Author Archive

Discourse about the challenges of technology development in three examples

Although the dominant view to technology is optimism, but there are some evidences that casts doubt it. Here are three examples that demonstrate this point :

1- Changing the models (curves) of  supply – demand: Studies show that use of the CFLs in the UK has led to increased power consumption in lighting sector. This situation can be explained by economic theory of  “William Stanley Jevons” . According to this theory, technological change leads to changes in the supply and demand curves. In other words, the demand curve of  lumen (lighting flux) changes due to the cheaper price of the lumen so that the final consumption increases. Thus, the electric utilities which switch from incandescent lamps to CFLs and LEDs lighting technology to reduce power consumption in the coming years, will be quite disappointed.

2- Changes in construction presuppositions: About two month ago, when the IEEE-519 2014 standard was published, electrical equipment manufacturers and  power system operators were amazed; because the limit of THDV increased from 5% to 8% to respond the development of renewable generation technologies. Thus a large variations in the design and manufacturing of electrical equipment in order to improve the electromagnetic compatibility, expected. Also it can be predict that meters manufacturers in the worldwide create more pressure on IC manufacturers to change their energy measurement model based on IEEE  1459–2010 standard. This standard follows the instantaneous power theory of Alexander Eiegeles Emanuel instead of  the of  Bodeanu’s power theory. With this action of IEEE power quality work group, it can be expected that the limit of THDV  increase to 20% until 2020. With such amount of harmonic distortion, the overall philosophy of the design and operation of power systems,  in the demand, generation, transmission and distribution sides will change.

3-Information overload: Smart grids is based on data more than anything else. The role of  the data in engineering systems can be analogized with the role of vitamins in biological systems. Excessive data, beyond the management capability of these systems, transforms to the load of system and prevents the flexible performance of it. The cost of building and maintaining data centers, as well as cyber security for information systems is very high and so the lack of value-added production makes these systems useless overload. Thus, the development of smart grids without having an effective strategy in benefiting from value-added  (such as improving utilization  and increase the life of electrical equipment), may tends to electric utilities bankruptcy.


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.

(continue reading…)


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.

(continue reading…)


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

 


Relationship Between Reliability and Power Quality

Reliability is a branch of power quality which investigates the impact of  “Electricity Interruptions” on customers. Interruption is an index of power quality which has two categories: short-term and long-term. In the “short-term interruptions”, indices of  momentary interruptions (with a duration between 30 cycles up to 3 seconds) and temporary interruptions (continued 3 seconds to 1 minute) and in the “long-term interruptions” category, the index of sustained interruptions (with continuity over than 1 minute) is defined. It must be mentioned that interruption refers to the reducing of voltage below the 10% of rated voltage.

In discussing the reliability of a power system, the dependent indices of interruption (eg. SAIFI, CAIDI, SAIDI, …), which evaluate the number of customers which is affected by the interruption and the duration of  interruption is studied.


Reclaim an Issue : Loss and Voltage Relationship

In studying of losses in power systems, often spoken that power loss decrease is proportional to the inverse square of system voltage increase. For example, if the voltage is doubled, the losses will be a quarter. It should be noted that this conclusion is correct only when that after increasing the line voltage (and so reducing the line current) conductor cross section remains the same as previous. But this assumption is unreasonable and unwise, because conductor cross section must be chosen based on current amount.

It is a well known relationship that conductor cross-section and the energy loss is proportional to the square of the current. So, if we assume that the correct  conductor cross sections is chosen, the following conclusions can be found (in the case of system voltage increasing) :

1 -Because the conductor cross section will reduce proportional to the current decreasing, the costs of conductors  purchasing will reduce also. Instead,  the cost of the conductors insulating will increase with voltages increasing.

2 – With assuming that the conductor cross section is chosen based on nominal current, then the loss will be proportional to the voltage inverse (instead  of the inverse square of voltage).

For example, with doubling of the line voltage, conductor cross-section and the energy loss are both reduced approximately to half (there are other parameters that complicate heat transfer conditions and so we say conductor cross section approximately will reduce to half).


All Rights Reserved To Farhad Yazdi