Maintaining all the equipment in our local grid – which spans 1,155 square miles – is an enormous undertaking.
Tucson Electric Power’s electrical system is an intricate network of power lines, substations, circuits and utility poles. Since 2021, we have invested about $1.7 billion and thousands of hours to maintain the integrity of our system and keep equipment in top working order.
“Over the past 130 years, our local electric grid has greatly expanded and become increasingly more complex,” said Ana Bustamante, TEP’s Vice President of Energy Delivery. “All of our 321 field operations employees are focused on the challenging task of testing, maintaining, upgrading and expanding this equipment that’s essential to powering our lives.”
Here’s what we do to maintain the major components of our electrical system to ensure the safe, reliable delivery of energy to homes and businesses, especially given forecasted growth in grid demand.
Keeping the Power Flowing
TEP’s transmission lines carry higher voltage electricity from generating stations across many miles into communities. They’re critical to maintain because any fault could cause a widespread outage.
Our transmission system includes 5,500 towers and covers a lot of ground. If you strung out all our overhead 500-, 345- and 138-kilovolt (kV) transmission lines end to end, they would stretch nearly from Tucson to Manhattan: 2,200 miles.
TEP conducts ground patrols as well as semi-annual aerial inspections by helicopter to check the condition of our high-voltage lines, towers, anchors and guy wires. Our inspectors also look for signs of vandalism and vegetation encroachment.
“Anything needing repair is assigned a priority level, with highest priority items addressed immediately. Other priority issues are addressed within 30 days,” said David Wagner, TEP Director of Transmission & Distribution Line Construction and Metering. “Less critical items are sent to our maintenance planner so that they can be added to the schedule and are grouped by geographical area for efficiency.”
As a proactive measure, TEP has been systematically replacing older 138-kV wood structures with steel poles since 2012 to harden our transmission system.
Tending to Substations
TEP’s 123 substations – which house transformers, switches and circuit breakers – serve as an important link between our transmission and distribution systems. Substation transformers “step down” high voltage electricity from transmission to lower voltages for distribution through circuits into neighborhoods. Each roughly $2 million substation transformer – which can take up to two years to procure and build – serves thousands of customers.
“We follow a well-defined and disciplined maintenance schedule that includes rating the condition of each transformer every year with a health index number to determine its equipment life,” explained Ernesto Ojeda, Director of Equipment & Asset Management. “We look at the oil condition, its maintenance and reliability history, age and other factors. This allows engineers to estimate its remaining life and plan a maintenance and replacement schedule.”
The condition of the oil in the transformers also is monitored and tested regularly by crews. Some of our transformers have an online monitor that samples the oil and sends an alert to system control if it detects gas buildup.
In addition to our installed substations, TEP maintains mobile substations and transformers for use during extended outages, times of high energy usage or when we’re making upgrades and improvements to equipment.
Maintenance for our most critical substation circuit breakers is scheduled based on the manufacturers’ recommendations, subject matter expertise, or as needed based on the results of diagnostic tests. “All our newer substations use telemetry to remotely monitor and detect faults and provide an alarm to help pinpoint problems,” Ojeda said.
If a circuit breaker needs maintenance or to be replaced, TEP uses spares while the breakers are replaced, relubricated or refurbished. As a proactive measure in 2011, TEP accelerated the replacement of aging breakers to improve system reliability. Each year, we replace about 23 breakers and overhaul another 30 or so to extend their useful lives.
Checking Distribution Lines and Cables
TEP’s distribution system consists of more than 3,100 miles of overhead lines and more than 4,900 miles of underground cables that carry lower voltage electricity from our substations through circuits to customers. Inspectors visually inspect the condition of the lines, crossarms and pad-mounted equipment on a three-year cycle.
Engineers conduct a critical circuit analysis each year to evaluate our 482 circuits for their reliability based on outage data, demand, capacity, age and load. Some 315 remote sensors installed in our system also detect power interruptions in real-time to identify faults so that repairs and upgrades can be scheduled.
While underground and feeder cables require less maintenance, the insulation breaks down over time because of the stress from the electric field and must be replaced more frequently than overhead conductors.
Our crews inspect them using a very low frequency test to gather information about the insulation quality and remaining cable life. This test along with statistical analysis based on the cable’s age and environmental issues are used to assess cables, identify any potential problems and proactively make repairs.
“In addition to all our regular maintenance, there’s a lot of proactive work being done by our engineers to reinforce the integrity of our system,” Wagner said. “They are constantly identifying heavily loaded circuits that are driven by hotter summers, new growth and development. As they reach their capacity, we may need to add a new substation or upgrade our system.”
Testing and Replacing Poles
More than 107,000 utility poles and structures dot the landscape of our service area and transmission corridors. Even though some of our poles were installed decades ago, they remain useful if they’re solid, sturdy and dependable.
To test the strength of our poles, crews perform a resistance test. This involves drilling three small holes in specific locations of the pole to assess its structural integrity and identify signs of rot or decay. Our engineers use the results from the test to determine which poles need replacement.
“All of the distribution system poles and pad-mounted equipment are visually inspected or tested every three years,” said Wagner. “We conduct a detailed wood pole inspection that includes resistance testing to pick which poles are next to be replaced for our pole replacement program,” Wagner said. “We are trying to convert wood poles to steel, but in some areas where bucket trucks have poor access, we use wood poles so crews can safely climb them to make repairs.”
Carlet Castro, Director of Enterprise Project Delivery, said TEP replaces about 1,200 poles a year, due to storm or vehicle damage, routine maintenance, system upgrades and line relocations. “This does not include new pole installations driven by new system reinforcement and business development,” she said.
Trimming Back Vegetation
Finally, a big part of maintaining our system involves vegetation management. Trees and vegetation that encroach on our lines or equipment must be trimmed back to ensure service reliability.
To provide a wide clearance for our transmission lines, employees inspect and monitor vegetation growth by ground and air. Vegetation is trimmed based on a five-year growth cycle to comply with mandatory North American Electric Reliability standards. Keeping our transmission lines free of interference from vegetation helps reduce potential fuel sources for wildfires and prevent power outages.
We also continuously monitor 120,000 trees in public rights-of-way and trim 20,000 a year to cover our entire service area over six years. Using mobile technology, we track historical vegetation growth patterns to identify areas of faster growth that might need more frequent trimming. Our tree trimming crews also are on standby for emergencies if downed branches or trees must be removed to help us restore power sooner.
TEP stepped up our wildfire prevention efforts this year with a new plan designed to reduce the risk of utility-caused wildfires in hot, dry desert areas. We expect to spend about $3.6 million this year on wildfire mitigation, including equipment, software, and training. We also anticipate additional investments to protect public safety in areas prone to wildfires.
“We expend enormous resources and effort into maintaining and enhancing our grid because we know our customers count on us,” Bustamante said. “We are honored and proud of our employee’s dedication to ensuring reliable service to the greater Tucson community.”
