Why is the Algood Transmission Line Needed?

The problem

There are three transmission issues in the Algood-Cookeville area.

• TVA’s West Cookeville 161kv Substation transformer bank is projected to be above its calculated capability by summer 2008.
• Upper Cumberland EMC’s Algood 69kv Substation is projected to be above its firm* capability by summer 2008.
• TVA’s West Cookeville-East Cookeville-Algood 69kv Transmission Line will exceed its capability by summer 2008.

*Firm means if one of the transformers is lost the other does not have the capability to feed the entire load. Therefore, it is overload.

TVA’s West Cookeville Substation

TVA’s West Cookeville Substation (161-69-13-kilovolt (kV)) is the major source of TVA power for the Cookeville area. It provides power to one Upper Cumberland EMC substation - Algood - as well as three Cookeville ED substations - Cookeville District, North Cookeville and East Cookeville. These four substations are 69-kilovolt. Cookeville ED also owns the South Cookeville 161-kV substation, which is powered from TVA’s West Cookeville-Peavine161-kV line.

TVA’s West Cookeville Substation contains four 1-phase 161-69-13-kV transformers with a total calculated capability of 153 megavolt-amps (MVA). Summer 2008 load is projected to be 155.3 MVA, which is 2.3 MVA above its capability.

Shifting load from any of the four 69-kV substations to another one does not solve the problem because all four substations are powered from the same source - TVA’s West Cookeville Substation transformer, which is nearing overload. As the area continues to grow and power demand increases, the equipment will become overloaded by even greater amounts unless improvements are made to the transmission system.

An additional 8 megawatts of new electrical load is projected for Algood by the summer of 2008. This will increase the load on TVA’s West Cookeville transformer bank to 163.1 MVA, which exceeds its capability by 10.1 MVA. The proposed new transmission line will power the Algood Substation from a different source, thereby relieving the overloaded West Cookeville equipment.

Upper Cumberland EMC’s Algood Substation

Upper Cumberland EMC has one substation that serves its entire electrical load. The Algood Substation serves the town of Algood, part of Cookeville, Tennessee and part of White County, Tennessee. The substation contains two 3-phase 69-13-kV transformers that were built in 1968. They have a firm capability of 18.67 MVA. During the summer of 2006 these transformers were loaded at 19.42 MVA, which is above capability.

The area served by the Algood Substation is experiencing both commercial and residential growth, which is expected to continue due to its proximity to Hwy. 111 and I-40. Growth of more than 30% over the next 3-5 years has been identified, including a 400 unit apartment complex, two housing developments (36 homes), school, bank, drug store and three industries.

With the addition of this new load, the firm capability of the transformers will exceed capability by 7.73 MVA. To meet this and future growth, Upper Cumberland EMC plans to replace the 69-kilovolt Algood Substation with an Algood 161-kilovolt Substation. The firm capability of the new substation will be 33.3 MVA.

TVA’s West Cookeville-East Cookeville-Algood Transmission Line

TVA’s West Cookeville-East Cookeville-Algood 69-kV Transmission Line is approximately 8.4 miles long and contains 636,000 ACSR (Aluminum Conductor Steel Reinforced)  conductor (transmission line), plus a section of double-circuit 397,500 ACSR conductor. This 8.4-mile section is capable of handling 77.1 MVA during the summer. (Summer loading is considered because the capability for equipment is usually lower (more limiting) in the summer due to the ambient temperature.)  With the additional 8 megawatts of new load, this line is projected to be 84.2 MVA, which exceeds its capability by 7.1 MVA.

The proposed new transmission line will power the Algood Substation from a different source, thereby relieving the overloaded West Cookeville equipment.

What will happen if nothing is done?

Transformers and other electrical equipment that are loaded above their ability to carry the current can be damaged or fail completely. The amount of damage depends on how heavily the equipment is overloaded.

If a transformer and/or transmission line fails, the result is a power outage. Sometimes power can be restored by routing it along other lines, although UCEMC can feed only a small portion of the Algood load from other sources. In addition, this could cause the remaining equipment to become overloaded and risk failure.

Overloading of a transmission line can cause heating and cooling of the material, which weakens the line over time. Overloading can also cause a transmission line to sag more than the line was designed to do. This means the clearance from the line to the ground is inadequate and potentially unsafe.

The solution

Upper Cumberland EMC plans to replace the 69-kV Algood Substation with a 161-kV substation, which would add capacity, solve the overloading issues at the substation and provide adequate capacity to the area.

Overloading of both TVA’s West Cookeville Substation transformer and the West Cookeville-East Cookeville-Algood 69kv transmission Line would be relieved with construction of the proposed 161-kv transmission line because power will be brought into the area from a second source -- TVA’s West Cookeville- South Cookeville-Peavine 161-kV transmission line. In addition, the new line would improve the reliability of power in Algood since the power source to the substation can be fed from two directions.