Derivation and Verification of a Calculation Method for the Overhead Line Voltage Measurement considering the Influence of the Earth Conductor

Monitoring of power grids is a central task of network operators. In order to ensure a high security of supply, disturbances in the network must be noticed and remedied. The Smart Grids approach is to increase efficiency, reliability, and security. An increasingly automated monitoring of power grids enables rapid detection of fault currents and increases the security of supply. For locating fault locations, sensors for current and voltage measurement can be used on lines at regular intervals. Currently, overhead line fault indicators are used in medium-voltage networks, which often only measure the current intensity and detect fault currents. In recent years, the proportion of decentralized generators, such as wind power or photovoltaic systems, has increased. As a result, the load flow direction in power grids is no longer clearly defined. In case of detecting a short-circuit current, it cannot be determined which side of the overhead line indicator the fault location is. The load flow direction helps indicate fault locations. Therefore, the motivation is to enable voltage and current measurements, which can be used to determine the load flow direction, and as result, fault direction detection. A simple measurement of the high voltage on overhead line indicators is not possible without reference to earth potential. A concept for earth potential-free voltage detection is thus developed and verified under lab conditions. The result of the investigation is a new measuring method using floating sensors near the overhead lines to calculate the actual high-voltage. Above all, the developed calculation method considers the earth wire of an overhead line arrangement and their suitability can be confirmed.