Iwatsu SS-293L, Instruction Manual

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Chapter 3 Measurement Principle
16
3.1 Rogowski Coil Sensor Part
Figure 3.1 shows that the current I flows through the conductor to be
measured. This section describes the principle of detecting this current by
the Rogowski Coil step by step.
Note) The above figure is a conceptual illustration to explain this measurement principle. The
Rogowski Coil Sensor part is actually covered with the insulating outer sheath. During
measurement, one end of the Rogowski Coil is inserted into the joint hole on the joint box
and locked by the screw lock.
Figure 3.1 Conceptual Illustration of Rogowski Coil
It is assumed that the conductor to be measured is placed inside of the loop
of the Rogowski Coil. A magnetic field is generated around the conductor to
be measured. It moves around the conductor in a clockwise direction in
relation to the current direction (Ampere
’s right-handed screw law).
The magnetic field changes with time, because alternating current flows in
the conductor to be measured. In the Rogowski Coil, magnetic flux changes
along the loop. When it changes, an electromotive force is generated and
current flows in the coil by electromagnetic induction.
Provided that the entire length of the wound Rogowski Coil is
l , small radius
of the coil turn is r , turn of the coil is N , and current flowing through the coil is
i , the electromotive force generated in the coil is expressed by Equation 3.1:
…… (3.1)
As shown in Equation 3.1, the electromotive force induced in the coil is
determined by the shape and turn of the coil and time differentiation of the
current. Thus, the electromotive force must be integrated to determine the
current.
Conductor to
be measured
Rogowski Coil Sensor part
Returning part
of windings
Signal that is
differential of input
current Output voltage (V)
(Current waveform)
Main unit
Observation with
an oscilloscope
and other
monitoring devices
In
se
rtio
n
Current (I)
M
M
a
a
g
g
n
n
e
e
t
t
i
i
c
c
f f i i e e l l d d
Integrator
Where,
(Permeability of Vacuum)