4.3 Earth measurement in live condition (REARTH). CHAUVIN ARNOUX C.A 6456
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4.3
EARTH MEASUREMENT IN LIVE CONDITION (REARTH)
4.3.1 DESCRIPTION OF THE FUNCTION
■
This measurement is made with a single auxiliary rod (voltage probe) connected to terminal (P), yielding a saving of time with respect to a conventional measurement with 2 auxiliary rods.
■
A specific additional current clamp is necessary to make a selective earth measurement.
he instrument automatically detects the connection of the voltage and current probes.
When the TEST key is pressed, the instrument:
checks that the amplitude and frequency of the voltages present are correct,
checks the resistance of the auxiliary rod,
interchanges L and N internally if the 2 conductors are reversed in the socket,
measures the voltage between the TEST key and terminal PE,
If these quantities are correct, the instrument generates, according to the user's selection, a high current
("tripping" mode ) or a low current ("non-tripping" mode on 30mA RCD or more) between terminals L and PE and measures the voltage drop between terminals P and PE.
■
If the user selects measurement without tripping ( ), the current generated is low : the instrument measures R
A
(global earth resistance).
Note : if, during a earth measurement at low current, a earth fault breaker in the circuit still trips, measure the leakage current with the current probe using the "current measurement" function of the instrument, then change the measuring current I
TEST
(see § 4.2.2) with allowance for this leakage current. Otherwise, shortcircuit the circuit-breaker concerned and make the next measurement at high current for greater accuracy.
■
If the user has selected measurement with tripping (or if they have connected the current probe to make a selective measurement), the current generated is high ( ): arrangements may have to be made to prevent the earth fault breaker from tripping (e.g. temporary shunting of the breaker). The instrumen measures Z
A
(the global earthing impedance), R
A
and L
A
(the resistive and inductive parts of Z
A
).
Remarks:
- If the user selects measurement without tripping ( ) and connects a current probe, the instrument reverts to measurement with tripping and reports the change.
- If the user connects the current probe, it is the current measured by this probe that is used to calculate
R
A
. The lower this current, the more unstable the measurement is likely to be: in this case, smooth the measurement using the "SMOOTH" function.
4.3.2
PREPARATION FOR THE MEASUREMENT (CONNECTION)
The instrument must be connected to the network in a live condition and the earth electrode to be measured must not be disconnected.
=> If necessary, set, in the SET-UP mode :
■
U
L
(see § 3.2),
25
■ the current generated for the measurement at low current :
PUSH btn
MORE x5
I
∆ n
12 mA
Selection of current
PUSH btn
MORE twice to exit from programming
■
■
■
The type of compensation of the measuring cables (see § 3.3) the alarm threshold Z
A
or R
A
: the number of measurements to be counted to smooth the measurement (see § 3.2).
=> Set the switch to the REARTH position,
=> Activate the alarm by pressing the ALARM key,
5
=> high ( ) for a greater accuracy:
- if there is no tripping of a earth fault breaker (measurement made upstream of the RCDs),
- if the earth fault breaker concerned is short-circuited for greater accuracy,
- in the case of a selective measurement using a current probe.
=> low ( ) for a quick check :
=> Make the connections as indicated below, according to the type of installation to be checked.
=> Compensate the measuring cables (see § 3.3),
Case of an installation with a TT type neutral situation :
=> Connect the mains socket (or the
3 separate cables) to the installation to be tested,
=> Plant the auxiliary rod at a distance
> 25 m from the earth electrode.
26
Case of an installation with a TN type neutral situation (selective measurement) :
=> Connect the mains socket (or the
3 separate cables) to the installation to be tested,
=> Connect a current probe to the terminal and encircle the earth of which the resistance is to be measured: the current used to calculate Z
A SEL by the probe,
is that measured
=> Plant the auxiliary rod PE as close as possible to the earth electrode to be measured for a measurement that is as accurate as possible,
=> Compensate the cables.
Note : without the current probe, what is measured is the global earth of the network, which is not very significant.
Connecting the clamp configures the instrument in the tripping mode (power-level current).
Case of an installation with an IT type neutral situation (not isolated) :
Preliminary remarks :
- the power supply transformer of the installation must not be completely isolated, but earthed through an impedance,
- the installation must also not be in first fault: start by checking the indication of the Permanent
Insulation Tester concerned,
- the "grounds to earth" R
A
and the earth of the power supply transformer must be separate to allow the circulation of the measuring current.
=> Connect the mains socket (or the
3 separate cables) to the installation to be tested,
=> Plant the auxiliary rod at a distance
> 25 m from the earth electrode.
4.3.3
MEASUREMENT PROCEDURE
The instrument first checks the resistance of the rod and measures the voltage between PE and earth, then measures the voltages U
LN
, U
LPE
, U
NPE
.
If these values are correct, pressing the TEST key starts the measurement.
Remark : to be sure that the auxiliary rod is located in a zone not influence by other earth electrodes, move the rod ( 10% of the distance and repeat the measurement. The result must not change. If it does, move the rod until the earth measurement remains unchanged.
4.3.4
MEASUREMENT RESULTS
After the measurement, the measured values and complementary results can be consulted using the
(The quantities accessible before the measurement is made are described above, in § 4.1.4)
27
Parameters accessible in earth measurement in live condition, mode (high current):
Initial display
(1
(2
(3 st nd nd press) press) press)
Initial display
R
A
Z
A
R
Z
A
R
A
Z
A
R
A
Z
A
A
MORE
(1 st press)
Z
A
L
A
Z
A
L
A
Z
A
L
A
L
A
Z
A
MORE
(2 nd press)
Hz
U
LN
Hz
U
LPE
Hz
U
NPE
Hz
U
P
MORE
(3 nd press)
R
A ALARM
U
F
R
A ALARM
U
F
R
A ALARM
U
F
R
A ALARM
U
F
MORE
(4 nd press)
R
U
L
L
R
∆
PE
U
L
R
∆
N
U
L
R
P
U
L
Parameters accessible in earth measurement in live condition, mode (low current):
Initial display
(1
(2
(3 st nd nd press) press) press)
Initial display
R
----
R
A
A
----
R
A
----
R
A
----
MORE
(1 st press)
Hz
U
LN
Hz
U
LPE
Hz
U
NPE
Hz
U
P
MORE
(2 nd press)
R
A ALARM
U
F
R
A ALARM
U
F
R
A ALARM
U
F
R
A AARM
U
F
MORE
(3 nd press)
R
∆
L
U
L
R
∆
PE
U
L
R
∆
N
U
L
R
P
U
L
Parameters accessible in selective earth measurement in live condition, mode (high current):
Initial display
(1
(2
(3 st nd nd press) press) press)
Initial display
R
A
Z
A SEL
R
A
Z
A SEL
R
A
Z
A SEL
Z
R
A
A SEL
MORE
(1 st press)
----
I
SEL
----
I
SEL
----
I
SEL
----
I
SEL
MORE
(2 nd press)
Hz
U
LN
Hz
U
LPE
Hz
U
NPE
Hz
U
P
MORE
(3 nd press)
R
A ALARM
R
R
R
A ALARM
A ALARM
A ALARM
MORE
(4 nd press)
R
∆
L
U
L
R
∆ PE
U
L
R
∆
N
U
L
R
P
U
L
28
4.3.5
CHARACTERISTICS
4.3.5.1 Measurement ranges and accuracy
Particular reference conditions : nominal voltage of the installation = 90 to 550 V, nominal frequency of use = 15.3 to 65 Hz, resistance in series with voltage probe: < 100
Ω inductive part < 0.1 x the resistive part of the impedance measured, resistance of the cable connected to terminal PE corrected, contact voltage < 5 V (potential of terminal PE with respect to the local earth).
Characteristics of the measurements:
Characteristics in "high current" mode ("tripping" mode ):
Charge duration : 300µs cycle
Display range
Specified measurement domain
Peak measuring current between
90V and 280V
Peak measuring current between
280V and 550V
Accuracy of the impedance measurement
Additional error for Rearth
0.20 - 1.99
Ω
1.06 to 3.25
Ω
40
± 10 % ±15 pt
Ω
2.00 - 19.99
Ω
0.90 to 3.25 A
1.27 to 2.73 A 1.20 to 2.71 A
20.00 - 39.99
± 0.3
Ω
Ω
0.79 to 2.83 A
1.13 to 2.57 A
± 5 % ±15 pt
400
Ω
40.0 - 399.9
0.24 to 2.47 A
0.55 to 2.42 A
± 5 % ±5 pt
Ω
Max. inductance acceptable for the measurement : 20 mH (display range 400.0 mH)
4000
Ω
400 - 3999
Ω
0.03 to 0.76 A
0.08 to 1.18 A
± 5 % ±2 pt
Characteristics in "low current" mode ("non-tripping" mode ):
Charge duration : cycle of one network frequency period.
Display range
Specified measurement domain
RMS measuring current
Accuracy of the resistance measurement (2)
0.5 - 1.9
± 15% ±
Ω
10 pt
400
2.0 - 19.9
Ω
Ω
20.0 - 399.9
(2) No measurement of the inductive part in"low current" mode.
±
Ω
15% ± 5 pt
4000
Ω
400 - 3999
6 - 9 - 12 mA (adjustable in «SET-UP» mode : see & 3.2)
Ω
29
Characteristic in "selective" mode: Charge duration : 300 µs cycle
Display range
Specified measurement domain
Peak measuring current (3)
Accuracy of the resistance measurement (4)
0.5 - 1.9
±
≥ 30 mA
15 % ±
Ω
5 pt 10 %
400
2.0 - 19.9
±
≥ 10 mA
±
Ω
Ω
5 pt
20.0 - 399.9
≥ 5 mA
(3) The measuring current is that measured by the current probe.
(4) No measurement of the inductive part in "selective" mode.
Ω
± 15 % ± 5 pt
≥
4000
2 mA
Ω
400 - 3999 Ω
-
Characteristics common to all measurement modes:
Max. resistance acceptable in series with the voltage probe: 15 k
Ω
- Accuracy of measurement of the resistance in series with the probe: 20 % + 10 pt
(resolution 0,1 k Ω ; display range 400.0 k Ω
4.3.5.2 Influencing conditions
Influencing quantities
Limits of the domain of use
Temperature
Relative humidity
-10 to + 55 °C
10 to 85 % HR at 45 °C
6.8 to 10 V Power supply voltage
Network voltage of the installation tested
99 to 101 % of nominal frequency
85 to 110 % of nominal voltage
Network voltage of the installation tested
Resistance in series qith the voltage probe ( earth in live condition only)
Contact voltage (Uc)
0 to 15 k Ω
0 to 50 V
Variation of the measurement
Typical Maximum
1 %/10 °C ± 1 pt 2 %/10 °C + 2 pt
2 % 3 % + 2 pt
1 % / V + 1pt 2 %/ V + 2 pt
0.5% 1 % + 1 pt
0.5% 1 % + 1 pt
0.1%/k Ω 0.2 %/ k Ω + 1 pt
0.1%/10V 0.2 %/10 V
30
4.3.6
WARNINGS OR ERROR REPORTS (EARTH MEASUREMENT IN LIVE CONDITION)
Preliminary remark: The complete list of coded errors is given in § 7.
Indication Cause possible
Hz
U
C
> 25 (or) 50V
Voltage > U is disabled.
L between the TEST key and PE: the measurement
Hz
<90 V
One of the voltages, U is impossible.
LN
or U
LPE
is < 90 V : the measurement
Hz
U
NPE
> 25 (or) 50V
U
NPE
is AC and > U
L
: the measurement is impossible.
< 15.3 Hz (or) > 65Hz
U
LN
(or) U
NPE
(or) U
LPE
The frequency of U
LN
, U
LPE
, or U
NPE
is < 15,3 Hz or >
65 Hz : the measurement is impossible.
NO rOd The rod is not connected, the measurement is stopped.
Er10
U
P
> 50V (or) 25V
U
P
> U
L
: the measurement is disabled.
R
P
> 15k
U
P
Ω Resistance of the auxiliary rod too high: the measurement is stopped.
Connection of a current probe after selection of measurement without tripping: the instrument automatically reverts to measurement with tripping and reports the fact.
During the measurement, U
F exceeds the value set in the
SET-UP mode: the measurement is stopped.
Er04
U
F
> 50V (or) 25V
Er05 During a selective measurement, the product of the current measured by the current probe and the measured voltage is too low: the measurement is stopped.
Er06
I = ----
During a selective measurement, the current measured by the current probe is too unstable: the measurement is stopped.
> 80°C
The temperature of the instrument is too high: the masurement is stopped. Pressing the TEST key has no effect until the
HOt temperature of the instrument is again below 60°C; another measurement can then be started.
Press the TEST key to exit from the error conditions.
31
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