Many ski areas have been upgrading the electrical drives on existing ski lifts. Most common among these upgrades is a complete replacement of an old motor and controls with a new DC analog or digital drive system. Some newer upgrades amount to “re-powers” that convert analog DC drives to digitally controlled DC drives. Another approach is to use new AC variable-frequency drives (VFD) as retrofits with high-tech controls that provide flexibility to both existing constant-speed fixed-grip lifts as well as variable-speed, fixed-grips.
A large base of working fixed-grip, AC-powered lifts exists in North America and throughout the world. Most of these fall into two categories. The first uses a hydraulic coupling to adjust the speed of the lift. Unfortunately, lift speed continuously changes with the number of passengers, and with the temperature and level of the hydraulic fluid. This type of arrangement is most often found on open ring-and-pinion gear reducer lifts. These lifts make it difficult for operators to adjust and maintain the lift’s speed.
The second category of fixed-grip lift gets its power from a wound-rotor motor. Its speed is changed by a drum controller that regulates a series of resistors that can be switched in and out of the motor circuit manually. The resistors in the controller are inefficient, dissipating energy in the form of heat inside the operator building, and adding to the ski area’s utility bill. Because most of these units are not built for continuous low speeds (less than 75 percent of max speed), this type of control system can also overheat. This tendency to overheat has inspired some personnel to dry clothing and warm lunches on the protective screen that makes up part of the large “toaster” cage that typically houses the resistor bank. In turn, those drying gloves and warmed lunches would catch fire, sometimes igniting the entire shack.
When a VFD is installed between the lift motor and the power source, either the hydraulic clutch or the resistors and controller are removed. Operations and maintenance become easier, lift speed is readily adjusted by the operator and the electric bill drops; at times substantially.
Case I
In 1999, Mohawk Mountain, Conn., retrofitted their Lift #4 with a 480-volt VFD. The Hall triple, originally installed in 1978, is 3,200 feet long with a vertical drop of 650 feet and has 120 chairs. The lift was installed with a 150 horsepower fixed-speed AC motor and transferred power through a Nelson fluid drive. Mohawk’s reason for undertaking the retrofit was to improve the lift’s speed regulation to make loading easier.
Steve Hedden, Mohawk’s vice president, led the project. First, his crew removed the fluid drive and put the existing motor in its place while moving the coupling. After removing the cumbersome cooling system and the reduced voltage starter, they installed a new VFD (an ACS 600) matched to the 150 horsepower induction-motor. Then it was a matter of reconnecting input and output power cables to the drive. Because Mohawk was able to connect the existing control panel’s handful of wires directly to the digital inputs of the new drive, the summer project took approximately two and a half days.
Hedden said his maintenance staff and lift operators were all pleasantly surprised with the results. The operators found that they were able to stop and start the lift smoothly regardless of the load. Fluid level and temperature were no longer factors. Mohawk personnel were also able to operate the lift at multiple speeds and make smooth changes at will, which dramatically cut the number of bad loads and improved their ability to load physically-challenged skiers and small children. Additionally, they increased overall capacity because the new controls significantly cut the number of full stops. Now, instead of stopping, they slow the lift down when guests need extra help. Besides making their jobs easier, the operators noted that the smooth ride resulted in increased comfort and overall guest satisfaction.
Maintenance staff at Mohawk found that the modified drive requires less attention to keep it running throughout the season and is also more efficient, saving on the ski area’s electric bill. Though no hard numbers are available (Mohawk has lighting and snowmaking on the same service as the lift), Hedden says the ski area is probably saving between 10 and 12 percent on its electric bill.
“To maintain constant speed prior to the retrofit,” Hedden says, “we had to have an operator standing by to constantly adjust the clutch settings. Now the lift runs at a constant speed, no matter what speed we select. We also noticed a dramatic reduction in the noise level in the lift shack. The original Nelson liquid drive was deafening.”
In addition to the ABB upgrade, Hedden and his crew have completed a retrofit on a wound-rotor motor powered lift. This one is a 100 horsepower Carlevario and Salvio that is 3,400 feet long, has 98 chairs and was originally installed in 1960. Hedden is planning a third upgrade for this summer.
Case II
In 1998, Boyne Highlands Resort, Mich., fitted a new VFD to a Riblet double called Amy’s Lift. The double, originally installed in 1967, is powered by a 125 horsepower GE, AC wound-rotor motor and is 2,160 feet long with a vertical drop of 370 feet and 95 chairs. Gordie Buynak, Boyne Highlands maintenance manager, oversaw the installation. After doing research on an alternative plan including buying a DC drive or a new AC motor conversion, he found that keeping the existing motor and going with a new VFD would cost much less.
First, he removed a room full of resistors and the old motorized drum controller. Then the resistors were replaced by external shorting bars in the motor’s rotor circuit. Next, Buynak’s crew connected the new VFD in the circuit in front of the existing motor.
Because the job entailed rewiring the entire terminal to connect to a new control panel, it took longer than simply adding a new VFD. “If you use the existing control panel,” says Buynak, “there are only about six pairs of wires to tie into the panel.”
Boyne Highlands experienced all of the benefits that Mohawk Mountain did, with one important addition; they no longer waste energy on the resistors and their power costs dropped even more dramatically than those at Mohawk. Buynak also found that the new drive was almost maintenance-free when compared to the old setup. The old parts were expensive and difficult to find and there are significantly fewer moving parts associated with the new drives. “We’ve noticed a big decrease in motor damage and replacement costs,” says Buynak.
“We had a coupler problem on Amy’s Lift,” he adds, “and without the variable-frequency drive, which allowed 100 RPM speeds, we never would have been able to pinpoint the problem. We were also able to heat the lift shack with an energy-efficient, thermostatically-controlled heater instead of the wasted energy of the grid resistors. Lastly, with the old drum controller, we had to hit the start button and hold the fast button for five seconds before the lift would even move. With the new VFD installed, we hit the start button and the lift takes off under a controlled acceleration ramp every time.” Boyne Highlands has also gone on to make similar improvements on two other lifts, Camelot and North Face, and has two more scheduled for this summer. And, the new drive also makes training new lift operators on the system much easier.
This type of retrofit is not limited to the U.S. In 1998, Cardrona Alpine Resort in New Zealand installed a VFD on a fixed-grip. The bonuses there were less maintenance and the ability to adjust speed for summer hikers and cyclists.
So when flexibility and efficiency are the goal and when line equipment is in good shape, a new VFD might be in order. However, because the new drives need to be carefully matched to existing power sources, the drive supplier should be called in early to evaluate motors for their compatibility. Not all AC motors can be re-used in upgraded variable-frequency systems.
For more information, contact Troy Miller at (262) 785-3352.
