Chuck Yung 
EASA Technical Support Specialist 

The problem:  We recently rebuilt a 2-pole motor and the centrifugal blower it drives. When the customer reinstalled them, he reported high vibration levels.  Everything runs smoothly for 10-15 minutes after a cold startup. Then the vibration starts to climb. We balanced the rotor and blower to G 1.0 tolerances. We even balanced each of the 7 blower impellers separately using a balancing mandrel. Shaft runout was less than 0.0002" on the motor and blower when we finished the job. The customer uses laser alignment. He is convinced that us to rebuild the blower again. What did we do wrong?

Tim Browne
Industrial Electric Motor Service, Inc.

Sospecho que casi todos en nuestra industria alguna vez han tenido el placer de reparar un motor “fabricado con requisitos especiales”. Este tipo de motor está construido para un propósito específico y tiene características que le pueden permitir funcionar bajo condiciones no habituales. Debido a la información limitada que algunos de ellos muestran en su placa de datos, la reparación de estos motores puede resultar un reto.

The repair of the various types of pumps represents an important segment of the service center repair market. Electric motors and pumps are the two most widely used industrial machine components.

Although there are two principle pump types (dynamic and positive displacement), this manual focuses on dynamic pumps and the fundamentals of dynamic pump repair. The information it contains will be helpful to both novice and experienced pump repair technicians, to supervisors and managers of pump repair operations, and to customer service and sales personnel who communicate with customers about pump repair issues.

Section 2 covers repair concerns and techniques common to most pumps, while the following sections focus on specific pump types and the unique concerns associated with repairing them. These sections include submersible pumps, vertical turbine pumps, end suction pumps and split case pumps. Where appropriate, these sections may reference the general repair information in Section 2.

Table of Contents- (Download the complete Table of Contents)

1. Nomenclature
2. General Pump Repair Procedures
3. Submersible Pumps
4. Vertical Turbine Pumps
5. End Suction Radial Split Pumps
6. Axial Split-Case Pumps
7. Seals
8. Pump Reliability
9. Glossary and Standards Organizations

Tom Bishop, P.E., and Chuck Yung
EASA Senior Technical Support Specialists

The typical service center repairs at least 300 motors per technician annually. Saving 8 minutes (0.133 hours) per job equates to: 300 x 0.133 = 40 man-hours per year—a full week of labor per employee. It is not unrealistic to expect twice that much savings, just by implementing some of these timesaving tips.

We all know that seemingly small time savings can significantly improve the bottom line. For a service center with a 12% return on investment (ROI), shaving a few minutes off each job is the equivalent of adding 2 manmonths of billing per productive employee.

For a 10-man service center, with a shop rate of $75 per hour, 20 man-months times 75 = $258,000. To add a quarter-million dollar account usually means adding personnel, sales maintenance, and risk of bad debt/warranty expense. However, steps that streamline efficiency continue to pay dividends.

Topics covered include:

• Layout and workflow
• Time killers
• Time: Is every hour on the job billable?
• Time-saving equipment
• Attitude and productivity
• Communicating effectively
• Training
• Lighting
• Calibration
• Storage/handling/procurement
• Parts storage
• Examples from real service centers

Tim Browne
Industrial Electric Motor Service, Inc.

I suspect that just about everyone in our industry at one time or another has had the joy of repairing a “purpose-built” motor. This kind of motor is built for a specific purpose and has characteristics that may allow it to operate under non-standard conditions. Due to the limited information that some of them display on the nameplate, the repair of these motors can be somewhat of a challenge.

Sometimes these motors possess differences such as the color of paint, the shaft size, the bearing size, or type. It can be the operating temperature and at times it can be the motor in its entirety. Following are a few useful tips we use when repairing a motor with so many question marks.

John Allen
Sheppard Engineering

Clachan Hydro Power Station (HPS) went into service in 1956. Clachan HPS is located on Scotland’s west coast about 40 miles north of Glasgow. The underground power station is at the head of Loch Fyne sea loch. See Figure 1. The tailrace discharges into the Fyne River, a salmon fishing river. Loch Fyne has a renowned fishery and seafood restaurant within a mile.

The 900 ft (275 m) head vertical shaft Francis turbine driven 50 MVA, 40 MW 428.6 rpm 11 kV generator was designed by English Electric. The generator stator was recored and rewound in 1984 by Peebles Field Services (acquired by Dowding & Mills in 1998).

During the 1984 rewind, the original split core stator was rebuilt as a complete annulus. And the Class B winding was replaced by a resin rich Class F epoxy winding. The turns were insulated with Samicaflex insulation tape and the slot cell would typically have been an S5 mica tape; this is a 180g/m2 epoxy mica tape on a glass fabric. The dielectric stress for the slot cell (wall) insulation was very conservative at 41.9 v/mil (1,650 v/mm).

The rewind used 5 mm (0.197”) epoxy glass wedges with Nomex 410 packing and 4 mm (0.157”) phenolic glass coil separators. The punched slot width was 22.15 mm (0.872”) which would typically have resulted in a built slot width of 21.8 mm (0.858”) and the specified slot cell width was 21.1 mm (0.831”).

As part of Scottish & Southern Electric (SSE) program of power station refurbishment, Clachan HPS was refurbished in 2000. The program included refurbishment of the generator stator with an option to rewind if the partial discharge levels could not be improved. 

Dowding & Mills refurbished the generator stator, re-insulated the rotor and replaced the DC exciter with a brushless excitation system. They also replaced the complete station control systems together with all the low voltage (LV) and high voltage (HV) electrical installations.

Presented by Ashutosh Kumar
Karsten Moholt AS

Learn how a fellow EASA service center interpreted different maintenance philosophies and put their own development in that curve. Their evolution has gone from workshop to predictive maintenance and beyond–to proactive maintenance, including 3D scan/print and the Internet of Things (IoT)

This recording addresses how the modern toolbox has changed–from an adjustable spanner (wrench) to sophisticated sensors. IoT is just a new tool in the box.

Ian Culbert (deceased)
Iris Power-Qualitrol

Editor’s Note:  The following article was written by Ian Culbert, an engineer with Iris Power - Qualitrol in Mississauga, Ontario, Canada. It was submitted for publication by John Letal of Iris Power - Qualitrol and member of EASA’s Technical Services Committee. Sadly, Mr. Culbert passed away recently. We appreciate his contributions to the industry. 

Introduction
Due to their ever decreasing costs, variable frequency drives (VFDs) are becoming more popular for energy conservation and the reduction in inrush currents during motor starting. The most widely used type of drive today is a voltage-source, with pulse width modulated (VS-PWM) inverter, since it tends to be less expensive than other possible topologies.

In the past decade, medium and high voltage motors rated 2.4 kV to 13.8 kV fed by VS-PWM drives have become more common. Currently motors rated up to 100 MW are being designed. Motors supplied from such drives have seen premature stator winding failures since the voltage impulses from the drive can lead to rapid insulation system aging. In most cases, as the aging progresses, the partial discharge (PD) activity increases. Thus, there is a desire for on-line PD detection for such motors. 

Unfortunately measurements with conventional electrical PD detectors tend to be masked by 1000-3000 V impulses created by multi-stage VS-PWM drives. The rise time of the voltage impulses from the multi-stage VS-PWM drives tend to be 500 ns or longer. This article describes the technical issues in on-line PD detection on motors fed by VS-PWM drives, and gives an example of one system that detected the PD successfully.

This presentation covers:

• Brief overview of disassembly and evidence of failure
• Discussion of possible failure scenarios
• Review of actual repairs, modification and reassembly
• Update of machine's present operation

Bret McCormick
Stewart’s Electric Motor Works, Inc. 
 
The following is an example of how Stewart’s Electric Motor Works was able to provide valuable new service to an existing customer. I hope you can benefit from this case study.

One of our municipal customers was experiencing diminished flow rates and severe leaking from an ITT 600 hp, 1200 rpm split case pump. The pump was brought to our facility for evaluation.

We found its overall condi­tion to be in serious disrepair. The rust and scale from years of service had built up around the packing; the inside of the pump had rust blooms through­out. The shaft sleeves were worn out and the sealing glands were bent. One of the bearing journals was worn and the other had broken.

John Allen
Sheppard Engineering

La Central Hidroeléctrica de Clachan, comenzó a funcionar en 1956. Esta central subterránea se encuentra localizada en la costa oeste escocesa, a unas 40 millas del norte de Glasgow y en la cabecera del lago salado Loch Fyne. Ver Figura 1. El ducto de descarga vierte el agua dentro del rio Fyne, en el cual se pesca salmón. Loch Fyne cuenta en una milla con pesca reconocida y marisquerías de renombre.

La turbina Francis de eje vertical con salto de agua de 900 pies (275 m) que acciona un generador de 50 MVA, 40 MW 428.6 rpm 11 kV fue diseñada por English Electric. En 1984, el núcleo del estator fue reconstruido y el estator fue rebobinado por Peebles Field Services (adquirida en 1998 por Dowding & Mills).

Durante el rebobinado de 1984, el núcleo original fabricado en secciones, fue reconstruido totalmente en forma de anillo y el bobinado Clase B fue reemplazado por un bobinado epóxico resin-rich Clase F. Las espiras fueron aisladas con cinta Samicaflex y el aislamiento a tierra generalmente estaba fabricado con cinta de mica S5; esta es una cinta de mica de 180g/m2 sobre un tejido de fibra de vidrio. La rigidez dieléctrica del aislamiento a tierra (Pared de aislamiento) de 41.9 v/mil (1,650 v/mm) era muy conservadora.

Durante el rebobinado se utilizaron cuñas epóxicas de vidrio de 5 mm (0.197”) con un relleno de Nomex 410 y separadores de bobinas de vidrio fenólico de 4 mm (0.157”). El ancho de la ranura perforada era de 22.15 mm (0.872”), lo que normalmente habría dado lugar a un ancho de ranura construida de 21.8 mm (0.858”) y el ancho de la pared de aislamiento especificada era de 21.1 mm (0.831”).

Como parte del programa para el reacondicionamiento de centrales eléctricas de la Scottish & Southern Electric (SSE), La Central hidroeléctrica de Clachan fue reacondicionada en el año 2000. El programa incluía el reacondicionamiento del estator del generador con la opción de rebobinarlo, si no se podían mejorar los niveles de descargas parciales. 

Dowding & Mills reacondicionó el estator del generador, re-aislando el rotor y reemplazando la excitatriz de CC por un sistema de excitación sin escobillas. Ellos también cambiaron completamente los sistemas de control de la estación, conjuntamente con todas las instalaciones eléctricas de bajo y alto voltaje.

Larry Payne
Heights Armature Works, Inc.

Most of us have had to battle with the occasional two-pole vertical motor and survived. The following case study is a story not only of survival, but of success. The background A few years ago, our service center had a customer with six, two-pole 4000 VAC 900 hp solid-shaft vertical motors; there were four installed and two spares. They were direct on-line start atomizer motors driving gearboxes in a coalfied power plant and were installed in the bottom of inverted conical structures supported from the roof of the building. The installation suffered from high ambient temperatures and a very marginal support structure for a vertical machine. Before coming to us, the customer had battled with the motor installation problems for years. The original motors, plagued with high vibration and frequent bearing failures, were replaced with another manufacturer's design. Unfortunately, that was no help. Several service centers had rebuilt these motors, but none of them had complete information regarding the installation and the high failure rate. Even motors returned to the OEM repair centers were extremely unreliable. The shortest run time was twenty minutes for one motor repaired by the OEM. The longest run time was less than two months. Cost had become virtually a moot point for the customer. The customer correctly decided to send all motors to one service center and communicate everything that was known about the problems associated with these motors. We were selected, possibly because of our close proximity to the plant.

Other topics discussed are:

• Grease and bearings
• Bearing problems
• Disassembly and in-process
• Assembly and test run
• Keys to success

This book was developed to help electric motor technicians and engineers prevent repeated failures because the root cause of failure was never determined. There are numerous reasons for not pursuing the actual cause of failure including:

• A lack of time.
• Failure to understand the total cost.
• A lack of experience.
• A lack of useful facts needed to determine the root cause.

The purpose of this book is to address the lack of experience in identifying the root cause of motor failures. By using a proven methodology combined with extensive lists of known causes of failures, one can identify the actual cause of failure without being an “industry expert.” In fact, when properly used,  this material will polish one’s diagnostic skills that would qualify one as an industry expert.

The book is divided into the various components of an electric motor. In addition to a brief explanation of the function of each component and the stresses that act upon them, numerous examples of the most common causes of failure are also presented.

For this second edition, the manual has been reorganized and updated with new information including a new approach to methodology, new case studies and a new section covering synchronous machine failures. This could not have been done without many contributions from EASA members and the Technical Education Committee. 

The all new “Root Cause Methodology” section goes into great detail explaining that effective root cause failure analysis must take place within the context of a practical problem-solving methodology or framework. It covers a modified Plan-Do-Check-Act process that emphasizes the importance of planning and the related problem-solving methodology components. This section also explains A3, a high-level reporting tool that is very effective for problem solving.

In addition, besides a systematic approach to problem solving, root cause failure analysis of motors and motor systems requires familiarity with contributing factors attributable to various kinds of applications, environments and industries. This includes how various stresses can affect motor components and the reciprocal impact the motor system may have on the motor. This section includes a table with a detailed summary of motor stresses. 

There also is a new section on “Synchronous Machine Failures” and an expanded “Case Studies” section. Readers are guided through eight case studies.

With 328 pages, the book provides extensive information, including a wide range of failures, the likely causes listed, and the methodology for confirming the probable cause of each failure. 

Members may purchase a printed manual and/or a PDF download. The printed manual is in black and white, while the download shows most of the failure photos in color.  

Sections in the manual include:

• Root Cause Methodology (all new)
• Bearing Failures
• Stator Failures
• Shaft Failures
• Rotor Failures
• Mechanical Failures
• DC Motor Failures
• Synchronous Machine Failures (all new)
• Accessory Failures
• Case Studies (expanded)
• References

This book is available as part of EASA's Root Cause Failure Analysis seminar.

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Gene Vogel
EASA Pump & Vibration Specialist

Increasingly, it is not enough to just “fix” that pump. Customers want and need to understand the “why” behind the failure. This pump failure case study looks at:

• Failure methodology and how it was used
• The possible causes of failure
• The final analysis
• How the analysis impacted the repair approach

Steve Skenzick
HPS Electrical Apparatus Sales & Service

By this time we should all know that stator core loss testing is a required part of a quality rewind.  A core loss test before and after burn-off is speci­fied in the EASA Recommended Practice for the Repair of Rotating Electrical Ap­paratus (ANSI/EASA AR100-2010) and The Effect of Repair/Rewinding on Motor Efficiency; EASA/AEMT Rewind Study and Good Practice Guide to Maintain Mo­tor Efficiency. I would like to share some core loss testing experiences we have had over the years in our service center.

Bill Gray
Control Concepts, Inc.
Houston, Texas
Marketing & Industry Awareness 
Committee Board Coordinator

My business in Houston is now 25 years old. At this time I don’t have any family members involved in it. And so this question has been on my mind lately:  Should I try to recruit family members?  
I started my business in 1984 when my family and I were very young. Thinking back, I have no recollection of my expectations.  I guess I thought I could support my young family better if I worked for myself. I’m sure I was also motivated by ego. It sounds cool to be a business owner. It really sounds cool when you are 27 years old.