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September 26, 2010

How are power factor correction capacitors available?

Three-phase motor power factor correction capacitors are sold by kVAR at a particular voltage rating. Normally they are sold in a trio of three capacitors, which may or may not be packaged in a single enclosure. When power factor correction capacitors are to be switched with an induction motor, the maximum value of corrective kVAR should not exceed the value required to raise the motor’s no-load power factor to unity

Avoid overcorrecting into a leading power factor condition. NEMA Standard MG1, Part 14 offers the following warning: “In no case should power factor improvement capacitors be applied in ratings exceeding the maximum safe value specified by the motor manufacturer. Excessive improvement may cause over excitation resulting in high transient voltages, currents, and torques that can increase safety hazards to personnel and cause possible damage to the motor or to the driven equipment.”

Capacitor boxes often contain some surge suppression circuitry. Experts widely agree that surge suppression also saves virtually no energy. Yet, it may be highly beneficial in protecting valuable equipment if there are actually serious voltage spikes on the circuit.

Q: How much energy can be saved by installing correction capacitors?

A: Power factor correction does not save much energy – usually less than 1 percent of load requirements – but even that benefit depends upon how low the power factor is to begin with and how heavily loaded are in-plant distribution system conductors. Note that power supplied to your motor driven-equipment is

Q: How significant is power factor correction in industrial settings?

A: Power factor is low in industrial settings where most of the plant energy is used to power electric motors. It is lowest when the induction motors tend to be over-sized and under-loaded. A lagging (less than 1.0) power factor causes some additional energy loss because more current is required – compared to an in-phase sinusoidal current – to deliver a certain amount of power. Correcting power factor can be an appropriate and cost-effective measure, but not because of energy savings.

September 23, 2010

September 2, 2010

Why, when birds sit on transmission lines or current wires doesn't get shock?

Answer: It’s true that if birds touch the single one line (phase or neutral) they don't get electrical shock... if birds touch 2 lines than the circuit is closed and they get electrical shock.

So if a human touch single one line (phase) then he doesn't get shock if he is in the air (not touching - standing on the ground if he is standing on the ground then touching the line (phase) he will get a shock because the ground on what we standing is like line (ground bed - like neutral) and in the most of electric lines the neutral is grounded..So that means that human who touch the line closes the circuit between phase and neutral.

August 26, 2010

What are the applications of Transformer?

1. Transformer can step up or step down the voltage or current in an A.C. circuit.
2. It can be used to prevent D.C. from passing from one circuit to the other.
3. It can isolates two circuit electrically.
4. It can increase or decrease the v...alue of capacitor, inductor or resistance in an A.C. circuit.

August 25, 2010

The two electric bulbs of 60W and 100W are given. Which one will be brighter when they are connected (i) In Series and (ii) In Parallel? And Why?

1. The resistance of a 60W bulb is much more than that of 100W bulb. When they are connected in series. 40W bulb will be more brighter (where P=I^2R).

2. When the two bulbs are connected in parallel, the 100W bulb will be more brighter (where P=V^2/R).

August 24, 2010

Why the Direction of Rotation of a TABLE Fan & CEILING Fan is different?

Actually ceiling fan can be designed to move either clockwise or anticlockwise direction.It all depend on whether they are set for winter or summer. A switch or extra connection may be needed to get both direction which has only one type of... direction.

For Summer they are so set so that the air moves downward to make us cool--- clockwise

For winter(when the air is cool) the air should move toward the ceiling to take away the cool air from us to give us comfort--- anticlockwise

The direction of rotation of a table fan is determined by the shape of the blades. A motor can be made to run in either direction but to force air to the front of the table fan, it must rotate in the direction that the blades will force the air properly.

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