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VLF sine 0.1 Hz – Universal voltage source for test-
ing and diagnostics of medium-voltage cables
A. Gerstner, M. Jenny; BAUR Prüf- und Messtechnik GmbH, Sulz (Austria)
1. Introduction
More and more operators of medium-
voltage networks are faced with the chal-
lenge of delivering high availability and
reliability at lowest possible costs. Evalua-
tion of the network condition
offers valuable
information for cost-optimum management,
grid expansion and maintenance. With the
help of information on the cable condition,
we can for example, identify highly aged
cable routes and prioritise these during
maintenance. But even
in newer cable
routes, the cable diagnostics delivers in-
formation on hidden faults, such as defec-
tive joints, water ingress and much more.
Testing cable routes is essential in order to
utilise the potential of condition evaluation.
Network operators that would like to carry
out diagnostics tests (see Section 2 Diag-
nostics procedures) in addition to power-on
tests, are subsequently concerned about
achieving significant diagnostic results with
as little time and
at the lowest cost as pos-
sible. In addition, they strive for the highest
possible significance of the measurement
results.
Among
other things, the significance of the
measurement results depends on the volt-
age source of the testing and measuring
device. Various sources are available on
the market, including 50 Hz resonance sys-
tems, VLF sine 0.1 Hz (VLF = Very Low
Frequency), DAC (DAC = Damped AC) and
VLF Cos-Rect (Cosine Rectangle).
The quality of the
respective voltage
sources - more precisely, quality of the
measurement results that can be achieved
with these sources - has already been a
subject of several studies and
even test
engineers discuss the relevance of the
voltage source for tests on field. In this pa-
per, we will interpret the results of a few
studies. In addition, we will present the
methods or method combinations that
could be useful in practice.
Moreover, we will show the impact that the
selection of the
voltage source and the
possible test and measurement methods
with it could have on everyday practice, the
cost factors that must be observed while
deciding on the measurement technology
and how the daily relevant criteria are af-
fected in practice.