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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 Coefcient of Resistance i.e. it has lower resistance 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 Starting Surge Current with consequent very heavy Starting Surge Power with
a value of up to 8 times the Maximum Continuous Running AC Power.
• 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 Utility / Grid e.g. in audio/video/
computing devices and battery chargers (Please see Section 4 for more details on SMPS). When this power
supply is switched ON, its internal input side capacitors start charging resulting in very high Inrush Current
for a few millisecs (Please see Fig 4.1). This inrush current / power may reach up to 15 times the Continuous
Maximum Running Power Rating. The inrush current / power will, however, be limited by the Starting Surge
Power Rating of the AC source.
Power Factor, (PF): It is denoted by “PF” and is equal to the ratio of the Active Power (P) in Watts to the Apparent
Power (S) in VA. The maximum value is 1 for resistive types of loads where the Active Power (P) in Watts = the
Apparent Power (S) in VA. It is 0 for purely inductive or purely capacitive loads. Practically, the loads will be a
combination of resistive, inductive and capacitive elements and hence, its value will be > 0 <1. Normally it ranges
from 0.5 to 0.8.
Load: Electrical appliance or device to which an electrical voltage is fed.
Linear Load: A load that draws sinusoidal current when a sinusoidal voltage is fed to it. Examples are,
incandescent lamp, heater, electric motor, etc.
Non-Linear Load: A load that does not draw a sinusoidal current when a sinusoidal voltage is fed to it. For
example, non-power factor corrected Switched Mode Power Supplies (SMPS) used in computers, audio video
equipment, battery chargers, etc.
Resistive Load: A device or appliance that consists of pure resistance (like lament lamps, cook tops, toaster,
coffee maker etc.) and draws only Active Power (Watts) from the inverter. The inverter can be sized based on the
Active Power rating (Watts) of the Resistive Load without creating overload (except for resistive loads with Tungsten
based heating element like lament lamps, Quartz/Halogen lamps and Quartz / Halogen Infrared heaters. These
require higher starting surge power due to lower resistance value when the heating elements are cold).
Reactive Load: A device or appliance that consists of a combination of resistive, inductive and capacitive elements
(like motor driven tools, refrigeration compressors, microwaves, computers, audio/ video etc.). The Power Factor
(PF) of this type of load is < 1 e.g. AC Motors (PF = 0.4 to 0.8), AC to DC Switch Mode Power Supplies (PF = 0.5
to 0.6), Transformers (PF = 0.8) etc. These devices require Apparent Power (VA) from the inverter to operate. The
Apparent Power is a vectorial sum of Active Power (Watts) and Reactive Power (VAR). The inverter has to be sized
based on the higher Apparent Power (VA) and also based on the Starting Surge Power.
SECTION 1.2 | Denitions
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