Students from The Infinity Math & Science Academy and Glenbrook South High School presented their Illinois Innovation and Technology Challenge solutions to Bison Gear and Engineering. The schools each proposed new ideas, identifying potential applications for Bison's new ServoNOW® motor.

Bison Gear and Engineering worked closely with associates from the Illinois Math and Science Academy (IMSA) as well as teachers from the participating high schools to bring this year's ILIT challenge to life. Each school was given a $250.00 stipend, a ServoNOW motor and tasked with producing a working prototype solution to a real-world application. Mike O'Donnell, a Bison servo expert, acted as a technical adviser. While the students took the lead on the project, Mr. O'Donnell was able to troubleshoot any issues the schools faced during the design process.

With only a few weeks to create a finished product, the students had to work fast to take their designs from initial concepts to working prototypes - both of which were inherently different. Using the ServoNOW to control the rotation of an extended output shaft equipped with special tooling for cutting, the students from Infinity Math, Science and Technology High School created a flavored ice maker where users could control not only the flavor of the ice, but also the size of drinks made.

The students from Glenbrook South took a different approach. They created a fun and unique gumball machine. Their design uses single and multi-axis movement, driven by the ServoNOW, to kick a gumball towards a pre-determined point into a waiting cup that was also driven by ServoNOW - adding a bit of entertainment while customers wait for their candy to be dispensed.

Both schools proposed their design in a creative, multimedia presentation where they highlighted what factors led to their idea, the challenges each school faced, the data they collected to test and refine their design and finally suggestions on how to market the product.

Bison Vice President of Business Development, Matt Hanson, reflected, "Since we wanted to introduce the ServoNOW as an easy way to integrate motion control into an application, it seemed like the perfect design challenge opportunity for the students. They came up with great ideas and even had suggestions for improvements to the product. All in all, it was a great experience for everyone involved."

A new site: www.motor-design-software.com, from Cobham Technical Services, helps engineers understand the contribution that finite element analysis (FEA) software can make to motor design cycle efficiency and design optimization. It provides a  engineers with a multi-faceted view of the ways electromagnetic FEA software can be used to design motors. Users can explore the underlying tools, looking at aspects such as the creation of design models or analysis of simulation results. They can also investigate the automated design approach for different types of design, by selecting a specific form of motor or related electromagnetic design topics such as magnetic gearing and linear motion. 

A range of interesting research material is available on the site including technical papers and details of training courses. Users may also register for a webinar on rotating machine design.

Contactors are traditionally used to start and control AC induction motors, where large power switching may occur and safety is a concern. The market for contactors generally follows machinery production forecasts and is tied in heavily to underlying GDP forecasts.

However, adoption of smart grid technologies drove 2010 volumes up higher than expected, and is forecast to continue to do so as smart grid initiatives gain momentum worldwide according to a study from IMS Research, entitled The World Market for Low Voltage AC & DC Contactors and Overload Protection Devices – 2011.

The global trend towards installing smart grid technologies is forecast to be the strongest market driver for low voltage contactors over the next five years, spurring contactor market revenues to over $5 billion by 2016. In IMS representative comments, “With more decentralized power generation, and more parties likely to act as electricity providers, the need for safe and reliable power switching is expected to increase. Growth in renewable energy, and related grid integration and management of renewable energy, is the single strongest driver for further adoption of contactors in power switching.”

2010 market revenues grew to an estimated $3 billion for contactors, with over a third of the revenues being for contactors sold into power switching. By 2016, revenues for contactors sold into power switching alone are forecast to reach $2 billion globally, or just over half the total projected market revenues.

The combined ball screw and linear guide markets were estimated to be worth $3.8 billion, nearly 45% of which came from the large, established sectors making machine tools and semiconductor production equipment, but established markets for these components have fluctuated considerably in recent years.

IMS is reporting that for more stable and high growth revenues, manufacturers of ball screw and linear guide products are developing products suitable for the industry sectors that will enjoy stable growth, such as those that produce equipment for pharmaceutical production, agriculture, and food & drink processing.

The report also suggests that Government-backed infrastructure projects, such as in power generation & distribution and mass transportation, will provide stable revenues, even during recession and in the face of austerity programs.

Linear motion companies are also identifying markets offering high initial growth with sustained long term revenues, in emerging regional markets and markets for new technologies, such as production machinery for lithium-ion batteries and photovoltaic panels. An IMS representatives is quoted, "Many companies are keen to gain a foothold in them, to make up for business lost in the recent downturn and to provide a stable revenue base in future downturns."

He adds, "competition within these markets will be fierce."

The new report, "The World Market for Linear Motion Products" considers in detail how this and other trends will affect the yearly development of this market through to 2015.

Most publications celebrate new, unproven ideas. But DrivesMag is all about work. So we like ideas that work.

Eaton has a clear winner in the Ampgard® SC9000.

The judging is complete and Eaton's Ampgard® SC9000 Medium Voltage Drive has won DrivesMag's first annual Old Idea Contest. Out of dozens of great submissions, the Eaton team showed why theirs was the best. Old ideas are at least 5 years old, and can been proven, by customer feedback, to be good and worthy of a recommendation.

What does a customer say about the SC9000?

The Benton Irrigation District in Washington state needed to replace a deteriorating open canal system. This included a reliable pump station at the Yakima River to supply water for 4,630 irrigable acres crucial to its agricultural industry. A new pumping station was constructed above the Yakima River to accommodate for current and future irrigation needs with six of Eaton’s Ampgard® SC 9000 medium voltage adjustable frequency drives.

Joseph Dinkel, the executive director of operations at the West View Water Authority tells the complete story:

Albeit that the pumps were new, modern pumps and they utilized state-of-the-art starters and pump control valves, we were still having a very large [energy] demand.

After visits to the [Eaton test facility] factory, where the products [Ampgard® SC 9000 medium-voltage drives] are manufactured seeing their [Eaton] availability to support us, we were quite satisfied that Eaton had the ability to handle this project.

We had Eaton products that serviced the original facility, and as a result the transition into the Eaton variable frequency drive (VFD) mitigated the amount of construction that was necessary for the project and made it a seamless transition into the new operation.

We rarely shutdown the units [Ampgard SC 9000] and they provide a very high degree of reliability on a 24 hour-a-day basis.

The Eaton drives allow us to operate 24 hours a day. When they [the Ampgard SC 9000] are online, we have less main breaks due to trauma placed on the system due to the starting and stopping of pumps.

With the new system, when the motor starts, there are no in-rush problems. It starts very slowly. Everything is under controlled circumstances. Where the motor [is], you can actually see the RPM start slowly. When it gets up to the point where we want it, it will produce the exact amount of water that we want with no wasted energy.

The very first month that the system was online, we documented that we were saving a thousand dollars a day, so that’s obviously thirty thousand dollars per month. And the way I prefer to look at it, over 3 years, we’re talking a million dollars in savings.

Eaton was tremendous to work with throughout the entire project. They provided excellent guidance for our electrical consultants during the design phase, for the specification writing, for the bidding process and for the implementation.

Our Eaton project has been such a success that we are totally convinced that the VFDs are the way to go in the future. We have a new plan that we are designing and it will be using VFDs at the intake, and throughout the treatment facility, and on the high-service end of the pumping operations.

As the winning company, Eaton will receive a free year-long banner on the DrivesMag home page, and the winning submitter will get a new iPod touch. Congratulations to the Eaton drive team, and thanks to Joseph Dinkel and the West View Water Authority for sharing your story!

Technosoft has announced a new family of very small and intelligent servo drives – what they are calling the iPOS Line – based on a new design concept offering higher power density on very compact boards.

How compact? Check this 75W module.

Designed to cover both low- and high-volume applications, the first version is a complete motion control and drive solution packed on only 21 x 54 mm of PCB space, offering 36 V, 2 A, 75 W. It combines all the basic motor control functions, motion control and PLC features on a a board slightly larger than a pencil.

CAN / CANopen interface is standard, optionally, EtherCAT interface is also available.

The company says the drive can control any rotary or linear brushless, DC brush or step motor.

A spokesman adds, "iPOS3602 is able to execute complex motion programs directly at drive level, using its built-in motion programmer and the high-level Technosoft Motion Language (TML), or it can operate as an intelligent EtherCAT and CANopen slave. In simple applications iPOS3602 works as a single-axis motion controller and drive in stand-alone mode, autonomously running the program residing in its non-volatile memory. In systems that request a host, the iPOS drive operates as an intelligent slave executing motion sequences triggered by input lines, or commands received via RS-232 or CAN bus. The motion capabilities of the iPOS card include position or speed profiles (trapezoidal, S-curve), 3rd order PVT and 1st order PT interpolation, electronic gearing and camming, analog or digital external reference, complemented with the cyclic synchronous position, speed and torque modes specific to EtherCAT. This enables you to reduce both the development time of complex applications, and the master’s task, by calling complex motion functions, pre-stored in the drive memory, or by triggering their execution via I/O signals."
It will be interesting to see where the miniaturization trend leads.

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 - see "Still More Room for Adoption of 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.

Source: ABB

What is the Difference Between Power Factor and Cosj?

Power Factor (PF) is an important measure for electrical systems and it is defined as ratio of Real or Active Power, in total kilowatts, to total Apparent Power, in kilovolt amps.

The Power Factor topic is of interest to a large number of people. An Internet search with one of the search engines gave more than three million hits. There sometimes seems to be confusion between the terms Power Factor and cosj (phi). Just remember that the cosj is equal to Power Factor only in cases where both system voltage (U) and system current (I) are sinusoidal (cosj is equal to Power Factor only when the voltage and current considered are at the same frequency). In real-world electrical installations, both voltages and currents contain harmonics and the Power Factor is not equal to cosj.

To understand Power Factor, it can help to consider phasor diagrams. An electrical circuit under consideration is shown in Fig. 1. The supply voltage U connected to the circuit is at a single frequency; that voltage causes current I to flow through the components. According to Ohms law, the voltage drop in each component is calculated by multiplying the current I (in Amps) by the resistance (in Ohms). The phasor diagrams for this circuit are shown in Fig. 2.

Figure 1. The three basic linear electrical components in serial connection with the voltage U, causing the current I to flow through the circuit. The components are:

• § Resistor R with resistance measured in Ohms and a voltage drop u_R
• § Inductor with inductive impedance X_L measured in Ohms and a voltage drop u_L
• § Capacitor with capacitive impedance X_C measured in Ohms and a voltage drop u_C

The voltages and currents in Fig. 1 can be illustrated in phasor form in Fig. 2. The current I is common for each component in the system, but the voltages are of different magnitude and their phasors are in different directions -- 90 degrees apart from each other’s. The three diagrams in Fig. 2. show the steps for defining the voltage phasors and the angle between the total voltage U and the current I. As result, we get the definition for the cos j:

 

Figure 2. The current phasor I rotates in phase with the voltage vector u_R, but it is lagging the voltage phasor u_L and leading the voltage phasor u_C. All phasors rotate counter-clockwise. Because the u_L and u_C are pointing in opposite directions, they are subtracted and the difference u_X is the reactive component of the total system voltage. The u_R is the active or real component and the phasor sum of these voltages is the total voltage U. The cosine of the angle j between total voltage U and the active voltage u_R is the Power Factor of an ideal system, which is known as cosj. If U and u_R have one single, fundamental frequency, cosj is sometimes called displacement Power Factor.

To understand, power factor is sometimes visualized with a horse pulling a railroad car down a railroad track. Because the railroad ties are uneven, the horse must pull the car from the side of the track. The horse is pulling the railroad car at an angle to the direction of car’s travel. The power required to move the car down the track is the real power. The effort of the horse is the total (apparent) power. The car will not move sideways. Therefore the sideways pull of the horse is wasted effort or reactive power. These three different power vectors are shown in Fig. 3.

Figure 3. The Power factor definition by using power vectors

In summary:

• Power Factor (PF) is the Real Power divided by Apparent Power
• Power Factor of the system with sinusoidal current and voltage is cosj
• In both cases, the value of PF is from 0 to 1, sometimes given as 0 to 100%
• The real-world PF is influenced by harmonic disturbances and other non linearity’s
• The real-world PF is therefore lower than with sinusoidal current and voltage

When Should the Power Factor be improved?

Power plant generators usually are designed for PF = 0.8 to 0.9. Therefore, if the actual demand-side Power Factor is lower than the designed (0.8), either the generator current increases above the rated current or the active power output has to be limited. For that reason, the power companies put limits on reactive power consumed by the customers. The limits usually are set for large industrial or public customers only.

Customers have to pay a power factor penalty if power factor falls below a certain limit. The limits can vary widely from 0.8 to 0.97. Electric motors connected to the power line is the main reason for reduced power factor. The rated power factor of a standard motor depends on its rated power and, typically, is around 0.85 but can be much lower if the motor is lightly loaded. This topic will be studied in the next section.

Why Do Electric Motors Cause Low Power Factor?

The use of AC induction motors is essential for industry and utilities. AC induction motors consume more than 50 per cent of the energy used in industry. As compared to other type of loads, motor loads have relatively poor power factor. Poor power factor causes higher line currents, which causes additional heat in line cables and transformers. The power factor is especially low in cases when the motors are oversized and are running with a light load.

Figure 4. Line current and power factor of a 55 kW AC induction motor as function of the motor load.

To produce the required rotating torque and speed, the induction motor takes both active current and reactive current from the power supply. The rotating torque of the motor is created as an interaction between the active current component and the magnetic field. The field is produced by the reactive current component. Light load takes less active current but the magnetic field, as well as the reactive current, stays constant. This means that the power factor decreases with decreasing load, as shown in the Fig. 4. At the full load, the current is mainly active but, at the light load, the current is mainly reactive.

How to Improve the Power Factor?

There are many different methods to improve the power factor or compensate for the reactive power:

• At the power plant, the excessive reactive power can be compensated by increasing the excitation of synchronous generators; or, by using separate rotating synchronous compensators.
• At transmission or transformer stations, the reactive power can be compensated by power- factor-correction capacitors. The capacitors can be installed to improve the power factor for a single load or an entire power system.
• At the plant level, the power factor correction can be accomplished by using power-factor-correction capacitors, or by using variable speed AC drives. When AC drives are used, power-factor-correction capacitors should not be used, because it is usually unnecessary, and because drive harmonics could damage power factor capacitors. See the next section.

The principle of Variable Speed AC Drives

On a so-called PWM (Pulse Width Modulated) drive with a diode bridge converter input, the Power Factor to the AC line is near unity (see Fig. 5). The output may have an inductive (lagging) power factor, due to the motor’s inductive reactance. However, the motor’s reactive current is circulated between the motor and the inverter bus capacitors – and not to the input line.

Figure 5. A Variable speed AC drive input consists of a rectifier bridge that converts the line AC voltage to DC voltage. The smoothing of the DC voltage is made via an inductor (L) and capacitor (C). The DC voltage (Ud) then is converted in the inverter to variable frequency and variable voltage AC that is connected to the AC motor. The switches V1 to V6 in the inverter are very fast semiconductors, usually IGBT’s (Insulated Gate Bipolar Transistors) in modern drives.

Because of the fast switching inside the AC drive, there is a risk of electromagnetic emissions. Emissions can be both conductive and radiating interference. International regulations set limits on both low- and high-frequency emissions. With the use of filters, screening and suitable mechanical construction inside the drive cabinet, it is possible to meet the Electromagnetic Compatibility (EMC) standards.

How Variable Speed AC Drives improve Power Factor

Let’s study the currents of the above mentioned 55 kW/400V motor and drive system:

Motor: Motor Mechanical Power = 55 kW,

Input U = 400 V, efficiency = 94.4% and power factor = 0.89

Motor Electrical Input Power= 55 kW/0.944 = 58.3 kW

Motor Electrical KVA = kW/PF = 65.5

 

 

AC drive: Output P = 58.3 kW, 94.5 A

Input U = 400 V, efficiency = 98% and power factor = 0.96

Drive Input Power = 58.3 kW/0.98 = 59.5 kW

Drive Input KVA = 62.0

One can see that the drive input current from the supply is 5 amps, or more than five percent (94.5 versus 89.5 amps), lower than the drive output current to the motor. The active power input, instead, is 1.2 kW (58.3 versus 59.5 kW) higher than the output from the drive.

The difference in drive input and output power factor is how the variable speed AC drive can improve the Power Factor and how the drive output current can be greater than the input current!

What Does This Mean in Reduced Losses and Saved Money?

The power losses in the power line, transformers and cables are proportional to the square of the current. We can estimate the following:

Assume the average load on the 55 kW motor is 35 kW.

From Fig. 4, the motor current at 35 KW is 65 amps; the AC drive input current

under these conditions is 60 amps.

The AC drive reduces the input current from 65 A to 60 A.

The reduction of losses when operating the motor from an AC drive is then:

If total losses on the supply side are 5% of the average load, the AC drive can reduce the losses to about 4%. The reduction on the total power consumption, as well as reduction on money spent, is one per cent.

(Note: The original reason to install an AC drive is not the power factor improvement but better process controls, energy savings in the process, and/or reduced wear of the machinery. PF improvement is a positive side effect.)

Power Factor Comparison Between AC and DC Drives

The main difference between standard AC and DC drives is that PWM AC drives have a diode rectifier on the front end while DC drives have SCR rectifier. The control principle of the SCR rectifier is based on phase control with line commutation, causing a phase shift between voltage and current. The lower the speed, the larger the phase shifts. This reduces the power factor of DC drives, especially in the lower speed ranges (as shown in Fig. 6).

Figure 6. Power factor of AC and DC drives as function of motor speed.

Conclusions

The power factor topic is interesting and important for a number of parties within the power generation and consumption marketplace:

• Industrial, commercial and domestic customers have a desire to get the most cost effective electrical installation to serve their machinery. Low power factor can mean extra losses and penalty payments to the utility for excessive reactive power.
• Power production and transmission companies want to sell as much active power as possible to their customers. Low power factor can reduce the generating and transmission capacity.
• Manufacturers of power-factor-correction equipment are willing to sell capacitor banks and automation equipment to help improve the power factor.
• Consultants have an interest to help the power companies, consumers and other interest groups with audits and plans for better energy economy and achieving higher power factors.
• Drives and motors manufacturers can also help to improve the power factor with variable speed drives. VSDs help solve the power factor problem -- while improving process control, saving electrical energy, and reducing machinery wear.

This video, by AC drive and motor expert James Shumberg, introduces induction motor theory and offers tips on proper motor selection for motors used on AC drives. Part I of 4.