|
The Aluminium Conductor Composite Core (ACCC) is a bare overhead conductor that was developed to increase the efficiency, capacity and reliability of the electric transmission and distribution power grid,〔''Engineering Transmission Lines With High-Capacity, Low-Sag ACCC Conductor'' (ISBN 978-0-615-57959-7)〕 which were three key objectives of the Energy Policy Act of 2005,〔(【引用サイトリンク】title=Energy Policy Act of 2005 )〕 specifically, Title XII, Section 1223 ''Advanced Transmission Technologies''. The ACCC is categorized as a high-temperature, low-sag "HTLS" or High-Capacity, Low-Sag "HCLS" conductor.〔(【引用サイトリンク】title=Energy Research and Development Division : Final Project Report )〕 The ACCC conductor uses a hybrid carbon and glass fiber core to replace the steel core strands found in several types of bare overhead conductors. The steel or composite core is used to augment the strength of the relatively weak but highly conductive aluminium strands used in bare overhead conductors. Because the ACCC conductor's core is lighter than steel, it can incorporate nearly 30% more aluminum without a weight or diameter penalty. The added aluminium content reduces electrical resistance which serves to reduce electrical line losses. Another important aspect of overhead power lines is conductor sag. The ACCC conductor's composite core offers a very low coefficient of thermal expansion ("CTE").〔Alawar A; Bosze EJ; Nutt SR. ''A Composite Core Conductor for Low Sag at High Temperatures'' IEEE Transactions on Power Delivery (2005); 20(3):2193-9.〕 As a conductor carries increased levels of current (amps), the electrical resistance of the aluminum strands causes them to heat up. As the strands heat up, their coefficient of thermal expansion causes them to elongate, resulting in conductor sag. Excessive conductor sag can lead to short circuits and power outages, as experienced during the major US/Canada Northeast blackout of 2003 and several other similar events. The economic impact of these events is often measured in billions of dollars. If high-capacity, low-sag conductors such as ACCC were utilized, these events may have been avoidable. The ACCC conductor's added aluminum content and low CTE composite core allow it to carry approximately twice the electric current of a conventional conductor without exhibiting excessive conductor sag. This makes it a good candidate for upgrade projects where increased electrical capacity is needed, but where pole or tower replacement is difficult. Replacing or modifying existing structures is not only expensive, it can require multi-jurisdictional permits, which can be very difficult to obtain. Increasing line capacity is often required to allow the integration of new generation resources such as solar and wind. It is also very important should an adjacent line be taken out of service for planned or unplanned reasons. In such a case, often referred to as an "N-1" or "N-2" contingency,〔(【引用サイトリンク】title=System Performance Under Normal Condition (Static Security) )〕 the ability of a non-impacted line to handle the extra load can help insure grid reliability and prevent power outages. In addition to enabling the connection of new generation resources and carrying additional current when adjacent lines might be taken out of service, the ACCC conductor's added capacity can also help alleviate "congested" transmission lines. A congested transmission line is a line that has reached its current-carrying limits and unable to carry more power from a potentially less expensive source of generation. The problem of congested transmission lines not only compromises grid reliability, it also increases the cost of delivered power to consumers. In 2005, Ontario Hydro conducted a sag comparison test on several types of bare overhead conductors. They installed each conductor (Drake size equivalents) on a 65 meter (215') test span at Kinectric's Lab in Toronto, Ontario, Canada and applied 1,600 amps of current. Differences in conductor sag were measured and recorded. In addition to the thermal sag measurements, it was also noted how much cooler the ACCC conductor operated compared to the other conductors subjected to the same electrical load.〔Goel,A. ''New High Temperature Low Sag Conductors'' NATD Conf & Expo May 9–11, 2005〕 Cooler operating temperatures reflect improved efficiency and reduced line losses, that can range from 25 to 40% or more depending upon electrical load. In early 2013, American Electric Power began upgrading ("re-conductoring") 240 miles of a heavily loaded 345,000 volt (345 kV) transmission line in South Texas, while the line remained energized. This milestone live-line reconductoring project, the largest live-line reconductor project in history, is being completed with the help of Quanta Energized Services. American Electric Power, who had previously installed ACCC conductor on eight smaller projects, selected ACCC for this project due to its high-capacity, low-sag, high-strength and corrosion resistance. This single project will utilize over 1,440 miles of wire. In addition to the corrosion resistant advantages of composite materials, they are also known to resist fatigue failure that often occurs on overhead power lines due to Aeolian (wind) induced vibration.〔Stowell E, ''A Study of the Energy Criterion for Fatigue'', Nuclear Engineering and Design, 1966: pp 32-40.〕 The vibration fatigue resistant properties of the ACCC conductor were confirmed by American Electric Power during their "Sequential Mechanical Conductor Test."〔(【引用サイトリンク】title=Sequential Mechanical Testing of Conductor Designs )〕 Considering bare overhead conductors are subjected to very harsh environmental conditions which include cyclic tensile and thermal loads, as well as Aeolian vibration and corrosive conditions caused by agricultural and industrial pollutants and salt air, the use of a composite core material is highly appropriate. While the ACCC conductor was the first bare overhead conductor to use a hybrid carbon and glass fiber core, the use of this type of composite material is not new, as Boeing, Airbus and several other manufacturers and industrial consumers have recognized their attributes for many years. Though many composite products are created by laminating various materials together to create, ''by definition'', a product that is stronger than the sum of its constituent materials, the ACCC conductor's core is created by a pultrusion process, wherein all of glass and carbon fibers run parallel. This is also known as a "uni-directional" composite which offers exceptional tensile strength required for overhead conductors that often span long distances over highways and rivers and between mountain peaks. While installing the ACCC conductor is not much different from installing most other conductor types, gripping the ACCC's composite core requires the use of a collet-type connector assembly (used inside conventional "compression" connectors) as shown in the adjacent photograph. While much was learned about the ACCC conductor in the lab and during initial installations there are a few noteworthy events that have occurred after the conductor was placed into service and energized. In May 2013, ACCC conductor took a direct hit from what developed into an EF5 tornado near Moore, Oklahoma. Though the outer aluminum strands were destroyed by flying debris in a few locations, the composite core was undamaged and did not fail. This prevented the conductor from falling to the ground, thus helping expedite repairs. In January, 2011, a firestorm near Reno, Nevada burned down several "H-frame" wood utility poles. The ACCC conductor dropped to the ground when the poles burned, but the ACCC conductor was undamaged and put immediately back into service after the wood structures and ceramic insulators were replaced.〔Lehan, J. ''NV Energy Experience with ACCC Conductor'', IEEE/PES T&D Conference, Orlando, Florida, March, 2013〕 ==Disadvantages== HTLS conductors are extremely expensive, compared with the all-metal ones. They probably cost less than putting things totally underground. They are also less bendy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ACCC conductor」の詳細全文を読む スポンサード リンク
|