By Ing. Frederick K. Bediako
CAUSE and EFFECTS
It’s July 1991, the clouds are gathering, the trees are whistling, birds are chirping; the wind blows stronger; a clear indication of a rainfall. As the temperatures drop and the sky becomes increasingly darker due to heavy cloud formation the possibility of rainfall becomes more realistic. A mother following this natural phenomenon closely and very much convinced of rainfall instructs her 11year old son in twi; “Kwabena, ko dum fridgi no” literally translated as “Kwabena, go and put the fridge off”. The boy does as instructed and just after that the rains come in and the lights go off.
On that day an impression was created on the boys mind…..these guys (ECG) must be very smart, they even put off the light automatically when it’s about to rain to protect their machines. He held on to this impression throughout his formative years, often times putting off important gadgets when it’s about to rain in anticipation of the lights going off, sometimes getting disappointed in ECG if the lights failed to go off.
I am sure a lot of you reading this article might have at one point of your life been in the shoes of this boy, and maybe still hold an improved version of this impression that ECG deliberately cuts off your power when it rains. Fast forward 25years later and this young 11year boy is now an electrical engineer and unfortunately works in the same company that had been putting off the light in the event of impending rain when he was a kid. As a technical person, he has come to appreciate the very reasons why the lights go off when it rains.
His mum after 20 years of sojourning in the States and experiencing how it feels like to live in the jurisdiction of a modern utility comes back home on Holidays and experiences this same phenomenon she had been saddled with all her life before she left for the States. In her shock, she decided to engage her son to know why this was still occurring in the twenty-first century in the face of all the technology and knowledge available to man. This is what ensued between mother and child:
In her acquired American accent, she says; “Kwabena, upon all the training, seminars and industrial attachments accompanied with fat per diems that you have had in America and other developed countries, you guys have not been able to solve this simple engineering problem.” Embarrassed and stunned by the question and knowing the mother has a lot of belief in him, Kwabena retorts; “but this is an act of God, we have no control over rain.” “An act of God you say,” she rebuts. “Yes you might not have control over rainfall, but you do have control over its effect on your network. Did you see this in the States when you were there?” She adds.
Sensing danger, Kwabena decides to confuse his mother in a bid to cower her argument. He pulls out a document and it reads; “In June 2011, President Obama released A Policy Framework for the 21st Century Grid which set out a four-pillared strategy for modernizing the electric grid. The initiative directed billions of dollars toward investments in 21st century smart grid technologies focused at increasing the grid’s efficiency, reliability, and resilience, making it less vulnerable to weather-related outages and reducing the time it takes to restore power after an outage occurs.
As you can see, he said, bad weather also affects the network in the States and other developed countries with first class networks. Noticing the propaganda bit of the quotation above, laughed and asked, would you compare the kind of bad weather in the States to anything in Ghana. The engagement between mother and son was becoming increasingly difficult for the son, not because he cannot answer all the questions and twists being posed to him, but there lies the small matter of how to answer those questions without becoming too technical and end up confusing his mother. Bottom line is, it rained and the lights went off. Is that something that is expected or something can be done about it? Will it ever stop completely, and what will be the cost of such an endeavour?
Many engineers have had a torrid time trying to explain this disturbing occurrence to our families, and mostly end up feeling embarrassed about it because deep down, you believe that this is very solvable. Let us try to break this down in simple terms to our cherished customers and inform them of our activities, if not to eliminate, to reduce the effect of weather conditions on our network.
While the majority of power failures from national grids last only a few hours, some blackouts can last days or even weeks, completely shutting down to our homes and slowing down production and operations in companies and critical infrastructures such as telecommunication networks, financial services, water supplies and hospitals due to severe weather conditions.
The overhead lines, underground cables, transformers and switching stations are the key components in the transmission and distribution network that are more susceptible to weather conditions. Among them, the overhead lines are the ones that face the strongest external pressures such as harsh weather conditions. Our monthly outage statistics gathered in all operational regions suggest that most distribution interruptions are initiated by severe weather–related interruptions in which inadequate maintenance is one of the main contributors. The study finds that failures in the distribution system are responsible for 80 per cent of all power interruptions.
Burke and Lawrence (1983) performed a four-year study of evaluating the faults (current) on distribution systems in 13 electricity utilities in the USA. They found out that around 40 per cent of all permanent faults happen during periods of adverse weather. In addition, the study finds that the faults occurring on underground distribution systems only account for about 5 per cent of all conductor-related faults. A study from Yu et al. (2009b) suggests that weather is a major cause of electricity blackouts. This accounts for 20 per cent, 14 per cent and 15 per cent of the total cases analyzed in the European, Latin American and Asian regions respectively.
The situation is no different in Ghana, in any other third world or developing country. Here the main weather variables that affect the normal functioning of the overhead lines in Ghana are lightning (flashes), wind, extreme weather temperatures, storms, rain and humidity. The high energy resulting from lightning strikes can burn the protective line isolators which subsequently may damage the transformers and switching devices. Damages in the transmission network are generally produced when lightning directly strikes the line. In the distribution network, the damage can be produced by a direct incidence and may also be due to the overvoltage induced in the lines when lightning strikes close to these lines.
The induced voltages, most of the time, far exceed the Basic Insulation Level of our insulators thereby resulting in flashover and the line tracking to ground. Pabla (2005) states that lightning is responsible for about one-third of all faults on HV and distribution systems during stormy days with about 75-80 percent of these faults being temporary. Lightning damage is one of the main concerns for many utilities because these cause the highest expense in breakdown of distribution equipment.
Winds can also damage the transmission lines. The wind speed combined with the line height and air density determines the dynamic pressure over the lines. Due to the low temperature, the equipment’s functionality can be reduced through cold. The load on the lines can cause higher traction, rope swinging and greater wind contact surface which can result in lines twisting or breaking. In addition, dynamic pressure increases due to the greater contact surface and the rope swing over time can cause a mechanical malfunctioning of the grid especially sectioned points connected with jumpers.
Humidity is also a concern due to the corrosion that it can produce to metal components such as pylons (towers). According to Pabla (2005), the tropical environment accounts for the majority of outages. This environment is characterized by high temperatures, dust, high humidity, heavy rainfall, high wind velocities and severe thunderstorms. Such environmental pollution forms a conductive film on the glazed surfaces of insulators and creates a means of tracking to ground in the event of a rainfall.
Strong winds have a devastating effect on the pole structures holding the overhead lines in place. It has the tendency of bringing the pole structures down thereby causing an outage when the bare conductors come into contact with either the ground or a nearby tree or even bringing the various phases of the conductors to ground. It must be noted that bare overhead conductors must be separated from each other at all times and also separated from either the ground or any nearby structure e.g. a tree branch so as not to cause a phase to phase (conductors coming together) situation or phase to ground (coming into contact with external material) situation. The effect of strong winds on the physical structures can be categorized as follows
- Foundation failures due to inadequate depths.
- Foundation failures due to using "standard" procedures in very soft soils. It should be noted that the long duration of a heavy mind and the accompanying heavy rainfall can soften clay soils to much greater depths than would occur in normal conditions.
- Pull-out (up trust) failures of stay anchors on poles.
- Breaking of poles, usually at the soil line, due to rotting of the wood.
- Breaking of poles at locations where they have been drilled to accommodate anchorages for cable attachments.
- Breaking of poles because they were overloaded with other services lines (e.g. combined circuits.
- Breaking of conductors.
- Failures due to flying debris and falling branches and trees.
With the exception of the last-listed item, all of the causes of failures are preventable by convenient means.
It is generally assumed that poor construction is responsible for most of the damage during rainstorms. Not everyone holds this perception. However, poor construction is a contributory factor in a significant minority of the failures. It can also be said that whereas poor construction can undo good design, analysis and detailing, good construction cannot make up for bad design, analysis and detailing.
Such attestation as described above should be buttressed by in-depth quality audits of projects randomly selected and also selected where there is prima facie evidence of under-design or poor construction.
It is becoming increasingly clear that the degree of effect of harsh weather conditions on any network is dependent on how resilient the network is. The question is, is there a universally resilient network capable of withstanding every weather condition? The answer is a big “No”. All networks are designed to withstand certain degree of safety based on the weather parameters available. Parameters such wind speed, humidity levels, level of pollution within the project site, frequency and magnitude of lightning strikes, and earthquake predominance are used to design the network with a certain degree of safety factor over and above the nominal figures. That is to say any condition that goes contrary to the accepted norm will definitely have an effect on the network one way or the other and might result in a momentary or sustained outage.
The studies into achieving network resilience is very important, as climate change increases the frequency and intensity of severe weather. Greenhouse gas emissions are elevating air and water temperatures around the world. Scientific research predicts more severe storms, heat waves, floods and other extreme weather events being among the changes in climate induced by anthropogenic emissions of greenhouse gases.
Severe weather is one of the leading causes of power outages in Ghana and costs the economy millions of Cedis a year in lost output and wages, spoiled inventory, delayed production, inconvenience and damage to electricity network infrastructure. Moreover, the aging nature of the network – much of which was constructed over a period of more than forty years – has made Ghanaians more susceptible to outages caused by weather conditions.
The number of outages caused by severe weather is expected to rise as climate change increases the frequency and intensity of storms, floods and other weather events.
To be continued....................
About the Author
Ing. Frederick Kwabena Bediako is an Electrical Engineer with over 10years experience in the Power Distribution Sector in Ghana.
He is the Manager for Major Projects in Ashanti Strategic Business Unit