Northfield Mountain Pumped Storage Station, Northfield, Mass.
FirstLight Power Resources’ Northfield Mountain pumped storage hydroelectric power station pumps water from the Connecticut river to an upper reservoir during periods of low power demand. Then, at times of high demand, water is released down a 1,100-foot pressure shaft to power a turbine generator.
Northfield Mountain’s power generators are maintained by two 202-ton overhead cranes, original equipment from 1972. Periodically the cranes are locked together using an umbilical cord to perform tandem picks of unwieldy components worth millions.
According to mechanical maintenance supervisor Brian Keir, the workload of the cranes with their 30-minute motors became more demanding over time. When Konecranes inspected the cranes they found burned insulation on wires for the brake systems and resistors, caused by the cranes running in creep speed for two hours or more to perform turbine repairs. Northfield Mountain was gearing up for a major outage, and it was clear their cranes were not up to the task.
“We began doing research for the upgrade,” said Keir. “We continuously had trouble with the cranes resistor banks and one motor. Konecranes representative Ben Poudrier showed us that the cranes were the wrong duty cycle for what we were trying to do with them.”
Based on Poudrier’s proposal, the facility had Konecranes upgrade all motors and controls on the cranes with continuous duty inverter controls that could run in creep speed for as long as was required.
New radio controls allowed the same operation from the floor as from the cab. Now when the cranes pick up a 22.5-foot rotor weighing 360 tons, they can use infinitely adjustable, inverter-controlled creep speed to prevent damage. Even more helpful, tandem picks of heavy, oversized and pricey components can now be done at the flick of a switch wirelessly through PLCs instead of physically wiring the cranes together, saving three days on each side.
Konecranes expedited the order and install to just 12 weeks to allow Northfield Mountain to build the cost of the major crane upgrades into their overall scenario for the outage.