Proposed 500-kV line will be TNB`s transmission backbone
Without additional transmission capacity, Malaysia will be unable to meet its growth for new electricity
John W. Harrison
Black & Veatch International
Leong Whye Hin
Tenaga Nasional Berhad (TNB), a private Malaysian utility, expects electrical capacity demand on its facilities to increase more than 450 percent over the next 20 years. A multi-company consortium will build the 500-kV electric transmission system necessary to accommodate such a generation increase. The system will eventually serve as the transmission backbone for TNB operations. In August 1993, TNB entered into an agreement with the consortium (Ranhill Bersekutu Sdn Bhd. and Black & Veatch International) to design and manage construction for the first phase of the multi-staged project. Power Technologies Inc., a subcontractor to Black & Veatch, was responsible for power system studies.
Phase 1, planned with five substations, will stretch approximately 380 km along Peninsular Malaysia`s west coast from Port Klang in the state of Selangor to Gurun in the state of Kedah. Phase 1A, another initial construction phase planned with four substations, originates at Pasir Gudang north of Singapore and proceeds northwesterly in the state of Johor for approximately 135 km to the Yong Peng area.
Phase 1 and Phase 1A are part of an overall scheme to provide reliable electric transmission within Malaysia. While all construction will suit double circuit 500-kV transmission, the utility will energize initially only one project section and two substations at 500 kV. TNB will energize the remaining construction at 275 kV. The system design allows for future conversion to 500 kV with minimized outage time. TNB must complete new construction on schedule because the existing transmission system can not support additional generation.
Establishing design standards
The primary challenge facing the design team during the initial design stages was to plan and design the system to meet the schedule. Conceptual design established parameters and determined preferred alternatives for detailed design. This was especially important for TNB`s new project since the country has no 500-kV system.
Although transmission line and substation designs are subject to the requirements of the Malaysian Electric Supply Regulations (MESR), the current regulations do not contain requirements for 500-kV safety, construction and operation. Using experience from other projects and references to acceptable 500-kV standards, the team established design criteria and included them in a Project Design Manual. Once submitted and accepted for inclusion in the next MESR edition, the criteria will serve as safety, construction and operation guidelines for future 500-kV construction in Malaysia.
Substation electrical design
The team designed switchyards for a 1.5 breaker configuration with bays consisting of three circuit breakers connected between two main buses, with a line or transformer termination between any two breakers. This arrangement gives TNB high reliability and achieves maximum flexibility during system operations and maintenance.
A typical substation arrangement allows for 15 500-kV circuit breakers associated with six transmission line positions and four transformer positions, and 21 275-kV circuit breakers associated with 10 line positions and four transformer positions. The 500/275-kV auto transformers are single-phase with a 750-megavolt-ampere capacity for each three-phase bank.
The design team established electrical clearances and insulation coordination for the outdoor air-insulated buswork in accordance with International Electrotechnical Commission (IEC) and industry standards. Designers developed electrical parameters, voltage ratings, installation level and clearances for substation design, as well as establishing parameters for bus loading and deflection. The bus design uses low profile aluminum bus with cable jumpers for major equipment including transformers, circuit breakers, disconnect switches and instrument transformers. Shield wires and lightning masts protect the substation from direct lightning strikes, and surge arrestors will shunt lightning strikes occurring outside the substation.
All substation equipment and material will conform to IEC standard requirements and will be suitable for operation at temperatures from 0 C to 45 C, at relative humidity levels between 80 percent and 100 percent, and at an altitude below 1,000 m. All equipment will operate on a three-phase, 50-Hz, solidly grounded system.
The substations will use a combination of existing conventional-style controls and a microprocessor-based computer control system in conjunction with the microprocessor numerical protective relays. A computer-based monitoring system and computer terminals operating in a two-tier hierarchical decentralized control scheme will control substation functions. The system will incorporate disturbance recorders and fault locators into the same enclosures as the numerical protective relays.
Protective relaying design for the substations includes overlapping and redundant protection for all lines, buses and equipment. The protective relaying schemes include transmission line relaying, automatic reclosing (single-pole and three-pole selectable), transformer relaying, high impedance bus relaying and breaker failure relaying. To make redundant schemes functionally separate, the relays will have separate dc power sources, different current and voltage transformer inputs, separate trip coils, separate communication paths and separation of control cables for each scheme.
An optical ground wire (OPGW) fiber-optic communication network installed on the transmission lines will provide the telecommunication and telecontrol path for an optical E-3 (34 megabytes per second) telecommunication system. The telecommunication equipment at each substation will be redundant and protected against any single failure point. The telecontrol will provide control and monitoring of each of the substations through remote terminal units and the computer-based control scheme.
Access to the substations and their sheer size were major design considerations. Some land requirements exceeded 100 acres. Designers used computer analysis to optimize the substation platform level by minimizing excess cuts and fill importing. Regardless, extensive earthwork will be required at all substation sites, so site access is critical. Road construction must be adequate to accommodate not only typical operation and maintenance (O&M) traffic, but also the heavy loads associated with transformers and other major equipment.
The transmission line routes considered have large variations in terrain, including hills and mountains (Figure 1), large rubber and palm-oil-producing plantations (Figure 2) and rice padis (Figure 3). Because there are relatively few roads in these areas, access can be difficult. Only a narrow pathway is anticipated along the right-of-way.
Typically, builders have constructed transmission lines for TNB using relatively small equipment and a high concentration of manual labor. For this project, it may be necessary in some areas to carry in water, concrete, aggregate, cement, tower steel and reinforcing steel. In determining construction procedures, subcontractors must balance the cost associated with available construction techniques with the need to complete the project on schedule. In addition, during line construction, builders must exercise care to interfere as little as possible with palm oil and rubber production. Construction will require a great deal of cooperation between the land owners and the subcontractors.
Rice padis present the greatest foundation and line construction challenge. Preliminary soil data indicate very poor soil conditions as deep as 20 meters (m). This is coupled with a high water table and flooding associated with rice production. While the rice padi areas are relatively accessible, the construction base in the field will be very soft. Finding suitable locations for structure assembly and wire pulling will be difficult.
Transmission line design
The Project Design Manual for the transmission line addresses electrical clearances, mechanical loading criteria, conductor, OPGW, insulators, hardware, accessories, structures and foundations. Of these items, the conductor, structures and foundations will account for approximately 75 percent of transmission line total costs. Optimization of these major items will result in significant savings to TNB.
During the system studies project phase, designers analyzed several acceptable conductors with respect to radio interference, television interference and audible noise. Designers also performed sag and tension analyses of the various conductors to aid in determining structure heights. In addition to electrical effects and sag/tension characteristics, the design team based final selection of the conductor (a bundle of four 1,033.5 thousand-circular-mils, 54/7 ACSR Curlew per phase) on economics that considered power flow losses over time and the effect of various conductor sizes on structure and foundation costs.
Team designers selected vee string insulator configurations for the towers because they are standard on 500-kV systems. Insulators will be ball-and- socket-type porcelain or toughened glass and will comply with IEC standards. Conductor arm spacing and length ensure proper clearances during system O&M. The dominant factor in determining the tower configuration was lightning performance. The team used a keraunic level of 180 in the design, considering both shielding failures and backflash analyses. A lightning performance analysis provided the information needed to determine the length of the shield wire arm.
Using the preliminary tower configuration, designers calculated electric and magnetic field (EMF) values to ensure that the system would not exceed EMF levels recommended during the system studies. The team has established maximum electric field limits of 12.5 kV/m within the right-of-way and 2.0 kV/m at the edge of right-of-way. They also established maximum magnetic field limits of 1,000 milligause within the right-of-way.
The project will use seven different double-circuit, galvanized lattice-steel structure types with varying line angles. Designers configured all tower types using a computer analysis that optimized the leg slope and tower weight by considering both mild- and high-strength steel. Figure 4 shows the final configuration of the light suspension tower.
The team designed the foundations for the towers using preliminary data from soil obtained along the route. Construction will include both pad and pedestal, and pile-type foundations, with rock anchor foundations used in isolated locations. The ground wire (earthwire) will be OPGW with 24 fibers per cable. The conductor will be suited for hotline maintenance tools and will have a strength equal to or greater than the mechanical and electrical rating of the insulators.
In addition to establishing the quality of materials, equipment and construction required, the design team prepared a Project Field Instructions Manual as a guide for all field personnel. Major sections included the following:
– Field administration–project scope, organization, communication, document control, quality control and daily logs;
– Planning and control–documentation, information management, schedule, cost, cost analysis and progress reports;
– Permits and licenses–construction constraints and contractor insurance;
– Design engineering–design control, drawings and related documents;
– Equipment and material procurement–revisions to contracts, status and quality surveillance, and material receiving and storage;
– Construction contracts–revisions to contracts, coordinating and monitoring of construction progress, outstanding work, processing of payments and contractor claims review;
– Construction support services–safety and loss control; and
– Project completion–transmission line and substation energization, and compilation of construction records.
Not only will this field manual help TNB, construction managers, and inspectors and project subcontractors work as a team, it will also allow them to construct a high-quality transmission system.
The “supply and construct” concept
In December 1993, the government established that the Malaysian Resources Corporation Bhd (MRCB) and Permodalan Nasional Berhad (PNB) could jointly negotiate with Tenaga Nasional Berhad (TNB) to provide the project supply and construction of the 500-kV system. To meet the requirements to initiate the negotiation, the 500-kV team prepared detailed specifications and drawings to provide a basis for the MRCB/PNB consortium proposal. Because of uncertainties regarding the structure locations and soil conditions along the transmission line routes, the team estimated bills of quantities to provide unit costs for the consortium.
It is intended that based on the unit costs, TNB will pay the consortium for items that are actually installed on the transmission lines. The design team is using a similar approach on the substations, where designers can more easily determine the actual quantities. Although the initial concept bases negotiations on the bills of quantity, the concept may change during final negotiations.
The MRCB/PNB consortium will develop local lattice steel fabricating and galvanizing facilities, and a hardware assembly plant. In addition, local sources will provide conductor and optical ground wire. The consortium plans to import only insulators and hardware as finished products for the transmission lines. However, the companies will import specific substation equipment and materials as finished products. The planning for locally provided substation equipment and materials is not yet final. Developing and using local facilities will help improve Malaysia?s competitiveness in the worldwide transmission and distribution market and will provide local job opportunities.
Figure 1. Hills and mountains presented transportation problems for transmission line construction.
Figure 2. Transmission lines were constructed in harmony with owners of large rubber and palm-oil-producing plants.
Figure 3. Soggy rice padis slowed construction activities.