Krzysztof Dobrzyński

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...

Effectiveness of the robust PSS design

The paper discusses robust PSS synthesis. The PSS is an H∞ controller, what means that minimises H∞ norm of transfer function between the exogenous signals such as reference inputs and disturbances, and the error signals which are to be minimised to meet the control objective. The dynamic properties of the plant are shaped by choosing appropriate weighting function applied to the plant output and input signals. Question appears: does such type of PSS design lead to effective PSS which can be applied in real power system?

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.

Resonance problems in UHV transmission lines

The paper presents resonance phenomena observed in 400 kV transmission lines in the Polish power system. Two events are analysed, when shunt reactors used for reactive power compensation, caused overvoltages and overcurrent protection tripping as a result of resonance. An oscillographic fault recordings from protection devices are compared to time domain simulation results. The obtained simulation results match fault recordings, which allows the cause of the observed disturbances to be explained. The paper indicates resonance risks which should be avoided to ensure safe power system operation.

Neutral earthing reactor protection

The IEEE and CIGRE recommend protection systems for high voltage shunt reactors. Unfortunately the recommendations do not include guidelines for the protection of neutral earthing reactors, which are often connected to shunt reactors to increase the effectiveness of single pole auto-reclosing. The paper discusses earthing reactor protection issues with particular emphasis on the detection of internal faults. An analysis carried out for a real power system which came into operation in 2015 is presented.

Low-frequency tripping characteristics of residual current devices

Fast development of various types of converters makes their utilization in industry and in domestic installations very common. Due to converters, an earth fault current waveform in modern circuits can be distorted or its frequency can be different than 50/60 Hz. Frequency of earth fault (residual) current influences tripping of residual current devices which are widely used in low voltage systems. This paper presents the behaviour of residual current devices when residual current of frequency lower than 50 Hz flows. The results of the analysis have shown that many of commonly used residual current devices are not able to detect residual current when its frequency is significantly lower than 50 Hz. Thus, protection against electric shock may not be effective.

Harmonics produced by traction substations – computer modelling and experimental verification

Voltage and current harmonics have a detrimental effect on the components of a power system. Current harmonics may result in the overload and damage to power transformers. Voltage harmonics may result in, for example, damage to capacitor banks used to compensate reactive power. Devices which contribute to both current and voltage distortion include traction rectifiers. This paper presents results of the computer investigation of the effect of these rectifiers on the power supply network. The results of the computer investigation have been compared with the result of experimental study.

Magnetic and capacitive couplings influence on power losses in double circuit high voltage overhead transmission line

Purpose The paper aims to discuss problems of power and energy losses in a double-circuit overhead transmission line. It was observed from energy meters’ readings, that in such a line, active power losses can be measured as “negative”. The “negative” active power losses appear when the active power injected to the circuit is lower than the active power received at the circuit end. The purpose of this paper is to explain this phenomenon. Design/methodology/approach Theoretical considerations based on mathematical model of the transmission line of π-type confirming that effect are presented. Power losses related to series impedance of the line and to shunt admittance are calculated. The theoretical considerations are confirmed by measurements done on the real transmission line. Findings The calculations allow to indicate components of the active power losses, i.e. related to electromagnetic coupling among wires of a given circuit, related to electromagnetic coupling between circuits and related to shunt capacitance asymmetry. The authors indicate the influence of the line/wires geometry on the active power losses in a double-circuit overhead transmission line. Originality/value Explanation of the effect of “negative” active power losses’ measurement in a double-circuit overhead transmission line is provided in this paper.