Static voltage stability analysis of eskom eastern grid

High voltage transmission line design requires careful insulator selection to ensure good operational performance. This paper reports on the in-situ measurements of leakage current (LC) on composite and glass insulators of the Cahora Bassa high voltage direct current (HVDC) transmission line in South Africa over a 6 - month period. The influence of temperature, humidity, dew, rain and the HVDC line's voltage and current on LC are investigated. The results show that the composite and glass insulator LC behaviour is similar, except in cases of high humidity or rain. At the commencement of rainfall and humidity (>90%), elevated LC levels are observed on glass insulators, while composite insulators demonstrate lower LC levels under these conditions. Under nominal weather conditions of no rain and low humidity, the LC measurements exhibit an almost square-wave behaviour with LC switching between lower (≈20 μA) and higher values (≈60 μA) with relatively short transitions on a daily basis. This phenomenon can be ascribed to condensation on the insulators, which is a primary determinant of the LC levels on contaminated insulators. The line current and voltage fluctuations do not influence the LC level.

In this paper, a dynamic (i.e., multi-year) hybrid model is presented for Transmission Expansion Planning (TEP) utilizing the High Voltage Alternating Current (HVAC) and multi terminal Voltage Sourced Converter (VSC)-based High Voltage Direct Current (HVDC) alternatives. In addition to new HVAC and HVDC lines, the possibility of converting existing HVAC transmission lines to HVDC lines is considered in the proposed model. High shares of renewable resources are integrated into the proposed hybrid AC/DC TEP model. Due to the intermittency of renewable resources, the planning of large-scale Energy Storage (ES) devices is considered. In order to accurately estimate the total TEP costs and hence capturing the scenarios of load and renewable generation uncertainty, using a clustering approach, each year of the planning horizon is replaced with four representative days. The proposed model is formulated as a Mixed-Integer Linear Programming (MILP) problem. Using Benders Decomposition (BD) algorithm, the proposed model is decomposed into a Master investment problem to handle the decision variables, and Sub-problems to check the feasibility of master problem solution and optimize the operation and ES investment cost. Three test systems are used as case studies to demonstrate the effectiveness of the proposed hybrid AC/DC TEP model.

Continental level power system interconnections using a High Voltage direct current (HVDC) transmission lines have been considered to bring economic benefits such as interregional power exchange. This paper describes the modeling process and studies the technical benefits of having multiple HVDC lines, including a grid of HVDC lines (macrogrid) configuration, connecting the North American Eastern and Western electric power interconnections. The models developed provide steady state and stability analysis for multiple HVDC overlay topologies and provide technical benefit analysis in terms of frequency response and congestions management. The paper also provides a comparison of different HVDC topologies performance and their grid support in case of major disturbances.

This paper proposes a novel control method for controlling voltage source converter (VSC) based high voltage direct current (HVDC) converters present in a network consisting of a Doubly Fed induction generator (DFIG) - wind farm (WF) connected to infinite bus via an HVDC line and a parallel tie line. A new idea has been presented where inertia emulation capability of capacitors present in HVDC network has been utilized with a nonlinear control such as sliding mode control method. In this method the DC voltage reference for the control is allowed to vary with the frequency deviations in the system for emulating the inertia characteristics of the DC link capacitance and thus controlling the power oscillations. The results of the proposed method are then compared with that of conventional PI control. The simulations results obtained in MATLAB proved the effectiveness in stabilizing the oscillations in case of various transient events such as fault and power reference variations of the DC link.

In this work, a method has been proposed for voltage source converter (VSC)-based high-voltage direct current (HVDC) transmission lines to detect the fault and find the fault pole during earthed and unearthed faults. Pre-processed features from DC voltage signals of both the poles and neutral to ground current signals from the rectifier end are taken as input to the proposed method. In this work, back-propagation neural network has been used as a classifier to detect the fault and to find the faulty pole. Three modules are designed—BNN-D for fault detection, BNN-P for fault pole identification and BNN-G for ground identification. The advantage of proposed method is that it not only detects the fault in a VSC-HVDC transmission lines, but it also identifies the faulty pole. Another advantage of proposed method is it does not need any communication link as it uses one-end measurement and the reach setting is up to 99.9% of the line length. Results of the proposed method have better selectivity, reliability, robustness and accuracy.

Polymer insulators traditionally used in HVAC (High Voltage Alternating Current) are used in HVDC (High Voltage Direct Current) transmission lines. For these polymer insulators, silicone insulating rubber, based on Polydimethylsiloxane (PDMS), is used in industry to manufacture high voltage insulators for power lines. Silicone rubber material ages due to pollution and environmental factors such as UV (ultraviolet light), rain, and temperature. Moreover, no international standard is available to standardize its functional characteristics to ensure its best performance in HVDC regime. Standards usually define the testing procedures to measure the resistance of the materials to these conditions. One of the tests used to evaluate the performance in AC (alternating current) of the housing material of polymeric insulators is the inclined plane test (IPT). This test has the purpose of assessing the tracking and erosion resistance of housing materials. However, for the IPT, no consensus is reached yet for this testing in Direct Current (DC) voltage. In addition, there are no indications whether the formulations that have been successfully used for HVAC work fine; also, in HVDC regime, or not. In this paper, an investigation of the tracking and erosion resistance under positive DC IPT is presented. In this way, the study was carried out on skirts of an HVAC commercial insulator and samples of a new outstanding composite silicone rubber formulation filled with micro and nano particles. The results show that HVAC silicone rubber formulations could not be suitable for HVDC applications under highly polluted conditions. In the case of the new enhanced composite, it is shown how nano particles used in this material significantly enhance the performance during DC tracking and erosion testing well above other materials tested in previous works. Also, thermogravimetric analysis (TGA) of the composites is used to correlate thermal stability with the DC IPT performance.

Recent developments in power semiconductor devices have made High Voltage Direct Current (HVDC) transmission systems the most crucial technology for future power systems. Today several HVDC projects have been commissioned around the world. The primary concern for such an advanced HVDC grid is to follow standard grid codes to maintain the safety and stability of the electrical equipment during transient and dynamic circumstances. Although the HVDC system has been recognized as the most prominent technology to transmit electric power, some issues must be addressed, such as selective and quick detection of faults. For selective fault detection, it is essential to look into the several fault detection strategies that fortify the HVDC system with time-frequency signal processing techniques. This research uses a time frequency-based method to identify the different HVDC transmission line faults. The most suitable mother wavelet for various transient states is selected by analyzing fault voltage and current signals based on variance, standard deviation, and range parameters. An experimental setup of a thyristor-based HVDC transmission system has been developed in the MATLAB/Simulink environment, and multiple fault scenarios have been analyzed. The simulation outcomes reveal that the most effective mother wavelet for detecting DC line, symmetrical and unsymmetrical faults occurs at the 6th level of fault signal decomposition. By examining current and voltage signals, our work has determined the best mother wavelet for various faults. Using more than one mother wavelet to detect faults is more reliable than using a single mother wavelet to detect all faults. Additionally, it has been noted that each fault's voltage and current signals have two distinct mother wavelets.

Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) technology is a very attractive power transmission technology. The VSC based HVDC transmission uses IGBT (Insulated Gate Bipolar Transistors) switches having turn-on and turn-off capability and having special characteristics compared to Current Source Converter (CSC) based conventional HVDC technology. Among various control methodologies used for VSC based HVDC, vector control, nonlinear control and independent P-Q controller based on analytic expressions have been developed and analyzed in this work for sending end control station 1. Similarly, in the receiving end station 2, DC and AC voltage controllers are realized with traditional PI controllers have been analyzed. The performance of the proposed controller has been investigated under different operating conditions including post fault recovery. The effectiveness of the proposed various controllers are demonstrated through digital simulation studies on VSC-HVDC transmission system, using PSCAD/EMTDC software package under short time Line-Ground fault in both AC systems in two terminal VSC - HVDC systems.

The area of high voltage direct current (HVDC) transmission line is very large, so using cable for electric field monitoring system is very inconvenient. Wireless sensor network (WSN) can solve this problem. Compared with the traditional communication network, WSN has the advantages of small volume, high flexibility, strong self-organization. So it’s more suitable for the construction of distributed electric field monitoring system which has long distance and high mobility. On the other hand, optical E-field sensors are passive devices and they have such advantages as compact structure, wide-band response and wide measuring range which mechanical sensors lack. A distributed wireless system with optical E-field sensor is designed for collecting and monitoring the electric field under HVDC transmission lines. This measurement system has been used in China’s state grid HVDC test base and power transmission projects. Based on the experimental results, this measurement system demonstrates that it can adapt to the complex electromagnetic environment under the transmission lines and can accomplish the accurate, flexible, and stable demands of the electric field measurement.

A hybrid 2D/3D numerical method is introduced to solve the ion flow field around a house near bipolar high voltage direct current (HVDC) transmission lines. At first, a 2D upwind finite element algorithm for the computation on the ion flow field near bipolar line structure is set up. Then a 3D method is used to analyze the ion flow field in the vicinity of a house under the HVDC lines. The 2D results serve as boundary conditions of 3D calculation in order to improve the computational efficiency.

Offshorewind farms inherently need alternating current (AC) grid connection withundersea cables. However, this requires reactive power compensation, which iscostly and not practical. Moreover, it threads the stability of the system. Forthese reasons, high voltage direct current (HVDC) transmission is a promisingsolution since no reactive power is needed. Furthermore, the DC power flowbetween offshore and onshore locations as well as the reactive power at eitherside can easily be controlled by voltage source converters (VSCs). In thispaper, the modeling and control of an offshore wind farm connected to themainland grid power with HVDC transmission is proposed. A control strategy isproposed to control active and reactive power at the offshore wind farmconverter and DC voltage at the onshore converter. The overall system,including wind farm, offshore and onshore converters, HVDC transmission, and ACgrid side, were tested and verified in a simulation environment. The designedcontrol systems of the VSCs were tested by various case studies.

Transmission of electrical power from the generator to the load is a very important part of the electric power system. In the transmission system, it is necessary to increase the voltage to minimize power losses. The transmission system commonly used is High Voltage Alternating Current (HVAC). However, in reality the HVAC system can cause large losses. There are other transmission systems besides HVAC, namely High Voltage Direct Current (HVDC). The purpose of this paper is to compare the performance of HVAC and HVDC transmission systems in distributing electricity to variations in transmission distance or conductor line length and transmission voltage variations. The performance of the HVDC and HVAC systems measured is the power losses in the line conductors. In addition, power losses in transformer 1, transformer 2, and active power in HVAC. In addition, power losses at station 1, station 2, and active power at HVDC. The type of power plant used in this paper is renewable energy. The renewable energy consists of photovoltaic and wind power plants. The results for very long transmission distances, HVDC has smaller power losses than HVAC. In addition, HVDC stations have higher power losses than HVAC transformers. Based on the total power losses, overall the total power losses in HVDC is smaller than the total power losses in HVAC.

The ±1100kV Ultra High Voltage DC (UHVDC) is characterized by large capacity, long transmission distance and low losses. It is an effective solution to long-distance and high-capacity transmission, implement of “Power Delivery from West to East” and relief from the Eastern air pollution in China. Due to the high voltage, large transmission capacity and hierarchical connection mode of inverter stations, inevitably, the operation of ±1100kV UHVDC will have a tremendous impact on power flow distribution and stability of the eastern receiving-end grid. In this paper, combined with the theoretical characteristics of UHVDC, the system parameters and control model of a ±1100kV UHVDC is designed. Meanwhile, the DC steady stability, monopolar trip, bipolar trip and the effects on DC when AC system faults are simulated and analyzed in detail by PSD-BPA. The corresponding stability control strategy is identified, which provides information for construction of ±1100kV UHVDC and hybrid operation of UHV AC and DC in the future.

High voltage direct current (HVDC) consists of two converters working as a rectifier and inverter which are connected, through transformers and high voltage equipment, to two high voltage AC (HVAC) power networks. Such electrical infrastructures are spreading thanks to the advantages they offer and the possibility of overcoming the limits of the most widespread HVAC technology. The first operational HVDC system dates back to 1954, created between the island of Gotland in the Baltic Sea and the mainland (Sweden), with a power of 20 MW which has over time been replaced with a 260 MW bipole transmission system. Other plants, all using mercury vapor valves, followed over the years, including: in 1965, the connection of Sardinia with the continent; in 1970, the Pacific DC Intertie, connecting the Pacific Northwest region and Los Angeles, United States; in 1973, the Nelson River Bipole in Canada. Only since the 1970s, with the development of high voltage semiconductor converters, HVDC transmission systems, which had already proven indispensable for crossing long stretches of sea or for connecting electrical systems with different frequencies, began to show competitiveness also for the transmission of great powers over very long distances. HVDC allows the long-distance transmission of large quantities of energy and installation costs are compensated by lower losses (breakeven point around 600-800 km). They are very useful in case of marine connections: being able to cross long stretches of sea, unlike HVAC which has limitations dictated by the need to compensate for the capacity of AC cables. Moreover, HVDC allows the interconnection between big consumption centers and geographical areas in which we have large availability of renewable sources (see for example the three DC corridors, made up of underground cable of ± 525 kV, which in Germany are being laid for transfer sustainable energy from the north of the country to the south). Finally, by crossing two converters directly facing each other (BackToBack) it allows the connection of alternating current networks that are not synchronous with each other (e.g. the first at 50 Hz and the second at 60 Hz). Among the main advantages, environmental impact aspects must also be considered, including those relating to electric and magnetic fields. After an introduction related to HVDC technology, the seminar will highlight the innovative aspects that need to be considered in simulations and measurements in electric and magnetic fields, considering that there are new aspects such as high static currents and voltages which are not present in traditional HVAC infrastructures. In particular, a couple of topics of interest are represented by the measurement of the static electric field due to the high voltage connection between the valve room and the power cables and the measurement of the disturbances generated by the harmonics along the DC lines.

Ion flow field is an important aspect of high voltage direct current (HVDC) transmission lines. In this paper, we apply the upwind finite volume method for solving the ion flow field of three HVDC configurations to clarify the effect of the wind and the role of shielding conductors. For the monopolar configuration installation, the ground current distribution with underbuilt shield wires was studied numerically and experimentally. For the ±250 kV bipolar configuration, the calculated peak electric field and current density are verified with the values in a reference. The ±500 kV bipolar configuration is used to investigate the change in electric field and ion current within the same corridors of the existing HVAC lines. We analyze the ion flow field with and without the dedicated metallic return conductor (DMRC). In the absence of wind, the maximum of the electric field is lower than that of the HVAC lines and the current density is very low on the ground. In the presence of wind, the electric field and the current distribution become unsymmetrical on the ground level. The peak current density increases significantly on the downwind side. The HVDC line without DMRC has the electric field peak higher than that of the HVAC lines. With the higher wind shear coefficient, the peak of the electric field and the current density increases on the downwind side. Overall investigations summarize that DMRC can effectively reduce the peak of the electric field to be lower than that of the existing 500 kV HVAC lines under all wind conditions.