“The impact on the Nugget was probably small compared to a lot of other businesses, especially restaurants,” Nugget Theater owner Jim Bedford said. “We had to give some passes back and some cash back. If the power had been out for 10 or 15 minutes we can hold people at the theater. A half an hour or longer we have to tell people we can’t serve them.”
San Miguel Power Association officials initially reported that a historic 32-megawatt demand on its system tripped the main breaker at its substation near Society Turn, but now aren’t sure exactly what tripped the main break and are continuing to investigate the outage.
As SMPA General Manager Kevin Ritter explained in an interview on Tuesday, it was a piece of protective equipment called a differential relay at the SMPA substation that tripped, causing the power outage. Ritter said all substations have this equipment to protect the system’s transformers, which are costly to repair if damaged. Once the differential relay detects a major variation in the voltages coming out of the transformer it will flip it off, as this could be an indication of an internal problem with the transformer.
After the outage occurred last week, a Telluride-based SMPA lineman was called in to investigate the outage at the Society Turn substation and to restore power. Ritter said restoring power isn’t as easy a just flipping a switch back on. Whenever the power is off for any period of time, especially in cold weather, when crews turn it back on there is a “rush current” for a short period of time. This “rush current” is a spike in usage where basically every motor, heater and appliance that has been off during the outage is just getting up an running. To manage this extremely high demand, especially during peak hours, the responding lineman had to open line breakers in sequence, causing some areas to have restored power sooner than other areas. Without systematically opening the power system on, the “rush current” would have more than likely tripped the differential relay again.
Although, Ritter said, the demand that evening was at historic levels, SMPA is still trying to figure out what caused the differential relay to trip. One of the last areas to be turned on was Mountain Village because a different fuse blew up there and that fuse could have caused the initial variation in voltage, which caused the outage.
“This is still under investigation,” Ritter said. “One of the theories is that the fuse in Mountain Village was the first thing to blow and that caused the difference in voltage. That could have been the trigger. It was the highest demand that we have seen at that substation so far.”
Ritter said that because the power outage occurred at a time of peak demand, the time it took to restore power was not unusual. He added, though, that every aspect of the outage and the response to restore power will be further analyzed.
“From SMPA’s standpoint, we are going to evaluate that and see if there is a better way to operate,” he said. “One merchant asked if we could have somebody on duty at the substation during peak times. We are going to look at that and see if there is a better way to respond. Having an outage during that particular time of night during that time of year is a very significant hit to the businesses up there and we want to say we are aware of that and we will take this very seriously.
“We are going to evaluate the technical aspects of the outage to improve the reaction of our equipment and we are going to take hard look at this and see how we can improve.”
Construction of New Transmission Line to Begin in May
SMPA officials have been warning for years that the region is vulnerable to power outages, and an upgrade of an existing transmission line from Nucla to Telluride is planned to provide an additional source of power. But even if that line were in place, it would not have prevented last week’s outage, Ritter said. “Since it happened at the substation and not at the distribution system, the new line would not have helped it,” Ritter said. “It wouldn’t have been any value to us in terms of backing us up in this instance.”
It’s been almost two years since San Miguel County, the Tri-State Generation and Transmission Assn., the Colorado Public Utility Commission, and a handful of private homeowners came to an agreement and ended a 10-year standoff on converting SMPA’s aging 69kV Nucla Power line to a modern 115kV transmission line.
The Telluride region’s primary source of power now is a 115kV transmission line that originates near Hesperus and crosses Coal Bank, Molas and Ophir passes in areas highly vulnerable to avalanches. If that line were to be taken out, it might not be reparable until the spring, forcing the area to depend on the 69kV line. That line is inadequate to meet demand, and rolling blackouts would be necessary. By upgrading to Nucla line to 115kV, a complete transmission line loop would be constructed, thus taking out the high risk of losing power for extended periods of time.
Tri-State’s Nucla to Sunshine 115 kV transmission project will replace the existing 69 kV line. The project is scheduled to begin construction in spring 2010 with completion expected in 2012. Tri-State will own and operate the line, as it is a transmission operator. The old line will be removed and a new line will be constructed, following some of the original alignment.
The new line will start at the Nucla Substation, west of Naturita and will terminate at the Sunshine Substation near Telluride. The project encompasses approximately 50 miles of new line and transmission facilities, including:
- • Constructing a new 19.9-mile-long, 115 kV line from the Nucla Substation to the Norwood Substation, across portions of Montrose and San Miguel counties.
• Constructing a new 30.4-mile-long, 115 kV transmission line from the Norwood Substation to the Sunshine Substation near Mountain Village on Ilium Road consisting of 20.4 miles of overhead line and 10 miles of underground line (across portions of Specie and Wilson mesas in San Miguel County).
• Expanding the Norwood Substation, near the town of Norwood on two acres of private land.
• Replacement the existing Wilson Mesa Substation.
• Modifying the existing Nucla and Sunshine substations.
• SMPA will remove the Oak Hill Substation on Wrights Mesa and Specie Mesa Substation, reclaiming the property to its original state.