As a device designer incorporating automation components into your product, or as a systems integrator combining disparate automation devices into a larger system, I2R is a term with which you should be familiar. The term is most commonly used in the phrase “I2R losses,” which refers to inefficiencies in power transfer and conversion (thanks to Ken Stead of Molex’s “The Connector” blog for that concise definition).
I2R loss is an issue for companies like Molex that offer interface connectors to reduce energy loss in device and systems design. According to Ken’s recent blog post on the topic, Molex has not yet received a lot of interest from engineers looking to reduce I2R loss with suitable connectors, but it is a concern they expect to appear on design engineers’ radar screen soon as energy efficiency receives greater industry focus (with a little help from Washington, D.C.).
For now, most engineers involved with automation typically encounter I2R when it refers to motor efficiencies in terms of stator and/or rotor I2R losses, both of which relate to conductor heating loss. To address this, motor designers commonly incorporate more copper and steel to create motor designs that run cooler and more efficiently.
Information from the Copper Development Association (which obviously has an interest in the push toward greater motor efficiencies, considering copper’s role) explains that energy losses in electric motors fall into four categories:
- Power losses;
- Magnetic core losses;
- Friction and windage losses; and
- Stray load losses.
Power losses are the I²R losses we’ve been discussing here and, according to the CDA, account for more than one-half of a motor’s total losses. These power losses appear as heat generated by resistance to current flowing in the stator windings and rotor conductor bars and end rings.
The CDA goes on to note that stator losses make up about 66% of power losses, and it is here that motor manufacturers have achieved significant gains in efficiency. Since increasing the mass of stator windings lowers their electrical resistance (therefore reducing I²R losses), highly efficient motors typically contain about 20% more copper than standard efficiency models of equivalent size and rating.
Design News has featured a number of articles recently with more information on energy loss reduction and I²R in particular. Here are links to two of those articles:
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