METREL Euro Z 440 V, Инструкция по эксплуатации

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MI 3143 Euro Z 440 V Test and Measurements
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6.2 Earth Potential [U]
AC
Voltage Measurement Test
Mode Test
Method Limit
U U touch single 4-wire yes
Table 6.6: Available Earth Potential measurements with the MI 3143
Note (acc.to IEEE Std 81):

Touch voltage - general definition. The potential difference between the GPR of a grounding grid
or system and the surface potential where a person could be standing while at the same time
having a hand in contact with a grounded structure or object.
6.2.1 U touch Measurement
Proposed measurement can be referenced to standard IEEE-81 par. 9.
The measurement is performed between an earthed accessible metal part and ground as shown
on
Figure 6.7 . The voltage between the probes is measured by a voltmeter with an external
resistance of 1
kΩ (adapter A 1597) that simulates the body resistance.
C1
P2
C2
MI 3143 Euro Z 440 V
V
A
R
E a r t h
Remote Power
Source
Current Probe (Cp)
Fence
Fence
Ground Grid Conductors
Um
Itest
S
P1
V
Itest
Itest
1k
Ω
A
1
59
7
Figure 6.7: U touch Measurement example
During the measurement, an internal resistance is connected between C1 and C2 for a period of
a half cycle.
The resistance of the current probe should be as low as possible in order to
inject a high test current. The resistance can be decreased by using more probes in parallel
or using an auxiliary earthing system as the auxiliary probe. A higher injected current
improves the immunity against spurious earth currents.
The instrument internal shunt resistor
measures the current (I
test
). A voltmeter measures the voltage drop across a 1 k resistor (A
1597). The (U
Touch
) voltage is determined from the fault current/ measured current ratio multiplied
with the measured voltage. In the example following U
Touch
voltage is measured:
𝑈
𝑇𝑜𝑢𝑐ℎ
= 𝑈
𝑚
×
𝐼
𝐹𝐴𝑈𝐿𝑇
𝐼
𝑡𝑒𝑠𝑡
where:
U
Touch
................................. Calculated Touch voltage in case of a fault current
I
FAULT
.................................. Set fault current (maximal earth current in case of a fault)
U
m
...................................... Measured voltage drop
I
test
..................................... Test current