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Internationally recognised standards by organisations such as ASTM and IEC are widely known and relied upon in all areas of engineering. One example in high voltage electrical engineering is the employment of standards giving material specifications to make decisions on the suitability of materials for a specific purpose. However, by their nature as reference documents, some of these standards lack reasoning and explanations about the derivation of the values stated. Others were written many years ago with only cursory updates being made at reviews since. [... ...] Standards relevant to silicone liquids used in CSE from the standpoint of theoretical and empirical research are discussed. This article aimed to identify and suggest reforms based on often unnoticed observations.

HVDC circuit breakers are of increasing importance, as multi-terminal high voltage DC (HVDC) transmission becomes a commercial reality. Multiple HVDC breaker technologies have been developed, and are starting to appear as proof-of-concept installations on real networks. Information about them is however distributed widely in the literature. This article describes the underlying challenges, the leading candidate solutions, and discusses the requirements and construction of the component sub-assemblies. Its goal is to provide a comprehensive overview of the field.

The aim of this study is the presentation of the results of an in-lab comparative study of electrical and thermal monitoring of artificially polluted, HTV-textured silicone rubber insulators, with different pollution levels. This work is a preliminary study of an in-situ monitoring of 400 kV SiR textured in a polluted environment. The results showed that the rms leakage current magnitude and pulses, and the average dissipated power depended on the pollution levels and the dry-bands formation. The discharge activity and their nature are governed by the pollution level and the voltage. A differentiation and a quantification between dry-band discharge onset and dry-band arc inception is highlighted.

Silicone oils are used in cable sealing ends owing to their combination of excellent dielectric properties, high oxidation resistance, and thermal stability. This paper aims to investigate how electrical stresses induced by sharp edges and protrusions inside the insulating device could lead to alterations in the chemical and dielectric properties of the silicone oil. Herein, electrical stress in the silicone oil samples is induced using a sonication technique. The physicochemical changes in the aged oil samples are analyzed using UV-vis spectroscopy, Fourier-Transform Infrared spectroscopy and dielectric response spectroscopy. The results provide experimental evidence that the proposed method can be adopted as an alternative method for reproducing the effects of electrical stress on oil samples.

This paper presents an experimental study on effects of moisture on partial discharge (PD) and breakdown characteristics of two silicone oils under AC stress. In this study, a needle-to-plane electrode configuration was employed to perform PD and breakdown tests in the silicone oils under three relative humidity (RH) levels, i.e. 5%, 30% and 90%. The experimental results revealed that as the RH is increased from 5% to 30%, the PDIV, PD magnitude and repetition rate and AC breakdown voltage do not change significantly. However, when the RH is further increased from 30% to 90%, it was found that both PD and breakdown characteristics are moisture dependent. The high RH results in a dramatic drop in the PD repetition rate. Compared to low RH oils, the 90% RH oil exhibits lower PD magnitudes and hence leads to a higher PD inception voltage; it, however, has higher PD magnitudes when applied voltage is increased, and as a consequence would have a lower breakdown voltage.

Silicone oils are widely used as insulating fluids in many high voltage applications, including cable sealing ends. However, the long-term effects of the service conditions on the properties of silicone oil are relatively poorly understood. Using a range of techniques, we report on the condition of ex-service silicone oils compared to new, unused oil and comment on the suitability of each technique for monitoring the aging process. Analysis of the oils will involve dielectric permittivity measurements, chemical analysis using mass spectrometry, two spectroscopic techniques, and viscosity measurements. We also consider the feasibility of obtaining accurate conductivity measurements: finite element simulations were used to analyze the effectiveness of a conductivity test cell.

In view of its widespread use in cable terminations, new results pertaining to electrical aging (i.e. exposure to repeated electrical discharge events) of silicone oil are reported. A new piece of equipment allowed the discharge characteristics to be controlled and the resulting blackening was correlated to the change in dielectric properties. End of life conditions were determined and the feasibility of a simple optical probe was explored. This could give the operator warning of when the oil is excessively aged, allowing remedial action to be taken.

This paper reports on a method combining the use of finite element simulations and external measurements to provide preliminary condition diagnosis of oil-filled cable sealing ends (CSEs) without requiring downtime. Good agreement has been obtained between the predictions from the electric field and thermal simulations and the measurements on a 132 kV oil-filled CSE. The electrostatic computation combined with electric field measurements can provide information regarding the electric field distribution inside the CSE and help in identifying potential issues with the CSE design, the materials or the cable termination process. The thermal computation combined with thermal imaging can reveal potential problems, such as high resistance connection to the busbar, and provide information regarding the cooling efficiency of the liquid dielectric. The method presented can provide the starting point for prioritizing maintenance operations on CSEs.

Two key problems in meshed high-voltage direct current (HVDC) transmission grids are managing line power flows and protection against dc faults. Current flow controllers (CFCs) will be required to balance cable currents in meshed dc grids, in order to prevent individual line power capacity limits restricting overall power flow in the grid. Direct current circuit breakers (DCCBs) will be also required to protect HVDC grids from dc faults. This paper demonstrates that the current flow controller functionality can be added into a hybrid CB's design. This paper proposes integrating an interline CFC into the load commutation switch (LCS) of a hybrid DCCB. The integrated design LCS/CFC is analyzed and a state-space model is derived. The control of the CFC is designed and the performance of the LCS/CFC during normal operation is verified by means of MATLAB Simulink and PSCAD simulations. A comparison of the integrated LCS/CFC and the separate design is given. The case studies show a reduction in total power losses, and improved protection operation times can be achieved.

This paper presents two insulation solutions for an AC to DC power transmission line conversion. The purpose is to maximise active power of both solutions, by maximising voltage. The method includes High Voltage Direct Current (HVDC) scheme selection, insulation dimensioning for HVDC energisation in polluted environments and switching surge overvoltage clearance calculation.

Existing polymeric cable sealing end (CSE) typically contain silicone oil as an insulating liquid between the cable core and the outside of the CSE. In recent years, a number of performance issues have been identified with silicone oil filled CSEs. To understand the reasons for the observed behavior of silicone oil, a range of characterization methods are reviewed, to allow investigation of the influence of moisture, potential chemical contaminants and the compatibility with CSE materials. The water content of all the oils studied was above the limit given in IEC 60836 (2015) for new silicone oil. There is no significant difference between the moisture content, whether the oil is used in CSE or new. Neither did the Fourier infrared (FTIR) spectroscopic analysis show difference between the oils. Preliminary results from gas chromatography connected to mass spectrometer (GC/MS) clearly show structural differences between unused expired oil and new oil samples particularly that species suspected to be cyclic siloxane appear to be present in the expired sample.

Circuit breakers for High Voltage Direct Current (HVDC) are seen as a required technological step in the development of HVDC grids. The development of several new HVDC circuit breaker prototypes indicate that this step may be achieved in the years to come. In order to facilitate the installation of HVDC circuit breakers, appropriate standards and tests need to be developed. These tests and standards must ensure that the technology is capable of functioning as required. In cases where direct testing cannot be carried out, a synthetic test circuit is used to recreate the conditions of the power system. Voltage testing envelopes are used to define the specification of these synthetic test circuits for Alternating Current (AC) circuit breakers. A similar concept can be applied to fault currents in HVDC networks, allowing specifications for HVDC synthetics test circuits to be defined. Testing envelopes which encapsulate the fault currents are analytically shown in this paper and compared to detailed simulations of faults in a VSC HVDC system. Testing envelopes can be drawn for a range of converter topologies in point-to-point and multi-terminal applications. Taking into account the large power electronic elements in the recently developed HVDC circuit breakers, discussion is given to the definition the worst case fault for a HVDC protection system. This paper demonstrates that a terminal fault is not necessarily the worst fault scenario for HVDC circuit breaker.

HVDC transmission systems using voltage source converters (VSC-HVDC) have been identified as an attractive solution for bulk power delivery over long distance. However if DC grids are to be built using this technology, fast DC circuit breakers are needed. This work proposes a new hybrid DC circuit breaker utilizing a series connected coupled inductor connected, which enables automatic current commutation from the mechanical switch to the semiconductor switch during a fault. The key advantage of the proposed DC circuit breaker is that the current in the mechanical switch automatically reduces to zero when a fault happens. This paper focuses on comparison of different mechanisms to commutate the current from the mechanical switch to the semiconductor switch and create a zero current for the mechanical switch. Three types of hybrid DC circuit breaker topologies including proactive hybrid DC circuit breaker, hybrid DC circuit breaker with commutation booster, and hybrid DC circuit breaker with coupled inductor for a 500 kV HVDC system are simulated and compared using Matlab/Simulink. A prototype hybrid DC circuit breaker with coupled inductor is designed and built. The prototype is capable of interrupting 200 A direct current within 4 ms. The automatic current commutation compensates for the fault detection and location time in the selective protection scheme, which provides faster fault current interruption.

Direct current (DC) circuit breakers are a key enabling technology for fault management in multiterminal high-voltage DC (HVDC) systems. DC fault isolation is challenging due to the high rate of rise of the fault current and the lack of natural current zero-crossings found in ac systems. In this paper, we present a novel superconducting hybrid dc circuit breaker that utilizes the intrinsic characteristics of the superconductor material. The automatic quench of the superconductor coil as a result of a high fault current transfers the current from the mechanical switch to the semiconductor switch. The isolating mechanical switch is able therefore to open at low current and recover its dielectric capability rapidly. A low voltage DC circuit breaker prototype has been built using a multistrand magnesium diboride (MgB 2) coil, a vacuum interrupter, and an insulated-gate bipolar transistor module. This prototype successfully demonstrated interruption of 500 A DC within 4.4 ms. This paper presents the design of the superconducting hybrid breaker prototype and a detailed analysis of the experimental results. This superconducting hybrid dc circuit breaker has significant potential for scaling up the high-voltage and high-current applications.

High-voltage direct current (HVDC) grids will require the development of dc protections that provide fast fault isolation and minimize the disturbance caused to the existing ac power networks. This paper investigates how the dc fault recovery performance of a half-bridge modular multilevel converter (HB-MMC) is impacted by different dc protection design choices. An HB-MMC point-to-point HVDC system that is protected with dc circuit breakers (CBs) is simulated on a real-time digital simulator using detailed switch models of the converters and switch gear. A dc CB controller has been developed and implemented in a software-in-the-loop fashion, and has been made available free for download. A novel blocking scheme for the HB-MMC is proposed, which limits the prospective dc-side fault current, benefiting dc switch gear. A comparison of circulating current controllers shows that the standard d — q controller is likely to be unsuitable for fault studies. Finally, benchmarking shows that a 48% reduction in power-flow recovery time and a 90% reduction in the energy dissipated in the circuit breaker can be achieved, along with other benefits, depending on the protection design.

Medium voltage direct current (MVDC) distribution networks have been considered for various applications, such as offshore wind farm collector systems, all-electric naval vessels, and aircraft. MVDC circuit breakers are a critical technology to directly manage faults in multi-terminal DC (MTDC) networks. However, DC current breaking is much more challenging than in AC systems because there is no natural zero-crossing of the current waveform to aid fault isolation. This paper reviews existing MVDC circuit breaker technologies and also discusses their advantages and disadvantages. This paper also introduces new topologies that can be applied in MVDC applications. The operation of several hybrid DC circuit breaker topologies with aided commutation is included. The paper illustrates that a hybrid DC circuit breaker with aided commutation can clear a fault within 2–5 msecs with low losses, this shows great potential for future MVDC applications. The implications for the practical design of commercial MVDC circuit breakers are also discussed.

The development of High Voltage Direct Current (HVDC) protection technology is a necessary step in the development of high power Voltage Source Converter (VSC) transmission grids. Presently, only a few industry prototypes have been developed for VSC HVDC grid applications[1-3]. However, before any piece of equipment can be installed, it must be subject to testing to prove it is capable of working. These tests are based upon operational experience and/or theoretical analysis of the system it is to be placed in. To date, no VSC HVDC circuit breaker is in commercial operation. Developing knowledge around the testing of the circuit breaker is an important step on the road to HVDC grids. This paper discusses the impact of traveling wave phenomena on the testing of HVDC circuit breakers for VSC applications, derives theoretical calculations to describe the phenomena and compares this to PSCAD simulations of a VSC under DC side pole-to-pole faults.

High Voltage Direct Current (HVDC) short circuit protection is a fundamental requirement for any HVDC transmission system. Presently, all point-to-point links are protected using circuit breakers on the AC side of the converters. In order to enable HVDC grids, a more advanced protection system must be developed. HVDC circuit breakers are one solution for the protection of future HVDC grids. Several designs have been proposed for DC circuit breakers but few are suitable for Voltage Source Converter (VSC) applications. To date, only a few industrial prototypes have been developed, which are seen to be suitable for the VSC HVDC applications. This paper presents analysis and simulations on one of these prototypes, the Proactive Hybrid Circuit Breaker (PHCB). Equations are derived from a state-space analysis of the circuit breaker. A model of the circuit breaker is suitably parameterized for a +/− 300 kV VSC system in PSCAD. Fault simulations are then performed and compared to the equations developed in a state space analysis. Discussion is then given to the design and testing of the Load Commutation Switch (LCS).

The use of VSC-HVDC grids for offshore wind farm integration will require the use of dc breaker systems and they, at present, will require dc reactors to limit the rate of rise of fault current. The introduction of large dc reactors throughout a VSCHVDC system can have significant impact on its stable operation and will require additional control. This paper analyses this problem and proposes a PSS-like control (DCPSS) to aid dc grid stability and cope with this effect. A generalized analytical model for studies on dc voltage control is presented. Key stability and transient performance issues caused by the use of the dc reactors in a multi-terminal system, are investigated by analyzing poles, zeros and frequency responses of both open-loop and closed-loop models. Design and location identification methods for the DCPSS are provided. Excellent damping enhancement is achieved by this controller. The analytical studies and time-domain simulations in this paper are performed based on two VSC-HVDC models.

Voltage-Sourced Converter (VSC) HVDC is attracting significant attention as the UK tries to meet its renewable energy targets. However, compared with the traditional Current-Sourced Converter (CSC) HVDC, VSC-HVDC is more vulnerable to DC faults due to the lower DC side impedances and more sensitive power electronics used in its construction. This paper investigates the equivalent two-level converter system response under a pole-to-pole fault. A three-terminal VSC-HVDC system is developed in PSCAD/EMTDC to evaluate the system fault response and to verify theoretical analysis. Based on the results, it is found that the AC grid will initially contribute relatively little to the DC fault current seen by the DC side circuit breakers during a pole-to-pole fault. The converter fault recovery strategy has also been studied in this paper. It is found that after successful operation of the hybrid DC circuit breaker, with the aid of bump-less transfer control, the DC system has a good voltage recovery response. The contribution of this paper is that it gives an improved understanding of the system response and offers some guidance for the design of DC protection systems.

Voltage Source Converter (VSC) HVDC transmission is receiving significant attention as the UK is trying to meet its renewable energy targets. However, VSC-HVDC is more vulnerable to DC faults compared to more traditional CSCHVDC transmission techniques, due to the low DC side impedances and sensitive power electronics within the converters. This paper investigates the two-level converter system response under different fault scenarios, i.e., pole-to-pole and pole-to-ground faults. A point-to-point two-level VSC-HVDC system was developed in PSCAD/EMTDC to evaluate the system fault response and to verify the theoretical analysis. The study details the system response of the DC side and AC side to pole-to-pole and pole-to-ground faults. The paper details parameters which are considered to be fundamental in the design of a DC protection system. This work is sponsored by National Grid.

Multi-terminal Voltage-Sourced Converter (VSC) High Voltage Direct Current (HVDC) transmission is expected to play a key role in future power transmission grids. Compared with AC transmission, DC transmission is more vulnerable to faults due to the lower DC side impedances and sensitive power electronics used in the converters. DC protection issues must be solved before any multi-terminal VSC-HVDC grid can be established. In terms of DC protection, apart from using a DC circuit breaker to interrupt and isolate a DC fault, a Fault Current Limiter (FCL) may be employed to limit the fault current. FCLs could potentially form an important part of any future DC protection system. This paper investigates such a FCL. The main contribution of this paper is that, the resistive type superconducting FCL (SCFCL) is modelled in detail to perform DC protection with the ABB hybrid circuit breaker, in a high fidelity four-terminal VSC-HVDC system model. The simulation results show that the SCFCL has great potential to be employed for DC protection.