November was wet and windy for many across the UK, leading to soaked streets, flooding and the risk of a terrible side effect: power outages. Once again, it is important to highlight the need for proper protection against water ingress into substations. Gavin Cornall, power and construction manager with cable seal manufacturer Roxtec, examines the issues and explains the importance of choosing reliable seals
The climate is changing and the UK is experiencing more intense rainfall. Since records began in 1931, three of the top five wettest years have occurred since the turn of the 21st century. This, coupled with ageing buildings across the power network, mean protecting substations is paramount to maintaining supply of electricity.
Substations are crucial
Substations are a vital part of the power transmission and distribution process, keeping the supply of electricity moving to homes and businesses. They transform voltage from high to low, or low to high, and perform other important functions.
Substations are built in various locations including housing estates, industrial sites and hospitals. They are also increasingly being built in remote locations, particularly in the renewable energy sector, where there is little drainage, and on sub-prime land such as flood plains.
In order to ensure constant operation, it is important the industry's awareness is increased of the best possible methods to protect substations. Prevention is always better than cure.
Humidity is the problem
Water ingress is one the biggest threats to the operational success of substations. One might just think of flooding, but with a relative humidity in the UK of 65% to 95%, even raised substations are vulnerable. This is because humidity is in the air.
You can say there are five stages in the process of a breakdown of a substation because of humidity. Rainfall leads to cable trench flooding which causes excessive humidity, prompting switch gear failure and eventually power outages.
Failing to meet the challenge
Traditionally, sealing compounds such as mastic have been used to seal cable entries into substations. These are, however, often not robust enough to support the weight of the cables, particularly the 'trefoil' layout of three cables.
Natural movement occurs during installation because the cables are not supported which makes it problematic to get an even seal around them. A natural travel or flex can also happen while in operation which can lead to water leakage.
Some substations are equipped with costly dehumidifiers, sump pumps, fans and air-conditioning units as it is necessary to keep the environment as stable as possible.
It is quite obvious only a good, reliable and properly installed cable sealing product will provide the power industry with a cost-effective, preventative measure so that the threat of disruption to power supply can be sealed out simply before the onset of the problem.
Reliable solutions against humidity
Roxtec cable and pipe seals are used to seal and secure entry points into a wide range of substations in for example electricity networks, renewable energy projects and wind farms. The seals protect against many hazards, including water, fire, explosion, flood, vibration, dust, electro-magnetic disturbances and vermin. They can be installed in any conditions and be used on retrofit as well as new-build projects. The seals are used in many applications, from protecting substations against water ingress from below ground penetrations through to preventing dust particles and pollution from reaching into the substation.
Roxtec seals are typically found in substation sites ranging from 11kV up to 400kV. They are most commonly used for all cables including HV, trefoil, LV, data, communications, multicore, scada and earth.
Modular-based sealing system
In substations the Roxtec sealing solutions consist of a round frame made of metal and a set of rubber sealing modules. The frames are cast, bolted or welded into place. The modules are easily adapted to cables of different sizes making it possible to efficiently seal multiple cables in the same opening. The idea is simple and ingenious: the more cables you can seal in the same opening, the fewer holes you have to drill, and fewer openings mean less risk of leakage.
The modules are then compressed and the seal ensures both tightness and cable retention. This eliminates the problem of cables moving and causing leak paths. Many Roxtec products are also openable which makes them useful in retrofit projects. They can also be installed into existing ducts or core drilled holes.
Roxtec has, among many other tailored cable sealing solutions, developed a seal for trefoil single core cables which places three cables through a wall in trefoil formation. It has been tested to 400KG pull-out forces, which is way beyond what a cable is ever likely to have to endure.
Roxtec seals in action
Roxtec seals have been supplied to a broad variety of substation projects all over the world, and there are a lot of references available. Three recent examples showcase the confidence shown in Roxtec solutions in the UK, the Netherlands and in Saudi Arabia.
Earlier this year, Roxtec was able to announce a new deal with Western Power Distribution, one of the UK's largest electricity providers. Roxtec supplies safety seals to a collection of the company's substations in the South West of England. Roxtec H3 trefoil seals are used to seal cable entry points into the substations to protect them from flooding.
The innovative seals are also used in a new type of substation in Ypenburg, a growing community in the suburbs of The Hague. Joulz BV, who was responsible for engineering, project management and installation, focused on safety and reliability looking into every component. Joulz chose Roxtec cable seals to ensure a guarantee of water-tightness.
Roxtec seals have also just been selected for one of the world's largest new petrochemical plants, called Sadara Project, which is being constructed on Saudi Arabia's east coast.
The Roxtec solution is also supported by the conclusion of a white paper by EA Technology.
Roxtec commissioned EA Technology to produce a white paper on the causes and effects of humidity within indoor substation environments. The white paper examined relative humidity and partial discharge as well as best design practice for avoiding these problems.
One of the issues facing substation operators is partial discharge, or electrical discharges occurring inside or on the surface of electrical insulation materials caused by high-voltage electrical stressing of the system when equipment is energised. Even a small amount of water in a cable trench can lead to increased relative humidity and, over time, cause partial discharge. This can leave switch gear vulnerable to circuit failures and power outages.
EA's report said the three most common sources of humidity, leading to the onset of partial discharge in substations, were ambient air with high humidity, water leaks and water in cable trenches. Dust can also cause partial discharge when found in considerable quantities, so switchgear chambers should be designed to prevent contamination.
For electricity distribution network operators, avoiding equipment failure and power outages is essential. If they cannot ensure energy being exported from the generating station, they will experience a substantial loss of income until the failed equipment is rectified or replaced. This could, for a large generator, cost upwards of £500,000 per day.
For manufacturing plants, the failure may cause a shutdown, resulting in loss of product passing through the production process, damage to the equipment and staff down time.
The mantra of prevention is better than cure could not be more relevant when companies are facing these kinds of costs.
Referring to best practice, EA concluded the substation building should be of sound construction and adequately water tight. Where it is in a location of extreme weather or flooding, extra measures to prevent water ingress such as robust sealing of cable entry points may also be required.
The report demonstrated why it is extremely important to control the substation environment and how it can be achieved by minimising moisture ingress and controlling the temperature and humidity within the building.
It concluded the design of the substation could have a major impact on the internal environmental conditions. Cable entry points are one of the main sources of water ingress to substations and they should therefore be effectively sealed.
The use of positive environment control in substations will maintain the humidity at an acceptable level and prevent sudden changes in temperature which can lead to condensation humidity, alongside routine inspection and maintenance for extra security.
