BAUR GmbH

Medium voltage networks up to 35 kV Diagnose with "viola TD”

BAUR cable testing device viola enhances measurement of the tan delta

The easy to transport cable testing devices from BAUR Prüf- und Messtechnik GmbH (Sulz/Austria) are now capable of interference-free diagnostics: Determining the tan delta (also called loss factor measurement) allows you to examine the aging condition without damage to the cable. With frida TD and viola TD, normal cable testing and measurement of the tan delta is possible. The "frida TD” is a device for diagnostics of network sections up to 20 kV. Now the even more powerful device, "viola”, is suitable for cable lines up to 35 kV and is available in TD version. In spite of its size, viola is easy to transport. The device can be disassembled in two easy-to-manage units and handled easily on site. Maintenance and assembly teams can now test network sections while laying new cables and during repairs with an integrated device. The help of the diagnostics functions look for weak points, without additional equipment. The TD versions are now available.

During the loss factor measurement, the ratio is determined from active output and capacitive reactive power. Test series across several voltage levels allow for assessment on the aging condition of insulation and thus offer the basis for status-oriented maintenance. For this, BAUR uses a low frequency voltage at 0.1 Hz. The unique BAUR true sinus generator ensures an ideal sinus curve and provides best prerequisites for good reproducibility and comparability of measurement results. The intuitive device operation and the BAUR PC software simplify recording and interpreting results as well as comparison with saved data for trend analysis.

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Technical Data of "viola TD”

Output voltage
VLF true sinus    1…42 kVrms (60 kVpeak)
DC/VLF Rectangular    1 … 60 kV
Frequency range     0.01 … 0.1 Hz
Option TD (integrated in device)
Precision    1x10E-4
Resolution    1x10E-5
tan delta measurement frequency    0.1Hz
Interface    USB 2.0
Dimensions    485 x 850 x 320 mm
Two device parts    Total weight 75 kg

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Detect water trees on time

In spite of their sturdiness, some plastic-insulated cables (PE, VPE) do reach their limits. The reason often is "water trees” (see Figure). They spread like little trees wherever there is a fault in the insulation, but don’t necessarily affect the functionality. They become "electrical trees” only from a certain size onward, structures where local discharges occur. The insulation effect is no longer adequate here. Early detection and evaluation of water trees is therefore important for the status-oriented maintenance of medium voltage networks. A suitable diagnosis method for this is the tan delta measurement. It determines the loss factor, i.e. the ratio of active power and capacitive reactive power. The active power in the ideal intact cable is almost zero. It grows during the aging process. A measured value alone – possibly recorded at low voltage – is not conclusive enough. Therefore, the tan delta measurement should be done with multiple voltages. When measured values over the voltage are applied, aged cables produce a characteristic curve, the height and course of which allows for conclusions on the status. Trend analyses based on regular measurements over a long period are also helpful. Therefore, it is recommended to always carry out the diagnostics together to create comparison options while evaluating cable lines. In this way, the existence of water trees can be detected early enough anywhere in the cable, before they become electrical trees. Should the tan delta measurement indicate an over-aged cable, the partial discharge measurement delivers information on the defective section so that only these can be replaced.

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Measurement series across multiple voltage levels (and the different phases) deliver a clear picture of the insulation status.

Other information / Press contact:

BAUR Prüf- und Messtechnik GmbH – Alexander Gerstner
Raiffeisenstraße 8 – 6832 Sulz (Austria)
Tel.: +43 (0)5522 4941-0 – Fax: +43 (0)5522 4941-8055
www.baur.at

Press’n’Relations II GmbH – Ralf Dunker
Guntherstraße 19 – 80639 Munich (Germany)
Tel.: +49(0)89 17999275 – Fax: +49(0)89 17999289