Purpose/Aim

Due to the lossy transmission characteristics, the propagation of PD pulses in power cables leads to length-dependent attenuation and dispersion, which is mainly caused by the cable semiconductor layers. Inevitably, for PD detection at the cable end, the sensitivity of the PD measurement decreases with increasing distance between the cable end and the PD fault position. Even worse, PD localization based on time-domain reflectometry (TDR) requires the detection of the reflected PD pulse from the far end of the cable. Depending on the fault location, the reflected pulse must travel at least one cable length and at most twice the cable length to reach the PD detector. Although the sensitivity can be significantly improved by synchronized PD detection at both cable ends, the cable length basically limits the achievable measurement sensitivity. In order to achieve acceptable sensitivity under on-site conditions, even for very long cable systems, distributed PD sensors are used on the cable accessories (end terminations and joints). This paper focuses on the properties and limitations of selected PD sensors. Examples of PD sensor application in HVAC cable systems show the advantages of distributed PD detection. For 525 kV HVDC cable systems with very long lengths, which are currently being installed in Germany, there arise new requirements for suitable PD sensors.

Experimental/Modeling methods

Measurements for characterization of the PD sensors are performed according to CIGRE TB728 (On-site Partial Discharge Assessment of HV and EHV Cable Systems, 2018). Complementary FDTD simulations provide information on the electromagnetic field generated by PD and coupled to the PD sensor.

Results/discussion

The results of our investigations should help to better distinguish between existing PD sensor types in order to make an appropriate selection for different application scenarios. The presented measurement setup can be used to characterize other types of cable PD sensors.

Conclusions

There are already numerous types of PD sensors for distributed PD detection on laid cables. The presented investigation and evaluation methods allow a quantitative comparison of PD sensors and should help to distinguish good from even better sensors.