When Kohler Co. established its new engine manufacturing plant in Hattiesburg, Miss., the company, through its Generator Div., planned on installing an emergency standby power system. The new plant's layout would also include plans to parallel with the utility for peak shaving and curtailable-rate savings.
Opened in January 1998, the production facility in Hattiesburg currently assembles Kohler's Command single-cylinder, vertical shaft engines. The air-cooled, four-cycle gasoline models are the mainstay of the company's product line and are used in a variety of consumer and commercial mowing equipment. The engines are also used to power agricultural, construction and recreational equipment, as well as selected models of Kohler generators.
Mississippi Power Co., the local utility, worked closely with Kohler's management and facilities engineering group to develop a standby generating system that would benefit both the company and the utility. With these guidelines, Kohler Power Systems began designing and manufacturing the generator sets and necessary paralleling switchgear. The final installation called for two generator sets operating in parallel with one another and the utility grid.
Each of the generator sets is housed within Pritchard Brown sound-absorbing, weatherproof enclosures with exhaust air ducted upward to aid in reducing the sound level near the sets. The enclosures incorporate 2500 gal. sub-base fuel tanks and 3 in. of acoustic insulation. Harco round pancake-style silencers were selected so they could be placed within the low-profile enclosures to further improve installation aesthetics. The silencers were also insulated to reduce the heat build-up in the enclosures.
The generator sets were installed in a courtyard near the plant and are positioned at a 90 [degrees] angle so the intake air is drawn from the side away from the plant, further reducing noise. Each enclosure is 33 ft. long, 13 ft. high and 12 ft. wide.
Two utility power lines were brought in underground through the courtyard to matched pad-mounted transformers that step down the utility voltage of 12,470 V to 480 V to match both the generated voltage and the plant utilization voltage. All synchronization and paralleling occurs at the 480 V level.
Kohler's paralleling switchgear contains two utility main circuit breakers, a main bus tie circuit breaker, two generator output circuit breakers, two tie circuit breakers that serve to isolate the generating system totally from the utility - if necessary - and 16 distribution (feeder) circuit breakers that distribute the power to the various areas of the plant. Power factor correction capacitors will ultimately be used as Kohler's engine plant expands in its production capability and more production machinery is added. These will be automatically added to maintain an overall plant power factor in excess of 95 percent.
Kohler Power Systems' engineers designed the switchgear, produced all the necessary drawings to build the assembly, and assisted in manufacturing the switchgear. The switchgear incorporates Cutler Hammer DSII drawout breakers. The generator sets and switchgear were systems-tested at Kohler's Wisconsin facility prior to installation at the Hattiesburg site.
The gen-sets' digital controllers, the Kohler Decision Maker 340, maintains communication among the generator sets, paralleling switchgear, and outside communication links. With the Decision Maker 340 controllers and operator interface terminals on the switchgear, together with PLC controllers in the switchgear, a communications system was implemented, allowing the generator sets and switchgear to be monitored locally and from Kohler's generator plant in Wisconsin. Synchronizing, load sharing and load transferring are accomplished using Woodward DSLC, and MSLC digital synchronizers and load controls. Utility intertie protective relaying is combined in a Beckwith multifunction relay.
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