 2014 EASA convention, deals with understanding IEEE Std 519 and various mitigation methods in order to meet those recommendations. It also reviews the types of filtering that is available to reduce the reflected waves, first turn insulation stress, and common mode voltages seen at the motor terminals.

• Overview of drives topologies
• The differences between 6,12,18 pulse and active front end drives
• How the differences in drives relate to harmonics generated
• Filters on either end of the drive to mitigate the effects of harmonics, as well as voltage spikes and other potential damaging effects on the motor

Jim Bryan
EASA Technical Support Specialist (retired)

Reclosure occurs when power to a motor is briefly interrupted and restored before the magnetic field has fully collapsed in the motor’s winding. If this occurs while the applied power is out of phase with the collapsing field, significant damage can result. This paper, presented at the 2014 EASA Convention, addresses how this can happen and what measures can mitigate damage potential. Topics covered include:

• Reclosing a switch or breaker before the magnetic field collapses
• Utilities’ automatic reclosure
• Contactor “chatter”
• Determining the time constant
• Remedies
• Time delay
• Zero crossing

Chuck Yung
EASA Senior Technical Support Specialist

This paper, presented at the 2014 EASA Convention, covers theory of operation, inspection, operation, and troubleshooting tips for AC generators. For the supervisor, field service technician or service center personnel, generators can present unique challenges. Topics covered include:

• Theory of operation
• Testing tips
• Stator winding cautions
• How to interpret the exciter rotor connection
• In-shop and on-site testing methods
• How to test the voltage regulator
• How to test a generator without the regulator