SOME “TRICKS” TO IMPROVE THE DESIGN OF EQUIPMENT FOR SUBSTATIONS
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- Mar 30, 2020 11:27 am GMT
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ABOUT EQUIPMENT DESIGN
There are known possibilities to optimize the equipment design, allowing for considerable cost savings. Most of them are simply by increasing normal and short circuit current carrying capabilities with small modifications. These techniques are used even for refurbishing old equipment. This allows to postpone investments in new equipment and even complete substations.
Often the equipment designers realize the opportunity to make the improvements but hesitates when think that will have to repeat the expensive high-power laboratory tests. It is more or less what happens with software developers like me . We receive suggestions for improvements of something that is working properly but could be better. However, the experience shows that when we add the improvements some other things , which were working, start to work differently, and it takes months to adjust everything again. So, in many cases we say, I will do it next year.
The new fact for designers is that nowadays it is possible , with short time training, to replace expensive laboratory tests by low cost testing simulations using small computers. I refer to tests like the temperature rise, internal arc and short-time current withstand(short-circuit electrodynamic forces). So, it is possible to check the effectiveness of an alternative solution without real tests. The limitation then is only the creativity of the designer.
Some examples of using these optimizations are in the next lines. These are techniques that do not require investments and just need creativity and good knowledge of engineering concepts:
- Create or increase the ventilation area to achieve the same temperature rises but using higher currents.
- Paint or coat buses to improve heat dissipation
- Improve electrical contacts to decrease unwanted heat generation and extend service life.
- Direct airflow to warmer points reducing temperature rises
- Modify some-part materials to reduce magnetic induction heating effects
- Modify geometries to reduce magnetic, electrical fields, and short circuit electrodynamic forces (and can increase bearable short circuit levels)
- Modify design to improve or increase the ability to support internal arcs.
- Use simple devices to reduce electric fields and thus use shorter phase-to-ground and phase-to-phase distances (more compact equipment)
THE TECHNIQUES AND “TRICKS” TO IMPROVE THE DESIGN
The key-points are the requirements for temperature rise, the supportability to electrodynamic forces the supportability to the overpressures of the internal arc and dielectric distances. All these ones have to do with the geometries, construction details and materials used.
To better understand them read IEC 62271-307. I participated in the meetings of the IEC working group for the creation of this document. There, the main design factors are described in detail.
“TEMPERATURE RISE” : the reference parameter for the design aspects is the rise, for conductive and insulating parts, that cannot be exceeded. If you exceed the limits specified in the technical standards, the equipment ages prematurely or may be even destroyed. For example, the allowable temperature rise limit for a silver-plated connection on a copper busbar is 75 K. For a bare, uncoated copper connection, this limit is 50K. Applying a permanent overload such that the temperature rise is only 6.5 degrees above these limits will result in a life loss of about 2/3. If we extrapolate this concept to overall life, it means getting two to three contacts and connections, rather than one, in the period. To understand the details of this aspect, see pages 101 to 116 of the complete free book at http://www.cognitor.com.br/Book_SE_SW_2013_ENG.pdf . This book is an useful publication for designers of equipment for substations.
ELECTRODYNAMIC FORCES: The smaller are the phase distances and the greater the distance between busbar supports, the greater are the mechanical forces which will arise during short circuits. Too many physical curves or change of direction of the conductors increase the forces to be supported and consequently the number o busbar supports.
INTERNAL ARC OVERPRESSURES: The smaller are the internal volumes and the smaller and slower the overpressure relief areas the greater are the overpressures. Higher and longer short circuit currents have more severe effects on the overpressure to be supported by the walls and doors.
In the link to follow you may download the complete article with test cases and references