Saturday, December 13, 2014

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

Monday, December 8, 2014

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.

Saturday, December 6, 2014

Comparison between LED Vs Incandescent VS CFL lights

LED vs CFL vs Incandescent Lights: Which is Better for You?

When it comes to choosing lighting solutions for homes or offices, the three most common options are:

Incandescent bulbs (traditional yellow bulbs),
Compact Fluorescent Lamps (CFLs), and
Light Emitting Diodes (LEDs).

Each has its own advantages and disadvantages, but LEDs have emerged as the most energy-efficient and sustainable choice. Let’s break down the comparison.

1. Lifespan Comparison

Incandescent Bulbs: ~1,200 hours
CFLs: ~8,000 hours
LEDs: ~50,000 hours

👉 Clearly, LEDs last up to 40 times longer than incandescent bulbs and more than 6 times longer than CFLs, which means fewer replacements and reduced waste.

2. Energy Efficiency (Power Consumption vs Lumens Output)

LEDs produce the same amount of light (lumens) with much lower wattage.

Lumens (Brightness)	LED (Watts)	Incandescent (Watts)	CFL (Watts)
450 (≈ 40W bulb)	4–5 W	40 W	9–13 W
800 (≈ 60W bulb)	6–8 W	60 W	13–15 W
1,100 (≈ 75W bulb)	9–13 W	75 W	18–25 W
1,600 (≈ 100W bulb)	16–20 W	100 W	23–30 W
2,600 (≈ 150W bulb)	25–28 W	150 W	30–55 W

💡 Result: Switching from incandescent to LED can cut energy use by up to 85%, and from CFL to LED by around 40–50%.

3. Cost & Payback Period

Initial Cost: LEDs are more expensive upfront than CFLs and incandescent bulbs.
Payback Period: Despite the higher price, LEDs pay back within 6–8 months (depending on electricity tariffs and daily usage). After that, they provide pure savings on electricity bills.

4. Environmental Impact

Mercury Content: CFLs contain toxic mercury, while LEDs are mercury-free.
CO₂ Emissions: Lower energy consumption by LEDs reduces greenhouse gases, sulfur oxides, and even nuclear waste.
Heat Emission: LEDs emit very low heat compared to CFLs and incandescent bulbs, making them safer and more efficient.
Cold Temperature Performance: CFLs fail below -10°C, while LEDs perform well in all temperatures.

5. Key Takeaways

✔️ LEDs are the most energy-efficient, eco-friendly, and long-lasting lighting option.
✔️ CFLs are better than incandescent bulbs but have mercury hazards.
✔️ Incandescent bulbs are outdated — high energy use, short life, and high replacement costs.

Related Resource

Want to know how LEDs work internally? Read here:
👉 Working Principle of Light Emitting Diode

Disclaimer

This article is for educational and informational purposes only. Technical specifications, lifespan, wattage, and electricity savings may vary depending on brands, usage conditions, and regional electricity tariffs. Readers should verify details with manufacturers or utility providers before making purchasing decisions.

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.

Friday, November 21, 2014

Regenerative braking in Three phase Induction motors

Regenerative Braking in Induction Motors

Braking of induction motors is essential for controlling speed, safety, and energy efficiency in industrial drives. Among the various braking techniques, regenerative braking is highly efficient since it converts the motor’s kinetic energy into electrical energy and feeds it back into the supply system.

Principle of Regenerative Braking

In a normal stator-fed induction motor, regenerative braking is possible if the number of poles of the machine can be changed during running conditions using special arrangements.
This technique is applicable in squirrel cage induction motors since:
- Number of poles in the stator = Number of poles in the rotor (though not necessarily equal to the number of phases).

Method of Operation

Pole Changing Method
- When braking is required, the number of poles is increased (usually by a factor of 2).
- The synchronous speed of the revolving magnetic field reduces to half.
- Slip becomes negative, and the motor enters the generating mode.
- Consequently, the motor speed reduces.
- Once the speed approaches the new synchronous speed, the power supply is switched off.
- Finally, mechanical braking is applied to bring the motor to a complete stop.
Energy Feedback
- During braking, the kinetic energy of the rotor is converted into electrical energy.
- This energy is fed back to the power supply mains.
- Hence, the method is termed regenerative braking.

Role of Variable Frequency Drives (VFDs)

With modern power electronics and VFD technology, regenerative braking has become more advanced:

Even without changing the number of poles, the supply frequency can be reduced.
The V/f ratio is maintained constant to avoid over-fluxing.
A reduced supply frequency lowers the synchronous speed, forcing the motor into regenerative mode.
This allows braking almost down to standstill conditions.
Applicable to both squirrel cage and slip ring induction motors.

Regenerative Braking Characteristics

At synchronous speed, slip = 0 → motor neither generates nor consumes active power.
When the rotor speed is slightly above synchronous speed → slip becomes negative, and power flows back to the supply.
This negative slip region corresponds to regenerative braking mode.

Advantages of Regenerative Braking

Energy saving since braking energy is recovered and fed to mains.
Smooth speed control without overheating resistors (as in dynamic braking).
Useful for frequent start-stop industrial drives, elevators, cranes, and traction systems.
Improves overall system efficiency and reduces operating cost.

✅ Summary:
Regenerative braking in induction motors is achieved by either pole-changing techniques or variable frequency supply methods. In both cases, the motor operates in generating mode when slip becomes negative, returning power to the grid. With the advent of VFDs, regenerative braking is possible even without pole changing, making it widely applicable to modern industrial drives.

Friday, November 14, 2014

Comparison between Shunt compensation and Synchronous phase modifier

⚡ Shunt Compensation

Shunt compensation is a method of controlling system voltage by connecting shunt capacitors or shunt reactors directly to the transmission network.

Shunt Capacitors → supply reactive power (kVAR) to the system, thereby raising voltage during light load or under-voltage conditions.
Shunt Reactors → absorb reactive power, thereby reducing voltage during no-load or light-load conditions when the voltage tends to rise.

🔑 Engineering perspective:

Simple, static, and reliable solution.
Provides step-by-step voltage regulation since capacitor banks can be switched in or out.
Widely used in transmission and distribution systems due to low cost and negligible maintenance.

⚡ Synchronous Phase Modifier (Synchronous Condenser)

A synchronous phase modifier (also known as a synchronous condenser) is essentially a synchronous motor running without mechanical load.

When under-excited, it draws reactive power → acts like an inductor.
When over-excited, it supplies reactive power → acts like a capacitor.