8 | SAMLEX AMERICA INC.
Maximum Continuous Running AC Power Rating:
This rating may be specifi ed as “Active
Power” in Watts (W) or “Apparent Power” in Volt Amps (VA). It is normally specifi ed in
“Active Power (P)” in Watts for Resistive type of loads that have Power Factor =1. Reac-
tive types of loads will draw higher value of “Apparent Power” that is the sum of “Ac-
tive and Reactive Powers”. Thus, AC power source should be sized based on the higher
“Apparent Power” Rating in (VA) for all Reactive Types of AC loads. If the AC power
source is sized based on the lower “Active Power” Rating in Watts (W), the AC power
source may be subjected to overload conditions when powering Reactive Type of loads.
Surge Power Rating:
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Electric Motors:
At the moment when an electric motor is powered ON, the rotor is
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ing design of the motor and the inertia / resistance to movement of mechanical load
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proportional to the RPM is generated in the windings and the current draw reduces
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Rating at the rated RPM.
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Transformers (e.g. Isolation Transformers, Step-up / Step-down Transformers, Power Trans-
former in Microwave Oven etc.):
At the moment when AC power is supplied to a transformer,
the transformer draws very heavy surge of “Magnetization Inrush Current” for a few millisecs
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Devices like Infrared Quartz Halogen Heaters (also used in Laser Printers) / Quartz
Halogen Lights / Incandescent Light Bulbs using Tungsten heating elements:
Tungsten
has a very high Positive Temperature Coeffi cient of Resistance i.e. it has lower resist-
ance when cold and higher resistance when hot. As Tungsten heating element will be
cold at the time of powering ON, its resistance will be low and hence, the device will
draw very heavy surge of current with consequent very heavy surge of power with a
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AC to DC Switched Mode Power Supplies (SMPS):
This type of power supply is used as
stand-alone power supply or as front end in all electronic devices powered from Util-
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tion 4 for more details on SMPS). When this power supply is switched ON, its internal
input side capacitors start charging resulting in very high surge of Inrush Current for a
few millisecs (Please see Fig 4.1). This surge of inrush current / power may reach up to
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/ power will, however, be limited by the Surge Power Rating of the AC source.
SECTION 2 |
General Information
