Tettex MIDAS 2881, Operating Instructions Manual

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140 Applications Guide
3 Phase Unshielded Cables Enclosed in a Common Metallic Sheath
Each conductor of an unshielded three phase cable should be tested individually with the other
conductors and the common sheath grounded. An overall test can be made with all conductors
connected together and energized with the sheath grounded. See the Test Procedure Example below.
3 Phase Individually Shielded Cables
The same procedure as for single conductor shielded cable can be applied for this type of cable.
Cable conductors not under test must be grounded. See also the Test Procedure Example below.
3 Phase Unshielded or Unsheathed Cables
In the case of a three phase unshielded cable a test procedure as outlined for a single-conductor
unshielded cable can be performed. Supplementary it is possible, by an UST mode, to perform
dissipation-factor measurements between two conductors, which are practically confined to the
insulation between the two conductors.
14.5.2 Test Procedure Example
The figure and table below shows the specific connections with the corresponding test modes of a
typical belted three-phase cable. It is assumed that no phase is left floating.
3 Phase Unshielded Cables Enclosed in a Common Metallic Sheath: Test connections to measure C
1G
, C
12
and C
13
Test Connections
DUT INPUT A
to INPUT B
to INPUT
HV GND
to Test Mode High Voltage
to
C
1G
2 3 GND shield GST gA+B 1
C
12
2 3 GND shield UST A 1
C
13
2 3 GND shield UST B 1
C
23
1 3 GND shield UST B 2
C
2G
1 3 GND shield GST gA+B 2
C
3G
2 1 GND shield GST gA+B 3
C
1G
+ C
2G
+ C
3G
- - GND shield GST gA+B 1 + 2 + 3