Datasheet

K6CM
16
Insulation Resistance Type Technical Data (Reference)
Method of measuring the value on the insulation resistance meter
Leakage current includes two types, namely capacitive leakage current (Ioc) that flows through the earth capacity, and resistive leakage current
(Ior) that flows due to the degradation of wiring and devices, and is the cause of electric shock and fire. The leakage current is determined by
detecting the value of the zero-phase current Io, which is the combined component of Ioc and Ior. (See the figure below)
About changes in the measurement accuracy
If there is almost no insulation deterioration in the motor, almost the entire constituent of Io becomes Ioc, and the measurement accuracy of Ior
declines. Further, if the Ioc based on the motor-specific electrical capacitance is larger than Ior, then the measurement accuracy will similarly
decline. Particularly, if the electrical capacitance increases in proportion to the capacitance of the motor, the measurement accuracy changes
depending on the motor capacitance.
The following items are the possible parameters affecting the measurement accuracy.
Increase in Ioc ......................Type of motor (manufacturer, structure), capacitance, number of poles,
and the length of wire between ZCT (IRT) and the motor
Other noise components.......Through-current, through-position
External factors.....................Voltage imbalance
[Effect of residual current]
Another noise component is the residual current* (hereinafter, specified as Ir). Ir increases in proportion to the through-current.
* Residual current
Residual current refers to the error that occurs as a result of an imbalance in the magnetic flux of each phase inside the core due to the
arrangement of the through-wire of ZCT.
Errors also occur as a result of the imbalance in the magnetic circuit of ZCT.
Ir combines with Io, and is output to the secondary side of ZCT. Ir is the same frequency component as Ior, and the amount of current or the phase
difference with respect to Ior changes depending on the through-position of the power line passing through ZCT. Therefore, isolation from Ior, which
must essentially be detected, becomes difficult.
If the position of ZCT and the through-wire is fixed once, the phase of Ir does not change. Moreover, by fixing the through-wire in the center of
ZCT, Ir can be reduced. Fix and install the through-wire in the center as much as possible.
Use the following holder to fix the through-wire in the center of ZCT.
Part name Manufacturer Model
Rubber holder Midori Anzen Co. Ltd. HZ-25
R
S
T
Io
ZCT
Ioc
Ioc
Ior
Ior
Ioc
U
V
W
Motor
Io
Ior
Ioc
Capacitance Low
No. of poles Less
Wire length Short
High
Many
Long