Digital controls provide synchronization function
The purpose of paralleling switchgear is to provide synchronization, load sharing and load management for a system with multiple generator sets. “Using traditional switchgear and controls would have added $300,000 to the project’s cost and taken up valuable floor space in the newly expanded plant,” said Greg Esau, sales engineer with United Engines, LLC. “To save cost and footprint, we designed a system without traditional switchgear, using the digital controllers on the mtu generator sets (enhanced DGC 2020 with auto-sync) and motorized breakers mounted onboard each generator set to provide the paralleling function.” Esau was one of the first mtu distributors to apply the DGC 2020’s paralleling function on a mission-critical application in the field.
The original plan was to parallel the existing 600 kW generator set with one new 1,000 kW generator set, but that soon became unfeasible. “The dilemma was how to synchronize the older generator with a newer generator set without having to make extensive modifications to the older unit,” said Joseph Baran, professional engineer with Innovative Engineering Group, LLC, Tulsa, designers of the expanded treatment plant. “Bypassing the original generator set made the project feasible, while saving money and adding redundancy.”
The DGC 2020 digital generator controller provides I2/t protection on the generator, which covers over-current due to shorts or other malfunctions. If a fault occurs on the system, the motorized breakers will take the units offline. In essence, the DGC 2020 is capable of typical generator set control protocols as well as functionality found in paralleling switchgear, providing an integrated, cost effective solution to paralleling applications.
Esau explained, “After the signal for the generators to start, the paralleling process works like this: The first unit to attain voltage and frequency within the nominal operational bandwidth will communicate to other units on the system and request dead-bus closure while inhibiting other units from closing on the bus. This ‘dead bus arbitration’ optimizes load acceptance and emergency power availably.”
Single fuel tank simplifies operation
Omitting switchgear significantly reduced the footprint of the entire system — good news for plant officials, because space was already allocated to pumps, controls and filters. Another plus is that three generator sets offer redundancy and higher reliability than one single generator set, but because of the absence of paralleling switchgear, the new system doesn’t add complexity. To further save valuable floor space, all three generators sit on top of a single 7,500-gallon fuel tank that provides a 72-hour runtime and reduces hassles during refueling.
With its expanded water treatment capacity, Rural Water District #3 will be able to deliver water to residents well into the future, no matter what the weather does to utility power. And relying on digital controllers instead of paralleling switchgear for its power system allows the district to minimize capital spending and simplify its operation today.