In my last post, I listed some of the aspects of extreme weather that are putting medium voltage switchgear in special service conditions affecting its ratings and lifespan. In this post we’ll have a look at some of the methods and innovations that are helping design engineers specify medium voltage(MV) power distribution systems that can withstand higher levels of temperature, humidity, and pollution with greater reliability and durability.
Scout your opponents
When going into battle, it’s important to know as much as possible about what you’re up against. The same goes for your electrical equipment. Switchgear is typically designed for ‘normal’ conditions, but environmental conditions onsite are often a different story. How and where switchgear is installed can have consequences on the stresses it has to withstand, including oxidation of metallic parts and degradation of insulating parts. Any specification of MV switchgear must pay attention to various stresses, as follows:
- Temperatures inside substations could daily vary by more than 20°C
- A high percentage of substations contain water in cable trenches, showing switchgear corrosion issues as early aging
- Environmental parameters in certain regions (dust, salt, vermin, etc.) will be more or less severe due to wind exposure.
- Environmental parameters can be more severe in certain applications, e.g. windfarm (wind), photovoltaic (irradiance), mine (sulfur, carbon, etc.), oil and gas (snow, sand, oceans, etc.)
Therefore, it’s important to identify potentially harmful environmental conditions at a planned installation site. To help in this effort, the IEC TS 62271-304 specification defines three condition classes: normal, light, and heavy. Temperature variations, condensation, water, dust, salinity, and other pollution elements in the atmosphere that can settle on components. To evaluate new construction sites, focus will mainly be put on the external environment – and how the operating room will transform these normal or special external conditions into normal service conditions – whereas existing sites can also be studied and monitored for visible signs of degradation that can help anticipate degradation.
From these evaluations, recommendations can be made regarding the installation as required. I mentioned some of these in my previous post, e.g. regular cleaning and use of baffles, filters, and minimum ventilation flow. Once this is addressed, the next step is to make sure the MV equipment specified is appropriate for the condition class of the installation.
Tougher gear for tougher places
Standard air-insulated switchgear (AIS) and shielded solid-insulated switchgear (SSIS) can be well-suited to normal or special conditions of installations. But, as they are designed for normal indoor service conditions, they may not perform with acceptable dependability in the most aggressive conditions where extreme levels of humidity, salinity, and pollution exist.
Many switchgear manufacturers are developing and testing designs with increasingly harsh environments in mind. Tests are typically based on existing standards, such as IEC TS 62271-304 for the MV electrical insulation system, which is completed by ISO standards dealing with corrosion withstand. Schneider Electric, for example, goes beyond this by using accelerated dielectric aging tests. Special ‘surface conductivity’ techniques performed in the laboratory simulate even harsher environments than defined in the standard, representing the effect of added pollution.
Based on the results of this testing, a number of new switchgear design innovations have emerged. One of these is the shielded solid insulation system (2SIS). This technology fully encloses all current carrying portions of the switchgear in an intermediate layer of high dielectric insulating epoxy, covered by a conductive layer that is connected to earth. This drastically reduces the probability of an internal arc or any other failure, even in the most ‘aggressive’ environments.
A feature of 2SIS protection means that dust, salt, pollution, and water cannot prematurely age the insulation and degrade the performance of the switchgear. This not only increases reliability, it maximizes service life while reducing maintenance. This all adds up to a lower cost of ownership.
Keep a close eye on conditions
There is a direct relationship between temperature, humidity, and aging of switchgear components. This is especially true when pollutants are present, including salt. As noted above, a new or installed switchgear where electrical insulation is exposed to atmosphere, an AIS can be monitored locally or remotely, enabling condition-based maintenance.
Compact, affordable sensors are now available that measure both temperature and relative humidity. Measured data is transmitted wirelessly – using Zigbee protocol, for example – to a data concentrator. This data is, in turn, shared with a local monitoring and control system, or uploaded securely to a cloud-based repository and artificial intelligence platform that provides advanced analytics.
Thermal sensors can be battery-powered or self-powered through inductive means if situated on a conductor within the switchgear. Multiple sensors can be located on busbars, circuit breakers, or power transformers to provide a complete picture of conditions throughout a substation. Sensors can be installed on new or existing equipment installations.
In this way, equipment conditions can be monitored on a continuous basis. Performance deviations can be configured to alert the operations team, while root cause analysis tools help improve response and recovery times. Data collected can be used to simplify and improve maintenance reporting and planning for critical assets. For example, continuously tracking equipment health will enable a predictive maintenance approach that can optimize performance, extend lifespan, and reduce time and costs.
Schneider Electric offers condition monitoring and fully connected switchgear as part of its EcoStruxure Power solution. To discover more about 2SIS technology, download the white paper ‘Breakthrough Technology in MV Switchgear: Shielded Solid Insulation System (2SIS)’ or visit our MV switchgear solutions page.
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