Stanislaw Czapp

The effect of earth fault current harmonics on tripping of residual current devices

The most popular means of protection against indirect contact in low voltage systems is automatic disconnection of supply, since it is a simple and economically attractive way to achieve safety in an electrical installation. As a protective device, residual current devices (RCDs) are commonly used. In certain conditions using the RCDs is obligatory. The widespread application of static converters, especially frequency converters, results in installing RCDs in circuits where nonsinusoidal earth fault current flows. The earth fault current in the output circuit of frequency converters comprises harmonics and interharmonics, whose order mainly depends on the PWM frequency. The level of higher frequency components in the earth fault current may exceed the fundamental one. The nonsinusoidal earth fault current influences tripping of the residual current devices. In the paper, results of the theoretical analysis and the laboratory tests of residual current devices operation are presented and discussed. They prove that in some cases higher frequency components cause improper tripping of the residual current devices and a real hazard of electrocution exists.

The impact of higher-order harmonics on tripping of residual current devices

Distorted line to earth voltage on the output terminals of the inverter of variable speed drives results in an earth fault current comprising harmonics. Higher-order harmonics in the earth fault current have a negative effect on tripping of residual current devices. In some cases sensitivity of residual current devices rapidly decreases and protection against electric shock is not effective. In the paper results of the laboratory testing of residual current devices sensitivity are described.

Nonlinear secondary arc model use for evaluation of single pole auto-reclosing effectiveness

Purpose – The purpose of this paper is to discuss two evaluation methods of single pole auto-reclosing process effectiveness in HV transmission lines. Secondary arc current and recovery voltage results obtained by load flow calculation are compared to the results obtained by the time domain simulations. Moreover, a nonlinear secondary arc implementation is presented. Design/methodology/approach – A computer simulation studies were performed using DIgSILENT PowerFactory® software to analyse phenomena during single phase to earth short circuit and during single pole circuit breaker opening. Possibilities of electric arc extinction for different earthing solutions of shunt reactors were examined. Findings – The authors indicate, that precise representation of secondary electric arc in power system studies could lead to different conclusion than analysis carried out on simplified arc models. Recommendations for line construction (i.e. earthing reactor installation) and line operation (i.e. prolongation of dea...

Computer-aided calculations of earth potential rise in high voltage overhead lines

High voltage overhead power lines with earth wires comprise towers made of conductive material. Some towers are in locations where people can be expected to be either for a long time or for a short time but very frequently. Evaluation of shock hazard near such towers requires calculation of line-to-earth short-circuit current, earth current and especially earth potential rise. Number of towers in high voltage power lines can exceed 100. Thus, evaluation of effectiveness of protection against electric shock is time-consuming, so computer software for fast calculation of earth potential rise can be useful. This paper presents a method of computerized calculation of earth potential rise and earth current distribution in overhead lines with earth wires. The example results of calculations are presented for two selected cases of transmission system.

The effect of PWM frequency on the effectiveness of protection against electric shock using residual current devices

In the paper spectral analysis of the distorted earth fault currents in circuits with variable speed drives is performed. The impact of these distorted currents on the fibrillation effect is evaluated. Effectiveness of protection against electric shock using residual current devices in circuits with variable speed drives for various PWM frequencies is discussed. Operational characteristic of the proposed residual current device is presented.

Numerical and experimental investigation of thermal convection near electric devices with vertical channels

This paper presents the results of numerical and experimental investigation of thermal convection near heat emitting surfaces of an electric device. For the intensification of thermal convection, special vertical channels were formed near the heat emitting surfaces of the device. An experimental test has proved that there is an optimal length of the channels - thermal convection is the most intensive then. Air velocity vectors close to heat emitting surfaces are presented with the use of Ansys software. Due to vertical channels, it is possible to increase the current-carrying capacity of electric devices.

EHV transmission lines wires location on line operation issues - case studies

Transmission lines towers construction affects the line parameters and influences on its operation in the future. Misguided design of the tower can lead to serious problems such as overvoltages, electric arc extinction difficulties, voltage asymmetry, resonance phenomena or increasing of magnetic field near the line. The paper points out those threats on example of 400 kV double circuit overhead transmission line with shunt reactors. The paper discuses the impact of circuits orientation of the transmission line, phase wires arrangement and line transpositions on above problems. The study includes steady state analyses and transient analyses (EMT simulations).

Influence of shunt compensation with SVC devices on resonance risk in power systems

Many analyses are required to locate a new reactive power source in a power system. The choice of a location is a very complex matter which requires various aspects to be considered. Selecting a location also entails the necessity to assess it from the point of view of the selected compensators structure as well as the systems performance in various states with the new device on. The paper presents the issues of assessing compensator location from the point of view of resonance phenomena. It indicates the factors which affect a circuits resonance conditions, including a change in network configuration and compensators structure.

Computer-aided analysis of induced sheath voltages in high voltage power cable system

This paper concerns the effect of configuration of high voltage power cables on induced voltages in their metallic sheaths. One, two or three cables per phase and phase sequence of the cables are considered. Computing of the voltages was performed for a normal operation and in case of earth fault. Various ways of the sheaths bonding are considered as well. Shock hazard and voltage stress of non-metallic outer sheath of cables are evaluated. Favourable configurations of the power cable system are indicated.

Tripping limitations of residual current devices in photovoltaic installations

In electrical installations with photovoltaic sources of energy, earth fault current may comprise alternating current component and direct current component. The waveform shape of this earth fault current mainly depends on the point of the fault and the properties of a photovoltaic power electronics converter. The waveform shape of the current influences operation of protection devices, especially tripping threshold of residual current devices. This paper considers the effect of the composite waveforms, which may flow in installations with photovoltaic sources of energy, on tripping threshold of residual current devices. Limitations and unexpected behaviour of these devices are discussed.