Resistance in Series and parallel

Resistance is only component availbale which converts current into voltage and voltage into current.

Resistance in Series:-

In Series resistance are additive and are as described below:-

If there are resistances are R1, R2, R3, R4 ----- RN are connected in Series then equivalent resistance is given as 

R (Eq.)= R1 + R2+ R3+ R4+ ---------------------+RN

Series resistance is known as voltage divider circuit in which voltage get divided but current remains the same.

Whenever resistance is added in series then equivalent resistance is getting increased.

To know about capacitors in Series and Parallel Visit:-
http://electrialstandards.blogspot.in/2015/05/capacitor-in-series-and-parallel.html

Resistance in Parallel:-

If there are resistances are connected in Parallel then equivalent resistance is given as :-

If there are resistances are R1, R2, R3, R4 ----- RN are connected in Series then equivalent resistance is given as 

        1      =   1   +   1   +    1     +    1    +  ------------- +    1 

    R(eq.)       R1     R2      R3         R4                              RN

Then parallel circuits are current dividers. They have same voltage in Parallel but current get divider.

Note that the equivalent resistance is always less than the smallest resistor in the parallel network so the total resistance,  Equivalent resistance will always decrease as additional parallel resistors are added. Parallel resistance will give conductance which is described by G and unites are Siemens S.

To know about how capacitors behave in Series and Parallel , Visit link

http://electrialstandards.blogspot.in/2015/05/capacitor-in-series-and-parallel.html

To know how electrical power will act in Series and Parallel, Visit link:-

http://electrialstandards.blogspot.in/2014/12/electrical-power-in-series-and-parallel.html

Light Emitting diode working principle; LED working principle

Lighting emitting diodes mostly known as LEDs are now becoming integrated part of every Industry, Household , Shops and everywhere as they offer plenty of advantages some of them main are such as power saving and long life.

There is curiosity arises how these LED’s will work?

Working principle of the same is as below:-

LED is capable of emitting a fairly narrow bandwidth of visible or invisible lights and LED emits lights usually of orange, red, yellow, or green colors. The invisible light that LED emits includes the infrared light.

LED consists of a P-N junction diode. When electric current is applied to that P-N junction then that junction emits light .This sensation is generally called Electro-luminance in electronics. Electro-Luminance is defined as the emission of light from a semi-conductor under the influence of an electric field.

At PN junction there are electrons at N- Region and Holes in P- region. These combine at PN Junction. Free electrons at N- Region are in the conduction band of energy levels, while holes in P-Region are in the valence energy band. When these high energy electrons combine with holes energy get emitted in the form of heat and light.

LED Symbol is shown below:-

The electrons dissipate energy in the form of heat for silicon and germanium diodes.

There are some semiconductors such as :-

àGalium- Arsenide-phosphorous (GaAsP)

àGalium-phosphorous (GaP)

In above semiconductors electrons dissipate energy by emitting photons. If the semiconductor is translucent, the junction becomes the source of light as it is emitted, thus becoming a light emitting diode (LED).

Infrared light is produced by using Gallium Arsenide (GaAs) as semiconductor.

Red or yellow light is produced by using Gallium-Arsenide-Phosphorus (GaAsP) as semiconductor.

Red or green light is produced by using Gallium-Phosphorus (GaP) as semiconductor.

Characteristics for the same is as shown below:-

Very Small voltage is required to operate the LED's and there consumption is also very small.

For comparison between LED and Conventional lights Visit link below:-

http://electrialstandards.blogspot.in/2014/12/comparison-between-led-vs-incandescent.html

Electrical Power in Series and Parallel circuits; Bulbs in series and Parallel

There is quite confusing question most of the time asked in interview is that if there are three bulbs having ratings as 60W, 30W and 20W and these bulbs are connected in parallel then which of these bulb will be brightest??

Answer to that question is that in Parallel

  1               =  1  + 1  +  1

R(eq)             R1   R2    R3

Multiply both sides by Rated voltage square i.e. (V _Rated) ²

We get

(V _Rated) ²   = (V _Rated) ² + (V _Rated) ²  + (V _Rated) ²

R(eq)              R1                R2               R3

This means

P(eq)= (P1)+(P2)+(P3)

This means in Parallel Power will be additive

In series we get

R(eq)= R1 + R2 + R3

Now divide both sides by (V _Rated) ²

We get

R(eq)      = R1 + R2 + R3

(V _Rated) ²           (V _Rated) ²

Thus we get

   1         =    1      +     1     +    1

P(eq)          P1           P2        P3

Thus we see that when all bulbs are connected in Parallel then 60W i.e. highest rating will be brightest and when all bulbs are connected in series then bulb with lowest rating i.e. 20W will be brightest.

Comparison between LED Vs Incandescent VS CFL lights

LED VS CFL VS Incandescent Light

Light Emitting diode is having Life span of 5000 Hrs , Incandescent light is having life span of 1200 Hrs and CFL has life span of 8000 Hrs.

LEDs use less power per unit of light generated (lumens).  LEDs help reduce electric bills LED’s consumes 6-8 watts against 60W in incandescent light and 12-15 watts in CFL for same lumens.

This will leads to huge power saving in a year against other available incandescent and CFL’s.

Although LED’s having initial cost against incandescent and CFL’s but payback period is from 6-8 months only depending upon usage and electricity charges in different geographies.

For knowing how LED works please visit the link below:-

http://electrialstandards.blogspot.in/2014/12/light-emitting-diode-working-principle.html

Also there are environmental effects also LED doesn’t use toxic mercury but incandescent and CFL’s contains mercury.

Lower energy consumption decreases: CO2 emissions, sulfur oxide, and high-level nuclear waste. 

LED’s uses less power also longer life which will leads to lower scrap.

LED’s doesn’t have sensitivity to lower temp. but incandescent and CFL’s have. CFL’s doesn’t work below -10 degree.

LED’s also emit very low heat in comparison to Incandescent and CFL’s.

Comparison Chart:-

	LED	Incandescent	CFL'S
Lumens	Watts	Watts	Watts
450	4-5	40.00	9-13
800	6-8	60.00	13-15
1,100	9-13	75.00	18-25
1,600	16-20	100.00	23-30
2,600	25-28	150.00	30-55

To know about How LED'S work visit link below:-
http://electrialstandards.blogspot.com/2014/12/light-emitting-diode-working-principle.html

Three phase Generator connected to load

Generator connected to Isolated load:-

When the prime mover I/p is increased while the excitation remains constant; it results in an increase in frequency. The increase in frequency increases the terminal voltage for the same excitation. The increase in  terminal voltage causes the static load to increase their respective demands as their power consumption is proportional to square of the voltage. The rotating load have their respective speed increases because of the increase in frequency that increases their synchronous speed.

The increase in voltage results to increase in their developed torque and consequently the power demand may increase particularly when they are driving constant torque load. The twin factors results in as increased power demand by the rotating power load as well.

The final conclusion is that an increase in prime mover I/P alone results in increase in frequency as well as increase in Unit loading.

If the excitation increases while the prime over I/P remains constant the terminal voltage increases. This results in increased power consumption by the connected loads as explained above. Since the increased power demand is not met by prime over, it is fed from the stored Kinetic energy of the rotating mass resulting in reduction of frequency to restore the frequency to the previous value; the prime mover i/p must be increased.

Regenerative braking in Three phase Induction motors

This type of braking is possible in normal stator fed Induction motors, if the no. of poles of machine can be changed during running condition by using a special arrangement.

àThis is obvious that this would be possible in squirrel cage induction motor.

No. of poles in stator= No. of poles in rotor (Not necessary no. of phases)

àThus when braking is desired the no. of poles is increased usually by a factor of 2.

àThe synchrounous speed of revolving field thus becomes half and therefore the induction motor goes into generating mode as the slip becomes negative.

Consequently the speed reduces and when it reaches near the new synchronous speed, Power supplt to the motor is switched off.

Subsequently it requires mechanical braking to bring the motor to rest.

àSince electrical power is fed to the main at the loss of kinetic energy of the rotor this method is known as regenerative braking.

àWith much progress in potential energy during the last cayed frequency drives are available for induction motors of the squirrel cage type as well as for slip ring type.

àTherefore even if the no. of poles remain unchanged the frequency of supply can be reduced keeping V/f variable constant to avoid the over fluxing.

àThis will reduce the synchronous speed causing regenerative braking as explained above thus the variable frequency supply regenerative braking must be possible to almost standstill & would be applicable to the squirrel cage as well as slip ring motors.

 Regenerative braking characteristics is shown as below:-

Comparison between Shunt compensation and Synchronous phase modifier

Below is comparison between shunt and Synchronous phase modifier.

Sr No.	Shunt Compensation	Synchronous Phase modifier
1.	A Separate Shunt capacitor and reactor is required for voltage control	A single unit of synchronous motor is used as an inductor with under excitation and used as a capacitor with overexcited for voltage control
2.	Step by step voltage regulation is possible	Smooth voltage regulation not possible
3.	No starting methods are required	Starting methods required for synchronism
4	Consume reactive power only	Consume active power
5	Transient stability improves	Transient stability reduced
6	Requires less maintenance	Requires more maintenance because of rotating device
7	They have very low cost	Cost is more
8	Most practical for voltage control	Not used practically due to above disadvantages