Why transmission line cables are loose ?

 

Why transmission line cables are loose ?

       Often when we look at the transmission lines going off the road, then we see all the lines slightly tilted. Also you can see in picture , there is a curve which is formed by transmission line due to losseness .

   After all, why are these lines kept loose? 

Before knowing the reason, we see some terms.

(01). The distance between two consecutive towers of an Overhead line is called span. 

(02)  Sag is the distance between straight conductor (which should be kept) and losse conductor (which is kept). The more tight the wire, the less the sag is. 

       

Inshort the Reason is  :  

       When this cable is loose, this cable allows vibration. Along with this, it also gives us protection from mechanical shocks that can come in our transmission.

     

Let's see how :

         You will know that our conductor, it expands when it is heated. It will expand and get bigger. Because if we heat a substance, then the millions of atoms in the subtance, they get energy in the form of kinatic energy. 

  Due to this, these atoms start to vibrate faster and the space between these atoms increases.

(1). Heat is generated due to the current flow in the conductor of our transmission line.

(2).On the other hand, according to the weather, heat is generated in it. Heat is generated in the transmission line due to the sun (like our metallic gate gets heated due to the sun.)

     

  Because of this, the amount of sag in the transmission line increases. But when the sun's ray is not there, then the value of the sag of the transmission line automatically decreases at that time.

    If we keep the transmission line tight, then heat will be generated in it, due to which there will be vibrations of atoms. And due to this mechanical shock on transmission line will be there to cut the transmission line by generating mechanical stress on it . That's why our transmission line is kept loose. 

Hope this helps you . Thank you ️❤️

why a bulb is called 0 watt?

 

Why a bulb is called 0 watt?

We all call a bulb as 0 watt bulb. But do you know why it is called 0 watt bulb? 

                       ---------   Zero watt bulb

Actually, no electrical equipment will do a work on 0 watt. To do work it will take electricity in either some points. 

Then why is it called 0 watt after all?

The reason for this is that the electrical meter we had till a few years ago was an analogue meter. And the analogue meter cannot read some watts.

 If that zero watt bulb is actually a 7 watt bulb, then people could not see anything rising on the meter. So this misconception had formed in the minds of the people that this is a 0 watt bulb.

And that's where this 0 watt bulb started. And this term became very popular in India.

Hope this helps you . Thank you ❤️.

Earth wire in transmission line।step and touch potential

 Earth wire Or ground wire in transmission lines:

Touch potential:

Conductors are not directly connected to the transmission tower. They are connected to tower by means of insulators. If overhead power lines are not properly insulated or insulation breakdown happened , the current will flow towards the ground through the towers .If someone accidentally touch the tower whole current will flow towards ground through his body which is very dangerous. 

Hence, Earth wire is connected to peak of the tower which has zero potential and the unwanted current present in tower flows through ground wire . Hence one can get protection against touch potential (shock due to touching electrical wires )

Protection from Lightening: 

 Ground wire is placed at topmost position (at peak) so that it can also provides protection against lightening. Ground wire has zero potential . Other conductors (except ground wire) have some potential let say it is 33 kV line. The typical voltage of lightening is 300 million V. As potential difference between ground wire and lightening is greater than 33kV conductor , lightening prefers high potential difference path I.e. it travels through ground wire. Hence ,line conductors are protected by using the ground wire. 

Step potential :

Due to earth wire touch potential is minimised ,but step potential cannot be minimised by Earth wire . Step potential (when we steps our feet we may fell high voltage shock ) happen when accidentaly conductor cuts and falls on the ground . The voltage is distributed over the ground. Near the conductor there is high voltage . And as we moves away from the conductor voltage decreases. 

Consider , 

          A place near to the conductor ( say at 10 cm) have voltage 33 kV , and at 20 cm it is decreased to 30 kV . 

If one kept his one foot at 10 cm and another at 20 cm , due to difference of 3 kV voltage ( we know current flows if there is voltage difference) person may get shock.

To avoid this one should stand with feet near to each other without keeping any space between them. And like astronaut one have to jump and escape to the safe place.  

Advantages of earth wire :

 (1) protection against touch potential

 (2) protection of Conductor against lightening

 (3) used for communication (plcc)

Voltage induced in a DC generator is AC or DC?

Q " Voltage induced in a DC generator is AC or DC?

 Hello Friends . We very well know that the machine which converts the mechanical energy into an DC electrical current is called as the electric generator. 

It is quite interesting , the induced voltage in the armature winding of a DC generator is not DC but it is AC .

Let us see how this is possible . To understand this concept we have to overlook the working principle of the DC generator .

Working principle:

When a conductor is moved through a magnetic field an e.m.f. is induced between its ends. 

Let the length of the conductor be 'L' m and the flux density of the field be B N/m^2 (refer above figure).

If the conductor moves with velocity 'v' (m/sec ^2 )at right angles to the field, then the flux cut per second will be BvL (since the conductor will sweep out an area vL every second).

But the rate of change of flux is equal to the e.m.f. induced in the conductor. Therefore,

E = BLv

If the conductor cuts through the flux at an angle θ( θ is the angle between the magnetic field and the direction of motion),

 the equation becomes,

E = BLv sin θ 

Hence ,if B,l and v are constant then  

E= k sinø 

Hence , E is directly proportional to sinø. Therefore ,shape of emf will be a sine wave . The induced voltage is maximum at ø= 90° and 270° and minimum at ø= 0° ,180° and 360° . One rotation of the armature conductor corresponds to one cycle of induced emf .

Thus it is interesting to note that, the induced voltage in the armature winding of a DC generator is not DC but it is alternating. 

To convert it into a unidirectional (DC) signal , we have to use a rectifying device called commutator. Thus it is a device used in the DC generators to convert alternating induced voltage to a DC voltage . 

I hope this helps you. Thank you ❤️.

why power generating voltage is always 11 kV?। generating voltage

why power generating voltage is always 11 kV?

The today's blog is about why power generating voltage is always 11 kV ? Means that whatever power we generate in our power station, why is it always 11 kV only?

   You must have heard this 11 kV voltage i.e. 11000 V many times, whenever we talk about how much voltage is being generated in this power station, then at that time we always take the name of 11 kV. 

So now the question comes that why 11 kV only? Why not more or less than this? 

So friends, it is not always fixed that our electricity can be generated on 11kV only. If you go to all the power plants and see, you will see power generation happening there even at 25 kV, 20 kV voltage. But in most of the cases you see only 11 kV generating voltage.

 There are chances of going to ask this question in an electrical interview. So what is the correct answer after all? Let us see. 

       The answer is that in order to make our system "economical", it means that we can take maximum output and efficiency by investing minimum money in our power plant. 

But here comes another question that whatever is our electricity, we have made 11 kV.Now after this, the power we have generated, we transfer this power from the power station to the substation.We use transmission lines to transfer to the substation. If the voltage of your transmission lines is not 11 kV. They are on our 400 kV or 220 kV means very high voltage.

      So the question arises that if we had to send such high voltage in the transmission line, then why are we generating 11 kV in the power station? Why not generate in direct high voltage only?

        By doing this we do not need a transformer to convert 11 kV to higher voltage. Now friends, this is a step up transformer, it is worth a lot. Now because of using 11 kV, we have to pay a different price for the transformer as well. 

 

        So this question must be coming in our mind that, how 11 kV generated voltage system becomes economical?

So friends, you must know that we use high voltage transmission line to reduce losses in transmission line.

Our 11 kV generator is of very large size. So if we make a generator of 40000V, its size will be very big. 

Now on increasing the voltage, why does the size of the generator increase? There are many reasons for this.

(1) winding turns are increased :

      Whenever we increase the voltage, the turns of our armature winding also increase.

Due to this the size increases.

(2) Increase in insulation :

You would know that if we have any high voltage machine, then the amount of insulation inside it also has to be given more.

If the generator will be so big, then the size of its rotor will also increase. More mechanical energy will have to be given to spin that big turbine.

With the increase in mechanical energy, the amount and cost of the source that generates mechanical energy also increases a lot. 

That's why we considered it right to do power generation under 11 kV by not selecting high voltage and considering 11 kV as standard.

But why only 11 kV? Why not less than 11 kV 4-5-6 kV? If we use them then our cost will be further reduced.

 The correct answer is, whenever we increase the voltage, the value of our current decreases. But if we decrease the voltage then the value of current will increase.

P = V * I

But if the value of current increases, then the size of the conductor carrying it will also increase. Due to increase in armature conductor, our rotor will become heavy. It will take high mechanical power to rotate it. Again our derived cost will increase.

And because the conductor is thick, it becomes difficult to give cooling to it.

To avoid all these things, we needed such a ratio which is economical and our overall power system gives more output with less input. That's why we chose a standard value of 11 kV as the generating voltage.

I hope this helps you. Thank you ❤️.

Use of one transformer as six types of transformer। 6tricky ways to use a step down transformer

 6tricky ways to use a step down transformer.:

Today's topic is how to use step down transformer in some different tricky ways .

Here I have shown one step-down transformer .let , Primary winding is rated for 240 V and 1 Amp . 

 And Secondary winding is rated for 24 V and 10 Amps .

     

     I will show you one by one all six ways ,but transformer quality had to be good for using the transformer in six different ways. 

(1) step up transformer :

      Here , secondary LV (low voltage) winding of step down transformer is connected to supply voltage and primary HV (high voltage) winding of step down transformer is connected to load .

          If you give 24V to primary of step up transformer (refer above figure) ,you will get 240 V as an output . In this case, we can't give input voltage more than 24V . Otherwise, Winding insulation will burn. 

(2)step up auto transformer:

     This is a 240 V /264 V step up auto transformer.  I have made only one extra connection (dark blue line ). If you give 24 V at input ,we will get 264 V . This output is more beacause primary and secondary windings are added .

 There is no isolation in this transformer in between input and output . Blue Dot indicates polarity. We have to be  careful for polarity during connection.

(3) step down autotransformer :

If we give 240 V input we get 218 as output . There is no any insulation between primary and secondary windings. 

Here , primary voltage is more than secondary voltage because primary and secondary winding turns are added . Also like step up transformer, blue Dot indicates the polarity of induced emf . 

(4) inductive load :

HV primary winding is shorted using wire . A secondary winding is used as a load . This will show R+L load  . Where R is Resistance of Winding wires . Better the quality of the Transformer the value of R will be less.

But if we keep primary open then Impedance will be very large and will behave like a step up transformer.

(5) step down current transformer : 

       Here Step down transformer is used as a current transformer (CT) . By 1st way , step down transformer is first make as step up transformer. 

      Then LV Winding is used as primary and is connected in series main wire. HV winding is used as a secondary. A load of 5  ohm is connected accross secondary winding . 

When 10 Amps current flows through main wire ,then 1 Amp current will flow through secondary winding and there will be 5V drop across 5 ohm resistor. 

(6) isolation transformer: 

     In fig ., isolation transformer 240V /240V is shown . I have used two transformers which are connected back to back . 

If we give 240 V , we will get 240 V as an output . There is double isolation . Percentage impedance of this transformer is double than the normal transformer . Therefore we will get more voltage drop at secondary .

I hope this helps you. Thank you ❤️.