MI 3143 Euro Z 440 V
Test and Measurements
18
6
Tests and Measurements
The MI 3143 Euro Z 440 V instrument is able to carry out different measurement methods. The
operator can select the appropriate one.
6.1 Impedance Measurements [Z]
When performing measurements close to the power transformer or inductance is present,
inductive part of impedance has a significant influence to prospective fault/short-circuit current.
Therefore, impedance instead of resistance has to be measured for correct calculation of
prospective fault/short-circuit current.
AC
Impedance
Measurement
Test
Mode
Test
Method
Limit
Z
Z line mΩ
single
4-wire
yes
Z loop mΩ
single
4-wire
yes
High Current
single
4-wire
yes
High precision line and fault loop impedance measurements are performed using high current
impulses to assure adequate voltage drop during the test.
Warnings:
The Euro Z instrument applies very high loading current into tested installation and it is
recommended to make rare measurements, typically one per 15 s to reduce problems
caused by such current.
Flickers can be observed due to high test current pulses.
6.1.1 Z line
mΩ Measurement
Line impedance is the impedance within the current loop when a short-circuit occurs:
Conductive connection between phase conductor and neutral conductor in single-phase
system,
Between two line conductors in three-phase system.
C1
P1
P2
C2
MI 3143 Euro Z 440 V
E a r t h
L1
L2
L3
N
Pe
R1
4 wire (Kelvin)
V
A
S
up
ply
R
Pe
Itest
ΔU
Z
R2
Figure 6.1: Z line
mΩ measurement example
During the measurement, an internal resistance is connected between C1 and C2 for a periode
of a half cycle. The instrument internal shunt resistor measures the current (I
test
). A voltmeter
measures the open circuit voltage with no load (U
UNLOADED
), followed by the second reading with
a load (U
LOADED
). The impedance Z is determined from the voltage dip / current ratio. In the
example following impedance is measured:
