Rotating Machine Design

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Inone complete volume, this essential reference presents an in-depth overview of the theoretical principles and techniques of electrical machine design. This timely new edition offers up-to-date theory and guidelines for the design of electrical machines, taking into account recent advances in permanent magnet machines as well as synchronous reluctance machines.

Outlining a step-by-step sequence of machine design, this book enables electrical machine designers to design rotating electrical machines. With a thorough treatment of all existing and emerging technologies in the field, it is a useful manual for professionals working in the diagnosis of electrical machines and drives. A rigorous introduction to the theoretical principles and techniques makes the book invaluable to senior electrical engineering students, postgraduates, researchers and university lecturers involved in electrical drives technology and electromechanical energy conversion.

Responding to the need for an up-to-date reference on electrical machine design, this book includes exercises with methods for tackling, and solutions to, real design problems. A supplementary website hosts two machine design examples created with MATHCAD: rotor surface magnet permanent magnet machine and squirrel cage induction machine calculations. Classroom tested material and numerous graphs are features that further make this book an excellent manual and reference to the topic.

Tapani Jokinen is a Professor Emeritus in the Department of Electrical Engineering at Helsinki University of Technology, Finland. His principal research interests are in AC machines, creative problem solving and product development processes. He has worked as an electrical machine design engineer with Oy Strmberg Ab Works. He has been a consultant for several companies, a member of the Board of High Speed Tech Ltd and Neorem Magnets Oy, and a member of the Supreme Administrative Court in cases on patents. His research projects include, among others, the development of superconducting and large permanent magnet motors for ship propulsion, the development of high-speed electric motors and active magnetic bearings, and the development of finite element analysis tools for solving electrical machine problems.

Valeria Hrabovcova is a Professor of Electrical Machines in the Department of Power Electrical Systems, Faculty of Electrical Engineering, at the University of ˇ Zilina, Slovak Republic. Her professional and research interests cover all kinds of electrical machines, electronically commutated electrical machines included. She has worked on many research and development projects and has written numerous scientific publications in the field of electrical engineering. Her work also includes various pedagogical activities, and she has participated in many international educational projects.

To achieve this, we will review the general concepts of force, stress, motion, and failure analysis first, followed by topics in the design of specific machine elements. There will be a decent amount of problem solving by hand calculations, followed by design of a mechanical system as a group project through hand and computer-assisted calculations.

Process technology involves a wide gamut of tasks comprising reactions, heat transfer, phase separation etc. The industry relies on a variety of equipment and components to carry out these processes. The design, optimization and modeling of these equipment is implemented with the help of simulation and design software. Such software helps design, visualize and simulate the products digitally. Generally there are three main types of equipment:

There are best practices and international codes governing the design of static equipment and rotating equipment. Some of the equipment have challenging parameters for design and tough testing and validation criteria. Software combined with engineering expertise is the key to quality, performance, accuracy and reduction in time to market and development cost.

The equipment design and modeling of static equipment the process needs to take into account the various fluids, their temperature, pressure and composition. It involves design of experiments, finite element analysis, Computational fluid dynamics and thermal concepts to optimize weight, cost and cycle times.

Rotating Equipment typically includes equipment like gas turbines, steam turbines, and other expanders; turbo-pumps and compressors, fans; motors, and centrifuges. These equipment are distinguished by the rotating motion caused by impellers or rotors. However, Rotary Equipment Design engineering has many challenges.

Rishabh Engineering has years of experience in Equipment Engineering in the Oil and Gas sector. We also follow international best practice and are conversant with the major codes and standards such as ASME Section VIII, API & TEMA.

Carefully define application requirements before choosing a replacement motor, or one for a new design: An undersized motor exhibits electrical stresses and premature failure. An overly powerful motor (with high locked-rotor and breakdown torques, for example) can damage the equipment it drives, and runs at less than full rated load, which is inefficient.

NEMA classifies general-purpose three-phase motors as A, B, C, or D according to their electrical design. For example, NEMA Design C motors have higher starting torque with normal start current and less than 5% slip.

In these devices, pulse-width modulation (PWM) is used to vary motor voltage. In turn, solid-state switches such as insulated gate bipolar transistors (IGBTs) or gate turn off SCRs (GTOs) execute PWM. Here, AC line voltage is converted to DC and then reshaped so that motor speed varies with the frequency of the pulses in the output voltage. PWM AC drives allow wide speed ranges, programmable acceleration and deceleration ramps, and good energy efficiency; speed and torque precision can in some cases match that of DC systems.

Even under sophisticated VFD control, AC induction motors exhibit inherent efficiency limitations and can require an encoder for feedback if low-speed accuracy is required. In addition, retrofitting an existing design with a new VFD can be troublesome, particularly when equipped with older motors.

In fact, the waste heat generated by any AC motor is capable of degrading the insulation so essential to motor operation. Stator insulation prevents short circuits, winding burnout, and failure: Magnet wire coating insulates wires within a coil from each other; slot cell and phase insulation (composite sheets installed in stator slots) shield phase-to-ground; stator varnish dip boosts moisture resistance and overall insulation.

Another consideration is cycling: Motors built for frequent reversals can withstand it, but start-stop cycles in others can cause overheating, because a typical motor under these conditions draws five to six times the rated running current, which accelerates heating. NEMA limits three-phase continuous-duty induction motors to two starts in succession before allowing the motor to stabilize to its maximum continuous operating temperature.

Finally, the VFDs commonly used to drive three-phase AC induction motors are sensitive to inertia, horsepower, motor lead length, and power quality, so must be programmed with full-load and no-load amps, base speed and frequency, and motor voltage when initially connected to a new motor. Typically VFDs also require tuning, during which motor response and electrical characteristics are logged.

One proliferating option, permanent magnet ac (PMAC) motors, has functionalities that partially overlap with those of both ac induction and servomotors for larger, higher-end applications requiring precisely metered torque, speed, or positioning.

In PMACs, magnets mounted on or embedded in the rotor couple with the motor's current-induced, internal magnetic fields generated by electrical input to the stator. More specifically, the rotor itself contains permanent magnets, which are either surface-mounted to the rotor lamination stack or embedded within the rotor laminations. As in common ac induction motors, electrical power is supplied through the stator windings.

Permanent-magnet fields are, by definition, constant and not subject to failure, except in extreme cases of magnet abuse and demagnetization by overheating. PMAC, PM synchronous, and brushless ac are synonymous terms.

PMAC-compatible drives (known as PM drives) substitute the more traditional trapezoidal waveform's flat tops with a sinusoidal waveform that matches PMAC back EMF more closely, so torque output is smoother. Each commutation of phases must overlap, selectively firing more than one pair of power-switching devices at a time. These motor-drive setups can be operated as open-loop systems in midrange performance applications requiring speed and torque control. Here, PMAC motors are placed under vector-type control.

Most manufacturers of synchronous motors hold pole count constant so input frequency dictates the motor's speed. For example, for a 48-frame motor with six poles, the motor's input frequency from the drive must be 90 Hz to obtain 1,800 rpm. To extract the same speed from a 10-pole 180-frame motor, input frequency must be 150 Hz. To calculate required input frequency (Hz) when the number of poles and speed are known:

PMAC motors are suitable for variable or constant-torque applications, where the drive and application parameters dictate to the motor how much torque to produce at any given speed. This flexibility also makes PMACs suitable for variable-speed operation requiring ultra-high motor efficiency.

In addition, PMAC motor control requires some technical knowledge for implementation: All commercially available PMAC motors require a PM-compatible drive to operate, although there is ongoing research in the development of a line-start PMAC motor.

Finally, high current or operating temperatures can cause the magnets in PMAC motors to lose their magnetic properties. Permanent magnets, once demagnetized, cannot recover, even if current or temperature returns to normal levels. PM drives reduce the risk of high-current demagnetization with over-current protection. Some motor designs further minimize the possibility of demagnetization with high-temperature magnets, integrated thermostats, and restricted motor operating temperature.

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