Roxtec are global-market leaders in the innovation, design and manufacture of cable and pipe penetration sealing systems. Roxtect solutions effectively seal against water and ducts ingress into safety critical and sensitive electrical equipment and buildings.
In this White Paper, Roxtec highlight the potential for electrical equipment failure resulting from high relative humidity within high voltage substations, typically operating at 11kV, 33kV, 66kV and 132kV voltages.
Roxtec are global-market leaders in the innovation, design and manufacture of cable and pipe penetration sealing systems. Roxtect solutions effectively seal against water and ducts ingress into safety critical and sensitive electrical equipment and buildings.
In this White Paper, Roxtec highlight the potential for electrical equipment failure resulting from high relative humidity within high voltage substations, typically operating at 11kV, 33kV, 66kV and 132kV voltages.
Roxtec commissioned EA Technology to produce a report on the causes and effects of high relative humidity within indoor substation environments and methods of mitigation.
This influential report covers relative humidity and the effect it has on the inception or level of partial discharge (PD). The White Paper discusses the factors affecting the environment within a substation and the best practice for the design of high voltage substations and internal environment control.
The findings in this White Paper have wide-reaching implications for the effective technical specification of cable sealing systems.
Cable sealing systems can reduce the risk of high voltage electrical equipment failure caused by partial discharge as a result of inadequate specification of cable transit systems.
The hard-hitting report concludes, "cable entry points are one of the main sources of water ingress to substations and they should be effectively sealed."
Who Should Read This ?
We summarise several of the Key Points below, however a thorough and careful complete read is recommended to electrical industry professionals. This White Paper should be mandatory reading for Lead Electrical Engineers, Electrical Project Engineers, Principal Electrical Engineers, Plant Engineers, LV HV EHV Cable Jointers, ATEX Inspectors, Substation Commissioning Managers, LV HV EHV Project Managers, Buyers & Procurement Managers, SAP's.
Environmental Conditions
Typical relative humidity (RH%) in the UK is between 65% – 95% in an internal substation environment. Where there are cable trenches and basement ducts adequate cable sealing must be adopted to prevent water ingress in “normal” and “flood” conditions. Even raised substations should seal all cable entries to prevent moisture ingress, the cause of high RH%.
Operational Conditions
Loads/faults can cause considerable cable expansion and contraction – which may lead to traditional cable seal failure as mastic sealants are often not able to provide sufficient cable retention. Due to lower ambient temperature and their location below ground, trenches and basements will experience a higher level of RH. For below ground enclosures and external penetrations, a vermin proof seal would also be advantageous.
Partial Discharge
PD’s are electrical discharges occurring inside or on the surface of insulation materials, caused by HV electrical stressing of the insulation. PD leads to progressive deterioration and plays a significant part in failures. Partial discharge affects all types of HV assets critical to network operation including high voltage switchgear, cables and transformers. High RH% and particle contamination (typically dust ) cause and accelerate PD. Large swings in RH% also have an adverse effect. Partial discharge is hard to detect unless invasive maintenance is carried out or a failure occures. The most common cause of high RH in electricity substations is water ingress through the structure and below ground cable ducts. Most common dust ingress points include below ground cable ducts and cable entries in walls and roofs.
Effects of Partial Discharge
PD can ultimately lead to a catastrophic equipment failure. This typically cannot be rectified through cleaning or minor refurbishment and can incur significant costs through the need to replace equipment, maintenance downtime and loss of supply.
Switchgear Specification & Design
IEC 62271-1:2007 & BS EN62271-1: 2008
Ambient air not polluted with gas, smoke, corrosive / flammable gases, vapours or salt
Average RH% over 24hrs not to exceed 95%
Average RH% over 1 month does not to exceed 90%
Design notes – highlights the use of “control measures” to manage RH%
All tests are short timescale, long term effects over several years are unknown
Environmental Requirements – Manufacturers Literature
Manufacturers recognise the design notes in the standards and use typical qualifying statements in equipment manuals.
Example: “RH% must not exceed 80% and the combination of temp and humidity must be such that condensation, in or on the equipment, will not occur. Where RH% exceeds 80% take special precautions to prevent.”
Example: “If the average air humidity exceeds 75% we recommend appropriate remedies are adopted.”
Example: “Ideal conditions – Humidity below 40% and no dripping water. Standard conditions – Humidity below 60%”
Ideal conditions can be as low as 40% normal conditions less than 60%
LOGICAL CONCLUSIONS
• RH% in UK between 65-95% as standard – manufacturers recommended operating levels may be below this.
• Water / dust ingress – mainly below ground cable ducts – but also through walls
• Cable retention is a key factor as movement will occur in normal operation due to expansion and contraction of the cables, the natural weight of HV power cabling and the disturbance caused by routine maintenance and engineering works.
• Beneficial to have vermin proof sealing
Many substations use costly control measures, such as sump pumps, heaters and de-humidifiers, to deal with the problem of RH without tackling the cause. The sealing of service penetrations is not highlighted in many standards, although these are the number one ingress point for water and dust. It makes sense to reduce operating costs and reliance on control measures to provide duct and service penetration sealing, which not only seals but remain tight under load and fault.
To repeat, "cable entry points are one of the main sources of water ingress to substations and they should be effectively sealed."
Roxtec Seals HV Electricity Substations, Transmission & Distribution
Roxtec have a track record in providing reliable Substation Cable Sealing to UK DNO's and overseas electricity authorities. Typical applications include sealing cables into control rooms, service rooms and control boxes at the electricity substation. Roxtec H3 Triplex Seals prevent water ingress generating increased humidity leading to partial discharge and eventual loss of power supply into 11kV, 33kV and 132kV substations.
Roxtec cable seals provide sealing solutions, with spare capacity for future cables, to prevent water and rodents from damaging substation electrical equipment and causing loss of power supply.
Dowload Whitepaper : http://www.cablejoints.co.uk/sub-product-details/cable-transits-roxtec/cable-sealing-substation-roxtec-transits?goback=.gde_4742617_member_257152961