At EPRI Labs: Tom Reddoch & Tom Geist


Senior Technical Executive & Principal Technical Leader

PUF 2.0 - November 15, 2017

Electric Power Research Institute Senior Technical Executive Tom Reddoch and Principal Technical Leader Tom Geist discuss alternatives to using power at the U.S. standard of 60 Hz, and what it could mean for efficiency and electrification strategies.

PUF's Steve Mitnick: We're talking about powering devices with electricity, but not with the standard AC frequency of 60 Hz that comes from the plug. Why would we do that? What would Nikola Tesla and Thomas Edison say?

Tom Reddoch: The reason we look at these other options is that we want to get the best and most efficient delivery solution, which may not be at 60 Hz. It could be at 400 Hz, as is used in motor drive applications. 

Tom Geist: The use of 60 Hz is historical and not universal. In Europe, the standard is 50 Hz. While 60 Hz is traditionally used for producing and shipping electricity, it is not the best form of electricity for powering end-uses. In fact, most loads require DC and a significant amount of energy is lost converting AC power into DC power. Our research is focused on identifying the form of electricity, AC, DC, or other, that's best for various applications.

Tom Reddoch: Here's some examples of what we're focusing on. First, we're looking at more efficient ways of coupling energy into a process. For some situations, the best choice is DC. Tesla would likely not be excited about DC solutions, but Thomas Edison would be thrilled!

PUF's Steve Mitnick: How do you determine whether to use 1400 Hz, or 140 Hz: do you have to test?

Tom Reddoch: There's no universal answer, but testing and analysis is part of it. We need to examine each application, keeping in mind such things as efficiency, controllability, safety, and reliability to determine the best choice.

Often, the electricity format is determined by the physical parameters of the workpiece or process. We're also looking at new, emerging technologies with interesting potential, such as pulsed power for distribution of electricity in residential and commercial applications.

Tom Geist: Pulsed power is a confluence of digital control and powered electronics to enable the safe delivery of power at a high voltage (380 VDC) in applications ranging from 100W up to tens of kW. Here's how it works. The circuitry is arranged to supply a pulse of power at 380 volts DC for a millisecond (0.001 second). Then the circuitry turns off the power for a shorter period, say 10 microseconds (.00001 seconds), during which time the circuity tests the impedance of the wires and end-use equipment.

The circuitry checks the safety of the circuit by determining if something changed. "Is there an open circuit? Is there a short circuit? Is something different than what we expected?" If nothing inappropriate has happened, the circuitry delivers another pulse, but if something has happened, the circuitry doesn't deliver another pulse and the wires and end load remain disconnected from the power source.

Tom Reddoch: The latter situation signals a safety problem. A change in impedance indicates that perhaps the wires are crossed, or worse, a person has come into contact with the distribution wires.

Tom Geist: What's interesting about 380 volts and 1 millisecond is that it's a significant amount of energy, but not so significant that an injurious amount of energy is delivered. In other words, if someone touches the wires, despite the high voltage, they will not receive a substantial shock. More like a tickle.

The benefit is increased safety and improved efficiency. And, because it's a form of DC, it enables more efficient integration of renewables and energy storage. Some estimates are up to 14 percent savings in energy.

PUF's Steve Mitnick: So where could customers use pulsed DC? What's next?

Tom Geist: Pulsed Power is ideal for appliances such as refrigerators, dishwashers and light emitting diode (LED) lighting in the home and in commercial buildings. EPRI has been involved with this technology for several years and, like any new technology, we are working to inform decision makers on all aspects of the technology. From safety standards to the potential for energy efficiency and demand response. More work is needed, but results are encouraging.