NF EC1000SA, Instruction Manual

Page: 83 / 283

4.2 Measurement of Inrush Current
EC1000SA 4-15
4.2 Measurement of Inrush Current
4.2.1 Inrush current
In such an electrical product as contains a capacitor input type rectifier circuit for the input power line,
a current that is larger than the rated current may flow for a short time immediately after the power
source switch is turned on. This current is called an “inrush current.”
If the power source is not able to supply such a large current, enough power is not supplied to the
product, and sometimes it does not start in the worst case.
On the other hand, when such a large current passes through the power source line, the supply voltage
is likely to decrease because of the voltage drop at the line impedance. There exists a standard to limit
this effect within a certain level.
Such a product should be driven by a power source with enough supply capacity
∗
Example of an inrush current
An electric drill
(rated 100 V AC/350 W)
Upper: Voltage (100 V/div)
Lower: Inrush current (10 A/div)
Even in a small electric drill, an inrush current of 14 Apk flows right after the power source is turned
on. Since the rated current is 3.5 A, this represents a fourfold increase in the current flow.
The EC1000SA can supply four times as a large peaked current as the maximum output current
supporting such a usage. There is no need to use a power source with an extra large capacity in order to
supply the inrush current (for a capacitor input circuit of CF = 4 or less).
The initial phase of the output AC voltage is adjustable from 0.0
°
to 359.9
°
(in 0.1
°
steps), so the user
can monitor how the current inrushes in the load under various phase conditions. The peak current
hold measurement function enables the measurement of the maximum peak value for the current
flowing at that time. The measurement value of the peak current is reference value.
When measuring the inrush current, set the peak current limiter to the maximum value. If the limiter
setting is lowered, the inrush current measurement may be incorrect.