Solar panel

The non renewable energy resources are decreasing, use of renewable resources for producing electricity is increasing. Solar panels are becoming more popular day by day. Solar panel absorbs the energy from the Sun and is stored in the battery. This energy can be utilized when required. Utilization of the energy stored in batteries is mentioned in below given applications. Solar panels should absorb energy to a maximum extent. This can be done only if the panels are continuously placed towards Sun direction. So solar panel should continuously rotate in the direction of Sun. This article describes about circuit that rotates solar panel.

Principle of Sun Tracking Solar Panel 

The Sun tracking solar panel consists of two LDRs, solar panel and stepper motor and ATMEGA8 Micro controller.

Two light dependent resistors are arranged on the edges of the solar panel. Light dependent resistors produce low resistance when light falls on them. The stepper motor connected to the panel rotates the panel in the direction of Sun. Panel is arranged in such a way that light on two LDRs is compared and panel is rotated towards LDR which have high intensity i.e. low resistance compared to other. Stepper motor rotates the panel at certain angle.

When the intensity of the light falling on right LDR is more, panel slowly moves towards right and if intensity on the left LDR is more, panel slowly moves towards left. In the noon time, Sun is ahead and intensity of light on both the panels is same. In such cases, panel is constant and there is no rotation.

Components in the Circuit:

• Solar panel
• ATmega8 micro controller
• Light Dependent Resistor.
• Motor driver IC
• Stepper Motor.

Automated Sun Tracking Solar Panel Circuit Design:

The proposed system consists of ATmega8 micro controller, Solar panel, Light Dependent resistors and motor driver IC.

ATmega8 is AVR family micro controller. It is based on advanced RISC architecture. It is an 8 bit controller. It has 4KB Flash memory, 512 bytes of EEPROM and 1Kb of SRAM. It has 23 programmable pins. It supports peripheral features like two 8-bit timers, one 16 bit timer, 6 channel ADC with 10-bit resolution, programmable USART, Serial peripheral interface, 2 wire serial interface, etc.

Solar panel is connected to Stepper motor. Solar panel consists of photovoltaic cells arranged in an order. Photovoltaic cell is nothing but a solar cell. Photo resembles light and voltaic is electricity. Solar cell is made up of semiconductor material silicon. When a light ray from Sun is incident on the solar cell, some amount of energy is absorbed by this material. The absorbed energy is enough for the electrons to jump from one orbit to other inside the atom. Cells have one or more electric field that directs the electrons which creates current. By placing metal contact energy can be obtained from these cells.

Light Dependent Resistors are the resistors whose resistance values depend on intensity of the light. As the intensity of light falling on the LDR increases, resistance value decreases. In dark, LDR will have maximum resistance. LDR will output an analog value which should be converted to digital. This can be done using analog to digital converter. ATmega8 has analog to digital converter internally. It has six ADC channels from ADC0 to ADC5.The two LDRs are connected to ADC pins i.e. PC0 and PC1. ADC conversion is done using successive approximation method.

Stepper motor rotates the panel in a stepwise angle. To drive this motor a driver IC is used. Driver IC amplifies the input voltage and protects the microcontroller from back EMF. Generally, motors generate back EMF. This may damage the controller. The driver IC used is L293D. It has H bridge internally made up of transistors. This IC has 16 pins. Output pins are connected to the stepper motor pins. Input pins are connected to the controller pins as shown in circuit diagram.

By connecting a battery to the solar panel, one can store the energy generated by the solar cells and this energy can be used when required.

some simple projects for Electrical&Electronics(EEE) students; for one-stop all electrical students for all electrical information's & projects...

Grounding Transformer or Earthing Transformer

Earthing

transformer on the Delta Side is outsides the Zone of protection the Earth

Fault(E/F)in the delta system outside Current Transformer(CT)

locations would produce current distributions as shown

which circulate within the differential CT secondaries and is kept out of

operating coils.

Zig-Zag

or inter connected star grounding transformer has

normal magnetising impedance of high value but for E/F, currents flow in

windings of the same - core in such a manner that the ampere turn cancel and

hence offer lower impedance.

In

cases where the neutral point of three phase system is not

accessible like the system connected to the delta connected side of a electrical power

transformer, an artificial neutral point may be created with help of a

zigzag connected earthing transformer.

This is

a core type transformer with three limbs. Every phase winding in zigzag

connection is divided into two equal halves. One half of which is wound on one

limb and other half is wound on another limb of the core of transformer.

1st

half of Red phase winding is wound on the 1st limb of the core and 2nd half of

same Red phase is wound on 3rd limb.

1st

half of Yellow phase winding is wound on the 2nd limb of the core and 2nd half

of same Yellow phase is wound on 1st limb.

1st

half of Blue phase winding is wound on the 3rd limb of the core and 2nd half of

same Blue phase is wound on 2nd limb.

End point of all three winding ultimately

connected together and forms a common neutral point. Now if any fault occurs at

any of the phases in delta connected system, the zero sequence fault current has close path of

circulating through earth as shown in the figure.

In

normal condition of the system, the voltage across the winding of

the earthing transformer is 1/√3 times of rated per phase voltage of the

system. But when single line to ground fault occurs on any phase of the system,

as shown in the figure, zero sequence component of the earth fault current flows

in the earth and returns to the electrical power system

by way of earth star point of the earthing

transformer. It gets divided equally in all the three phases. Hence, as

shown in the figure, the currents in the two different halves of two windings

in the same limb of the core flow in opposite directions.

And

therefore the magnetic flux set up

by these two currents will oppose and neutralize each other. As there is no

increase in flux due to fault current, there is no change of dφ/dt means no

concluded like that, the zigzag type earthing or grounding

choking effect occurs to impede the flow of fault current. So it can be

transformer maintains the rated supply voltage at normal current as

well as when a solid single line to ground fault current flows

through it.

The

rated voltage of an

earthing or grounding transformer is the line to line voltage on

which it is intended to be used. Current rating of this transformer is the

maximum neutral current in

Amperes that the transformer is designed to carry in fault condition for a

specific time. Generally the time interval, for which transformer designed to

carry the maximum fault current

through it safely, is taken as 30 second.

Auto Transformer

Auto transformer is kind of electrical transformer where primary and secondary shares same common single winding.

Theory of Auto Transformer

In Auto Transformer, one single winding is used as primary winding as well as secondary winding. But in two windings transformer two different windings are used for primary and secondary purpose. A diagram of auto transformer is shown below. The winding AB of total turns N₁ is considered as primary winding. This winding is tapped from point ′C′ and the portion BC is considered as secondary. Let's assume the number of turns in between points ′B′ and ′C′ is N₂. If V₁ voltage is applied across the winding i.e. in between ′A′ and ′C′. Hence, the voltage across the portion BC of the winding, will be, As BC portion of the winding is considered as secondary, it can easily be understood that value of constant ′k′ is nothing but turns ratio or voltage ratio of that auto transformer.

When load is connected between secondary terminals i.e.between ′B′ and ′C′, load current I₂ starts flowing. The current in the secondary winding or common winding is the difference of I₂ & I₁.

Copper Savings in Auto Transformer

Now we will discuss the savings of copper in auto transformer compared to conventional two winding transformer.

We know that weight of copper of any winding depends upon its length and cross - sectional area. Again length of conductor in winding is proportional to its number of turns and cross - sectional area varies with rated current.

So weight of copper in winding is directly proportional to product of number of turns and rated current of the winding. Therefore, weight of copper in the section AC proportional to,

and similarly, weight of copper in the section BC proportional to, Hence, total weight of copper in the winding of auto transformer proportional to, In similar way it can be proved, the weight of copper in two winding transformer is proportional to, N₁I₁ + N₂I₂   ⇒ 2N₁I₁    (Since, in a transformer N₁I₁ = N₂I₂) Let's assume, W_a and W_tw are weight of copper in auto transformer and two winding transformer respectively, ∴ Saving of copper in auto transformer compared to two winding transformer,

Auto transformer employs only single winding per phase as against two distinctly separate windings in a conventional transformer. Advantages of using auto transformer. For transformation ratio = 2, the size of the auto transformer would be approximately 50% of the corresponding size of two winding transformer. For transformation ratio say 20 however the size would be 95%. The saving in cost is of course not in the same proportion. The saving of cost is appreciable when the ratio of transformer is low, that is lower than 2.

Disadvantages of Using Auto Transformer

But auto transformer has the following disadvantages:

1. Because of electrical conductivity of the primary and secondary windings the lower voltage circuit is liable to be impressed upon by higher voltage. To avoid breakdown in the lower voltage circuit, it becomes necessary to design the low voltage circuit to withstand higher voltage.
2. The leakage flux between the primary and secondary windings is small and hence the impedance is low. This results into severer short circuit currents under fault conditions.
3. The connections on primary and secondary sides have necessarily to be same, except when using interconnected starring connections. This introduces complications due to changing primary and secondary phase angle particularly in the case-by-case of delta / delta connection.
4. Because of common neutral in a star / star connected auto transformer it is not possible to earth neutral of one side only. Both their sides have to have their neutrality either earth or isolated.
5. It is more difficult to preserve the electromagnetic balance of the winding when voltage adjustment tappings are provided. It should be known that the provision of adjusting tapping on an auto transformer increases considerably the frame size of the transformer. If the range of tapping is very large, the advantages gained in initial cost is lost to a great event.

High Voltage Transformer

The transformers are normally used in high voltage laboratory for extra high voltage testing purpose. This transformer is subjected to transient voltages and surges during their normal operation when the insulation under test breaks down. To withstand these impulse voltages, the insulation of transformer is carefully designed. This high voltage transformer is single phase, core type. This type of transformer is generally oil immersed. Bakelite sheets are used for separating high tension and low tension winding. The high voltage transformers used for HT cable testing purpose are to supply also sufficient electric current and that is why the cooling system of these transformers is very carefully designed. Special cares also to be taken for voltage regulation of transformers. For insulator testing purposes, the required current is very tiny but, while the insulator breaks down during testing, there would flow huge current through the transformer. To limit this current, a high resistance is connected in series with transformer. As the current required is very less during insulation testing, this high voltage transformer needs not to have high KVA ratings. The table below shows, the rating of transformer used for various testing purposes.

Up to voltage 500 KV, generally single one high voltage transformer is used. But for higher voltage more than one transformer, are connected in cascade to produce required high voltage. Actually for getting such high voltage, a single transformer has to be very huge in size which is not at all economical. The figure below shows the typical cascading connection of two transformers. Low voltage is supplied to the low voltage winding of a step up transformer 1 as shown in the figure below. The tank of this transformer is earthed. The secondary of this transformer, is connected to the earthed tank and other end comes out through a high voltage bushing. The bushing is so specially designed and manufactured, that it can withstand full secondary high voltage, in respect of earthed potential of transformer tank. Another tapping terminal also runs through this high voltage bushing. The high voltage end and tapping terminal ends are connected across primary of the second transformer. One end of the secondary winding of second transformer is connected to its tank. The tank of second transformer is not earthed like first transformer. This is isolated and insulated from earth for full secondary voltage of the transformer. One end of the high voltage or secondary winding of second transformer is connected to the earth and other end alone comes out from the high voltage bushing for feeding high voltage to the equipments and insulators under testing.

Single Phase Transformers for Three Phase System

some simple projects for Electrical&Electronics
(EEE) students; for one-stop all electrical students for all electrical information's & projects...

It is found that generation, transmission and distribution of Electrical power are more economical in three phase system than single phase system. For three phase system three single phase transformers are required. Three phase transformation can be done in two ways, by using single three phase transformer or by using a bank of Three single phase transformers. Both are having some advantages over other. Single 3 phase transformer costs around 15% less than bank of Three single phase transformers. Again former occupies less space than later. For very big transformer, it is impossible to transport large three phase transformer to the site and it is easier to transport three single phase transformers which is erected separately to form a three phase unit. Another advantage of using bank of three single phase transformers is that, if one unit of the bank becomes out of order, then the bank can be run as open delta.

Connection of Three Phase Transformer

A verity of connection of three phase transformer are possible on each side of both a single 3 phase transformer or a bank of three single phase transformers.

Marking or Labeling the Different Terminals of Transformer

Terminals of each phase of HV side should be labeled as capital letters, A, B, C, and those of LV side should be labeled as small letters, a, b, c. Terminal polarities are indicated by suffixes 1 & 2. Suffix 1’s indicate similar polarity ends and so do 2’s.

Star-Star Transformer

Star-star transformer is formed in a 3 phase transformer by connecting one terminal of each phase of individual side, together. The common terminal is indicated by suffix 1 in the figure below. If terminal with suffix 1 in both primary and secondary are used as common terminal, voltages of primary and secondary are in same phase. That is why this connection is called zero degree connection or 0° - connection. If the terminals with suffix 1 is connected together in HV side as common point and the terminals with suffix 2 in LV side are connected together as common point, the voltages in primary and secondary will be in opposite phase. Hence, star-star transformer connection is called 180°-connection, of three phase transformer.

Delta-Delta Transformer
In delta-delta transformer, 1 suffixed terminals of each phase primary winding will be connected with 2 suffixed terminal of next phase primary winding. If primary is HV side, then A₁ will be connected to B₂, B₁ will be connected to C₂ and C₁ will be connected to A₂. Similarly in LV side 1 suffixed terminals of each phase winding will be connected with 2 suffixed terminals of next phase winding. That means, a₁ will be connected to b₂, b₁ will be connected to c₂ and c₁ will be connected to a₂. If transformer leads are taken out from primary and secondary 2 suffixed terminals of the winding, then there will be no phase difference between similar line voltages in primary and secondary. This delta delta transformer connection is zero degree connection or 0°-connection.

But in LV side of transformer, if, a₂ is connected to b₁, b₂ is connected to c₁ and c₂ is connected to a₁. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings, and then similar line voltages in primary and secondary will be in phase opposition. This connection is called 180°-connection, of three phase transformer.

Star-Delta Transformer

Here in star-delta transformer, star connection in HV side is formed by connecting all the 1 suffixed terminals together as common point and transformer primary leads are taken out from 2 suffixed terminals of primary windings. The delta connection in LV side is formed by connecting 1 suffixed terminals of each phase LV winding with 2 suffixed terminal of next phase LV winding. More clearly, a₁ is connected to b₂, b₁ is connected to c₂ and c₁ is connected to a₂. The secondary (here it considered as LV) leads are taken out from 2 suffixed ends of the secondary windings of transformer. The Transformer connection diagram is shown in the figure beside. It is seen from the figure that the sum of the voltages in delta side is zero. This is a must as otherwise closed delta would mean a short circuit. It is also observed from the phasor diagram that, phase to neutral voltage (equivalent star basis) on the delta side lags by − 30° to the phase to neutral voltage on the star side; this is also the phase relationship between the respective line to line voltages. This Star delta transformer connection is therefore known as − 30°-connection. Star-delta + 30°-connection is also possible by connecting secondary terminals in following sequence. a₂ is connected to b₁, b₂ is connected to c₁ and c₂ is connected to a₁. The secondary leads of transformer are taken out from 2 suffixed terminals of LV windings,

Delta-Star Transformer

Delta-star transformer connection of three phase transformer is similar to star – delta connection. If any one interchanges HV side and LV side of star-delta transformer in diagram, it simply becomes delta – star connected 3 phase transformer. That means all small letters of star-delta connection should be replaced by capital letters and all small letters by capital in Delta-star transformer connection.

Delta-Zigzag Transformer

The winding of each phase on the star connected side is divided into two equal halves in Delta zig zag Transformer. Each leg of the core of transformer is wound by half winding from two different secondary phases in addition to its primary winding.

Star-Zigzag Transformer

The winding of each phase on the secondary star in a star-zigzag transformer is divided into two equal halves. Each leg of the core of transformer is wound by half winding from two different secondary phases in addition to its primary winding.

Choice Between Star Connection and Delta Connection of Three Phase Transformer

In star connection with earthed neutral, phase voltage i.e. phase to neutral voltage, is 1/√3 times of line voltage .e. line to line voltage. But in the case of delta connection phase voltage is equal to line voltage. Star connected high voltage side Electrical power Transformer is about 10% cheaper than that of delta connected high voltage side transformer.

Let’s explain,

Let, the voltage ratio of transformer between HV & LV is K, voltage across HV winding is V_H and voltage across LV winding is V_L and voltage across transformer leads in HV side say V_p and in LV say V_s.

In Star-Star Transformer

Voltage difference between HV & LV winding,

In Star-Delta Transformer

Voltage difference between HV & LV winding,

In Delta-Star Transformer

Voltage difference between HV & LV winding,

For 132/33KV Transformer K = 4

Case 1 Voltage difference between HV & LV winding,

Case 2 Voltage difference between HV & LV winding,

Case 3 Voltage difference between HV & LV winding,

In case 2 voltage difference between HV and LV winding is minimum therefore potential stresses between them is minimum, implies insulation cost in between these winding is also less. Hence for step down purpose star–delta Transformer connection is most economical, design for transformer. Similarly it can be proved that for step up purpose delta-star Three phase transformer connection is most economical.