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) )
Thursday, February 20, 2014
Understanding Type 2 Coordinated Protection in Motor Branch Circuits
The new IEC (International Electrotechnical Commission) standard, publication
947 “Low Voltage Switchgear and Control, Part 4-1: Contactors and Motor Starters,”
has been recognized by UL (Underwriters Laboratories) and is becoming
widely accepted by designers and users of motor control in the U.S. This standard
addresses coordination between the branch circuit protective device and the motor
starter. It also provides a method to measure performance of these devices if a short
circuit occurs. This standard defines two levels of component protection in the
event of a short circuit: Type 1 and Type 2 coordination.
This Product Data Bulletin describes:
_ How to conformto the new standard using motor controls built to meet
NEMA and IEC standards
_ Related benefits associated with Type 2 coordination
The IEC standard for motor starters and contactors, 947-4-1, defines two levels of
protection/coordination for the motor starter (contactor and overload relay) under
short circuit conditions. Each level of protection is achieved by using a specific
combination of motor starter and short circuit protective device.
_ Type 1 Coordination
Under short circuit conditions, the contactor or starter shall cause no danger
to persons or installation and may not be suitable for further service
without repair and replacement of parts.
_ Type 2 Coordination
Under short circuit conditions, the contactor or starter shall cause no danger
to persons or installation and shall be suitable for further use. The risk
of contact welding is recognized, in which case the manufacturer shall indicate
the measures to be taken in regards to equipment maintenance.
Faults in electrical systems are most likely to be of a low level, which are handled
well by motor controllers built to meet Type 1 coordination standards. After the
fault is cleared, the only action necessary is to reset the circuit breaker or replace
the fuses. In situations where available fault currents are high and any period of
maintenance downtime is crucial, a higher degree of coordinated protection may
be desirable.
Many industries are dependent upon the continuous operation of a critical manufacturing
process. In these conditions, it is especially important to understand that
Type 1 protection may not prevent damage to the motor starter components. In order
to ensure that high level fault or short circuit does not interrupt a critical process,
it may be prudent to consider implementation of Type 2 coordination in the
selection and application of low voltage motor controllers.
Type 2 coordination, which has no equivalent U.S. standard, does not permit damage
to the starter beyond light contactwelding, easily separated by a screwdriver or several
coil operations. Type 2 coordination does not allowreplacement of parts (except fus-
es) and requires that all parts remain in service. Beyond providing basic electrical and
fire protection, it also minimizes lost production, reduced productivity and unscheduled
disruptions resulting fromdowntime needed to replace or repair a starter.
SQUARE D Product Data Bulletin
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