4th Quarter 2013Electrical switching & drive systems & components
Single-phase motors are typically used on farms, office buildings and residential applications where low output power is required and no three-phase system is available. However, with the ongoing improvements in technology and lowered cost of smaller variable speed drives (VSDs), three-phase motors can now be used in these applications.
“Single-phase motors have a single winding and are fed with a single-phase voltage. There are various arrangements that can be used but the most common design is the one that uses a starting capacitor or a starting and a run capacitor, both equipped with a centrifugal and a stationary switch,” explains Edson Cristofolini, product and projects manager at Zest WEG Group.
Three-phase motors, on the other hand, have three windings and are fed with a three-phase voltage. The interaction between the magnetic field on the stator and the induced magnetic field on the rotor makes the motor run. “When using a single-phase VSD you would still have a single-phase feed to the drive allowing the existing installation to be used without any modification, however there would be a three-phase voltage feed to the motor,” Cristofolini continues. “This is possible because the VSD will rectify the single-phase voltage from its input and switch the voltage on and off with IGBTs, from a DC link provided by a capacitor bank, to create the three-phase signal on the output to feed the motor.”
In general, three-phase motors present a better efficiency and power factor than a single-phase motor and they are also more reliable, lighter and require less maintenance, as no capacitor or internal switches are needed. “Added to the performance and reliability of three-phase motors, when they are run on a VSD it eliminates the need for a DOL starter with contactors and thermal relays, since all the protection is now built in the VSD,” continues Cristofolini.
WEG manufactures a variety of VSDs which also provide additional features not available on a normal starter for single-phase motors. These include current and speed reading, under voltage and phase protection, fault history and speed variation, which contributes to power savings. “The VSD also incorporates analogue inputs and outputs as standard and allows communication with a PLC or scada system,” Cristofolini adds.
“Whilst cost comparisons between a single-phase motor and a three-phase motor typically focus on the cost of the single-phase motor, one also needs to take the cost of the starters into account. A comparison undertaken by Zest WEG Group indicated that in most cases, based on current market prices, it is more cost effective to use a three-phase motor with a VSD than to use a single-phase motor with a starter. In addition, there is a higher off the shelf availability of three-phase motors and VSDs,” Cristofolini points out.
“It is important to remember that the VSD has on-board electronics, thus requiring additional care in use. In spite of this fact, VSDs are becoming increasingly more user friendly and require little maintenance. This makes them the perfect cost effective alternative to a single-phase motor with starters,” he concludes.
Understanding standby, prime and continuous gensets WEG Africa
Electrical switching & drive systems & components
The increasing reliance of South African businesses on generator sets to mitigate power disruptions highlights a crucial need for proper selection based on specific operational demands. Despite their growing usage, there is still widespread confusion about how to choose the appropriate genset, often leading to inefficient and costly decisions.
Read more...PC-based control for advanced hydrogen storage technology Beckhoff Automation
Editor's Choice Electrical switching & drive systems & components
The proportion of renewable energies from solar, wind and water is rising continuously. However, sufficient storage options are of the essence to use these energies as efficiently as possible. GKN Hydrogen offers a particularly compact and safe option, low-pressure metal hydride hydrogen storage systems with PC-based control from Beckhoff.
Read more...Axiom reaches new heights Axiom Hydraulics
Editor's Choice Electrical switching & drive systems & components
When Rula Bulk Handling could not source a cable tensioner large enough for a new cableway, the engineers knew they had to come up with an inventive solution. After discovering that no such tensioner was immediately available, Rula approached Axiom Hydraulics and ifm to assist with building their own.
Read more...Local range of planetary units SEW-EURODRIVE
Electrical switching & drive systems & components
s SEW-EURODRIVE South Africa actively extends its offerings to customers, the SEW PPK and SEW P2.e industrial gearbox ranges are good examples of solutions that are well suited to the local business environment.
Read more...At least 60 million strokes Horne Technologies
Editor's Choice Electrical switching & drive systems & components
Designing and constructing compact automation systems is one of the core activities of the Austrian machine manufacturer, STIWA. Its modular LTM-CI system has been optimised for small parts assembly. Linear and rotating micromotors from Faulhaber perform key tasks in these systems.
Read more...Innovative five-axis laser precession scanner
Electrical switching & drive systems & components
Motion control specialist, Aerotech has launched the AGV5D, an innovative five-axis laser precession scanner specially developed for laser micromachining. This makes it possible to create high-precision bores, contoured slots and other complex geometries with dimensional tolerances in the sub-micrometre range.
Read more...Minetruck with electric drivetrain combines power and innovation
Electrical switching & drive systems & components
The new Minetruck MT66 S eDrive is the first of Epiroc’s large-capacity mine trucks to feature the latest generation electric drivetrain. Along with an upgraded and powerful diesel engine, the hauler combines the cost-effectiveness of a traditional mine truck with the productivity of an electric one, without requiring changes to a mine’s infrastructure.
Read more...Modular hydraulic control blocks for brake actuation
Electrical switching & drive systems & components
Electrohydraulic brake release valves are exposed to extreme loads, and can become uncontrollable in the event of a power failure. The experts at WEBER-HYDRAULIK GMBH have developed a practical, modular solution that ensures the safety of construction machinery, and is also suitable for a wide range of other vehicles with hydrostatic drive systems.
Read more...Modular assembly platform for clean manufacturing Beckhoff Automation
Electrical switching & drive systems & components
JR Automation delivers custom automated solutions for numerous industries. It has done this through its scalable, modular automation platform, FlexChassis, which speeds up time to market while cutting costs. The company chose the XTS linear transport system from Beckhoff because of its speed, and modular design that allows for multiple configurations.
printer friendly version