There are several regions of the globe where environmental pollution represents a serious challenge to the reliable operation of power networks – from the petrochemical complexes of western Algeria to the deserts of northern Kuwait. Ranking high among these are parts of Pakistan, such as south of Karachi, whereat times it can be difficult to distinguish system voltage of different lines due to dense smoke from nearby power plant and industrial chimneys. INMR Contributor and Insulation Specialist, Raouf Znaidi, recently visited Pakistan’s National Transmission & Dispatch Company (NTDC), where engineers have to deal with a combination of challenges to reliable operation of the overhead grid. Apart from heavy pollution and corrosion, these also include snow and icing in steep mountainous terrain.
Environment & Power Generation
Located between Asia and the Middle East, Pakistan has a blend of diverse climates and landscapes, from plains to deserts to forests to the towering Karakoram Mountains. The country’s south includes over 1000 km of coastline running along the Arabian Sea and Gulf of Oman. Some 40 independent power producers contribute significantly to electricity generation and combined deliver up to 34,520 MW, predominately from natural gas (31%), coal (16%) and oil (14%).
Almost all this power is transferred to the NTDC, whose transmission grid is now undergoing significant expansion through ongoing double circuit 500 kV projects expected to be commissioned in upcoming months. General Manager of Design & Engineering, Khawaja Riffat Hussain, reports that apart from the focus on expanding the transmission system, another priority has been improving existing infrastructure to assure more consistent as well as higher quality service, especially in the south where there are frequent outages due to the impact of severe industrial and marine pollution.
NTDC Transmission System
The NTDC was incorporated in November 1998 with the mission to build, operate and maintain the transmission network owned by Pakistan’s Water and Power Development Authority (WAPDA). This network includes almost 5900 km of 500 kV lines and over 11,100 km of 220 kV lines.
Muhammad Iqbal, Chief Engineer of Line Design, explains that NTDC’s Transmission Line Div. faces two different types of extreme insulation challenges. In the south, particularly near coastal areas, industrial pollution mixed with salt spray causes frequent outages in spite of costly regular insulator washing. In the north, with its towering mountain ranges, engineers confront challenges in selecting and dimensioning insulators for new 500 kV double circuit lines that will run through areas with heavy snow and ice exposure.
Most transmission lines in Pakistan have traditionally been insulated with locally manufactured anti-fog type porcelain disc insulators. To cope with the severe service conditions, NTDC has adopted a strategy of over insulating all lines running along the south coast by using more than 43 U160CP discs. This corresponds to a unified specific creepage distance (USCD) of as high as 74 mm/kV. By contrast, systems in the north typically do not exceed 40 mm/kV USCD and strings consist of only 23 discs.