Chapter 1 Overview - Mitsubishi Electric MELSEC-Q series User Manual

CHAPTER 1
(1) CT
A CT means "Current Transformer" and is a current sensor which is necessary to measure an alternating current.
A CT is used for the following purposes widely.
• To control a load or monitor an operation of equipment and devices
• To control or monitor of an electric power system
When a high current is measured in an electric power receiving facility, measurement devices cannot be wired
directly. A CT is used for such a situation.
(a) Mechanism of a CT
A CT utilizes characteristics of an alternating current.
Primary current (I
( Current transformation
ratio (CT ratio)
There are two CT types: the contact type and noncontact type. The noncontact type is classified into the
window-type and split-type which is easy to be retrofitted.
(2) Operation of a CT input module
A CT input module measures an alternating current by converting a secondary current input from a CT to a digital
value after carrying out an effective value operation.
The above flows are defined as "digital conversion" in this manual.
OVERVIEW
Primary coil
K
Primary current (I )
1
Primary windings (T )
1
L
Primary and secondary coils winded an iron core are isolated
electrically. When a primary current (I
core, a secondary current (I ) can be extracted depending on
2
the turn ratio (current transformation ratio).
The following shows the relationship of a primary current, a
secondary current, and windings
) Windings (T ) = Secondary current (I
1 1
Primary current (I
)
=
Secondary current (I
Iron core
Secondary coil
k
Secondary current (I )
2
Secondary windings (T )
2
I
) is applied to the iron
1
) Windings (T
2
) Secondary windings (T
1
) Primary windings (T
2

CHAPTER 1 OVERVIEW

)
2
)
2
)
1
15
1