Briggs & Stratton: Power Regeneration System

The system consists of a group of 12 test stands of various horsepower limits. This is a subset of the 105 test stands in the reliability lab, and 312 total in the Wauwatosa plant. The test stands are equipped with alternating current (AC) electric motors operated from variable frequency drives (VFD’s) on a common 180 amp regenerative bus. The regenerative bus is bi-directional, meaning it can supply AC power to the motors and also regenerate power to the AC line. The motor and drive systems start the engines and test them at various operating conditions by varying the loads on the engine. Previously, the power generated by the motors was dissipated as heat and lost. The new regeneration system captures the power output from the rotational energy of the gasoline engines and creates electricity. All 12 AC motors and drives convert the rotational energy of the engine to electricity, which is then sent to a common direct current (DC) bus supply. The DC bus supply then converts the DC to AC, and synchronizes to the AC line, where all the power is directed back to the internal grid—reducing the need for electricity from the outside utility.

The team installed new control hardware and software that increases productivity, efficiency, and safety. An automated data acquisition system monitors engine heath and diagnoses engine glitches, which eliminates human collection errors and frees technicians for other tasks. Most importantly, it improves safety by providing warning signs and automatic shutdown in the unlikely event of catastrophic engine failure. The user friendly system enables technicians to instantly determine when an engine is not operating normally or when a test is set up incorrectly. Briggs & Stratton estimates that productivity and efficiency gains associated with the data acquisition system equate to about $40,000 per year.

The power regeneration system is expected to generate 533,000 kWh annually and reduce energy costs by $48,000 a year as electricity is fed back into the plant’s internal grid. The savings equate to an almost 25% improvement in energy intensity within the Test Building, which is where the reliability lab is located. Additionally, the electricity savings are estimated to reduce the plant’s greenhouse gas emissions by 442 tons per year. This project was implemented on 12 test stands, but has the potential to expand to other test stands and laboratories for additional energy savings. The company is considering implementing the power regeneration system at another 36 test stands in the next two years. Expanding the power regeneration system to include these additional 36 test stands would save an additional $100,000 per year, with implementation costs of about $475,000, according to Briggs & Stratton.