During the summer of 2016 articles from our growing archive will be republished. This one was first published in April 2011.
Most of us don’t give a great deal of thought to the functioning of static frequency converters, known as “drives.” But for companies that manufacture electric motors — and for the much larger number of industrial users — these speed controllers are of crucial importance in saving energy and reducing operating costs. And it’s no exaggeration to say that drives are fueling a minor revolution in electric motor technology.
Ranging in output from a few watts to several megawatts, these silent gadgets contribute to significant savings in any equipment where continuously regulating speed and torque is key to operating efficiency. This can include everything from washing machines, fans and hand tools to small electric vehicles, refrigerators, heating plants, light rail trains and more.
Big electricity consumers
The electric motor has been with us for more than a hundred years with little change to its basic design. It’s a fantastic invention and a true workhorse that can stay on the job continuously for years. An electric motor converts electrical current into mechanical energy through electromagnetism. The key parts of an electric motor include a stator that generates the magnetic field and a rotor that converts the resulting power into motion.
For years engineers have faced the problem of how best to custom-tailor electric motors for specific tasks. Take the example of an electric motor-driven water pump that needs to be able to regulate water flow. This issue is normally solved with a throttle valve that allows flow to increase or decrease as the motor spins at full power. It’s like driving a car at full throttle and adjusting speed with the brake pedal — hardly energy efficient.
Many electric motors found in industrial equipment, power plants, office buildings, hotels and water and sewage plants are major energy users. Over-sized motors are often used, requiring throttle valves, dampers, switches or strap systems to control rotation speed. About 20 percent of the energy consumed by industry to drive electric motors is wasted by these throttling devices, but there are two basic approaches to making more efficient electric motors:
Increasing efficiency through optimal engine speed. Small speed reductions make a big difference in energy consumption.
Making the engines themselves more efficient, through proper material choices such as thinner housing plates and more copper in the rotor and stator.
Drives cut power consumption
“Connecting a drive to an electric motor makes it more efficient,” says Stellan Rosenquist, product marketing manager for low voltage motors at ABB, the Swedish-Swiss electrical engineering conglomerate. “The drive controls the motor speed. Replacing the throttle valve in a water pump with a drive reduces electricity consumption by about 45 to 60 percent,” he adds. “In a single year, our converters reduce global greenhouse gas emissions by 85 million tons, equivalent to the emissions from 31 million cars. The electricity savings add up to the annual consumption of 42 million households.”
Drives can be controlled in different ways, and applications need not be advanced. “It may be just a standard sensor that detects a temperature increase in a room and increases the motor speed on a fan,” Rosenquist says. “But it can also be an advanced automation system in which all changes are continuously coordinated between the controllers and the operations. The control accuracy can be down there in milliseconds to make everything work.”
Reducing carbon footprint
A properly functioning heating, ventilation and air conditioning (HVAC) system is essential to a pleasant stay for hotel guests, as well as for staff comfort and safety. But the electric motors driving the HVAC system can account for more than 60 percent of a building’s total energy use. Hotel Jumeirah Beach in Dubai has recently installed ABB technology to increase energy efficiency and reduce environmental impacts.
The motors in the existing HVAC system were set up to run at fixed speed, so the hotel replaced start switches with ABB’s ACH550 drives. The system runs the motors efficiently, optimizing speed according to changing requirements, or stopping and starting at varying power requirements. The drives are connected to the building’s central control systems, where they’ve helped reduce and carbon dioxide emissions by 35 percent per year.
As the first drive designed to cut energy consumption in AC appliances for HVAC systems, the ABB ACH550 has won several awards for outstanding engineering.
Article published in April 2011