Megger VLF SIN-45 - VLF tan Delta Loss Factor Measurement (Optional); Preparing for Measurement

Operating Modes
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5.3 VLF Tan Delta Loss Factor Measurement (Optional)
5.3.1 Preparing for Measurement
Underground medium and high voltage cables are continuously subject to thermal,
electrical and mechanical stresses over the course of their use.
This fact inevitably leads - despite the use of durable materials - to increasing damage
or ageing of the cable, which in turn leads to dielectric losses.
A measure of these dielectric losses is the so-called loss factor tanδ, which can be
determined within the scope of a tan delta step test.
On the basis of the measurement results, integral ageing effects, such as the degree of
humidity, can be diagnosed and cables with critical ageing identified.
To start a tan delta step test, the submenu of the test operating modes must be opened
using the menu item and from this, the menu item must be called up.
Upon entering the operating mode, some parameters (phases, test standard, insulation
type and nominal voltage) are automatically queried, which however can still be
adjusted until the actual start of the measurement (see the following table).
The following test parameters can be set (some of which are in the submenu ):
Button /
Menu item
Description
During phase selection (see page 28), all the phases must be selected on
which a tan delta step test is to be performed.
The test is carried out − starting with the lowest phase − successively on
all the selected phases.
The phase selection menu must be closed using the function button .
Nominal voltage Uo of the connected cable type as RMS value.
Once the value is confirmed, a calculation of the respective voltage values
of the individual levels is carried out and displayed on the screen.
The maximum nominal voltage that can be set depends on the
maximum output voltage of the test system as well as on the set
voltage levels (see the next page).
If the nominal voltage of the cable is above the maximum value
that can be set, the number of the voltage levels would have to be
reduced accordingly first.
Introduction
Selecting the operating
mode
Setting the test
parameters