Mt. Pleasant electric substation goes online

Mt. Pleasant's new electric substation is up and running.

The Iris Street substation project was officially completed in October and is now distributing electricity to about half of the city, according to Mt. Pleasant Municipal Utilities General Manager Jack Hedgecock.

'Initially, we're going to load half the town,” Hegecock said. 'Everything east of Grand will be on this sub (short for substation).

'This sub will carry the entire town if we have an anomaly, we lose transmission source or have a catastrophic failure at one of our other subs, we can feed the whole town off this.”

The new 'sub” sits on about an acre of land on Iris Street, just south of East Washington Street.

The approximately $4 million project has been in the planning stages for nearly a decade.

Hedgecock said that not long after he came to work for the utility in 2011, they conducted a study on the city's electricity distribution system.

'We started looking at what might happen if some of this (east side) development if we started plopping additional load down,” he said. 'It would cause us more concerns. To better serve our customers and to be able to provide redundancy and get some of that exposure down, we started the plans to build this new substation.”

Hedgecock explained that the city's other two substations provide enough capacity to serve the city's electricity demands, which he said is in the 20 megawatt range.

'The issue we have is that all the load growth in the city of Mt. Pleasant is in the wrong place,” he said. 'It's over in the far east corner of our town. We've got a lot of development over here.”

He said that the Park substation, which previously fed the east side of the city, is about 7.5 circuit miles away.

'There's a lot of exposure to critters getting up in the line and things like that,” Hedgecock said. 'There's also a lot of voltage drop between there and where all the load is at.”

A one-acre site for the new substation was purchased in December 2014.

In an effort to protect rate-payers, the utility spread the capital investment out over time.

'You don't want to have to do it all at once,” Hedgecock said. 'We were able to save money and spread the expense over time, so we wouldn't have to raise rates to do this.”

The utility's chief financial officer Randy Neff said that they did not want to have to borrow money to pay for the project.

'We've been saving for this substation for almost a decade, and we paid cash for it,” Neff said.

Neff said that the utility was able to do that by funding its depreciation to the tune of about $800,000 annually.

'That's how we can do these projects,” Neff said. 'We build our budget to have money available to us to do these kinds of things.”

Neff estimated that the utility saved about $400,000 in interest by not having to use revenue bonds to finance the project.

'That's money our rate-payers, our customers, don't have to pay embedded in the rates,” Hedgecock said. 'We haven't raised rates in a long time, and we don't intend to.”

Hedgecock said that additional money was saved by the utility acting as the general contractor on the bulk of the project.

'We didn't hire somebody and let them sub it out to somebody else and pay the markup,” he said. 'We solicited the bids, and we helped with the technical specs.”

They worked with Shermco Industries on some of the higher-end engineering for the project, while the ESCO Group won the bid for the construction in 2019.

A substation transforms high voltage service delivery down to lower voltage that can be safely delivered to customers.

'It takes 69,000-volt transmission voltage down to 7,200 single-phase and 12,500 three-phase, which is distribution voltage,” Hedgecock explained. 'Then, you have transformers at your home that take it from that level down to 120/240, which is what you have in your home.”

Part of the project was the design and construction of one mile of high-voltage transmission line to feed the substation at a cost of about $1 million.

The new lines feed into a circuit switcher inside the substation, which Hedgecock said is a protective device that looks for faults in the electricity.

The circuit switcher sends the electricity to the transformer, which converts the electricity down to distribution levels.

Hedgecock said that the transformer is capable of handling up to 25 megawatts of power and has 4,600 gallons of mineral oil in it.

There is a containment vault under the transformer that can hold the entire 4,600 gallons if there is a leak to keep it from spreading to the nearby creek.

The transformer sends the power to the control house via underground cables.

The control house has several compartments, each one with a feeder that controls distribution to designated areas of the city.

Hegecock said that the substation was built with safety in mind.

'We have the most technologically advanced relays that you can realistically buy,” he said. 'If there's a wire on the ground or there is an anomaly, the protective devices in the sub will clear it effectively.”

With that project done, the utility is now eying future projects.

Hedgecock said that there are plans to increase the city's power-generating capability, as well as a new water well project that is expected to start in the spring.