Tuesday, February 25, 2014
Terms AC1 and AC3
AC-1 - This category applies to all AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as heating. Breaking the arc remains easy with minimal arcing and contact wear.
AC-3 - This category applies to squirrel cage motors with breaking during normal running of the motor.
On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor.
On opening, the contactor breaks the rated full load current of the motor.
Monday, February 24, 2014
Advantages of LED light bulbs
How far the light bulb has come. For years incandescent bulbs were the only game in town. But in more recent times consumers have seen new choices come along, such as compact fluorescent light bulbs (CFLs) and light-emitting diodes (LEDs). Sometimes people prefer a certain type of light bulb for the impact they hope it will have on the environment, and other times people choose bulbs based purely on the kind of light they cast. LEDs compare favorably versus incandescent bulbs in some areas. They produce their light from the movement of electrons across a semi-conductive material, while incandescent bulbs have a filament that glows when heated by an electric current. LEDs are said to last as long as transistors -- that's much longer than incandescent bulbs. LEDs have a typical life span of about 30,000 hours, as opposed to the 750 hours that a traditional incandescent bulb will last.
Furthermore, an LED's plastic construction is much more durable than glass bulbs. Their small size enables them to be used in more applications, such as in electronic circuits. However, the biggest advantage of LEDs boast over incandescent bulbs is their greater efficiency. LEDs produce light without heat, saving all of the energy that goes into heating filaments for incandescent bulbs. A 2007 study by the Alliance to Save Energy determined that if half of all incandescent decorative Christmas bulbs were replaced with LED bulbs, for example, this could save the U.S. some $17 billion dollars a year in energy costs.
So the LED bulb uses much less electricity and causes much less waste than do their traditional incandescent light bulb counterparts, producing much less carbon dioxide. As with most things, however, there is an unfortunate downside and that's immediate cost. LEDs cost much more per bulb than incandescent bulbs, and regardless of the long-term savings they might offer, it's hard for people (especially during difficult economic times) to put so much of their monthly cash flow into expensive light bulbs. Time, and lower prices, may change that equation, however.
Source : How stuff works
Friday, February 21, 2014
KW to Ampere calculation
DC kilowatts to amps calculation
The current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by the voltage V in volts (V):
I(A) = 1000 × P(kW) / V(V)
AC single phase kilowatts to amps calculation
The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by the power factor PF times the RMS voltage V in volts (V):
I(A) = 1000 × P(kW) / (PF × V(V) )
AC three phase kilowatts to amps calculation
Calculation with line to line voltage
The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by square root of 3 times the power factor FP times the line to line RMS voltage VL-L in volts (V):
I(A) = 1000 × P(kW) / (√3 × PF × VL-L(V) )
Calculation with line to neutral voltage
The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by 3 times the power factor FP times the line to neutral RMS voltage VL-N in volts (V):
I(A) = 1000 × P(kW) / (3 × PF × VL-N(V) )
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