Unique real time reactive compensation (RTRC) bank helps automotive plant avoid costly downtime and production disruptions.
A few years ago, Chrysler Corporation faced a dilemma that defied a cost-effective solution: how to reduce secondary load current and boost bus voltage at its Toledo Machining Plant without completely overhauling its electrical distribution system.
The automotive giant found the answer in a unique technology that instantaneously compensates for reactive and harmonic currents. The Square D REACTIVAR AV9000 Real Time Reactive Compensation (RTRC) Bank consists of three AV9000 and six AV7000 Automatic Filter Systems installed within the plant's nine roof-mounted 15kV/480V substations.
The first of its kind installed in a North American automotive plant, this system allowed Chrysler to proceed with expansion plans without building new substations and busways. In the long run, management expects to save several hundred thousand dollars in annual downtime at the plant.
The first RTRC shipped to the field was installed in Substation No. 4B at the Perrysburg, Ohio facility. The bank is rated at 600kVAR, and comprises six individually switched, discrete 100kVAR steps. Electronic switching elements provide transient-free connection or disconnection within one cycle (16.6 ms) of a load fluctuation. The unit compensates for rapidly changing reactive currents required by inductive loads as well as high-frequency, non-linear harmonic currents generated by welders, VFDs, motor soft starters, etc.
According to Chrysler Plant Engineer Ken Reeves, prior to installing the RTRC, power factor in Substation No. 4 (the most heavily loaded in the plant) varied between 47% and 60% as unsynchronized spot welders were operated and other equipment was cycled.
"That meant reactive current was nearly as high as active current; a condition that overloaded busways, cables, and transformers and wasted perhaps 2% energy as I2R losses. The other substations weren't much better," says Reeves. "Bus hot spots, as measured by a portable infrared detector, could exceed 300 DegrF."
Until now, correcting power factor proved to be impossible because engineers were shooting at a moving target with the welding loads, says Reeves. Power factor typically changed two or three times per second when viewed on a digital meter in the substations. Contactor-actuated banks designed to switch incremental amounts of capacitance (even every 30 sec) were too slow and would also generate transients. Reeves says the only practical solution was brute force; installing sufficient transformer and bus ca pacities to handle the unwanted currents.
Payback is proceeding at a rate of $45,000 to $50,000 per month from higher production, fewer scrap parts, and a reduction in power factor penalty charges. Based on these outstanding results, the system has proven both efficient and productive.