Electrical Engineering Related
Discourse about the challenges of technology development in three examples
Choosing the right lighting for outdoor restaurants and entertainment venues
One of the most complex subjects in lighting design, is related to restaurants, docks and other recreation areas which provide service in outdoor landscapes. Lighting design of these spaces is a real paradox.
One of the main consequences of inappropriate design of lighting in these cases, is accumulation of insects such as mosquitoes around the lights which threats the family hopes to spend a pleasurable evening outdoors …
In general, the light-sensitive insects are divided into three categories which are photo-negative, photo-positive and photo-tactic. Photo-positive insects, which encompasses the majority of known insects, are attracted to ultraviolet light. Conversely, photo-negative insects, which live in the soil, escape from the light.
Finally, photo-tactic insects are including the insects, such as bees, which absorb to light and use it for purposes such as generating thermal energy and navigation.
Studies which is conducted on the lights shows that mercury vapor lamp is the most attractive one for the insects. After it, fluorescent lamps (including CFLs), incandescent lamp, sodium vapor lamp and LED lamps are in the next level of attraction respectively.
So, in such cases, it is better to use the LED lights (despite the relatively high-price). Because , in addition to their lower ultraviolet radiation and so very little attraction to insects , they have a better CRI in comparison with sodium vapor lamps. Furthermore, in the long term, LED lights, due to lower power consumption, offset a part of high cost of initial investment.
A New and Comprehensive Classification of Fault Related Operations in Power System
Generally, operating procedures associated with faults in the power system can be classified as follows:
1-Pre-fault stage :
Operations in this stage aimed to preventing of faults and so interruptions in the power system. In this way, power system’s reliability will increase. So this operations is called reliability centered maintenance (RCM). This type of operation itself is classified into three categories : preventive maintenance (PM), predictive and preventive maintenance (PPM ) and condition monitoring (CM).
2-Concurrent with fault stage:
At this stage, the fault must be detected and isolated from the power system. This operation is done automatically by the protection system.
3- Before fault locating :
At this stage, the approximate range of fault locations will be determined. This stage is called power system step restoration. In this stage, operators by re-closing of some circuit breakers in power system and monitoring that they trip again or not, can estimate a more accurate range of fault locations.
Even in some cases, because of transient faults, the whole of system may be restorated (fault natural clearance). Sometimes auto-reclosers and sectionalizers is used to do this step automatically.
Comparison of the reliability of low voltage and medium voltage networks
In all books written about the reliability of power systems, it is explicitly stated that the reliability of medium voltage networks is lower than similar (overhead/underground) low voltage networks. In the other words, the failure rate in the unit length of a medium voltage network (in a definite period) is more than the similar low voltage network. However, these books does not explains why this is so.
One of the main reasons that cause to decreasing of medium voltage networks’ reliability, is the electric field intensity. Two important phenomena are the main source of faults in the overhead and underground networks respectively, fault path carbonization and water treeing (polymers reaction with water in XLPE cables).
Figure 1 : Water treeing in a XLPE cable joint
It is worth noting that these two phenomena can form only in the presence of voltages higher than 5 kV. In the other words, the voltage gradient plays both the activator and catalyst roles in water treeing and fault path carbonization mechanisms. For this reason, in low voltage networks, the occurrence probability of water treeing and fault path carbonization (the most important factors that tends to network aging and fault occurrence in MV networks) is almost zero.
Right Choosing Of Film Capacitors for Outdoor Installation (Pole Mounted Capacitors)
Dissipation factor of capacitors is a function of temperature and frequency (of supply voltage). In the other words, capacitors’ losses vary with temperature and frequency. Dissipation factor of capacitors has three additive components. The first and second components are related to changing of capacitors’ parallel and series (ESR) resistances due to temperature. Since both of these resistances increase with temperature, so these two components always are positive. The third component is related to intrinsic characteristic of dielectric material. Dielectric dissipation factor may increase, decrease or even remain constant with increasing temperature. So, cleverly choosing of film capacitors may decrease the probability of capacitor overheating and extends its overall life.
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Temperature Monitoring with Chromogenic Polymeric Covers (Smart Paints)
“Over-heating” is one of the major causes of malfanction and damaging of electrical equipments. Specially, considering expensive electrical equipments such as generators, motors and transformers, reveals that by proper “temperature monitoring” of these electrical equipments, we can avoid a lot of unexpected costs.
“Chromogenic polymers” are a general group of polymers which are “excitation-respective”. A cathegory of “chromogenic polymers” are “thermo-respective polymers” which their color change in response to the temperature variations. “Thermo-respective polymers”, have two main cathegories which are “thermo-chromic” and “thermo-tropic” polymers.
“Thermo-chromic” polymers are a kind of “LCPs” (Liquid Crystal polymers) which also named as chiral nematics and can show a vast and high resolution color spectrum in response to the temperature changes.
Application of these special polymers as the “painting cover” of expensinve electrical equipments* may increase reliability of power systems and reduce the operational costs of industries. These special paints are named “smart paints” and is expected to be used in “smart grids”.
* Comparing “smart paints” and “fixed thermo-graphic cameras” is a separate subject that is investigated in my book “survey of electrical contacts in power systems-ISBN : 978-964-8479-59-1”.
Future of Power Industry, Captured by Polymers
The picture of the future power industry may be very different from that we imagine. The power industry probably will change totally in a decade. The extraordinary progress of polymer science may has an important role in this massive change. It is not far from reality to imagine a world where the power lines and ground wires, lighting bulbs, turbine blades, batteries, electrical equipment frames, panels paintings, advertising lights, fuel cells, substation enclosures , … change to polymers. So , power lines and ground systems which are made from conductive polymers will not be degraded by the exposure to the corrosion and oxidation.
Polymeric photo-luminescent lights for advertising
Why go so far? Which electrical engineer could imagine polymeric fuses? Re-settable fuses which are innovated by “Tyco Electronics Corporation” does not need to be replaced at all. The resistance of these fuses increases when the current exceeds the nominal rate and tend to infinity. When the current gets its normal conditions, then fuse recovers its normal conductivity again. On the other hand, smart polymeric sensors will be an inseparable part of any smart grid. The polymeric sensors of temperature, voltage, PH, moisture and … are sensitive, reliable and appropriate sensors that doesn’t need to any external supply. Supplying sensitive electronic sensors in proximity of high power networks is a challenge for implementing of any smart grid. The intrinsic properties of Thermo-respective, Photo respective, photo-luminescent, electro-luminescent, Ph-respective, shape-memory and other smart polymers make a great potential for making a modern polymeric power industry.
Eigenvalues and Eigenvectors
The effective analysis of any of complex dynamic system requires understanding the concepts of “eigenvalues and eigenvectors” . These concepts generally are introduced during linear algebra course in university. Innovative and beautiful presenting of these concepts at “MIT’s Open Course of Linear Algebra” at the following address (specially lectures 21 and 22) will build deeper and more subtle attitude which is necessary to the engineering courses such as Power Systems Dynamics .
http://ocw.mit.edu/courses/mathematics/18-06-linear-algebra-spring-2010