COMMERCIAL FEATURE Cable diagnostics… the next generation N etwork operators can now get faster and significantly more reliable information about the quality and the condition of their cables. This is made possible thanks to the brand-new 50 Hz Slope technology. For the first time, it has become possible to immediately locate faults in underground cables during the actual partial discharge (PD) measurement. With the 50 Hz Slope technology, for the first time worldwide a withstand test with very low frequency cosine- rectangular (VLF CR) voltage and PD diagnosis with damped alternating voltage (DAC) is combined in one unit. This allows an efficient and integrated solution for precise inventory of the network infrastructure. The important fact here is that the PD measurement data, gained with the VLF CR or with the DAC test voltage, can be compared directly with the 50 / 60 Hz network voltage. This facilitates reliable decision making. TDS NT – test and diagnosis system TDS NT consists of a multifunctional, compact voltage source and a modern PD detector. It can be used to test cables according to the international standards (e.g. IEC 60502-2 and IEEE 400.2) with VLF CR. In addition, a PD diagnosis using the new 50 Hz Slope technology can be performed simultaneously with the help of the PD detector. Alternatively, the TDS NT can also be used for PD diagnosis with the proven DAC. In practice, the PD diagnosis 46 has been established nationally and internationally as an effective method of measurement. It is especially useful for commissioning testing, as it is the only way to reliably check the quality of workmanship of the accessories. SebaKMT is widely known for its powerful VLF test systems. The high testing capability is achieved through the patented energy recovery principle. Now, in addition to the VLF waveform, which is ideal for commissioning tests, there is also the option of generating a DAC voltage. The DAC voltage has proven to be the ideal voltage waveform for a non- destructive PD diagnosis. In addition the TDS can also be used for DC tests and sheath tests in compliance with IEC 60229. Furthermore, in combination with the step voltage sensor ESG NT, it can also be used for precise pinpointing of sheath faults. The 50 Hz Slope technology principle For both voltage waveforms, these two fundamental conditions are present; the charging phase and the resonance phase. During the charging phase the test object is charged to the desired voltage, or the voltage losses of the cable during measurement are recharged. During the resonance phase the TDS and the cable form a resonant circuit whose natural resonance frequency is determined by the fixed inductance and the support capacitor of the power source, and the capacitance of the test object. The support capacitor has been designed in such a way that the resonance frequency will always fall in a specific frequency window comparable to that of the network frequency – thus a 50 Hz slope – is attained for every test object. The new PD detector PDS 60 combines many years of field experience, customer demands and innovations in one device. That makes it possible to carry out a VLF test along with a PD diagnosis. This not only increases the reliability of the withstand-test, since partial discharges are simultaneously recorded, but is also cost- effective. If a PD-free cable is detected during the withstand-test, a PD diagnosis for quality control is no longer required. The operating software is designed so that any user will come to grips with it immediately. It features an integrated database, simplified searching, browsing and administration of measurement and cable data. Live PD mapping means the PD evaluation algorithm enables a reliable automatic detection and precise location of partial discharges (PD mapping) whilst the measurement is taking place. ESI ESI AFRICA ISSUE 2 2014