Solar Power for Homes

 

With cost of living going up every day, it’s time to change things & become aware about the efficient usage of our natural & earthly resources. As the cost of electricity is boosting, let us now think to make use of solar energy for homes. Since Sun will come up daily, it will keep our solar appliances getting charged and remain fully charged and when it’s winter season or raining days and Sun veils away, still it would be better enough to get all the way through till next dawn or so, otherwise we can make use of regular power as backup.

When in general talking about that why I require using electricity formed by solar energy for my home, you would also consider that every appliance that is functional with the help of electricity will be bringing into play solar power electricity. If you want that every appliance in your house run on solar power then you will require solar panels, solar grid-tie, Inverter or charger and Battery.

Why We Use Solar Power for Homes?

When deciding for being solar, every home owner will have their individual precise grounds for making use of solar energy for home, but the maximum of the home owners can be classified into 3 main categories -

1. Environmental Impact
2. Financial Benefits
3. Energy Independence

Comprehending why solar energy usage is vital for you will assist you to develop a solar energy plan that can fetch your solar visualization to existence.

1. Environmental Impact:

Many home owners make up their mind to use solar energy just because of the positive impact it gives to our environment. Global warming and climatic alterations are some major problems which the world is facing now a day… and you can be a fraction of the way out by captivating benefits of solar energy!

Not like fossil fuels, solar energy does not bring into being the injurious pollutants liable for raising the greenhouse effect which directs to global warming. Solar energy is a fresh and prolong energy source that you can bring into play for solar heating, solar electricity, solar lighting and solar cooling. By making use of solar energy, you -

• Will decrease your carbon footstep,
• Can experience a satisfaction about being an environment friendly responsible citizen.

2. Financial Benefits:

An additional key reason for home owners bearing in mind solar energy is the monetary feature. The financial gains of solar energy can be observed in condensed utility expenditures as you bring into play solar energy for electricity, cooling, lighting and heating. Additionally, by sinking your domestic operating expenditures you are also escalating the rates of your residence.  As you can witness, captivating benefits of solar economics will -

• Save you a lot of funds in present as well in future,
• Endow you with a sturdy investment for your upcoming future.

3. Energy Independence:

A final answer to the query “Why make use of solar energy” is the energy freedom it will provide you.

By bringing into play solar energy, you will decrease your reliance on the utility firms. You no more require having electricity supplies to your residence as you will be capable to manufacture your individual solar power electricity. Solar expertise will also liberate you from making use of customary energy supplies for heating as well as for cooling, etc. All of this implies you will at last be liberated from increasing utility prices & bills!

Solar energy also provides you a plane of dependability and safety that other energy resources cannot counterpart. When your neighbors do not have electric power owing to an outage, you would not be concerned as your residence produces its individual electricity and heat (this is also acknowledged as micro generation). Additionally to the individual safety you will get free from your neighboring utility firms, you will also facilitate to eradicate our dependence to overseas energy manufacturers which, in present day’s world, is dangerous for national safety.

Solar Energy (Solar Panel) Installation for Home:

Installing a photovoltaic (solar or PV) power structure is an awesome technique of imprisoning the Sun’s vast solar energy to produce electricity for our individual homes. Once your solar system is fitted properly, it will facilitate you to lessen your electrical energy bills and together with will lend out your hand to keep your environment clean & green. Solar power arrangements are also low at maintenance and can boost the cost of your home.

 

Solar power systems can be coupled to the main electricity network or can be set up as a separate structure. If you attach solar power system to the main grid you still have to pay an electricity bill. If you are yet utilizing some electricity from the main electricity network, think about purchasing Green Power so that your residence electricity supplies are fulfilled from renewable resources. If you get installed a solar power system at residence, you might be entitled to obtain renewable power benefits in the outline of STCs (Small-scale Technology Certificates).

How to Install Solar Energy Systems:

1. Find out where the installation of your solar panels will be appropriate. To get the maximum out of the solar energy system, you are required to maximize their exposure to the Sunlight so that they may get direct as well as maximum daylight all year round.
2. Make certain that all your solar panels are mounted on a rafter.
3. Fasten the solar panel mounts to the roof with sturdy lag bolts. Position mounts in such a manner that solar panels will have a minimum of three inches of air-flow underneath them. This checks the system from getting overheated.
4. Fix metal flashing above the solar panel mounts to evade leakages. Fasten the metal bars to the mounts with steel screws.
5. Fix the solar panels above the metal bars. Unlock the connection box on each & every solar panel and attach the boxes by uniting their cables collectively on the suitable terminal bolts. The cables will keep the panels together in series. Run the cable on the very last solar panel to the charging controller for the solar panel unit.

Once your system is installed successfully, set up the final inspection and here you solar energy is ready to be used. So, it is actually an easy and uncomplicated course of action. The only significant point to make a note of is that you should bring into play a MCS licensed solar power systems in order to avail the benefits and grants. That’s a compulsory condition.

اقرء المزيد

Mark the ground with an X and say Dig Here!

Figure 1 - Acoustic surge detection

No matter what method is used for fault locating on direct buried underground cable, at some point an “x” must be marked on the ground to say “dig here.” The most commonly used prelocation methods such as arc reflection or current impulse will get reasonably close to the fault, but are not accurate enough to define the exact fault location.

Before digging, in order to repair the faulted cable, some type of pinpointing technique must be used.

The classical methods all revolve around a way to zero in on the sound produced by the thump or discharge of energy at the fault created by a surge generator. A simple and well-used method is the fault-locator-ear-on-the-ground-butt-in-the-air technique. Under some conditions such as after a rain or heavy morning dew this can be a shocking experience, literally. Under certain conditions such as created by a corroded neutral, when surging the cable, current will flow in the earth itself rather than back to the generator through the neutral.

When this occurs, a voltage drop is produced between the spread hands of the fault locator each time the surge generator discharges. Other less painful approaches involve old reliable tools such as traffic cones, shovel handles, and modified stethoscopes.

Slightly more sophisticated equipment uses an acoustic pickup or microphone placed on the ground, an electronic amplifier, and a set of headphones.

This setup amplifies the sound and helps to zero in on the source at the fault. An improvement on this technique is the addition of a second pickup. See Figure 1 above. A switch and meter on the amplifier allow comparison of the magnitude of the sound from each pickup. The higher signal is from the pickup closest to the fault and the sensors are moved in that direction. With pickups straddling the fault, the sound levels are equal.

These acoustic techniques all assume that the sound produced at the fault travels directly to ground level unimpeded and that the loudest sound is heard precisely above the fault. If the cable happens to be in duct or conduit, under paving or surrounded by tree roots, this assumption may not be valid. In duct or pipe, the loudest sound occurs at either end or at a break.

If the fault is under paving, the loudest sound may be at a crack or seam. Root systems seem to carry the sound off in all directions.

اقرء المزيد

Alternating Current (AC) Home Wiring

Homes typically are powered with both 220-volt and 110-volt alternating current (AC) electricity. Modern outlets have three different shaped holes to assure plugs can only be inserted in one way. Two of the holes are considered grounds, for reasons of safety. Proper grounding and the use of fuses are important to maintain electrical safety in the home.

Questions you may have include:

• What is the configuration of home wiring?
• What do the holes in the wall outlets represent?
• What safety features are necessary?

This lesson will answer those questions.

 

Home wiring

Typically, homes receive 220 volts of AC electricity. Certain high-power devices, such as an electric stove, use the full 220 volts. The rest of the outlets in the house use 110 volts.

Wires into home

Usually, three copper wires come into the home. Two are covered in black insulation and one has white insulation. Sometimes one wire is red instead of black. Each black or red wire is called a "hot" wire and has 110-volt AC. The white wire is called the "common" and is grounded at the power station. Measuring across the two hot wires results in 220 volts. Measuring the voltage between a black (or red) and white wire, results in 110-volt AC.

Wiring configuration

Copper wire

Copper wire is used because it is a good conductor of electricity. Materials that do not conduct electricity as good usually have a higher resistance. This results in wasted energy and the tendency to get hot, which could be a safety hazard.

In the 1960s many electrical contractors started to use aluminum wire instead of copper. Aluminum is almost as good of a conductor as copper, but it is much less expensive. After a number of years, it was found that this type of wiring caused a potential fire hazard. Problems due to expansion caused overheating at connections between the wire and switches, outlets, or splices. Many homes had to be re-wired, although there still are many that still have aluminum wiring but have never had problems.

Wall outlets

The wall outlets usually have a one wide slot, one narrow slot and one round-with-flat-bottom hole. This is to assure that each part of the plug will be used as it is supposed to and to increase safety. Older outlets have both slots the same size and no round hole.

Typical wall outlet

Outlet slots

The narrow slot is considered "hot" and is where the alternating current power comes out. The wiring behind the outlet to this slot is usually black in the U.S. The wide slot is considered the "common" and is supposed to be grounded. Using the white wire as a common grounded wire, means that everyone is working from the same zero voltage position.

Round hole

The hole that is round on the top and flat on the bottom is an extra ground. Usually the wire behind the wall outlet has green insulation. Sometimes it is a bare wire. This extra ground is to make sure your utensils are properly grounded in the situation that someone had improperly wired the house. It is an extra safety measure.

Common wire

Although the white wire is not supposed to be a "hot" wire, in some cases it is used that way, especially in older homes that have the old style outlets. In general, this is acceptable, but it can result in problems. If you touch a common wire that is properly grounded, you should not get a shock. But if that wiring has made it hot, you can get a shock. Also, by using the white wire where the black should be used, you may cause a short circuit.

Safety

Proper grounding and the use of fuses are important for protection against shock, as well as to prevent electrical overheating and fire hazards

Grounding

Correct grounding is very important. Often ground wires are connected to water pipes that normally go into the ground. Connecting to a hot water pipe means that the water heater is between the connection and the ground. The water heater may have plastic parts that would insulate the connection to ground. Thus, using a hot water pipe is not a good idea.

Another consideration in using water pipes to ground the circuit is that plastic piping is often being used in plumbing. You must make sure there are no plastic pipes between your connection and the outside earth or ground.

Fuses

Fuses and circuit breakers are used as a safety measure in case of short circuits. A fuse or circuit breaker will break the connection if more current is passing through the wire than is considered safe. This will prevent the house wiring to overheat and start a fire.

Most homes now use circuit breakers instead of fuses. One reason is because people with bad wiring in their homes that constantly blow out fuses, would then force pennies in the fuse receptacles, thus bypassing the requirement for a fuse. This removed the aggravation, as well as the expense of buying new fuses, but it also often resulted in serious electrical fires in the house.

Summary

Most homes use both 220- and 110-volt AC electricity. Wires have black, red, white or green insulation, depending on their use. The holes in modern outlets assure plugs can only be inserted in one way. Proper grounding and the use of fuses are important to maintain electrical safety in the home.

اقرء المزيد

استار دلتار بطريقه مبسطه للمبتدئين بالصور

السلام عليكم ورحمة الله وبركاته

بشرح دائرة استار دلتا بالصور

 

ملاحظه : ممكن ان يكون هذا الموضوع معروف لبعض الاخوه لكن هناك الكثيرون لا يعرفونه ,وممكن ان يكون الموضع مكرر ولكن ليس بهذا السياق

1- المكونات



2- رسم للدائرة البور كنترول

3- مرور التيار الكهربائى فى وضع الايقاف مع عمل لمبه ليد بالون الاحمر

4- بعد الضغط على مفتاح البدء وتحرك التيار فى الدائره ,عند تشغيل المحرك يبدا التيمر بالعد ليقوم بعكس النقاط المشار اليها فى الصوره

5- بعد عد التيمر وعكس النقاط وتشغل المحرك دلتا

اقرء المزيد

10mistakes people make working on electrical systems

1. Thinking that it's "only 120 volts" or 208 volts or 480 volts or...

"It's only low voltage." Okay, I'll admit that you can have an open casket with a low-voltage hit, but you'll still be dead. The only difference between low and high voltage is how fast it can kill you. High voltage kills instantly; low voltage may take a little longer.

Dr. A.G. Soto, consulting physician to Ontario Power Generation presented a paper at the 2007 IEEE Electrical Safety Workshop discussing low-voltage shock exposures. In that paper, he stated that a 120-volt shock can kill up to 48 hours later. He also stated that many emergency room physicians are unfamiliar with electric shock and that an EKG may not show a problem. The injury to the heart muscle tends to spread over time and cannot always be identified using EKGs.

2. Working on energized systems or equipment when it can be de-energized.

This is a "man-thing". When I was working in a power plant (back in the 70s), we never de-energized anything, whether it could be or not. My boss had a great contempt for anyone sissy enough to actually ask to de-energize before working. He would tell anyone foolish enough to suggest turning it off, "You're an electrician, work it hot! That's what you're trained to do!" His other favorite saying was, "If you want to be here tomorrow, you'll get this done today". Can you feel the love?

De-energizing is the only way to eliminate hazards. Arc flash personal protective equipment (PPE) just increases your chances of survival; it doesn't guarantee it. Just be aware that until equipment and systems are placed in an electrically-safe work condition, proper PPE and procedures must be used to protect the worker. See Article 120 in NFPA 70E 2009.

3. Not wearing PPE.

This could go into number 2 above, but people really don't like wearing rubber insulating gloves or arc flash PPE and equipment. It's hot, uncomfortable, restricts movement, and slows the entire work process down -- not only by wearing it, but by selecting the correct PPE and putting it on and taking it off. It will also save your life. One of the most likely times people neglect to wear their PPE is during troubleshooting. The rationale seems to be, "I'm not really working on it; I'm just testing it." Yet, CDC/NIOSH studies have found that 24% of electrical accidents are caused by troubleshooting, voltage testing and like activities. We have a tendency to ignore hazards associated with tasks we consider "safe".

Back at my old job, when I was surveying a 480-volt 250 amp molded-case circuit breaker, the worker I was with put his bifocals up on his forehead so he could read the label on the breaker. He dropped his glasses back to his nose and immediately the breaker blew up! Luckily, he only had some red dots on his face and some singed hair, as he was backing his head out when it let go. Metal droplets were imbedded into the lenses of his glasses, but because of them, he wasn't seriously injured. We investigated why that breaker might have failed and never found a good reason; it was just time for it to fail. Carbon buildup from earlier fault interruption, eroded contact materail that gets sprayed up into the arc chutes, weakened dialectric due to the extreme heating of arc interruption; all of these weaken circuit breakers and could have caused what seemed like a perfectly good breaker to fail suddenly. You never know.

4. Going to sleep during safety training

Nothing like a good nap to get you ready for a hard day's work! Every Monday morning Shermco does a one-hour safety meeting for all technicians. We call it the "Monday Moaner", because the technicians really want to be at their job sites, not getting "preached to". We like to do what we are comfortable with, even it there's a better way to do things. Add that to the fact that wearing PPE and filling out forms are port of the required steps, and fugettaboutit!

The other side of the coin is that a lot of safety training is sooooooooooooooooo boring! I've been to some sessions that, by the end, you're praying for a mercy killing - either me or the instructor, I don't care which! Safety training has to be focused, concise and interesting, otherwise everyone tunes it out.

5. Using outdated or defective test equipment to troubleshoot.

When the leads are frayed or the meter's doggy, it's time to replace it. I worked with a technician who used the same Wiggy (solenoid tester) for seven years. You couldn't read the faceplate, the coil was so weak that it didn't even vibrate and the leads had been pulled loose from the bottom. Almost every time he used it he got nailed! One day, right after he was shocked (for the kazillionth time) I said, "Hey, let me see your Wiggy". He handed it down and I twirled it around my head and smacked a concrete column with it. The coil came springing out and he charged down the ladder like an enraged bull! I handed him my new Wiggy and said, "Take this new one - that one's going to get you killed", to which he said, "I've had that since I was an apprentice!" Don't get emotionally attached to inanimate objects. If you really love your old voltage tester, take it home and make a little shrine to it - just don't bring it to work.

The NFPA committee was concerned enough to put two different requirements for using only portable electric tools and test equipment that were properly rated.

110.9(A)(1) Use of Equipment, Rating states, "Test instruments, equipment and their accessories shall be rated for the circuits to which they will be connected".

Each of these statements are followed by a reference to ANSI/ISA 61010-1, Safety Requirements for Measurement, Control and Laboratory Use - Part 1: General Requirements for rating and design requirements for voltage measurement and test instruments intended for use on electrical systems 1000V and below."

6. Not wearing the right PPE.

No, I'm not repeating myself. Some people think that if they wear anything by way of PPE, that should be enough. While it is true that the injuries that you sustain probably won't be quite as severe as if you didn't wear any PPE, there's a high probability that if the right PPE was worn, you'd have no injury. This could also probably go under number 4, because if you aren't paying attention during safety training, you probably can't choose the right PPE, either. Do you know how to interpret arc flash labels? What do you do if there's no arc flash label on electrical power equipment? Do you know how to use the tables in the NFPA 70E? Do you refer to the notes when you use the tables? If you answer "no" to any of these questions, you aren't choosing the right PPE. As a matter of fact, you probably would not be considered qualified by OSHA. Your company has the responsibility to provide training so you meet OSHS's definition of a qualified electrical worker, but you have the exposure to the hazard. It's your biscuits that'll get burned; you need to do the homework to protect yourself!

7. Trusting someone else for your safety.

An OSHA compliance officer I know investigated an arc flash incident where two electricians had been working together for years. The one who was injured asked his buddy if the circuit had been checked and was dead, to which his buddy replied, "Yeah". He really didn't think that it had been done, but he didn't want to offend his partner, so he didn't pursue the question. When he started working on it the circuit blew up, causing severe arc flash burns. He stated, "If I had to do it over again I would have checked it myself and not worried about so-and-so's feelings". Actually, those weren't his words, but they won't allow me to print what he really did say. You get the idea, though.

Sometimes relationships cause us to not follow through when we should. Either we don't want to offend someone, like the above example, or we don't want to look less than manly to our coworkers. "Nothing personal, I'd just like to make sure I don't get my face blown off." However you want to put it, don't neglect to prove systems dead personally.

8. Not performing required maintenance of power system equipment.

Too often companies look at maintenance costs as an overhead expense. Nothing could be further from the truth. The problem is, it's difficult to put a savings on things that don't happen. unscheduled outages, loss of production, buying equipment at premium pricing, overtime, disposing of the cratered equipment, etc. Those of us who've been through the maintenence wars have seen the costs associated with neglect, but for newer managers and accounting types, it's really difficule to appreciate. Liken it to automobile maintenance. You go out and buy that new ZR1 and then do no maintenance for 100,000 miles. What condition do you think it will be in?

9. Not carrying your gloves with you.

During my safety training classes I like to ask how many people actually carry their rubber insulating gloves with them? Maybe one or two will raise their hands. Well, guess what, if you don't carry them, you aren't using them. This might go along with thinking low voltage won't hurt you. We get buzzed and it's no big deal. At the beginning of 2008 in Athens, Texas three TXU workers were working on a 120/208 volt transformer. One of the workers stood and said, "Well, boys. Looks like I got bit again", took three steps and was dead. Carry your gloves and use your gloves, always.

10. Not using an Energized Electrical Work Permit system.

People tend to hate paperwork, including myself. This is one great exception. OSHA wants us to plan each job, have the right tools and equipment to do the job safely and follow our work plan. How do we document the Hazard/Risk Analysis or our PPE Assessment? The OSHA Field Safety Compliance Officers I know all tell me the same thing; if it's not documented, you can't prove that you did it. The Energized Electrical Work Permit provides the means to plan the work, assess the hazard and the risk, choose the proper PPE for the job and document it. The side bar shows an example of Energized Electrical Work Permit and has a brief description of each section and its purpose.

Summary

There's always something else that could be included in this list, but 10 gets you thinking. We go through life making small mistake after small mistake and nothing happens, until we happen to get the wrong alignment of small mistakes and we now have an accident. Once the accident starts, we have no control over it, so the best thing to do is to avoid the small mistakes and tighten up the way we work.

اقرء المزيد

How To Make A Dark Sensor

 

Step 1: Things You Need

 

Parts:-
1) 1x BC547 transistor
2) 1x 220 k resistor
3) 1x 330 ohms resistor
4) 1- small perf board
5) 1x led (any colour )
6) wires
7) 9v battery
8) battery clip
9)ldr(light dependent resistor )

Tools:-
1) soldering rod and wire
2) wire stripper 

Step 2: Getting started

solder the transistor on the perf board and solder one wire of the ldr to the emitter and other to the base  , solder the negative wire of the led to the base of the transistor with a 330 ohms resistor and also solder 220k resistor with the one side of the 330 ohms resistor

 

 

Step 3: Finishing touches

 

you can use a SPDT switch it is optional, it used to pin headers as the connectors for the power .

 

اقرء المزيد

Effective Resistance Of Busbars

System with two copper bus bars

Busbars made up of flat bars

The construction of busbar is usually carried out by putting together several flat bars in parallel for each phase. The spacing between the bars is made equal to their thickness for practical reasons, and this leads to skin and proximity effects.

Figure 1 - Extra loss coefficient in groups of flat bars

If one refers to published results, no accurate quantitative estimations of these combined effects can be found. An order of magnitude forthe extra loss coefficient K is given in figure 1 for 2 cross-sections of copper: 100 x 5 and 100 x 10 mm.

For each group of 1, 2, 3 or 4 bars, points corresponding to published results encircle a shaded area in which the probable value of K must be situated. In the absence of any more accurate results, the search for a value of K for a set of bars of any size can be made using the curves of figure 1, and equating the set to a single bar of the same height but of a width equal to the overall width of the whole set. The resistance Rc is the equivalent to that of all the bars in parallel.

The coefficient K is here found by excess, but this extrapolation is only valid for bars which are not separated by more than their thickness.

In effect, a generous spacing and a judicious positioning of the bars lead to a reduction in the loss coefficient; for example in figure 2 are shown the coefficients K for groups of 3, 4, 6 and 8 bars of 100 x 6 mm; the closest bars are 6 mm apart, the furthest 60 mm. The relative gain on the losses is 20% for 3 bars and 40% for 4 bars, according as to whether they are in one or two batches. It is rare that the use of 5 bars grouped together is considered because of the high loss coefficient caused by inadequate use of the central bar.

Figure 2 - Extra loss coefficient in groups of 3 to 8 flat bars according to their disposition

It has also been proposed to place the 4 bars of a phase along the edges of a square, a solution which gives the advantages of a tubular conductor, but the supports and the tappings become fairly complicated here. 

All these indications concern the skin effect acting simultaneously with the proximity effect, in a group of several bars of the same phase; for 3 phases, if the distance between the closest bars of 2 different phases is less than twice the height of these bars, an inverse proximity effect acts in addition to the two previous effects.

In order to obtain a value for the coefficient K giving the increase in the corresponding losses, one should refer to the DIN standards no. 43.671 [23] which give the coefficient K4 for bars of 5 or 10 mm thickness, or to reference [24] in which the average geometric distances of various shapes of conductor make it possible to carry out the relevant calculation.

An arrangement which is of particular interest in the case of 3 phase system is the so-called sandwich: busbars inter twined or permuted. The bars of each of the phases are not placed in independent groups for each phase, but are on the contrary placed in between each other.

Figure 3 - Busbar having 2 bars per phase (J, R, V)

A busbar having 2 bars per phase (J, R, V) is thus arranged as in figure 3 ; the proximity effects are eliminated, the current density in each bar is almost identical and the coefficient K is little over 1.

Two disadvantages limit the general use of this process: certain complications in the connection and joints, and the difficulty of obtaining isolation of the phases, even at low voltages.

An additional advantage is the reduction in the electrodynamic stresses, to which can be added a decrease in the inductance per phase by a factor of 10;  this last characteristic of sandwich type busbars has a favorable effect on the induced voltage drop in normal operation, but leads to an increase in the value of short-circuit current.

 

Minimal heating, or reduction in the extra losses?

Up till now the effects mentioned have only been analysed from the point of view of the increase in the effective A.C. resistance, that is of the extra losses produced by the Joule effect.

The normal consequence is increased heating of the conductors, but this is sometimes compensated for by adopting an arrangement  which favors cooling by radiation or convection. 

Now the heating is at present time the only important criterion taken into consideration for the designing of a high current conductor; however the minimal heating is not always found in conjunction with the lowest loss coefficient; it can be seen from figure 15 that the coefficient K is more or less the same for one 100 x 10 bar or two 100 x 5 bars, but because of the larger cooling surface in the latter case, it is possible, at equivalent heatings, to obtain a current of 10% greater, and thus losses which are 20% greater.

Another characteristic example is the tubular conductor whose optimized shape guarantees a coefficient K close to 1; however this tube has the smallest cooling surface (without any forced ventilation on the inside) and it can be seen in Figure 4 that it is far from having the profile which carries the highest current, for a heating and a cross-section the same as other configurations.

Figure 4 - comparison of profiles having equal total cross-section

The designer of a high current conductor will sometimes be advised to choose a technology not only according to the heating produced, but also according to the total losses.

 

Resistivity of the metal, copper or aluminium?

It was assumed in what has preceded that the metal used was copper; it now should be noted that the skin and proximity effects become more marked as the resistance decreases.

A copper conductor will thus have a higher loss coefficient than the same conductor made of aluminium, but the latter, requiring a cross-section 1.6 times greater to obtain the same resistance (for a direct current), losses this advantage over the copper conductor because the two conductors have the same coefficient K for the same shape and the same resistance Rc.

In practice, the replacement of copper by aluminium is not done on the basis of equivalent resistance or voltage drop but rather on that of equivalent heating; this amounts to multiplying the cross-section by 1.4 to 1.5 only, in order to take into account the improved cooling of the larger surface.

To sum up, for equal heating, an aluminium conductor has a better loss coefficient than an equivalent copper conductor; it must not be forgotten however that this entails higher losses which must be evacuated and also paid for.

 

The price per kilo and the much lower density of aluminium are the determining factors which lead to the metal being chosen to high current intensity conductors.

 

Influence of the frequency

Only the industrial frequency of 50 Hz has been taken into consideration in the preceding calculations; their accuracy which is only relative however makes them valid for frequencies of up to 60 Hz. Extra loss coefficient for the skin effect in cylindrical conductors (tubes and flat rods) at 50 or 60 Hz can be used for any other frequency with the corrections given.

Amongst these frequencies 25 Hz is hardly ever used; as for 16 2/3 Hz it can be assimilated to direct current. Serious problems of skin effect are set by the 400 Hz frequency which is used for special circuits (marine, aviation, etc.), as soon as the current reaches a few hundred amperes: the “skin ” of the copper is reduced to 3 mm at this frequency.

In industrial networks, harmonic currents having frequencies which are multiples of 50 Hz (the harmonics 3 and 11 cause the most nuisance) can be superposed to the fundamental frequency. These currents encounter an effectively increased resistance and significant losses and heating occur.

SOURCE: Schneider  Electric Cahier technique no. 83 – Extra losses caused in high current conductors by skin and proximity effects .

اقرء المزيد

الخلية الشمسية أو الضوئية أو الكهروضوئية

 

جهاز يحول الطاقة الشمسية مباشرة إلى طاقة كهربائية مستغلا التأثير الضوئي الجهدي.

تستخدم التجمعات من الخلايا الشمسية (وحدات الطاقة الشمسية) لالتقاط الطاقة من ضوء الشمس, عندما يتم تجميع وحدات متعددة معاً (حيث تكون أولوية التركيب بنظام تعقب قطبي محمول) يتم تركيب هذه الخلايا الضوئية كوحدة واحدة يتم توجيهها على سطح واحد وتسمى بلوح الطاقة الشمسية (solar panel.).. إن الطاقة الكهربائية الناتجة من الوحدات الضوئية (Solar power). وتعتبر مثالأ على استخدام الطاقة الشمسية(solar energy)..

 إن الخلايا الكهروضوئية هو مجال التكنولوجيا والبحوث المتعلقة بالتطبيق العملي في إنتاج الكهرباء من الضوء، لكن وعلى الرغم من ذلك غالبا ما يستعمل على وجه التحديد بالإشارة إلى توليد الكهرباء من ضوء الشمس.

 توصف الخلايا بالخلايا الضوئية وإن لم يكن مصدر الضوء هو الشمس ومثال ذلك (ضوء المصباح، الضوء الاصطناعي، وغيرها..). وتستخدم الخلايا الكهروضوئية للكشف عن ضوء أو غيره من الإشعاع الكهرومغناطيسي بالقرب من مجموعة ضوئية مرئية، كالكشف عن الأشعة تحت الحمراء، أو قياس شدة الضوء..

خلية شمسية صنعت من بلورة أحادية من السليكون.

السيليكون كثير البلورات في لوح شمسي.

الفولتية الضوئية (بالإنجليزية: Photovoltaics PV) التي تعرف ب الخلايا الشمسية أوالخلايا الفولتضوئية photovoltaic cells. من خلالها يتم تحويل أشعة الشمس مباشرة إلى كهرباء، عن طريق استخدام أشباه الموصلات مثل السليكون الذي يستخرج من الرمل النقي.

 وبصفة عامة مواد هذه الخلايا إما مادة بلورية سميكة كالسيليكون البلوري Crystalline Silicon أو مادة لابلورية رقيقة كمادة السيلكون اللابلوري (Amorphous Silicon a-Si) و Cadmium (Telluride CdTe)أو (Copper Indium Diselenide CuInSe^2, or CIS) أو مواد مترسبة كطبقات فوق شرائح من شبه الموصلات تتكون من أرسنيد(زرنيخيد) الجاليوم (Gallium Arsenide GaAs).

وتعتبر طاقاتها شكلا من الطاقة المتجددة والنظيفة، لأنه لايسفر عن تشغيلها نفايات ملوثة ولا ضوضاء ولا إشعاعات ولا حتي تحتاج لوقود. لكن كلفتها الابتدائية مرتفعة مقارنة بمصادر الطاقة الأخرى. والخلايا الشمسية تولّد كهرباء مستمرة ومباشرة (كما هو في البطاريات السائلة والجافة العادية).

تعتمد شدة تيارها علي وقت سطوع الشمس وشدة أشعة الشمس، وكذلك على كفاءة الخلية الضوئية نفسها في تحويل الطاقة الشمسية إلى طاقة كهربائية. يمكن لهذه الخلايا الشمسية إعطاء مئات الفولتات من التيار الكهربائي المستمر DC لو وصّلت هذه الخلايا علي التوالي. كما يمكن تخزين الطاقة الناتجة في بطاريات الحامضية المصنوعة من الرصاص أو القاعدية المصنوعة من معدني النيكل والكادميوم. ويمكن تحويل التيار المستمر DC إلي تيار متردد AC بواسطة العاكسات ال Invertor للاستعمال وإدارة الأجهزة الكهربائية المنزلية والصناعية العادية.

من ميزتها أنها ليس بها أجزاء متحركة تتعرض للعطل. لهذا تعمل فوق الأقمار الصناعية بكفاءة عالية، ولاسيما وأنها لاتحتاج لصيانة أو إصلاحات أو وقود, حيث تعمل في صمت, إلا أن اتساخ الخلايا الضوئية نتيجة التلوث أو الغبار يؤدي إلى خفض في كفائتها مما يستدعي تنظيفها على فترات.


وهذا كتاب يشرح  كيفية توليد الكهرباء من الخلايا الشمسية
الجزاء الاول
الجزء الثاني
الجزاء الثالث

اقرء المزيد

How a simple Tesla coil works

A Breif description of how spark gap tesla coils works.
Some electronic or technical terms are of course un-avoidable.

Voltage is applied , the primary capacitor (C) charges , the voltage across the primary capacitor increases.
Spark gap (SG) fires, when the voltage across C reaches the spark gap break down voltage.
Capacitor (C) is discharged through the spark gap (SG) and primary coil (P).
The magnetic field in the primary (P) increases as the voltage across the capacitance (C) decreases.
When the voltage across the capacitor (C) is zero, the field in the primary coil (P) starts to collapse, creating a voltage which re-charges the capacitor (C). This creates an alternating current in the primary coil (P).
Because the secondary coil (S) is connected (by transformer action) to the primary coil (P). The alternating current in the primary coil is transferred to the secondary coil (S). It takes a few of the above cycles for all of the power to be transferred into the secondary coil (S).
The topload (T) and the secondary coil (S) are designed to swap power between them in the same way and at the same rate as the primary capacitor (C) and the primary coil (P). This matching of frequencies multiplies the induced voltage in the secondary coil (S).
When there is more voltage than the topload can hold on its surface. The voltage breaks out into an arc.
This process continues until there is no more power in the primary capacitor (C) and primary coil (P). As there is now not enough voltage to maintain the arc across the spark gap (SG), The arc extinguishes. This alows the capacitor(C) to charge again and the sequence repeats.

اقرء المزيد

اختبار قياس الموجات فوق الصوتية

 

ثمة مشاكل كهربائية أساسية يمكن التعرف عليها وكشفها:

حدوث القوس الكهربائي : يحدث القوس الكهربائي عند تدفق التيار الكهربائي في المكان. والإضاءة خير مثال على ذلك

الكورونا الضوئية : وهي عندما يقوم الفولت للموصل الكهربائي ، مثل الهوائي أو خط انبعاث الفولت العالي يزيد على قيمة خط النقل الكهربي وهو يزيد على قيمة العتبة المقدرة، فإن الهواء المحيط بها يبدأ في التأين ليشكل توهج أزرق أو أرجواني

إبقاء الترددات على نسبها المضبوطة : يشار إليها غالبا على أنها " بداية حدوث تقوس" يتبع العزل التالف

وبالرغم من أنه من الناحية النظرية، فإن الكشف بالموجات فوق الصوتية يمكن استخدام جهد كهربي منخفض أو جهد كهربي متوسط أو جهد العالي فإن معظم التطبيقات تميل إلى استخدام نظم الفولت الكهربي المتوسط والعالي

فعندما تتسرب الكهرباء في خطوط الجهد العالي أو عندما تقفز عبر الفجوة في الوصلة الكهربائية فإنها تقطع جزيئات الهواء حوله وتولد موجات فوق صوتية. ويمكن إدراك هذا الصوت من خلال القرقعة أو تشويش الكهرباء ، وفي حالات أخرى يمكن سماع صوت أزيز. وتشمل التطبيقات : عمليات العزل والكابلات ومحطة التحويل والموصلات والمرحلات ومفاتيح التلامس وعلب التوصيلات الأسلاك  الكهربائية. في المحطات الفرعية يمكن اختبار المكونات مثل العوازل والمحولات والكابلات

ويمكن استخدام الاختبار بالموجات فوق الصوتية  لتقييم الجهد ا لكهربي الزائد عن 2000 فولت، وخصوصا في محطات التحويل . و هذا مفيد بشكل خاص في تحديد تتبع الأعطال. أما في محطات التحويل، فإن تتبع الذبذبات التي تفوق التردد للأعطال الخطيرة يمكن تحديدها من خلال قياسها بالأشعة تحت الحمراء. وينصح باستخدام الاختبارين معا مع محطات التحويل المغلقة

.

ملاحظة: عند اختبار الآلة الكهربائية، يجب إتباع إجراءات السلامة الخاصة بالشركة أو بالمصنع. وفي حالة عدم التأكد يجب الرجوع إلى المشرف.  لا تلمس الجهاز الكهربائي المرتبط بالنظام.

إن الطريقة المستخدمة للتنبؤ بالقوس الكهربائي وتسرب إكليلي تشبه الإجراءات المذكورة في عملية التنبؤ بالتسرب. وبدلا من الاستماع إلى صوت اندفاع ، فإن المستخدم سوف يستمع لصوت قرقعة أو أزيز . ففي بعض الحالات ، كما هو في محاولة لتحديد مصدر التشويش الراديو والتلفزيون أو في المحطات الفرعية ، يتم تحديد المنطقة التي تسود فيها التشويش باستخدام  كاشف ضخم مثل جهاز لا سلكي نقال أو جهاز تحديد التشويش . فما أن يتم تحديد المنطقة العامة، يتم استخدام وحدة المسح وذلك لعمل المسح الشامل للمنطقة. وتقل الحساسية إذا كانت الإشارة قوية في خلال تتبعها على جهاز القياس حتى يتم تحديد أعلى نقطة

وتحديد وجود العطل من عدمه باعتباره عطل بسيط نسبيا . فمن خلال مقارنة جودة الصوت ومستويات الصوت بين الآلة المماثلة، فإن مشكلة الصوت قد تكون مختلفة تماما

ففي نظم الجهد الكهربي المنخفض، فإن عملية المسح السريع لقضبان التوصيل سوف تلتقط التوصيل الضعيف . وفحص صناديق التوصيل يظهر عملية التقوس الكهربي. ومع كشف التسرب فإن أقرب موقع  للتسريب ، يرتفع صوت الإشارة . فعندما لا يظهر فحص خطوط الطاقة أي إشارة قوية لكشفها من الأرض ، عندئذ تستخدم وحدة مكثف شكل الموجة فوق الصوتية ( عاكس مكافئ المقطع ) والذي يضاعف مسافة الكشف للنظام ويظهر نقطة الكشف المحددة.

اقرء المزيد