Impact Of Qatar's Harsh Environmental Conditions On Power System Stability And Maintenance

Power System Elements and the Need for Maintenance

Discuss about the Electrical Power for Transformers and Underground Cables. 

The stability and quality of the power have a direct impact on the power system planning, control, and operation. The network power system is made up of expensive and massive elements among them generators and their associates, transformers, underground cables as well as overhead cables that are used in the transmission of electrical energy from the point of generation to the load center. For this reason, there is need to protect these elements from the operation and human faults which would otherwise render them completely damaged. Protective and predictive maintenance is thus needed to ensure that the most appropriate steps are taken in a bid to reduce the rate of fault in a transmission network (Chowdhury, 2011). Voltage stability is about the operation of stable loads and acceptable levels of voltages across the network nodes. 

Tremendous growth is being experienced in electrical power systems with regard to the size and the complexity across all the sectors including transmission, generation, distribution as well as load systems (Ziegler, 2012). Severe economic losses are experienced in the cases of occurrences of faults which also serve to reduce the reliability of an electrical system. An electrical fault is defined as an abnormal condition that results from failures of equipment such as transfers and rotating machines. The abnormal condition may also result from environmental conditions and human errors. All the various types of faults result in disruption of electric flows, damages to the equipment and may even lead to the death of people, animals, and birds in the worst case scenarios.

The power system environment of Qatar is such that the country is surrounded on its three sides by the coastline and has a direct connection with Saudi Arabia to the south (Zhang, 2012). The landscape of the state is mostly flat and barren desert which is mostly covered by gravel and sand. Going to the geographical location and the climate, Qatar is thus classified as a hot subtropical desert that experiences very long summer between June and September. The summer is normally characterized by alternating cycles of humidity and dryness as well as immense heating. The temperatures are normally very high, over 55?C with negligible annual rainfall. The relative humidity ranges 71% in the morning and 43% in the afternoon (Hase, 2012). Qatar also experiences sudden dust storms that at times descend onto the peninsula. These sandstorms can be very dangerous and destructive to the extent of blocking the sun, resulting in wind damage and even disrupting the transmission and distribution networks of the power systems.

The transmission system of power in Qatar is mainly through overhead power networks which function at various levels of voltages such as 33kV, 66kV, 132 kV, 220 kV and 400 kV. The power transmission of Qatar works under very harsh environmental conditions with very heavy pollution levels which are normally higher than the specified levels in the IEC 60815.  The climatic variables are also a contribution to the harsh operating environments (Ziegler, 2012). The state receives extreme temperatures that can at times go higher than 55?C during July and August. The state experiences high solar radiation, very large daily temperature and seasonal temperature variations besides fog and dew.

Tremendous Growth and Economic Losses from Faults

Relative humidity goes as high as 100% during these summer month with the precipitation during the shortest winter not exceeding 80 mm. the presence of frequent sandstorms blows sand and dust of various sizes into the air adding to the pollution levels on the insulating surfaces. Following this is the classical wetting phenomena which are associated with frequent early dew during the months of summer and fog during the months of winter. Challenges with insulation flashover resulting from salt spray from the sea are also experienced (Blume, 2011).

A period of the poorest insulation selection was experienced in the 1990s during which serious problems were experienced on the 132 kV line as a result of the failure of the low-quality glass insulators. The failures were severe in some cases to the extent of causing droppings in the conductors (Chowdhury, 2011). This failure has a serious impact on the future decisions with regard to requirements for dimensioning besides other criteria that need to be observed when specifying insulators. The focus was thus shifted to finding an insulator that was best resistant to the abrupt changes in the temperature as was the frequent case in the typical desert environment. To be precise, the search was aimed at finding a shed that was most suitable in terms of its geometry and profiling and had a high self-cleaning capability. Several preventive techniques were adopted since then to avoid the occurrence of such insulation problems in the future. These techniques included over-insulation techniques and over-designed 220 kV and 132 kV towers. In addition, a decision was reached to replace the lines that were worst affected with underground cables that even included the installation of a submarine cable that was 7 km long along of the arguably most important streets in Doha (Zhang, 2012).

These climatic conditions of Qatar result in overheating in the power generation, distribution and transmission systems and hence power faults. Overheating results from a rise in the temperature of an electrical circuit and can result in fire explosion or even injury. A rise in the temperature of a transmission or power system above the operating system may result from the production of heat that is higher than the expected amount for the case of short-circuits or form poor dissipation of heat. Poor heat dissipation results in the poor drainage of the waste heat generated (Hertem, 2016). 

As a result of the 1990s experience, the whole Qatar Transmission System had been insulated and reinsulated using aerodynamic insulators which have led to higher distances of specific creepage. An example is an insulation mounted on the 66 kV lines that have gone to 35 mm/kV from 27 mm/kV and the specific creepage insulators use d on 132 kV having increased from 31 mm/kV to 35 mm/kV. 220 and 400 kV transmission lines have been insulated using strings whose lengths are 24 and 45 respectively of aerodynamic insulators. In other circumstances, insulators made from alternating shed silicone rubber have been adopted which correspond to a specific creepage distance of about 41 mm/kV. This is equivalent to 70 mm/kV of a Unified Specific Creepage Distance (Bayliss, 2011). As a result of the increase in the distance of specific creepage, a need for additional insulator discs has risen and hence over the design of the traditional towers that were meant to support the 132 kV and 220 kV transmission lines. Some of the over the design of these traditional towers have seen the towers become as high as those that are used for 400 kV. 

Other than insulation as a preventive mechanism for the power system faults in Qatar, the state adopted rigorous corrective and preventive maintenance programs that were applied to all the transmission lines (Bayliss, 2011). The program included climbing and ground-based inspections besides numerous additional diagnostic measures and countermeasures to pollution. Despite the positive improvements recorded as a result of adoption of insulation for the transmission cables and the elaborate maintenance program, some of the transmission lines, especially those that are located close to the coastal areas and dunes and in the open gas flares from the industries of gases still experienced flashover problems that are related to pollution. Due to this, live washing was started with the introduction of a program that was aimed at coating the strings of glass insulator using RTV silicone (Ziegler, 2012).

Live line washing was a program that was associated with additional manual cleaning of the insulators. This was aimed at improving the availability and reliability of the overhead transmission line system. Following the programs of reinsulating on the 66 kV, 220 kV and 132 kV lines, all insulators of uncoated glass and porcelain were to be washed after every three months. Infra-red thermography inspection is used in the conduction of annual inspection to each of the towers in the network (Ali, 2016). The resulting thermograms from the inspection are studied to establish the efficiency of the washing efforts. Besides the infra-red thermography inspection, the country is considering acquiring the latest generation ultraviolet camera. This insulator comes with a high cost which is approximately $79 for every kilometer for a five-lane washing. Live line washing has proved to be quite reliable to the old equipment as has been recorded from the experience of the washing.v

References

Ali, H. (2016). Wind Energy Systems: Solutions for Power Quality and Stabilization. Sydney: CRC Press.

Bayliss, C. (2011). Transmission and Distribution Electrical Engineering. London: Elsevier.

Blume, S. W. (2011). High Voltage Protection for Telecommunications. London: John Wiley & Sons.

Chowdhury, A. (2011). Power Distribution System Reliability: Practical Methods and Applications. Sydney: John Wiley & Sons.

Hase, Y. (2012). Handbook of Power Systems Engineering with Power Electronics Applications. New Delhi: Wiley.

Hertem, D. V. (2016). HVDC Grids: For Offshore and Supergrid of the Future. London: John Wiley & Sons.

Zhang, B. (2012). Methodology and Technology for Power System Grounding. Beijing: ohn Wiley & Sons.

Ziegler, G. (2012). Numerical Differential Protection: Principles and Applications. New York: John Wiley & Sons.