Motors & Drives Information

An updated version of Baldor's interactive electronic motors and drives catalogue has been published.
An updated version of Baldor's interactive electronic motors and drives catalogue has been published. With the new Version 8 CD-ROM, users are able to instantly access comprehensive technical information on over 6500 motor and drive products. Product information includes performance and test data, DXF and PDF format dimension drawings, nameplate data, replacement parts and installation and operating manuals.

An interactive search function allows users to find motors and drives with only limited information.

The CD-Rom additionally includes a useful energy savings analysis program for PCs or Palm Pilots that calculates an existing motor's annual electricity usage based on its nominal efficiency, and contrasts it with the annual usage of a 'standard efficiency' or 'premium efficiency' alternatives.

Baldor Europe has released a new 36-page catalogue overviewing its industrial motors and drives service - supported by large and comprehensive local stockholdings.
Baldor Europe has released a new 36-page catalogue overviewing its industrial motors and drives service - supported by large and comprehensive local stockholdings. Free on request, the catalogue details hundreds of DC and AC motors, drives and spares - with many small to medium power ratings available for immediate delivery - providing a valuable resource for automation builders and maintainers alike. The selection is exceptionally broad, and includes permanent-magnet and shunt-wound DC motors, as well as AC motors.

The catalogue details both IEC frame sizes and Baldor's exceptionally broad range of NEMA motors (including large-frame options up to 1120kW/1500hp), helping companies who build for international markets or maintain equipment manufactured overseas.

The catalogue goes on to cover AC and DC drives, gearboxes and inverter-duty gearmotors, tachometer options, and washdown-duty motors for clean processing environments.

It concludes with reference material on IEC and NEMA sizes, and imperial/metric conversions.

PML is exhibiting an exciting new range of electric motors and drives at Drives and Controls.
PML is exhibiting an exciting new range of electric motors and drives at Drives and Controls on stand D132, Hall 9. On show will be the world's first truly brushless 'pancake' flat motors, a new intelligent servo drive and electric vehicle wheel motors. PML's joysticks will also be on show.

Slimline and compact, PML's new brushless pancake motors are ideal for applications where precise speed control, space saving designs and a long maintenance free life are essential.

They feature PML's novel printed stator technology for extremely smooth cogging free torque.

The main advantages over brushed motors are faster running speeds and an extended life due to the lack of brushes.

The range comes in four sizes, from 6 to 16cm diameter.

The new PMC 90 intelligent servo drive can operate brushless (AC) or brushed (DC) motors from a single, cost-efficient package.

Brushless motors are controlled automatically when hall sensors are connected.

The unit's 40kHz PWM switching frequency is double that of most conventional drives and enables direct connection to the low-inductance printed stator motors with no external choke.

A high-speed RS485 connection allows up to 31 drives to be linked to a central controller.

Built in safety features include short circuit protection, over travel limit switch inputs, emergency stop input, over and under voltage shutdown.

The new electric wheelmotors are ideal for electric vehicles, low-speed heavy vehicle movement, high-speed materials handling, elevators, reeling/winding and direct drive turntables.

Developing high torque at low controlled speeds, these robust, compact motors save on battery power by being extremely energy efficient.

Standard flange fittings accommodate different wheel rim sizes, and the heavy-duty tapered roller bearings can withstanding heavy radial loads.

Five sizes are available.

PML first made its name in flat servomotors for those applications with confined spaces.

From high specification motors in defence and aerospace industries, to affordable high quality versions in processing and printing industries, the list of applications also extends to instrumentation, medical and general industry areas.

If you use hazardous area motors with drives, there are a few things you need to think about: but with a motor and drive from ABB, they have already worked out the details for you
If you use hazardous area motors with drives, there are a few things you need to think about. However, if you get the motor and the drive from ABB, there is no need for further action - we have already worked out the details for you. ABB has blanket certification for motor and drive combinations for hazardous areas.

This means that no further testing is required once on site.

But if you match your own drive and motor combination, it may need to be independently tested by a notified body.

Variable speed operation gives higher temperature rise and higher voltage stress on the motor insulation, in combination with reduced cooling in self-cooled motors.

These factors combined could create a heat source powerful enough to ignite an explosion.

At ABB, we have designed our motors for use with variable speed drives for the last 30 years.

We have the experience to guarantee safe operation in hazardous areas - and we have the certificates to prove it.

If you want more information about using motors in hazardous areas with variable speed drives, order your FREE information leaflet.

Matched pairs of ABB high efficiency motors and drives will reduce energy consumption at the new Coventry Hospital by over 1400MWh per year for the ventilation system in block A.
Matched pairs of ABB high efficiency motors and drives will reduce energy consumption at the new Coventry Hospital by over 1400MWh per year for the ventilation system in block A, when it comes fully into service in 2006. Similar savings are expected for the planned blocks B and C. Ranging in size from 0.55 to 45kW, the 230 drives and motors packages are being supplied on a just-in-time basis by ABB, being produced and delivered to meet the installation time table of Air Handling Systems, supplier of the ventilation system.

Wes Campbell, Senior Project Manager for Air handling systems says: "We chose ABB because we have worked with them before.

We know we can trust their products to arrive on time and to operate reliably".

"Buying a combined motor and drive package makes sense because the two products are exactly matched to each other, giving the most efficient power consumption, and if there is a problem in any part of the system, ABB has full responsibility and we know where to go to get things put right".

Using variable speed drives to control the flow of air and water in the HVAC system can save well over 50% of the energy, compared to using traditional control methods such as throttling valves and vanes.

On a large site like Coventry Hospital, this can have a significant impact on running costs.

The GBP 150,000 contract is one of a number of recent large projects for ABB's sales organisation for dedicated HVAC drives, which was set up 18 months ago.

In addition, ABB is also delivering low voltage switchgear to the hospital.

The just-in-time production posed no problems for ABB.

"We are used to products being called off in this way for major projects", says Nick Thorne, Sales Manager, HVAC.

Although some of the equipment is already installed, the majority of the drives will be installed once the hospital is more complete.

The drives will be mounted on the side of the air-handling units and are enclosed to IP54.

ABB will commission all the drives to make sure they are optimised for the applications and that the energy optimisation programme contained in the direct torque control is activated.

Support for the drives is also vital.

Says Campbell: "With such a critical application as a hospital, we need fast service if things go wrong".

Local warranty support and after sales service will be provided by Sentridge, ABB's local Drives Alliance Partner located in Coventry, offering a 24-hour service.

The hospital is being built under the Private Finance Initiative (PFI) by a consortium led by Skanska, Europe's second largest construction company.

The consortium will build the new acute hospital, a new mental health facility, a new clinical sciences building and a number of other ancillary buildings, as well as keep those buildings fully serviced and maintained to agreed standards for 35 years from the end of the construction period.

Aiming to save downtime costs of up to GBP 10,000 per hour, Imerys Minerals in Cornwall has entered an agreement with ABB to supply motors and drives to its UK plants.
Aiming to save downtime costs of up to GBP 10,000 per hour, Imerys Minerals in Cornwall has entered an agreement with ABB to supply motors and drives to its UK plants. Extraction and processing is a 24/7 continuous process, using high-pressure water systems in the quarries. Imerys is the largest user of motors in the South West, employing more than 5000 motors and over 27MW of installed power driving pumps and handling systems for the extraction of 2Mt of china clay per annum.

The company makes extensive use of condition monitoring and failure mode analysis as any motor failure can lead to extended downtime.

Quality and delivery problems from their previous suppliers prompted Imerys to look for a new supplier of motors and drives.

The company carried out its own exhaustive tests to satisfy itself that the prospective vendors could meet its demanding requirements.

ABB motors and drives were ultimately selected on the basis of mechanical build quality, reliability and low running costs due to high energy efficiencies.

Dave Constance, Electrical Manager for Imerys, says: "In our experience of running motors we have never come across a motor as reliable as these from ABB".

"They are well designed for the harsh environment we work in, with better protection against ingress of dust and water and improved cooling".

"The drives work well in the wet and harsh environment found in our quarries and are well protected against ingress of water or slurry, which could otherwise cause expensive damage and downtime.

"We didn't take what we were told at face value".

"We examined motors and drives from a number of manufacturers and conducted compatibility tests to see if they were suitable for our environment".

"We stripped the motors down to look at how easy they were to maintain and how this would affect the running costs".

"Efficiency tests were also an important part of our investigation".

"For all criteria, ABB came out on top".

"We were particularly impressed with the company's technical support, which was excellent, as was the order processing".

"We have had no problems at all".

The five-year agreement covers the supply of ABB's process performance motors and industrial drives.

The motors, designed originally for the pulp and paper industry, have an IP56 rating, making them particularly suitable for the constant wet and abrasive conditions of the quarry.

Imerys expects to spend between GBP 200,000 and GBP 300,000 a year on motors and GBP 150,000 on drives.

Lifetime cost of ownership is important to Imerys and so getting maximum time between maintenance sessions was vital.

The company made suggestions to improve the sealing on a motor bearing to reduce its maintenance needs and ABB altered the design of a casting to accommodate this as part of its policy of continuous improvement based upon customer feedback.

"We were impressed with the access we had to ABB's design team".

"Overall ABB has delivered as quoted and with the quality we need", Constance concludes.

Contrary to what many believe, OEM (Original Equipment Manufacturer) motorcycle parts are not inherently better than aftermarket motorcycle parts. Like any product in a dynamic marketplace, aftermarket motorcycle parts manufacturers often find a way to improve upon the performance or the look of the part. A comparison of the two types of parts is often contrary to what many people assume.

OEM Motorcycle Parts:

An OEM part is part made by the same company that made the part for the original vehicle. Oftentimes, auto and motorcycle manufacturers don’t make the parts themselves, but contract the job to a manufacturing company. A comparison of the two different types of parts shows the strengths and weaknesses of each.

Aftermarket Motorcycle Parts:

The manufactures of aftermarket motorcycle parts must apply for the rights to reproduce a part. Aftermarket motorcycle parts manufactures operate under strict guidelines and by nature of their profession must be absolutely precise in their design.

Good aftermarket motorcycle parts often can’t be distinguished from the original. Additionally, manufacturers of aftermarket motorcycle parts have the flexibility to improve upon the design and the quality. Normally, aftermarket motorcycle parts are sold for much less than OEM parts. The possible downside to using aftermarket parts is, that if installed by a non-certified technician, could impact the warranty.

Finding Quality Aftermarket Motorcycle Parts:

Different company’s aftermarket motorcycle parts will differ in look and quality. Your best bet is to find a highly reputable aftermarket motorcycle parts dealer who is in the know about all of the latest parts and manufacturers and who only offers the best quality after market motorcycle parts.

Who Uses Aftermarket Motorcycle Parts:

Those who build custom motorcycles use aftermarket parts to build bikes with fresh new designs and unique looks. Those with older model bikes often choose aftermarket motorcycle parts because parts for older models have often greatly improved since the original part was manufactured.

Insurance companies almost consistently choose identical aftermarket motorcycle parts to replace damaged bikes after an accident. When the price is cheaper and the quality is as good, if not better than the original, it makes sense to use aftermarket motorcycle parts.

Custom Aftermarket Motorcycle Parts:

Aftermarket motorcycle parts are essential for customized bikes. Aftermarket parts like wheels, tires, handlebars, frames, foot pegs, mirrors, etc. offer a great number of options in terms of customization. The wide variety of aftermarket motorcycle parts available today makes it easy to create an original looking bike.

There are lots of after market motorcycle parts to make fixing or customizing your bike inexpensive and simple. Before forking out too much cash on a comparable part, take stock of your aftermarket options.

Any decent motorcycle racer or extreme hobbyist will tell you that the natural laws of physics do indeed matter. Whether you ride for fun, challenge or even race there is no doubt in your mind that the laws of gravity, acceleration, centripetal force and kinetic energy are very real.

In fact they can be your best friend or worst nightmare depending on how you chose to use them and there are plenty of broken bones and road rash scars to prove it out there. In Motorcycle racing you can feel yourself pulling from the turn due to centripetal force when you let off the throttle. So you get onto the brakes before coming into the turn and then feed the throttle thru it, while counter steering.

You can take a system of a combination of natural laws and change it around to fit your need for control; same with anything. Whether you are flying, sailing or skiing. Consider wind turbulence in an aircraft while flying straight and level. Your perfect system encounters an outside force, wind shear or other wake turbulence.

You were doing perfectly fine, aircraft trimmed up, nothing to do, but look outside, suddenly secondary forces. But provided every thing is correct no controls will put the aircraft into another stable system upon the disappearance of the secondary force. Or if it is strong it could turn you upside down into chaos if you are too close to the ground. You lose. Chaos wins.

There is no difference in motorcycle racing you set up for your turn correctly and prepare to adjust if anything changes or some squid loses the front end ahead of you sliding off the track. Either you adapt or end up eating pavement. Hey you decide, but do not ever believe you are above the natural laws of physics out there. Consider this in 2006.

If you are an auto detailer who specializes in detailing older cycles such as Harley Davidson's then perhaps you might like to detail than at trade shows. This can be an incredible marketing opportunity for your company and it also pays very well.

Other people in the industry and region will see you if you wear company shirts with your name and phone number on them. Also it pays to have some business cards for each motorcycle detailing person on your crew.

Motorcycle manufacturers and aftermarket accessory part makers need and desire motorcycle detailing services at trade shows and they are willing to pay top dollar. Often they pay in cash and how can you beat that? What does it take to get such accounts?

Well, you may be surprised actually, as it is very easy to score such bonus type accounts. If you live in a city that has tradeshow activities is important to watch which groups are coming out in the future for trade shows. Then you need to go to the industry association web sites promoting the show and make sure you somehow get on the vendors list or go through the vendors list of all the people who will be at the tradeshow in contact them directly and let them know you are in the local area and ready to serve.

It is best to contact the marketing department of the motorcycle manufacturer or aftermarket accessory company and pitch them the ability that you have to keep everything clean even though the ventilation system will be pushing dust all over their equipment. If they know they can count on you that you become part of their team.

There are many additional benefits and bonuses to working with motorcycle manufacturers and aftermarket accessory part makers at trade shows. For instance the food is excellent and the parties are even better. Please consider this in 2006.

Adjustable Speed Drives are used in any application in which there is mechanical equipment powered by motors; the drives provide extremely precise electrical motor control, so that motor speeds can be ramped up and down, and maintained, at speeds required; doing so utilizes only the energy required, rather than having a motor run at constant (fixed) speed and utilizing an excess of energy.

Since motors consume a majority of the energy produced, the control of motors, based on demands of loads, increases in importance, as energy supplies become ever more strained. Additionally, end users of motors can realize 25 - 70% energy savings via use of motor controllers. (Despite these benefits, the majority of motors continue to be operated without drives.)

Here are 10 additional benefits users realize when operating motors with drives:

1. Controlled Starting Current -- When an AC motor is started "across the line," it takes as much as seven-to-eight times the motor full-load current to start the motor and load. This current flexes the motor windings and generates heat, which will, over time, reduce the longevity of the motor. An Adjustable Speed AC Drive starts a motor at zero frequency and voltage. As the frequency and voltage "build," it "magnetizes" the motor windings, which typically takes 50-70% of the motor full-load current. Additional current above this level is dependent upon the connected load, the acceleration rate and the speed being accelerated, too. The substantially reduced starting current extends the life of the AC motor, when compared to starting across the line. The customer payback is less wear and tear on the motor (motor rewinds), and extended motor life.

2. Reduced Power Line Disturbances -- Starting an AC motor across the line, and the subsequent demand for seven-to-eight times the motor full-load current, places an enormous drain on the power distribution system connected to the motor. Typically, the supply voltage sags, with the amplitude of the sag being dependent on the size of the motor and the capacity of the distribution system. These voltage sags can cause sensitive equipment connected on the same distribution system to trip offline due to the low voltage. Items such as computers, sensors, proximity switches, and contactors are voltage sensitive and, when subjected to a large AC motor line started nearby, can drop out. Using an Adjustable Speed AC Drive eliminates this voltage sag, since the motor is started at zero voltage and ramped up.

3. Lower Power Demand on Start -- If power is proportional to current-times-voltage, then power needed to start an AC motor across the line is significantly higher than with an Adjustable Speed AC Drive. This is true only at start, since the power to run the motor at load would be equal regardless if it were fixed speed or variable speed. The issue is that some distribution systems are at their limit, and demand factors are placed on industrial customers, which charges them for surges in power that could rob other customers or tax the distribution system during peak periods. These demand factors would not be an issue with an Adjustable Speed AC Drive.

4. Controlled Acceleration -- An Adjustable Speed AC Drive starts at zero speed and accelerates smoothly on a customer-adjustable ramp. On the other hand, an AC motor started across the line is a tremendous mechanical shock both for the motor and connected load. This shock will, over time, increase the wear and tear on the connected load, as well as the AC motor. Some applications, such as bottling lines, cannot be started with motors across the line (with product on the bottling line), but must be started empty to prevent breakage.

5. Adjustable Operating Speed -- Use of an Adjustable Speed AC Drive enables optimizing of a process, making changes in a process, allows starting at reduced speed, and allows remote adjustment of speed by programmable controller or process controller.

6. Adjustable Torque Limit -- Use of an Adjustable Speed AC Drive can protect machinery from damage, and protect the process or product (because the amount of torque being applied by the motor to the load can be controlled accurately). An example would be a machine jam. With an AC motor connected, the motor will continue to try to rotate until the motor's overload device opens (due to the excessive current being drawn as a result of the heavy load). An Adjustable Speed AC Drive, on the other hand, can be set to limit the amount of torque so the AC motor never exceeds this limit.

7. Controlled Stopping -- Just as important as controlled acceleration, controlled stopping can be important to reduce mechanical wear and tear -- due to shocks to the process or loss of product due to breakage.

8. Energy Savings -- Centrifugal fan and pump loads operated with an Adjustable Speed AC Drive reduces energy consumption. Centrifugal fans and pumps follow a variable torque load profile, which has horsepower proportional to the cube of speed and torque varying proportional to the square of speed. As such, if the speed of the fan is cut in half, the horsepower needed to run the fan at load is cut by a factor of eight (1/2)³ = 1/8. Using a fixed speed motor would require some type of mechanical throttling device, such as a vane or damper; but the fact remains that the motor would still be running full load and full speed (full power). Energy savings can be sufficient to pay back the capitalized cost in a matter of a couple of years (or less), depending on the size of the motor.

9. Reverse Operation -- Using an Adjustable Speed AC Drive eliminates the need for a reversing starter, since the output phases to the motor can be electronically changed without any mechanical devices. The elimination of a reversing starter eliminates its maintenance cost and reduces panel space.

10. Elimination of Mechanical Drive Components -- Using an Adjustable Speed AC Drive can eliminate the need for expensive mechanical drive components such as gearboxes. Because the AC Drive can operate with an infinite variable speed, it can deliver the low- or high-speed required by the load, without a speed-increasing or reduction devices between the motor and load. This eliminates maintenance costs, as well as reducing floor-space requirements.

Figure 1. Drive configuration with:

a) conventional induction motor drive, gearbox and jackshaft

b) DriveIT Direct Drive Solution

Over the past several years, the networking of drives has gone through several phases of evolution. Today, web-enabled Ethernet communications represents the latest, and most powerful, of all of these phases. The level of control and the amount of information available are significantly improved over earlier methods. Most importantly, with web-enabled Ethernet, the ease of both getting information and displaying it is on an entirely new level than was possible with older technologies

To help in understanding the power of this new development, the earlier phases could be broken down as follows:

Phase One - Network connection to an intelligent device.

The intelligent device (such as a PLC or a Building Automation System) would talk to the network, and then it would "communicate" with the drive via traditional dry contacts and proportional signals (4-20mA, 0-5VDC, 0-10VDC). In basic systems, the system only told the drive what to do, as if it were a mechanical actuator like the damper controls and valves that the drive replaced. In more sophisticated systems, the drive would feed back some information, such as dry contact closures for drive status (i.e.: power status, run status, fault status) or proportional signals (i.e.: for speed confirmation, motor amperage, or motor kW)

Phase Two - Network connection to the drive - one way communications.

The drive is directly connected to a serial network such as Modbus, FIPIO, N2, etc. and is used for control only. The network simply tells the drive to turn on or off and how fast it should go when it is on.

Phase Three - Network connection to the drive - two-way communications.

The drive does all of the control described above. The link is also used for monitoring the status of the drive or for reading data (i.e.: fault logs, variable states) to aid in troubleshooting the drive in the event of a fault. Sometimes this link is used to re-program or tune the drive.

All of these phases require special software, special network knowledge, and special wiring for the network involved. For example, the wiring, junctions, and terminations of Modbus are quite different from that of ControlNet. Technicians that support such equipment must be trained in all of these areas.

In addition to the issues above, any computer that is going to use or display this information must be specially configured for the software and network connection. Anyone using the software will need specific training on how to use it. In order to create a graphical display even more technical software is required.

The next step in the network evolution is to make all this detail transparent to the typical user. That is what web-enabled Ethernet is all about.

There are many advantages to using Ethernet. The simplicity of the "Ethernet" part of this concept, the network, is the first benefit. Each of the standard industrial control networks has it's own wiring and addressing peculiarities that require training. Any implementation issues associated with Ethernet are all well understood by the IT department of any company or facility. There have been many debates about the relative levels of determinism between older industrial control networks and Ethernet, but it is fairly well understood today that this is a function of how an Ethernet network is switched and not of the network itself.

The second advantage to this approach revolves around the "web-enabled" part of the concept and is even more significant. Pure data by itself is not meaningful if it is simply sitting in the data registers of a Drive or a PLC. If that data can be put into the proper context, something interesting happens. Data evolves into Information and Information evolves into Knowledge. The communications link goes from being a simple control network to being a true HMI that anyone can use.

For a long time, there have been a number of HMI packages and Drive control programs that provided this function. The software would display information in a meaningful manner and make the programming of the drive much easier than using a keypad. Because such software had to run on dedicated computers, configured for and wired to, the specific industrial control network involved, the usability of this software is limited.

With a web-enabled Ethernet connection, a Drive can provide the HMI functions as well as a superior programming capability without any special software running on the computer involved. The software is resident on the communications card in the drive, meaning that the user can access it with nothing more than a browser such as Internet Explorer or Netscape Navigator. As an added advantage, this connection will work from anywhere that the user can connect to their own intranet. If a user is inside of their corporate firewall and has the correct addresses and passwords, they could monitor and control a Drive in San Francisco from a computer in France.

Some advantages of web-enabled Ethernet for Drives are simplified wiring and software, but there are even more benefits available as the concept evolves. To illustrate this, the tuning of a PI loop could be considered. To many people that work with Drives, tuning a PI or PID loop is almost more of an art than a science. Doing such tuning just based on data is very challenging and needs a high level of expertise.

In a typical example of a simple loop, there is a Drive controlling a fan that feeds into ductwork in an HVAC system. There is a pressure sensor in the duct and the drive is configured to maintain a set point using PI control.

Using web-enabled technology, a screen can be setup in the drive to provide a real time plot of both the set point and the feedback signal for a Drives control scheme. The screen would also provide tools for setting up the various PI control variables. An example of such a screen from an actual system using simple Java beans for the display is shown below

With this type of a display, the user can instantly see the effect that variable changes are having on the overshoot and dampening of the system. The time required to tune the system is sharply reduced and the user has a much better feeling for what is going on. All of this is done with nothing more than a web browser and no special software running on the computer.

Web-enabled Ethernet represents a significant advance in the control and operation of Variable Speed Drives. The advantages that this technology offers users will lead to fundamental changes in the use of communications with Drives.

Up to 10 issues may need consideration, not necessarily prioritized in this order, when selecting a flexible coupler:

Does it provide adequate misalignment capability?

Can it transmit the load torque?

Do I need axial compliance?

Can it sustain the required speed of rotation?

Will it fit within the available space envelope?

Can it operate at the designated ambient temperature?

Does it provide the required torsional stiffness?

Does it provide electrical isolation between shafts?

Will it have the required life expectancy?

Will it meet my cost expectations?

The issues of misalignment and torsional stiffness will be discussed here.

Misalignment Compensation & Axial Motion

These properties differentiate a flexible coupler from a solid sleeve type. The nature of the enabling mechanism (i.e., bellows, membrane, sliding disc, etc.) determines almost every other performance characteristic of the coupler, including its tolerance of misalignment and/or axial motion.

Sliding disc and universal/lateral types can tolerate large misalignments but their backlash-free life may reduce as a result; bellows types can absorb significant axial motion but their misalignment capacity may suffer accordingly; membrane couplers are irrevocably damaged if axial motion exceeds the catalogue specification, but can accommodate large misalignments with no reduction in life expectancy if the distance between membrane centers is increased, typically by linking a pair of single-stage couplers with an intermediate shaft.

Incidental misalignment is caused by manufacturing tolerances, thermal expansion, wear, fitting difficulties and structural settlement. The resultant errors are small, generally in the range 0º - 1/2º angular and 0-0.2mm parallel, and are difficult to predict. Be aware that a 0.2mm (0.008") parallel error can grow substantially due to adverse interaction with the angular component.

When misalignment is incidental, it is more realistic to consider the effective radial error, being the radial distance between shaft center lines measured midway along the length of the coupler. In effect, this is the composite error and is what matters when determining a value for maximum misalignment. Only a radial value need be specified.

Axial motion can result from axial clearances in the shaft bearings, or from shaft growth due to thermal expansion. It is usually beneficial to absorb this with a suitable coupler. In some cases, however, it may be preferable to resist the axial motion of an unrestricted shaft, particularly if this has a positioning function, and anchor it to a stable motor shaft. Couplers such as the universal/lateral can be useful in these cases.

The reason we use flexible couplers is to protect the shaft support bearings from destructive radial and thrust loads due to misalignment and axial motion, respectively. Since all couplings resist misalignment and axial motion, it follows that those with least resistance can better protect the bearings. Fig. 1 compares the radial bearing loads of a number of popular couplers. Excluding the 30mm (1.125") jaw coupler, all results were obtained with couplers of nominal outside 25mm (1").

Fig. 1

Load, Torque, Inertia and Torsional Stiffness

Applications in which couplers are used for driving so-called frictional loads, for example pumps, shutter doors, textile machinery, and so on, are not generally sensitive to coupler torsional stiffness because angular synchronization of the shafts is not an issue. Where resonance is a problem, it is possible to reduce the coupler s torsional stiffness and thus avoid conflict with the natural resonant frequency of the machine which is most likely operating at constant speed.

This is not a solution when the loads are inertial, typified by position and velocity control systems, where registration of input and output shafts is critical throughout the operating cycle.

In these systems motor, coupler, and load form a resonant system. Its resonant frequency depends on the load inertia and on the coupler s torsional stiffness. Increasing the load inertia, or decreasing the coupler s torsional stiffness, lowers the resonant frequency.

To control a resonant system you have to be working well below its resonant frequency. Imagine you are holding an elastic band with a weight suspended from it. You can control the vertical movement of the weight provided you move your hand slowly. Speed up the movement and the weight barely moves.

To improve response, you need a less elastic band, or you need to reduce the weight at the end of it Substitute a coupler for the elastic band, and an inertial load for the weight, and you have a good analogy for an inertial system.

When the focus is on performance, a stiffer coupler reduces settling times, improves positional accuracy, and raises the upper limit of dynamic performance.

Fig. 2 compares torsional deflection (the inverse of torsional stiffness) for a number of popular couplers tested with 8mm shafts. Excluding the 30mm (1.125") jaw coupler, all results were obtained with couplers of nominal outside 25mm (1").

Fig. 2

This article was written and provided by Huco Engineering Industries, Ltd, manufacturers of the world's most comprehensive range of precision couplers.

Many professionals who work with AC motors consider their operational behavior a mystery. This month I'll try to clear up some of the questions and address typical concerns.

Question

I have a 20hp motor running at full load producing 20hp of torque and the motor is rated as 90% efficient. Does that mean that the motor actually pulls 16.4 kW in order to produce 14.9 kW worth of work? If that is correct then how does a power factor of 0.60 versus a power factor of 0.90 affect the motor?

Discussion Group Answers

Input power to the motor increases as the motor efficiency falls. Power factor will not affect the input power, but it will affect the input current. If the motor input power is 16.4 kW at a power factor of 1, it will be the same with a power factor of 0.6. The current however will increase as the power factor drops due to the addition of reactive currents, harmonic currents, or both. In the case of an induction motor fed from a standard supply, the additional current is inductive and does not add to kilowatt usage.

If my understanding is correct, then what someone pays for is the true power and not the kVA and electric companies just have an additional charge for the increased current being used to deliver the power as a result of a low power factor.

Standard electrical meters measure true kilowatt hours and electrical utilities bill for each of these hours. Utilities may have surcharges designed to minimize line losses due to poor power factor and reduce maximum demand. Surcharges vary by region. Some utilities use thermal meters and bill based on maximum demand (Amps). In such cases, charges are calculated based on the highest current draw in a three-month period. Thus, a single high current draw for 30 minutes would be used to as the basis for the entire 3-month power bill. Some utilities charge extra when your maximum demand coincides with the maximum load on the power distributor. Such fees provide a major incentive to draw a constant load 24/7.
Efficiency is dependent on motor loading. If motor loading is 50%, for example, the efficiency will drop according to the manufacturer-provided efficiency versus loading curve. At low loads, the motor becomes less efficient. If the motor shaft load is equal to zero, the motor efficiency is equal to zero.

The power factor is dependent on the motor load. It decreases rapidly with smaller loads. The magnetizing branch of the motor significantly influences the power factor decrease for small motor loading. In many cases, power factor versus motor loading curves are available from manufacturers.
Power factor issues relate only to AC machines. Windings represent an inductive load, and this produces a lagging power factor. (A pf = 1 is perfect; this means that, for example, that 0.9 is better than 0.6.) Because circuits must be capable of supplying this unwanted current, cables and switchgear must be sized up to carry it. Improve power factor by installing power factor correction capacitors. They produce a leading current that offsets the lagging current produced by the motor windings. Electricity tariffs often have power factor penalty clauses in the billing structure.
Clarifications

In the question, 20hp of torque is misleading. The motor could produce from 30 lb-ft of torque to 120 lb-ft of torque, depending on the base speed of the motor. A standard 4-pole motor (1750rpm base speed) would produce about 60 lb-ft of torque.

Application of AC motors requires an understanding of both the power demand by the motor and the duty cycle demand by the motor. Users have a tendency to oversize motors for a given application. Motors are designed to operate best at their nameplate rating.

However, it is also important to consider that the cables feeding power to the motor are an important factor. Losses in any cables should be kept below 5% voltage loss in all cases, and as close to 3% as possible. Whenever possible, power factor correction should be applied at the motor to reduce distribution system losses due to reactive currents. In cases where the motor loading varies widely, the changes in power factor will not typically result in additional utility penalties as long as peak power levels are below maximum demand levels.

Motor manufacturers have improved efficiency by increasing the cross sectional dimension of the wire used in the windings. Since this reduces the I²R losses, less heat is lost in the motor. The downside to this improvement is that inrush currents are greater than with many older motors. In addition, since a lower slip occurs in the induction motor, the actual speed of the motor, when operated across the line, is greater. This increase in speed may have a negative effect in the application.

In applications where pulse width modulated (PWM) AC drives control the motors, input power factors are almost unity under all motor loading conditions. Although some concerns exist regarding harmonic currents, additional distribution system loading is generally less when compared to the current when the motor is operated across the line.

Questions concerning various applications where variable frequency drives and AC motors often arise. Discussions with and answers from various users indicate that the operational behavior of some applications are still a mystery. This article will clarify some of the concerns raised by typical users.

Typical Question

I am an electrician in a can manufacturing plant. Requirements for cooling water used to be around 100gpm for our ironers. There have been several modifications, and we need to increase the flow. Our superintendent wants to know if we can regulate the flow of a bigger pump and motor with a variable frequency drive (VFD). He wants to replace a 100gpm pump and a 5hp motor with a 200gpm pump and 10hp motor and regulate flow by changing pump speed. Is this something you should do with a centrifugal pump?

Discussion Group Answers

"It is best to have the pump Torque-speed characteristics properly aligned with the motor Torque-speed characteristics to establish appropriately integrated motor-pump set. You select your operating points on the pump curves and then determine the maximum motor rating you need. You then select the VFD for the motor."

"Check your requirements. If you need 5 hp at 100 gpm, then depending on your system requirements, it is probable you will need more than 10hp for 200 gpm. Centrifugal pumps have a power/speed relationship that is cubic, the power requirements of the pump reduce dramatically as the speed is reduced. The reduction in speed also affects your pump delivery. In general, variable speed control offers excellent pump and process control."

"Precise control of pump processes is possible with VFDs. Pressure in water can be maintained to closer tolerances. A VFD is an electronic controller that adjusts the speed of an electric motor by varying frequency/voltage and then the amount of power supplied. That allows the motor to continually adjust to work just hard enough, rather than running full speed all the time."

"Depending on the actual power requirements and a number of other issues, if the present pump is not heavily loaded, you might try just adding a drive and running the pump motor in excess of 60 Hz. Due to current limiting and maximum available voltage, the maximum torque will fall off as the speed increases, but you might not actually be using all 5 Hp in the present installation."

"Using VFDs you can control the speed of the motor and hence the flow of the pump. The advantage lies in the fact that power decreases by the cube of the speed decrease. Thus a 5% (0.95) speed decrease will cause the power requirement to decrease by cube of the decrease (0.95x0.95x0.95 = 0.86).

"This is provided that the motor is suitably matching the pump (10hp for 200gpm @ a certain head) and also make sure that the motor you buy is an inverter-rated motor. But you have to check the economics behind this, since the power decrease in a 10hp motor would be lot less than the investment done in buying an inverter and an inverter-rated motor, even if you are considering a couple of years for payback."

Clarifications

We live in a fixed frequency world. All standard pumps and motor are designed to operate at a constant frequency (50 or 60 Hz). However, variable frequency drives allow fixed speed motors and connected loads to operate at other than those standard frequencies.

Changing the frequency and associated voltage allows the motor to change its operating speed. As long as the voltage-to-frequency ratio is constant, the torque is reasonably constant. In most cases, the motor's operating speed range, for constant torque, is 3 or 4 to 1. In centrifugal pump applications, the torque requirement deceases rapidly as the speed decreases and the motor's operating speed range can expand to 10 to 1 or more. Operating speeds from 180 to 1,800 rpm are not unusual for AC motors used in centrifugal pump applications.

Hammering in low flow situations using valves for flow restriction are normally not a problem when variable frequency drives are used to directly control the motor/pump speed. Most variable frequency drives reduce the volts-per-hertz ratio as the speed deceases. This results in cooler operating motors.

Since less horsepower is required as the speed deceases, the demand for torque also deceases and the volts-per-hertz ratio can be reduced. Typically values are 115 volts at 30 Hz for a 460-volt, 60Hz-rated motor. An unknown fact is that input current to the variable frequency drive is less than the typical no load rated current of the AC motor. Also, where some line voltage unbalance is present, some phases may not indicate any current. This "unbalance current" presents no problem but may disturb some plant electricians.

Questions concerning various AC motors and drives often arise. Discussions with and answers from various users indicate that the operational behavior of AC motors and drives remains a mystery. This article will clarify some of the concerns raised by a typical user question.

Typical Question

I am using VFDs with dv/dt filters installed. Each VFD has eight motors attached. The motors are standard—1/2 HP, 200-230/460V, 3-phase with class B insulation. All motors are started together.

We have had a failure rate of about 10% failure of these motors, mostly on startup. The motors are new and fail on startup or with less than 2 weeks run time.

We are still doing failure analysis on them, but so far there have been bad lead connections, and one burned out motor coil. I have talked with some motor experts, and they say the motors do not show the "typical" signs of VFD compatibility failures. My customer is insisting that we change to VFD rated motor to fix the problem.

Discussion Group Answers

• "Finding inverter-rated motors in small sizes can be difficult. The extra insulation simply takes too much space. The dV/dt filter should be all right. There should be damping resistors parallel to the reactor's to prevent ringing between reactors and cable capacitance.
  
  "This is not the reflected wave phenomenon, but pure LC ringing. The frequency is usually not more than 10 or 20 kHz. It depends on the total cable capacitance and the length of the cables. The ringing not only heats the motors, but also it heats the reactors in the dV/dt filter.
  
  "Try to operate the VFD with the lowest possible carrier (switching) frequency. This will reduce any adverse effects that the switching can have on the motors. Eight motors on one VFD means that you have to run the inverter in scalar (volts per hertz) mode. Motor protection has to be outside the inverter (one thermal for each motor). The motor protection function of the VFD cannot protect the eight motors individually."
  
  
• "It is possible there is too much slip. Measure speed with a stroboscope and compare to the rated speed. If there is too much slip at nominal load, then your voltage/frequency ratio may be on the low side and should be adjusted.
  
  " The thermal protection becomes important when there are several motors connected to one inverter. The inverter has to supply power to all motors and cannot tell if one single motor is working too hard. You need thermal protection for each individual motor."
  
  
• "Marginal interactions among motors should not be ruled out, since each motor is manufactured within certain manufacturing tolerance, which influences the motor parameters. If different motor parameters exist, there will be marginal currents flowing among motors. This is necessary to treat as a system of interacting loads on the VFD output."
  
  
• "The total cable length with 8 motors involved will possibly be quite long. Check this and confirm if you are using screened cable or not. If you are, there are practical limitations to screened motor cable lengths due to the increased high capacitance effect. In some cases, the capacitance effect can cause problems with motors or the actual drive itself. If you have a dv/dt filter then this should minimize the effect."

Clarifications

When dealing with today's IGBT-based PWM VFD, under a specific set of installation conditions, there exists the potential for motor insulation damage. The most significant impact is the possible occurrence of high voltage spikes at the motor terminals that can produce destructive stress of the motor insulation.

Output waveforms consist of repetitive pulses. Motor waveforms can have high peak voltages with amplitudes of 2 to 3 times the DC bus voltage of the VFD. For 460-volt VFDs, the DC bus voltage is about 650 volts. For 230-volt VFDs, the DC bus voltage is about 350 volts.

There is less likelihood of motor insulation stress with 230-volt VFDs. Filters located on the VFD output or at each motor will reduce the effects of the peak voltage seen by the motor, however, these devices will not guarantee that the motor will not suffer an insulation breakdown.

Most motor insulation systems are designed to operate in a utility-supplied voltage environment. The typical utility voltage would be a 460-volt sinewave. A motor insulation system capable of 600 volts would offer suitable protection.

Most motors manufactured today provide a minimum of 1,000 volts insulation protection. Some inverter-rated motors (VFD-rated motors) provide 1,600 volts or 18,000 volts of protection. In almost all cases, the weak insulation point in the motor exists where the motor terminal leads enter the motor frame.

A motor insulation system consists of magnet wire insulation, resin insulation, slot insulation, and coil head insulation. In addition, there are variations in assembly techniques used. An insulation system is much more than the sum of its components.

Several factors could contribute to standard motors failing shortly after being operated. There have been cases where small HP motors began to fail when IEC contactors began replacing NEMA contactors. The faster switching time constant of the IEC contactor placed more stress on the existing motor insulation.