To meet an already large and rapidly growing electricity demand in one of Russia’s most important industrial centers, the primary power provider of the city of Perm has been vigorously researching and evaluating new technologies.
The city of Perm is often referred to as the gateway to the Urals and is situated on the banks of the Kama River, the largest tributary of the Volga. The city’s electricity needs are supplied by PermEnergo, a subsidiary of MRSK-Urals, the primary utility providing power to the Ural Region, a huge area in Western Russia.
PermEnergo is responsible for the operation of 360 substations, having a voltage range from 35 kV to 110 kV, and some 12,784 distribution substations. The total installed transformer capacity is more than 11,000 MVA, and the transmission system and distribution network extends to 45,800 km (28,460 miles) operating voltage levels up to 110 kV. The company supplies electricity to the production enterprises and households in a territory of 160,000 sq km (61,776 sq miles), which has a population of 2.82 million people.
Mainly due to its location on the deep and easily navigable Kama River, which provides access to the prolific mining operations of the Urals, Perm has emerged as a major manufacturing hub for many of the nation’s most critical industries. These include oil refining, metallurgy, machine building, chemicals, aerospace, wood processing and foods. Additionally, several branches of the Russian Academy of Science and seven universities conduct research in and around this city.
One of the most significant issues facing MRSK-Urals has been the limited load transfer capacity of the existing overhead lines. Installing additional generating capacity is not difficult, but delivering the output to the load center is a major problem in a densely developed city like Perm, where line clearance and new tower construction present daunting challenges.
This limitation became especially evident when PermEnergo planned the construction and commissioning of a 124-MW combined-cycle gas turbine that tripled the generating capacity of the existing HPP-6 hydro-electric power plant to 175.7 MW. Distributing the additional capacity required a substantial increase in the load transfer capability of the existing 8-km (5-mile) double-circuit 110-kV line between the power plant and the 110/10/6-kV substation.
Uprating the Existing Line
Initially, the MRSK-Urals overhead line engineers believed that the required current-carrying capacity of the overhead line could be achieved by reconductoring the existing circuit with 300-sq-mm (0.465-sq-inch) cross-section aluminum conductors. However, this proposal would require the overhead line to be upgraded to 220-kV and require new towers be installed in dense urban areas. Also, the new conductor would fail to provide the necessary safety distance to ground for populated areas. Following due consideration of all the engineering variables and the restriction on the increased land use required by taller towers, the overhead line engineers sought an alternative solution.
As a result of further research, MRSK-Urals identified a more desirable solution: a new lightweight conductor manufactured by 3M — an aluminum conductor composite reinforced (ACCR). This conductor was being deployed in other Russian cities where overhead line upgrades involved challenges similar to those in Perm. In Moscow, for example, one circuit upgrade using this conductor had already been energized and a second similar installation was being planned.
Before its commercial launch in 2004, the ACCR conductor was subject to extensive field testing in extremely harsh climates for several years. The 3M ACCR conductor is now widely used by utilities in the United States and other countries for overhead line upgrades, especially in cases where tower construction and rights-of-way expansion present serious economic and logistical challenges.
This lightweight conductor is capable of more than doubling overhead line transfer capacity, often without needing larger towers. Additionally, the low coefficient of thermal expansion reduces the problems associated with conductor sag.
MRSK engineers compared the 3M ACCR solution with the originally proposed aluminum composite conductor and found it to be lighter and stronger, with an increased current-carrying capacity rated for continuous operation at very high temperatures. An equally important benefit of the comparison was the low sag eliminating the problem of infringing the statutory conductor to ground clearance.
Although the ACCR conductor is lighter than the AC 150/24 conductor, they both have similar cross-sectional areas. However, the composite in the ACCR conductor core and the aluminum alloy in the outer wires are designed for conductor temperatures above 200°C (392°F). Therefore, when the ACCR conductor is operated in the long-admissible mode, the current-carrying capacity is 195% higher than that of the AC conductor, 896 A compared with 450 A. Also, following cooling, the ACCR conductor features the same mechanical and physical properties.
The increased elongation created by the higher operating temperature is within the conductor’s elastic deformation, which is compensated by its greater rigidity and lower thermal expansion coefficient. This makes it possible to heat ACCR conductor without increasing the mid-span sag. When heated above 90°C (194°F), the AC conductor deforms the outer aluminum conductors creating the commonly referred to “birdcage effect.”
Based on the superior collective characteristics of 3M’s ACCR conductor, the Ostrich 300 T-16 was selected by MRSK-Urals for the Perm overhead line upgrading project.
Line Upgrading Project
The reconstruction of the 110-kV double-circuit high-voltage power line between the power plant and the Perm substation was completed in early 2011. The use of the ACCR conductor requires special software to calculate the design parameters as there are significant differences between overhead lines constructed using composite and standard aluminum conductors. The ACCR conductor allows a utility to design the most efficient and cost-effective overhead line supported by the minimum number of towers to upgrade an existing circuit because of its light weight.
The existing 110-kV double-circuit overhead line was supported by double-chain metal and concrete structures that were erected more than 40 years ago, so the utility was not confident of the continuing reliability of these supports. Therefore, a majority of the towers, 41 out of 53, had to be replaced, which enabled to utility to benefit from all the advantages offered as a result of selecting the ACCR conductors for the circuit upgrade.
In the course of the circuit reconstruction, the monolithic foundations of the towers that had to be replaced, requiring the use of a hydraulic hammer to split the existing foundations to facilitate removal. Special attention was given at the project planning stage to the conductor tension and the supporting and fitting frames required. As the core of 3M’s ACCR conductor can be damaged if the specified bending radius is exceeded for conductor stringing, the utility employed a leader cord and larger-diameter puller tensioners in addition to over-sized stringing blocks.
The 3M ACCR conductor used in this upgrading project has proven to be an efficient and highly reliable solution to the utility’s need for increased capacity in Perm. Moreover, the utility regards this installation as a milestone as it is the first application in the Urals of a new conductor technology that will help to meet the growing load demands from the expanding industrial, commercial and residential customers.
Alexey Aleksandrovich Pravkov ([email protected]) is the head of the high-voltage lines maintenance department of the Directorate of Operation, Maintenance and Repair of PermEnergo, a branch of IDGC of Urals JSC. He has been working in the energy sector since 1996, beginning as an electrician repairing 35-kV to 500-kV high-voltage lines. Pravkov holds advanced degrees from the Moscow State Industrial University and Perm National Research Polytechnic University.
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PermEnergo | www.mrsk-ural.ru