Operation Manual

44 GMC-I Messtechnik GmbH
11 Measuring Insulation Resistance
Attention!
!
Testing Systems with RCDs
Insulation tests in electrical systems with type B RCDs may
only be conducted while the RCDs are switched off.
In the case of insulation testing, it’s advisable to discon-
nect AC/DC sensitive RCDs for safety reasons, because the
electronics required for detecting DC residual current
may be destroyed by these tests.
(Excerpt from ABB brochure 2CDC001003C0109).
11.1 General
Select Measuring Function
Connection
2 pole adapter or test
plug
Note
If you use the test plug together with a plug insert, insula-
tion resistance is only measured between the phase con-
ductor terminal designated “L” and protective conductor
terminal PE!
Note
Checking Measurement Cables Before Measurements
Before performing insulation measurement, the test
probes on the measurement cables should be short-cir-
cuited in order to assure that the instrument displays a
value of less than 1 k. In this way, incorrect connection
can be avoided and broken measurement cables can be
detected.
Set Parameters
* Freely adjustable voltage (see section 5.7)
Polarity Selection
* AUTO parameter (see section 5.8)
Breakdown current for Ramp Function
Limit values for Breakdown Voltage
Limit Values for Constant Test Voltage
q Test voltage
A test voltage which deviates from nominal voltage, and is usually
lower, can be selected for measurements at sensitive compo-
nents, as well as systems with voltage limiting devices.
q Voltage Type
The “U
ISO
” rising test voltage function (ramp function) is used to
detect weak points in the insulation, as well as to determine
response voltage for voltage limiting components. After briefly
pressing the ON/START key, test voltage is continuously increased
until specified nominal voltage U
N
is reached. U is the voltage
which is measured at the test probes during and after testing. This
voltage drops to a value of less than 10 V after measurement (see
section entitled “Discharging the Device Under Test”).
Insulation measurement with rising test voltage is ended:
• As soon as specified maximum test voltage U
N
is reached and
the measured value is stable
or
• As soon as specified maximum test voltage is reached, e.g.
after sparkover occurs at breakdown voltage).
Specified maximum test voltage U
N
or any occurring triggering or
breakdown voltage is displayed for U
ISO
.
The constant test voltage function offers two options:
R
ISO
Voltage type: constant
Test voltage: 50 V / 100 V / 250 V / 500 V / 1000 V / xxx V*
Voltage type: rising/ramp
Earth leakage resistance:
2-pole meas. (relevant for report generating only):
Measurements between
Lx-PE / N-PE / L+N-PE / Lx-N / Lx-Ly / AUTO*
where x, y = 1, 2, 3
Limit value:
I > I
Limit
U
INS
STOP
low limit:
U
INS
input range:
> 40V ... < 999 V
upper limit:
Limit value:
R
INS
< Limit Value
U
L
 R
L
U
INS