Earth Leakage Current - Eaton Holec Clink II User Manual

CLINK II SCU MANAGER
Table 8: Motor current parameter
Name
Motor Current L2
Motor Current L3
Calculation
The Starter Control Unit calculates the effective value of the current using the following formula:
In order to calculate this value, 16 samples are taken so that up to and including the 8th harmonic is taken into
consideration in the calculation. To attain the required accuracy, it must be synchronised with the mains
frequency using a so-called Phase Locked Loop circuit, abbreviated to PLL
I = RMS value of the current
i = Instantaneous value of the current
Note
The accuracy of the measured value is ± 2.5% of I
5.2.3

Earth leakage current

The purpose of this measurement is to detect an earth leakage current caused by a.o.:
• Disruptive discharge between motor winding and earth
• Deteriorated insulation between motor winding and earth
• Short-circuit between one of the phases and earth.
The earth leakage current is measured with a so-called 'core balance' current transformer. The three phases
conductors are led through the hole of the transformer so that the transformer measures the vectorial sum of
the 3 phase currents. Under normal operating conditions the vectorial sum is 0. If, due to a fault, the sum current
is no longer 0, this will be detected in the secondary winding.
Earth leakage current serves as input signal for the earth leakage protective function and can be read-out via
LCU-5. Select:
SCU Manager - Module Measurement
Table 9: Earth leakage current parameter
Name
Earth leakage current
Calculation
The Starter Control Unit calculates the effective value of the earth leakage current using the following formula:
I = RMS value of the earth leakage current
i = Instantaneous value of the earth leakage current
functional description scu
Range Unit
0-1,200.000 A
0-1,200.000 A
Range Unit
0-6.0 A
Parameter
type
Actual
Actual
T
1
∫
2
-- -
I = i t d
T
0
n
.
Parameter
type
Actual
version 5.0 17