Download PDF: Case Study: Finding a Power Quality Needle in a 30-Mile Haystack
Measuring tools: Fluke-RPM Recorder, ScopeMeter??, 41B Power Harmonic Meter
Operator: Bill McConnell, Var+Technologies and Vaughn DeCrausaz, Starboard Electric
Inspections: Power quality/harmonics logging at site, voltage distortion at multiple feeder lines
At the end of April 2005, Crystal Mountain Resort in Washington suffered catastrophic failure of two power filters associated with their chair lifts. The ski resort had just closed down for the season. Maintenance personnel were doing the end of the season maintenance and cleanup when they smelled the overheated reactors on the power filters. Crystal Mountain has four Var+Controls harmonic power filters located in the lift houses of their highest horsepower chair lifts. All of the filter units are programmed with two fixed steps to adjust to loading and power conditions to absorb harmonic distortion, and the rest of the steps automatically turn on to obtain unity power factor for the greatest electrical efficiency when the lifts are in operation.
Crystal Mountain's electrical personnel measured the harmonic current in the power filters to determine the damage to the units. With the help of Bill McConnell of Var+Technologies, the team found that only the C-phase reactors in two of the power filters were damaged. They replaced those reactors and continued investigating the cause of the failure throughout the summer. The filters were louder than usual but seemed to work.
At the start of the 2005 - 2006 ski season, the electrical maintenance personnel noted that, as more chair lifts were brought on line, the more overloaded the power filters became. They turned the filters off in an attempt to save the equipment and decrease the noise and smell in the lift houses. With the power filters off line, the lift dc drives were noisy, pumping systems on the mountain malfunctioned, variable frequency drives on conveyors tripped off-line and data capture credit card systems failed. At that point, the team called Bill McConnell of Var+Technologies and Vaughn DeCrausaz of Starboard Electric to help troubleshoot the ski area's overall power system. Given the approaching Thanksgiving and Christmas holidays, finding a solution was of paramount importance.
The team consulted the local utility company to verify whether any changes in their system had occurred at the end of April. Were any new underground lines installed? Had any capacitor bank been installed or modified? Had any large loads been installed or removed?
The utility felt that the problems were caused by some of the old 12 kv underground line located on the ski area. So, the team tested this theory by starting the mountain's 2000 kw backup generator at night with no lifts running and monitoring the voltage and current at one of the power filters. With the generator on in parallel (co-generating) with the utility, the 5th harmonic current to the power filter reduced to 60 amps, 72 amps and 88 amps, on phases A, B and C respectively. With the utility removed from the circuit, the 5th harmonic current was further reduced and balanced to 25 amps, 22 amps and 24 amps. This test proved the problem was on the utility system between Greenwater and the backup generator and not on Crystal's property.
Later at the ski area, the following voltage waveform was recorded at Lift 11 with the mountain shutdown for the evening. Note the amount of distortion still on the utility system. That evening at the ski area, all the power filters were put on-line and measurements taken to prove their health. The voltage distortion at the area was reduced to 3.1 % THD. The next day, technicians turned on all of the lifts with all four filters and all of the pumping stations and conveyors online. The voltage waveform below is at Lift 11 with all the lifts and filters on line.
