E. Wiedenbrug, Consulting Engineer, SKF USA, and M...
Keep your motor-testing options open
This paper presents current methods of electrical test and trend analysis of the operational health of electric motors in the context of successful predictive maintenance programs.
Reducing servomotor instability
Instability in a motor is uncontrolled and unintended motion at the motor shaft and can occur at any frequency. It's caused by excessive gain in the speed controller of the drive, and the gain setting of the speed controller determines how much torque the drive will generate. As servo drives become more prevalent in industry, they are being applied in a wider range of applications. Servo motors sometimes make a "growling" noise, which can be eliminated by reducing the gain on the speed controller, but lower speed controller gains can lead to an increase in position error and a decrease in performance. This paper looks at the methods that can be used to eliminate servo instability.
Advances in low-voltage motor control center (MCC) technology help reduce arc flash hazards and minimize risks
Measures to increase equipment and personnel safety in manufacturing are reflected in new approaches and technologies designed to help minimize the risk of workplace dangers. One rapidly growing area of focus is reducing the potentially serious hazards associated with arc flash events. This white paper examines the causes of arc flash, discusses the standards guiding arc flash safety and details the role arc-resistant motor control centers (MCCs) play in helping contain arc energy. It also highlights the key features of an effective arc-resistant MCC design.
Motor efficiency and fault zone analysis
Given the sometimes frenzied movement in the effort to go green, maintenance management may overlook the fact that maintaining reliability can pay dividends towards efficiency while improving the bottom line.
Intelligent motor control centers lay the foundation for improvements in manufacturing efficiency and reliability
Measures to increase equipment and personnel safety in manufacturing are reflected in new approaches and technologies designed to help minimize the risk of workplace dangers. One rapidly growing area of focus is reducing the potentially serious hazards associated with arc-flash events. This white paper examines the causes of arc flash, discusses the standards guiding arc-flash safety and details the role arc-resistant motor control centers (MCCs) play in helping contain arc energy. It also highlights the key features of an effective arc-resistant MCC design.
Managing safety hazards and reducing risks are top priorities for manufacturers across all sectors of industry. With a multitude of potential dangers and new ones continuously emerging, companies must be diligent in their ongoing efforts while considering new approaches and technologies to improve plant safety. One rapidly growing area of focus is implementing techniques and practices designed to reduce hazards and minimize risk for workers who must enter an area with an electrical arc-flash potential.
Today's machine designer must evaluate more factors than ever in approaching a new project. Likewise, the integrator and retrofit engineer has expanded options, not only as a result of new technologies, but also because of critical areas of focus such as reduced energy consumption, faster assembly time, vendor reduction and smaller footprint achievement.
In the realm of motion control, one type of motor with a relatively short history has made significant advancements that necessitate a new look at its potential in many application areas. These applications range from machine tool rotary tables to various packaging, printing, converting, extruding, papermaking, plastic film and materials handling machinery, anywhere direction must be reversed with a very high degree of accuracy, no backlash (hysteresis) and the maintaining of motion control, contrasting the necessary decoupling of a conventional motor and gearbox.
Enter the often-overlooked permanent magnet, synchronous torque motor. Torque motors are direct drives built for rotary axes where high torque and high precision are required at relatively low speeds. With significantly lower installation time, maintenance requirements, component part count and space allowance, these motor types are frequently viable alternatives to geared motors.
Rapidly increasing energy cost and strong global interest in reducing carbon dioxide emissions are encouraging industry to pay more attention to high-efficiency motors.
Permanent Magnet (PM) motors have higher efficiency than induction motors because there are no I2R losses of the rotor. But widespread use of the PM motors has been discouraged by price and requirement of a speed encoder.
Recent release of low-cost high-performance CPUs and establishment of the speed sensorless control theory (hereinafter referred to as an open-loop vector control method) enables the advent of a general-purpose open-loop control PM drive. In this white paper, the open-loop PM motor control technology is introduced and its characteristics and major application fields are described.
High slip braking software
The techniques for braking of high inertial loads to a stop traditionally involved either Dynamic Braking or DC Injection Braking technology.
This article examines a new load-braking alternative called High-Slip Braking (HSB). We identify the different aspects of HSB, look at what it does, how it works, and how it is different from other braking methods. We also provide examples of "real-world" successes, and discuss the new technology's cost effectiveness.
Evaluation of an alternate soft charge circuit for diode front end variable frequency drives
Variable Frequency Drives (VFDs) with diode rectifier front end are typically equipped with a resistorcontactor arrangement to limit the inrush current into the dc bus capacitors, thereby providing a means for soft charging the dc bus capacitors. Because of the mechanical nature of the magnetic contactor typically used in VFDs, there exists a concern for fatigue. In addition, during a brown out condition, typically the contactor remains closed and when the voltage recovers, the ensuing transient is often large enough to possibly cause unfavorable influence to surrounding components in the VFD. Many researchers and application engineers have thought about this issue and many are actively seeking non-mechanical solutions in a cost effective manner.
In this paper, a new topology to soft charge the dc bus capacitor is proposed. Other techniques that have been evaluated are also introduced. The relative advantages and disadvantages are discussed. Experimental tests to show the feasibility of the proposed idea is also provided.
Mahesh Swamy, Tsuneo J. Kume and Noriyuki Takada
A hybrid 18-pulse rectification scheme for diode front end variable frequency drives
Diode rectifier with large DC bus capacitors, used in the front ends of variable frequency drives (VFDs), draw discontinuous current from the power system resulting in current distortion and hence voltage distortion. Typically, the power system can handle current distortion without showing signs of voltage distortion. However, when the majority of the load on a distribution feeder is made up of VFDs, current distortion becomes an important issue. Multi-pulse techniques to reduce input harmonics are popular because they do not interfere with the existing power system either from higher conducted EMI when active techniques are used or from possible resonance, when capacitor based filters are employed.
In this paper, a new 18-pulse topology is proposed that has two six-pulse rectifiers powered via a phase-shifting isolation transformer, while the third six-pulse rectifier is fed directly from the AC source via a matching-impedance. This idea relies on harmonic current cancellation strategy rather than the flux cancellation method and results in lower overall harmonics. It is also seen to be smaller in size and weight, and lower in cost compared to an isolation transformer. Experimental results are given to validate the concept.
Mahesh Swamy, Tsuneo J. Kume and Noriyuki Takada
Passive techniques for reducing input current harmonics
Events over the last several years have focused attention on certain types of loads on the electrical system that result in power quality problems for the user and utility alike. Equipment which has become common place in most facilities including computer power supplies, solid state lighting ballast, adjustable speed drives (ASDs), and uninterruptible power supplies (UPSs) are examples of non-linear loads. Adjustable speed drives are also known as variable frequency drives (VFDs) and are used extensively in the HVAC systems and in numerous industrial applications to control the speed and torque of electric motors. The number of VFDs and their power rating has increased significantly in the past decade. Hence, their contribution to the total electrical load of a power system is significant and cannot be neglected.
The case for regenerative AC drive motors
During the operation of any converting machine, whether for film, foil, wire, paper or board, plus most large printing presses, rolls of materials are handled by unwinds, often still driven by pneumatically operated braking systems. The traditional tension control system for an unwind stand is a simple mechanical brake. In principal, the unwind brake mechanically operates much like the braking system on your car, with a disk, caliper and pads, but is controlled by a tension sensor linked to a set point controller. As the roll unwinds, the tension is maintained by the brake for smooth passage of the material through the dies or rollers, resulting in better package alignment, less wrinkling, better print registration, even more consistent wire dimensioning and other production positives. These mechanical brake unwinds are effective in controlling the tension, but have inherent problems of heat and power loss, plus mechanical wear and constant maintenance needs, substantially impacting machine uptime.