Single Wire Earth Return Lines Research Articles

Narrowband Modeling of Single-Wire Earth Return Distribution Lines

The implementation of powerline communication (PLC) on single-wire earth return (SWER) grids requires high-frequency earth path characterization. The empirical determination of these characteristics is not practical for large grids. Analytical expressions may be used to estimate the high-frequency characteristics of earth paths; however, this paper shows that this approach can lead to errors when modeling line-to-earth path PLC channels. Therefore, a hybrid empirical/analytical earth path characterization method, based on heuristic correlations of measurement results with a lossy capacitor model, is hereby proposed. Further measurements on an experimental SWER line using two types of conductors were carried out. The results indicate that narrowband PLC implementation on SWER grids is feasible, and that conductors with similar size and material composition may have similar high-frequency characteristics, regardless of the construction method used. The proposed earth path characterization method was verified by comparing measurements with simulations of frequency-dependent analytical and constant parameter hybrid, per-unit SWER transmission line models.

Rural Single Wire Earth Return distribution networks – Associated problems and cost-effective solutions

Single Wire Earth Return (SWER) systems are used for supplying electricity at low cost, where electricity supply is required for small populations of people dispersed across wide geographical areas. It is principally used for rural electrification, but is also used for other isolated loads and light rail. The existing SWER distribution systems have been stretched with the sharp growth of their loads because of customers’ change of lifestyle, which has introduced additional load of air conditioning equipment, motors driven by variable-speed drives and inverters. This paper proposes cost-effective solutions to address the problem of voltage regulation and compensation of the unbalancing effect of SWER lines on the three-phase feeder of these lines, which have been exacerbated by this load growth. To improve the voltage regulation problem, a LV switchable reactor has been designed, a prototype made and tested in the field. Also, an unbalance compensator has been designed to reduce the unbalancing effect of SWER lines. Two case networks have been used to perform simulation studies on the effectiveness of both proposed solutions. At first, a case study is used to demonstrate the impact of a switchable reactor on improving voltage regulation. Then, another case study shows that installation of a switchable reactor and an unbalance compensator simultaneously on a SWER distribution system effectively improves voltage regulation and reduces unbalancing effects.

Impact of distributed generation on protection of single wire earth return lines

Distributed generation (DG) inclusion within the grid system potentially introduces problems related to control, protection, harmonics, and network transients. This paper analyses one of the key issues: protection of the network, by ascertaining the impact of rotary DG inclusion on existing protection system of SWER (single wire earth return) lines and the DG sensitivity during faults. The analysis is carried out by estimating fault-sensitivity for the worst-case situation, determining the DG impact on the existing protection scheme, and comparing the network situation with and without DG during the fault. A model of arc voltage is used to represent a fault on a SWER scheme. The size of DG is selected based on the SWER capacity and SWER load. The study is conducted on an example SWER system by considering the SWER lines with and without DG and faults on the SWER backbone and laterals, and simulation results are reported. In every case studied, the fault current from the DG significantly exceeded the DG rating and the DG would have tripped. Thus the system reverts to the case with no DG. Even if DG did not trip, the fault current from the source would be largely independent of the DG, and thus the original feeder protection would continue to provide the same quality of performance. Hence, net sensitivity and existing protection system will not be adversely affected by DG inclusion in SWER lines.