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A protective relay is a device which initiates the circuit breaker to cut or off the faulty circuit from the healthy system. It acts just like a ‘ silence guard’, when any fault occurred in a system, the relay operates to close the trip circuit of the breaker and the breaker disconnects the faulty circuit.
Relay is the sensing unit of the electrical power system just like the brain of a human being which senses cold and hot things by touching it similarly, relay sense the abnormality in the system and gives trip command to the circuit breaker in order to disconnect the faulty section from healthy section.
A typical relay circuit is shown in fig. There are three parts in the relay circuit :-
First part is, the primary winding of a current transformer (C.T ) which is connected in series the line.
Second part , secondary winding of C.T is connected in series with relay operating coil.
Third part is the tripping circuit which may be either AC and DC source of supply, trip coil of the circuit breaker and relay stationary contacts are connected in series connection.
Now describe, how the relay disconnects the faulty circuit .
Suppose when a short circuit occurs at a point F, on the line, the huge current flows in the line. Hence, a heavy current flow through the relay coil, causing the relay to operate by closing its contacts. Result complete the tripping circuit of the breaker and making the circuit breaker open.
Relays are very important for protection of the electrical system and any damage occurring to the costly equipment's of a substation of any industry.
In a variety of ways, usually, depending on the region. The vast majority of it is generated by magnetic induction, but some is generated by the photoelectric effect. I'll try to be comprehensive in this answer.
First, generation of electricity by magnetic induction:
The concept is relatively simple, and in practice it's surprisingly simple, too. While the generator depicted above is a pretty poor generator, it demonstrates the concept okay. The math behind magnetic induction is, in differential form (easier from an electromagnetics standpoint),
or in integral form (easier from a systems analysis standpoint)
Where B is magnetic flux density, phi is total magnetic flux through the coils, the big E is electric field and the curly E is voltage.
Here's how they do it in practice. By far the cheapest per kilowatt-hour is hydro-electric power.
Quite simply, it uses gravity to naturally let water fall, and the moving water turns a turbine to generate electricity by magnetic induction. It's cheap per kilowatt-hour because there's no throttle time issues and no fuel. It can provide both baseline (low-power usage) and peaking (high power usage) generation. As long as it rains enough in the region, the reservoir will fill up without any human energy input.
A lot of our electricity is generated in coal power plants.
This power plant takes coal and burns it, using the heat to boil water and create high-pressure steam, which high pressure steam gets forced through a turbine, which generates electricity by magnetic induction.
Coal is pretty disgusting, by the way, but it's cheap unless you charge for the pollution. Coal power plants usually provide baseline power, since it requires incrementally more coal per extra bit of power. Coal for peaking is more expensive.
There are other systems in a coal power plant to make the process more efficient and have cleaner output, but those are a discussion for another question.
For peaking power, we often use natural gas generators.
It's similar to how the coal power plant works, except that it gets to double-dip on power generation -- first, the combustion reaction turns a turbine, and second, the hot exhaust boils water to turn a steam turbine.
Gas is expensive compared to coal, but the first turbine throttles up really quickly and the second within a few minutes, and it can be throttled up and down very easily compared to coal. As such, it makes for a great peaking generator.
In some areas, baseline power is provided by nuclear power plants. Nuclear power is remarkably similar to the others, as it's a thermal power generator.
The major conceptual difference is that the heat comes from Radioactive decay. Nuclear makes an excellent, clean baseline power source, and the major issues are failsafe systems (prevent meltdowns) and where to store the spent (still radioactive, but not enough to work in this configuration) fuel rods. However, it isn't very good at throttling up and down, so it sticks to baseline power generation for the most part.
I believe the biggest obstacle to deployment of more nuclear power is NIMBYism -- "Not In My Back Yard" opposition.
Next up, we have wind power.
In principle, it's even simpler than a hydroelectric plant. For newer systems, it's pretty cheap. The wind turns some great big blades, which turn a generator. The most expensive part of wind power is probably the land area that it has to take up per unit of power. Another issue with wind is that in most places it can be pretty variable, meaning you can't at-will throttle it up and down, and it may not be producing power all the time. If you have a very diverse set of locations for wind generators connected to a grid, it can work well, but if you rely on a single location the generation is a little intermittent.
If you want to know a lot more about wind power, ask Michael Barnard.
Keeping with magnetic induction, some companies have been using concentrated solar-thermal power. The concept is, again, a thermal power system, but instead of burning fuel it concentrates sunlight on to a target to heat it up. Think of the way you used to burn ants with a magnifying glass, only switch the magnifying glass for a parabolic mirror, and make it a lot bigger, and that's how solar-thermal works. It comes in different forms, but the concept is the same in all cases.
Modern systems have a salt target that melts and stores the heat, allowing the power generation process to continue for several hours after the sun goes down.
Last, I'll talk briefly about photovoltaic power, which uses the photoelectric effect instead of magnetic induction.
The basic concept is that light can knock charge carriers out of a bound state in a material, if individual photons comprising that light have enough energy to do so. In a photovoltaic panel, we use a semiconductor p–n junction and make the light get absorbed in the depletion region of that junction where there are no native free charge carriers. The light "generates" charge carriers (knocks them off of the atoms holding them) and they diffuse to the electrodes. It generates DC power.
I personally have a lot of interest in photovoltaics. (See: Jacob VanWagoner's post in X-Ray Visions for an interesting lecture on conversion efficiency, Jacob VanWagoner's answer to Is solar power becoming more efficient? and many other things I've answered related to solar panels.) While they suffer the same limitation of not having 100% uptime as wind power, the two major advantages I see are distributed power generation that takes up no real usable space, and that the panels tend to generate the most at the time of highest demand -- the afternoon, when everybody is running air conditioning.
Which ones are used most? Depends on where you live.
Solar technology is not a new technology, it was developed in 17th century B.C, and this technology has marked its presence in both developing as well as developed countries. Electric Street lights consume more energy as they use HD lamps. Today we have everything that work with solar energy like solar-powered buildings, vehicles, solar LED street lights, etc., for energy conservation.
Nowadays a new range of solar LED Street lighting make their presence felt everywhere and these lights are environmentally friendly and are easy to install and give high-intensity LED output. The solar LED street lights system convert sun energy to electricity and the system is prompted to turn on as the darkness approaches. Therefore, these lights automatically switch on after the sunset and after sunrise it switches off.
Solar Street Light
Design of Solar LED Street Light System
Design of Solar LED Street Light
The solar street lights operate from night until morning. The LED lamp automatically switches on after the sunset and switches off after the sunrise. This system design consists of the following parts:
Solar panels
LED light
Rechargeable battery
Controller
Pole
Interconnecting cables
Solar Panels
In solar street lights, the solar panel is one of the most important parts, and it is also known as solar photovoltaic cell. These cells are of two types: poly crystalline and mono crystalline. Compare to the poly crystalline, mono crystalline conversion rate is higher. Solar panels use light energy from the sun used to convert solar energy into electricity, which can be used to run many applications.
Electrical connections are made in series to accomplish an output voltage and to provide a current facility connections are made in parallel. The majority of modules use silicon or wafer based crystalline silicon but most of these solar panels are inflexible.
LED Light
In modern solar street lights, LEDs are used as lighting source and LED provide much brighter light with lower energy consumption. The energy utilization of LED fixture is lower than the HPS fixture, which is generally used in traditional street lights. Compare to the other HD lamps, and these lights do not emit light in all directions. The directional uniqueness of the LEDs will affect the design of lamps.
The output of the single LEDs is less than the other lamps like compact fluorescent and incandescent lamps but a set of LED lights gives bright light than these two. LED lights offer many benefits like Long life, durability, Eco-friendly and zero UV emissions.
Rechargeable Battery
Rechargeable battery is a type of electrical battery or accumulator and its electro mechanical reactions are reversible so it is called as secondary cell. Usually, there are two types of batteries: lead acid battery and gel cell deep cycle battery.
In solar LED street lights, a battery is used to store electricity from the solar panel during the day time to provide energy in the night time. The capacity and lifetime of the battery is very important as they affect the backup power days of the lights.
Controller
In solar LED street lights, a controller is very important as it usually decides to switch on or switch off the lighting and charging. Some modern controllers are programmable and are used to decide a suitable chance of lighting, dimming and charging. The Controller consists of a battery charger, a secondary power supply, a Led lamp driver, a driver, a protection circuit and a MCU.
The controller also controls the battery from overcharging and under charging conditions. By receiving the power from solar panels it continuously charges the battery in day time and while in evening it supplies the battery power to set of LED street lights.
Pole
For every street light, a strong pole is necessary, especially for a solar street light, there are some components like fixtures, batteries and panels mounted on the top of the pole, and input power consumption is 7.2 watt (LED). In solar street lights, the input operating voltage is 12V DC nominal system voltage, and the light output at the height of 12 feet is min of 09 LUX (unit of luminance).
Interconnecting cables
The battery box, Led light and solar panel are all fixed on the top of the pole and they are interconnected with cables. The cable for this LED system includes a PV module to the controller, and from controller to the battery and lamps. The cable size and lengths depends on the current being carried to the lights and the height of the pole.
With assembling all the above components into a one integrated system results the complete solar LED light system which uses sunlight energy to power the LED lamps fitted on street poles.
Solar LED Street Light Applications
Area lighting
Airport lighting
Hospital parking
Parks and playground parking
Parking lot lighting
Highway road way lighting
Street lighting
Security light
Highway and ramp lighting
Bridge lighting
Residential lighting
Industrial lighting
Commercial lighting
LED Lights offers the following Advantages:
Require fewer systems for installation.
Offers high lighting output when compare to the conventional lights.
Requires less time for installation and needs fewer systems.
Offers Long shelf life and low maintenance.
Offers pollution free ambience.
Provides provision of portability.
Comes with two year full system warranty.
Disadvantages
Initial investment is high when compared to the conventional lights.
The dust, snow or moisture can mount up on the PV panels, and thus reduces the energy production.
The rechargeable batteries need to be replaced several times.
Solar system costs reasonably high, and therefore,, the risk of theft is higher.
This is all about the solar LED Street light and its applications. We hope that you have got clear understanding of this topic, and if you have any doubts on this topic, you can contact to us. And, don’t forget to post your views and feedback on this article in the comment section below.
Chinese state-owned developer CECEP has completed a 70MW floating solar project - the largest in the world - at a former coal-mining area of Anhui Province, China, in collaboration with French floating solar specialist Ciel & Terre.
The project, spread across 13 separate islets on an area of 140 hectares, was completed in late 2018, with grid-connection, tests and commissioning carried out this month at the project site in the Lianghuai mining subsidence area, Yongqiao District, Suzhou City.
EPC services were provided by China Energy Conservation Solar Technology and the China Energy Engineering Group Shanxi Electric Power Design Institute. A brand new 18km 110V overhead line was also built for the grid connection of the plant, which is expected to generate up to 77,693MWh of electricity in its first year, equivalent to the power consumption of nearly 21,000 households.
While the complete facility in Anhui is said to currently be the largest floating PV plant on the same reservoir in the world, nearby, China-based firm Three Gorges New Energy has already partially connected a 150MW floating PV project to the grid, which is likely to become the largest plant globally once fully commissioned.
Equipment
The CECEP system was built using Ciel & Terre's Hydrelio floats, which are locally produced to minimize emissions, optimise logistics costs and offer local employment.
The project uses monocrystalline modules from Chinese manufacturer LONGi Solar, as confirmed by a C&T spokesperson to PV Tech. Central inverters have also been put on stilt platforms on the shoreline of the quarry lake so as not to interfere with neighbouring farm activity. Concrete poles support the electrical installation and 1,500 helical anchors were used for the project and buried at an 8-15 metre-depth to match the water body.
Ciel & Terre has already supplied its floating structure solution to GCL's 32MW FPV plant in Anhui province. It has also recently supplied a 9.8MW PV project featuring rooftop and floating elements in Cambodia.
Deep in the center of the sun, intense nuclear activity generates huge amounts of radiation. In turn, this radiation generates light energy called photons. These photons have no physical mass of their own, but carry huge amounts of energy and momentum. Different photons carry different wavelengths of light. Some photons will carry non-visible light (infrared and ultra-violet), whilst others will carry visible light (white light). Over time, these photons push out from the center of the sun. It can take one million years for a photon to push out to the surface from the core. Once they reach the sun’s surface, these photons rush through space at a speed of 670 million miles per hour. They reach earth in around eight minutes. On their journey from the sun to earth, photons can collide with and be deflected by other particles, and are destroyed on contact with anything that can absorb radiation, generating heat. That is why you feel warm on a sunny day: your body is absorbing photons from the sun. Our atmosphere absorbs many of these photons before they reach the surface of the earth. That is one of the two reasons that the sun feels so much hotter in the middle of the day. The sun is overhead and the photons have to travel through a thinner layer of atmosphere to reach us, compared to the end of the day when the sun is setting and the photons have to travel through a much thicker layer of atmosphere.
This is also one of the two reasons why a sunny day in winter is so much colder than a sunny day in summer. In winter, when your location on the earth is tilted away from the sun, the photons have to travel through a much thicker layer of atmosphere to reach us.
(The other reason that the sun is hotter during the middle of the day than at the end is because the intensity of photons is much higher at midday. When the sun is low in the sky, these photons are spread over a greater distance simply by the angle of your location on earth relative to the sun.)
DELTA-STAR and Distribution Transformer Unbalanced Loades
There are two types of unbalanced load. One type can be connected line-to-neutral and the other can be connected line-to-line. Although both unbalances can occur simultaneously during transformer loading, let us consider each separately.
Given a Dyn1 transformer, if a single phase load is connected line-to-neutral, the currents can be shown as follows:
When the load is connected to phase-a and neutral, the resulting load current will flow in only one of the three transformer secondary windings. On the primary side, the current flow will appear as a line-to-line connected load. Current will have the same phase angle as the load current and . Thus, a single phase load connected between any phase and neutral on the secondary side will appear as a line-to-line connected load on the primary.
If a single phase load is connected line-to-line, the currents can be shown as follows:
This type of unbalance is a bit more complicated. The load current flows in two of the secondary windings and each will have equal magnitude but opposite phase angle. On the primary side, current will appear in each of the three lines. Line current will have twice the magnitude as and but opposite phase angle. Thus, a single phase load connected line-to-line on the secondary will produce imbalanced line currents on the primary side. Two of the line currents will have equal magnitude and phase angle. One of the line currents will have twice the magnitude and opposite phase angle.
The unbalanced loading of a transformer is typically analyzed using the method of symmetrical components, but the approach shown above might be more intuitive for those not familiar with that method.
