Geomagnetically induced currents (GICs) in power systems are conventionally modelled as direct currents, based on their commonly described quasi-DC nature. For more representative power system dynamic response modelling, it is necessary to model GICs using low-frequency AC. After analysing spectra of geomagnetic field measurements and GICs in several power systems, preliminary results indicate that the GIC spectra depend on the magnitude and frequency spectrum of the geomagnetic disturbance, the earth conductivity and the electrical characteristics of the network. In this paper, analysis based on measured GIC power spectra suggests that the dominant frequencies to use in GIC modelling and simulation are typically below 50 mHz. The associated error introduced by only using these frequencies is also quantified. The results have implications for modelling the geoelectric fields inducing GICs, dynamic models of power system response and the need for GICs and their associated driving fields to be measured at intervals not exceeding 10 s.

Geomagnetically induced currents (GICs) in conductors connected to the Earth are driven by an electric field produced by a time‐varying magnetic field linked to magnetospheric‐ionospheric current perturbations during geomagnetic storms. The GIC measurements are traditionally done on the neutral‐to‐ground connections of power transformers. A method of inferring the characteristics of GIC in power lines using differential magnetic field measurements is presented. Measurements of the GIC in the power lines connected to a particular power transformer are valuable in the verification of the modeling of GIC in the power transmission network. The differential magnetometer method (DMM) is an indirect method used to estimate the GIC in a power line. With the DMM, low‐frequency GIC in the power line is estimated from the difference between magnetic field recordings made directly underneath the power line and at some distance away, where the magnetic field of the GIC in the transmission line has negligible effect. Results of the first application of the DMM to two selected sites of the Southern African power transmission network are presented. The results show that good quality GIC measurements are achieved through the DMM using Commercially‐Off‐The‐Shelf magnetometers.

This paper discusses the currently used generator systems in wind energy conversion systems and some of the newer concepts with their technical features. The Brushless doubly fed induction generator, Brushless doubly fed reluctance generator and the Switched reluctance generator are viable alternatives for wind power applications. This paper also highlights the hybrid wind generator solutions which is an emerging trend in hybrid renewable energy solutions. Using the appropriate control techniques, these generator technologies unlike the conventional wind turbine generator can produce constant wind power irrespective of the changes in velocity of wind speed. This has tremendous application in Africa as the installed capacity increases and the need to provide remote communities with electricity remains paramount. The merits and demerits of the various technologies are uniquely grouped in a novel way to aid decision making based on available resources.

Geomagnetically Induced Currents (GICs) are induced after a complex interaction between the sun and earth’s magnetic field. GICs may cripple power systems leading to voltage collapse and a drop in power quality. While the commonly-used dc model for GICs is valid for steady-state analyses of power systems and transformer responses, GICs must be represented with their continuously varying magnitudes and frequency components to understand the dynamic power system’s response to solar storms. In this paper, we used measured GIC data from the 2003 Halloween storm to compare several signal processing techniques. The Fast Fourier Transform (FFT) with a fixed window size, Short-Time Fourier Transform (STFT) with a variable window size, wavelet transform, and Particle-Swarm Optimization (PSO) methods were used to identify the GIC frequency characteristics. To understand the effects of these GIC characteristics on voltage stability, a multi-machine network was modelled on a digital real-time simulator (OPAL-RT). The results reveal the limitations of fixed window FFT in capturing the dominant high-frequency GIC bandwidth arising during peak solar activity. Wavelet and STFT are recommended for GIC data analysis as they provide time-frequency localization. High-frequency GICs during sudden storm commencements and pulsation activity are more of a concern for voltage stability than lower frequency components. Novel results from this study suggest that limiting contingency analysis to only high magnitudes of dc/GIC does not cater for the underlining GIC dynamics. In addition to magnitude thresholds, contingency analysis should incorporate GIC characteristics such as frequency which affect voltage dynamics and thus power system stability.

This paper deals with the effect of DC faults on the transient stability of a multi-machine power system with two transmission line configurations; HVDC and a hybrid HVAC-HVDC transmission line. The faults are located at the DC terminals of the HVDC converter station. In order to carry out this study, two case studies are presented. In the first case study a double HVDC transmission line is used to transmit 2000 MW to an area of the power system called Pookland which has a total load demand of 2440 MW. In case two, a parallel hybrid HVAC-HVDC transmission line is used to transmit the same amount of power to Pookland. In both cases, the impact of a short term converter DC fault on the transient stability of the entire system was investigated. This was done by studying the response of the rotor angle of G2 in Pookland, G3 in the Bing Coal plant and the voltage profile at the terminals of the generators to the DC fault at the HVDC converter station. Amongst other results, it was established that in case 1 which has a double HVDC transmission line, the rectifier side (in the Bing coal plant) has less rotor angle oscillations when compared to the inverter side (in Pookland), but the rectifier side took longer than the inverter side for the rotor angle of the generators to stabilize. In case 2, the voltage at G2 in Pookland took six times the amount of time it took G3 in the Bing coal plant to stabilize while the voltage in the Bing Coal plant dipped by 0.35 pu (smaller than case 1 which dipped by 0.4 pu). In conclusion, the converter DC fault had a smaller impact on the transient stability of the multi-machine power system when the hybrid HVAC-HVDC transmission line was adopted.

Geomagnetically induced currents (GIC) caused by abnormal space weather have traditionally been modelled as balanced dc in low-frequency transients studies. Existing transformer models can be used to investigate a power system with GIC but the extent to which these models are consistent is unclear. This paper investigated the differences between the three-phase five limb (3p5L) power transformer models in MATLAB Simulink and PSCAD/EMTDC when they were subjected to dc (dcGIC) and low-frequency GIC (acGIC). The simulation protocol used a simple 4-bus power system with a generator, two transformers, a line, and a PQ load. An IEEE 1459 power calculation block was developed in MATLAB for non-ideal conditions whereas waveform data was post-processed from the PSCAD simulations. The results showed that even though the transformer models were calibrated with the same magnetization characteristics, the 3p5L PSCAD models with inter-phase magnetic coupling yielded a slightly different magnetization curve for each phase. By contrast, the MATLAB model yielded the same magnetization curve for each phase under the same conditions. As a result, there were differences in the performance with dc or acGIC, with the PSCAD model being more responsive to phase unbalance, simulating greater distortion in the transmission line, and voltage drop at the end.