Direct Current Fault Protection

Electricity delivered by alternating current (AC) has a long and colorful history [1]. This method, which alternates the flow of electricity back and forth many times per second, has dominated the transmission and distribution system in the world for over a century. AC proliferation has been driven by the ease and lower cost of voltage conversion as compared to direct current (DC). However, DC electric power offers several benefits over AC, reducing system power losses due to improved electrical conductivity and utilizing fewer power cables with higher power carrying capacity (as shown in Table 1.1) [2, 3]. In addition, controlling of DC electric power could be easier since frequency and phase synchronization requirements are eliminated.

This chapter provides a brief overview of DC fault scenarios and fault detection and interruption technologies. A new classification of various DC fault interruption concepts, including simple mechanical means, solid-state circuit breaker (SSCB), hybrid circuit breaker (HCB), converter-based breakerless protection, and fault current limiter (FCL), is introduced, based on the fundamental topology and operation principle. Their advantages and disadvantages for different DC applications are discussed.

This chapter provides an overview of ABB’s recent technology development in solid state circuit breakers.

This chapter provides a brief overview of a new class of intelligent solid-state circuit breakers (SSCBs) using wide bandgap (WBG) semiconductors, referred to as iBreakers. The iBreaker concept explores the use of WBG switching devices in low-voltage (up to 1000 V), mΩ-resistance SSCB designs and new converter-based topology and control techniques beyond the conventional ON/OFF configuration to integrate intelligent functions. iBreakers adopt a distinct PWM Current Limiting (PWM-CL) state in addition to the standard ON and OFF states to facilitate soft startup, fault authentication, fault location, and selective coordination functions. Key design considerations, such as use of WBG switches, tri-mode operation, combined digital and analog control, and universal hardware/software architecture, are discussed in detail. Two iBreaker design examples, one rated at 380 V/20 A and based on GaN switches for data center applications and the other rated at 750 V/250 A and based on SiC switches for hybrid electric aircraft applications, are discussed in this chapter to highlight the iBreaker design methodology and functionality. Greater than 99.95% transmission efficiency, passive cooling, and μs-scale response time are demonstrated experimentally in both cases.

This chapter introduces the T-type modular dc circuit breaker (T-Breaker) for future dc grids. The T-Breaker has a scalable modular structure with locally integrated energy storage devices. T-Breaker is a paradigm shift from traditional solid-state circuit breakers (SSCBs). It has strong capability in limiting fault current, high tolerance to control signal mismatches during breaking events, and unmatched ancillary functions including power flow control, power quality improvement, and transient stability enhancement.

The growing technology of solid-state circuit breakers (SSCBs) has been reported as one of the driving factors in developing MVDC systems. This chapter deals with the capacitive couple-based transient current commutation technique in SSCBs. The state-of-the-art active injection circuits are introduced, and their applications in wide bandgap-based SSCBs are illustrated. In addition, the technology of capacitive coupling interface in transient current commutation is explained, and the advantages are highlighted. Along with developing mathematical investigations, MVDC experiments are also presented. Applying transient current commutation in SSCBs achieves a soft turn-off in the main switch during DC current breaking. Eliminating the transient power on solid-state switches and mitigating the gate voltage oscillations are two significant outcomes, which help to enhance the reliability and lifetime of the breakers in long term.

This chapter presents a brief discussion of solid-state dc circuit breakers followed by a description of the Z-source circuit breaker. The primary distinction of this breaker is that it automatically responds to a fault, not requiring fault sensing circuitry. This is accomplished by a Z-source impedance network which was introduced in the power electronics arena in the early 2000s. The basic principle of operation is described followed by popular variations that have appeared in the literature. Z-source breakers with coupled inductors are then illustrated. It turns out that the coupled-inductor versions have many advantages such as the ability to tune the sensitivity to a fault using the turns ratio and also require fewer passive components. Finally, the incorporation of the Z-source breaker into power converters is shown. Examples of a buck and boost converter with built-in Z-source breakers are presented.

This chapter presents the key design challenges for medium voltage solid-state circuit breaker related to the aviation hybrid electric propulsion applications. The technical approaches to address such challenges, including extremely high specific power, high efficiency, reliability, and high-altitude insulation capability, are explained in detail with a 2 kV 1.2 kA solid-state circuit breaker example design.

This chapter describes the design, simulation, fabrication, and characterization of a solid-state DC circuit breaker based on a normally-off, light-triggered, gallium nitride photoconductive switch combined with a cascaded, normally-on, silicon carbide junction field-effect transistor circuit leg. This design provides a very fast response time to fault events. Simulations of the various parts of the breaker and their predicted behavior in system designs have guided a first hardware demonstration. Circuit breaker voltage and current timing diagrams illustrate the interplay between different parts of the breaker and the sensitivity of the timing. The experimental performance closely matches the predicted behavior, allowing voltage and current scaling for future designs.

This chapter presents two recent projects performed at ABB within the area of hybrid circuit breakers where mechanical contacts have been combined with semiconductor components to increase the performance. The first project includes a traditional parallel hybrid topology that is utilized in a medium voltage fault current limitation application in an AC-distribution network where the functionality has been proven in field during a 2-year long trial. The second project uses small scale semiconductor components in a resonant configuration to create a local zero-crossing and enable DC-interruption in a mechanical contact system.

This chapter provides a brief overview of the development of a 6-kV/200-A hybrid circuit breaker for medium-voltage applications based on a concept of power electronically modulated transient commutation current injection (TCCI). The TCCI circuit in the parallel electronic path remains in a standby mode with near-zero power loss under normal conditions but can rapidly generate a counter-pulse current to force the fault current in the primary mechanical path to zero or near zero and therefore facilitate current commutation from the mechanical to the electronic path. The TCCI circuit then ensures a near-zero voltage and a small high-frequency AC ripple current condition for the main mechanical contacts to separate arclessly. Exhibiting ultralow on-state resistance by virtue of having no semiconductors in the primary conduction path, the topology achieves minimal on-state losses and greater than 99.97% efficiency. The HCB design also employs a specially designed high-speed actuator/vacuum contactor combination enabling sub-millisecond interruption as well as a modular MVDC power electronic interrupter (PEI) design in the electronic path.

The development goal for EDISON was to design and build a hybrid circuit breaker that minimizes the continuous power losses, limits the rate of rise of current during a fault at the earliest possible time, achieves sub-millisecond fault clearance, and minimizes maintenance requirements. EDISON consists of N submodules of insulated gate bipolar transistors (IGBTs) and metal oxide varistors (MOVs), a fault current commutation circuit (FC3), as well as a fast mechanical switch (FMS). The assembly of all submodules is also known as the power stack. The FMS is a new device based on a piezoelectric actuator that is integrated directly into the switching chamber, allowing switching speeds of less than 250 μs, while the on-state power losses are less than 0.01%. Supercritical CO₂ is used as the switching medium to enable high dielectric strength at unprecedented short contact travel, combined with outstanding heat transfer and low viscosity. Furthermore, EDISON introduces a new topology with no semiconductors in the main current path. Commutation of the current to the fault current commutation branch is achieved by a novel FC3 voltage source, which allows to substantially reduce steady-state losses compared to hybrid circuit breakers with commutation circuits in the main current path. A variable inductor in FC3, located in the main current path, holds the current flowing through FMS at a low level near the end of the commutation process. It allows the FMS to open and therefore to gradually establish the voltage withstand capability for the following MOV insertions while reducing the rate of rise of fault current. Finally, a new control scheme sequentially turns off the submodules as the dielectric strength between the opening contacts in the FMS increase. This control scheme dramatically reduces the peak fault current levels, enabling a more reliable, more cost-effective, and more power dense solution than comparable existing technology. The modular design allows to implement redundancy and reach the desired voltage and current ratings.

This chapter introduces a practical engineering application of hybrid circuit breaker (HCB) in detail. The 535 kV/25 kA HCB developed by Tsinghua University for Zhangbei flexible DC transmission project is one of the highest voltage class DC circuit breakers in the world. Every part of this HCB is introduced and key issues are analyzed. Finally, the engineering prototype passed the relevant inspection and is working fine in the grid.

DC fault current interruption speed, low on-state resistance, reliability, and efficiency are critical key metrics for DC circuit breakers. Mechanical breakers typically provide low on-state resistance via high-conductivity metal contacts but are relatively quite slow in their opening and closing operations. SSCBs have opening and closing times in the microseconds; however, their on-state resistance is quite high resulting in lower efficiency. Hybrid circuit breakers are a combination of both mechanical circuit breakers and SSCBs resulting in a circuit breaker solution that provides the best properties of both breakers individually. However, challenges exist in the coordination and control between the mechanical and electrical components of the hybrid circuit breaker. It is crucial to drive the current to zero through the mechanical breaker before opening to mitigate any chances of arcing forming between metallic contacts. Furthermore, it is very difficult to produce the significant forces required to move mechanical contacts while obtaining opening and closing times in the 100s of microseconds. This chapter will review hybrid resonant DC circuit breakers and present past and recent advances.

This chapter provides an overview on the potential benefits of gas discharge tube switches and circuit breakers as an enabling technology for medium- to high-voltage direct current power systems. High-voltage, high-power gas tubes are a recent development in a long line of proven gaseous electronic devices for power conversion and transmission systems that includes thyratrons and mercury-arc rectifiers and valves. In their present state of development, they are best suited for high-voltage (up to 500 kV), moderate-current (up to 1000 A) applications. Electrical opening and closing times are both fast (<5 μs), and the devices are compact and amenable to high-temperature operation. The device capabilities and critical design criteria are discussed with a view toward target applications that would appear to benefit from implementation of this technology. We also outline the key technical challenges to make gas tubes viable in various electric power system applications.

This chapter provides a brief overview of breakerless MVdc fault protection based on different power electronic converter topologies and fault controls. An MVdc breakerless architecture for a shipboard power system and the need for breakerless approach are also introduced. The comparisons between breaker-based method and breakerless approach are discussed at the end of this chapter.

The effective fault current limiting is very significant for the fault ride through of the dc system. This chapter provides a brief overview of dc fault current limiters (FCL), including directly installing dc reactors, superconducting FCL, and power electronic FCL. The technical requirements of FCL and the parameter configuration methods are analyzed in detail in this chapter. A classification of these FCL methods based on fundamental topology and operation principle is introduced with an extensive reference list.

This chapter provides a brief overview of SF₆ use in medium- and high-voltage gas-insulated electrical equipment and the outsized environmental impact of SF₆ which has prompted a decades-long search for alternative gases and gas mixtures. Section 2 summarizes the key gas properties required for gas insulators, the early SF₆ gas mixture alternatives that were considered, and the recent successes in the development and testing of gas mixtures based on 3 M’s Novec™ 4710 and Novec™ 5110 gas. Section 3 briefly summarizes the life cycle challenges associated with the use of SF₆, including leak detection and end-of-life disposal. Section 4 describes the hardware development of new electrical equipment when near drop-in SF₆ replacements are not possible or desirable.

Conventional SSCBs use transistors in an undesirable way—continuously dissipating power except during infrequent fault interruption throughout their service life. Conventional HCBs offer a relatively long interruption time that is limited by the finite amount of force applied to the mechanical contacts. Innovative solutions are needed to overcome these fundamental limitations for future DC grids. This chapter introduces a new series-type hybrid circuit breaker (S-HCB) concept as an example to stimulate other new fault interruption ideas. The S-HCB conducts its load current through metal wires instead of semiconductor switches and curtails its fault current to near zero throughout the entire opening process of a series mechanical switch. It offers the low on-resistance of conventional mechanical contacts for normal operation and μs-scale fault interruption speed which is even faster than fast-acting SSCBs.

This chapter covers a study of the medium-voltage direct current (MVDC) market, including the value proposition, market and segment opportunities, channels and barriers to entry, and speed of adoption. A variety of existing and promising MVDC markets are evaluated in the grid distribution, transportation, and commercial and industrial sectors. A regulatory framework is introduced, with guidelines and standards that will help shape emerging MVDC markets.