The cost to travel ten miles doesn’t seem expensive: most people drive more than ten miles every day for less than the cost of a gallon of gas. But to a utility company faced with extending three-phase distribution to rural parts of the country, ten miles is quite expensive, at a total cost of somewhere near $200,000 per mile. When faced with the need to deliver three-phase power to a sand mine in rural Georgia, the local utility company chose to get creative.
With a single low power three-phase user in the area, the cost was prohibitive. Rountree Construction had been using rotary phase converters at another nearby sand mine that was now closed down. Rountree was not pleased with the past maintenance history of those rotary converters which caused disruptions for the mine when the converters shut down. The Principle Engineer with the local utility explained that the high amps generated when starting each converter on the weak line were causing power quality problems downstream. With multiple rotary phase converters on-site, the downstream power quality concerns were amplified.
A 1-to-3 MicroGrid Power Source™ from Single Phase Power Solutions provides clean, stable three-phase power from the single-phase utility service on-site, addressing the needs of both the power utility and the end customer.
Mining for sand, and more power
The sand mine operates two production lines six days a week, 360 days a year. A dredge pumps material from the lakebed to a processing plant, where sand is washed, drained, dried and prepared for delivery. All said, upwards of ten different motors, with a combined total of 220Hp, run 10-12 hours a day, creating a sizable demand for consistent power.
For years, the open dredge system at the now-closed sand mine ran multiple rotary phase converters to convert the single-phase service to three-phase power. The power supply was inconsistent, vulnerable to lightning strikes and voltage sags in the summer. A slight disruption would cause one or more of the converters scattered around the site to kick-off,
creating problems for the continuous operation. Depending upon the severity of the problem, the site would be down from 15 minutes to 6 hours, so it was not only a nuisance, it was expensive.
The sand mine was the only business around for miles, and with its limited service life (approximately 10 years), it wasn’t profitable for the utility company to extend three-phase service for the 10-miles required.
Shockingly simple solutions
According to the Principle Engineer, rather than extend three-phase service the entire ten miles, the utility company extended the line half the distance, in order to better balance out the single-phase loads, and chose to install a pair of 1-to-3 Microgrid Power Sources TM utilizing the patented BELLE TM Written-Pole motor for the sand mine. Generating clean, stable, three-phase power with the pair of 100-HP 1-to-3’s has simplified the power generating process and resulted in more reliable and consistent power, even in the heat of summer. And the skid-mounted 1-to-3’s can be moved to a
new site when the mining venture has run its course and the mine ceases production.
Before the utility company installed the solution on-site, they wanted to make sure the 1-to-3 Microgrid Power Source TM could successfully start the plant’s largest motors. That capability was tested at the Electric Power Research Institute’s test facility in Knoxville, Tennessee. The testing produced positive results, so the company had a concrete slab poured on-site and awaited the shipment of two 1-to-3 Microgrid Power Sources TM.
A utility company crane offloaded and positioned the two skid-mounted generators. Each of the 100-HP 1-to-3 Microgrid Power Sources™ generates 75kw of total power which can power several motors. The largest motor that the plant powers is a 30 HP freshwater pump that feeds the wash plant.
Previously, when the operators started operations at the sand mine, each of the dozen or so rotary converters created an in-rush of amps on the system, causing voltage flicker on the system and an inefficient poor power factor. At the sand mine, the fickle rotary phase converters were unable to handle the voltage fluctuation inherent with being at the end of the line.
Because of the multiple rotary converters scattered around the old plant, it was possible for a single converter to shut down while the others kept operating. If crews were unable to re-start the converter before a jam was created, they’d have to manually clear the jam, which often meant unbolting pipes, unplugging the pipes, rinsing the system, and restarting the production line. A labor-intensive and time-consuming process that resulted in lost production. The stable power generated by the 1-to-3’s has eliminated the jams.
The utility spent close to $300,000 in the project, including equipment, pre-installation testing, and site prep—which is far less expensive than running three-phase power for ten miles to the site.
“Our primary goal when we undertook this project was to find the best cost solution to provide reliable three-phase power in a rural area of our service territory where there was no expectation of three-phase load growth.,” the Principle Engineer explained.
With no other demand for three-phase power in the area, the setup was an effective, simple solution, with powerful results.
Loads of compliments, all around
The 1-to-3 TM delivers strong three-phase power with excellent voltage regulation capable of starting and running large three-phase motors while providing a high power factor load typically at 0.95 that does not create any harmonics which can be harmful to sensitive loads. The sand mine three-phase motors produce a poor power factor in the range of 0.65. The utility line is isolated from that poor power factor from the sand mines partially loaded three-phase motors because the 1-to-3 TM generator is providing that while being mechanically coupled to the high power factor BELLE TM Written-Pole motor the utility has as a load.
“What the actual load looks like to us is a huge advantage, these two Written Pole Motors are presenting a power factor that’s better than 0.95,” the Principle Engineer said.
The Written-Pole® Motor that drives the 1-to-3 TM produces clean, balanced voltage even while starting multiple smaller 3-phase motors. Written-Pole® Motors start using only 1.7x their rated running current, minimizing the voltage “flicker” that can cause problems on long distribution lines. Starting the equipment now just requires two-starts on the system, decreasing the likelihood of in-rushes that cause voltage inconsistency.
The efficiency rating of the motor is 95.5% and generator efficiency is 93.5%. The result is an overall efficiency of 89%, which keeps the sand mines equipment running efficiently and turning out product. The utility company is immune to the in-rush, the power factor is much better, and the sand mine gets stable, clean power all day: a true win-win situation. Surge protectors installed on the input and output of the system defends the 1-to-3 TM from lightning strike voltage surge, ensuring consistency in foul
weather.
Ordinarily, the utility company targets to maintain within 5% of the voltage, but because the 1-to-3 TM has built-in voltage regulation, the sand mine stays at 470 volts with less than 1% voltage imbalance all day, every day, even in the heat of the summer.
The solution that the utility company designed is a unique combination of new 1-to-3 TM technology with standard Written Pole Motors—so unique that the utility company has nominated the project for an innovative technology award at the Southeastern Electric Exchange.
Since the installation, the Single Phase product has run consistently, just as the testing suggested. The 1-to-3 Microgrid Power Source™ provides true, balanced, three-phase power that helps the sand mine stay up and pumping, not down and out. The sand mine owner is pleasantly surprised with the uptime that the plant achieves due to the stable power supply.
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