1
ANALYSIS OF POWER QUALITY OF SUPERCONDUCTING FAULT CURRENT LIMITER WITH IGBT IN RECTIFIER WITH HVDC CIRCUIT BREAKERS
SHANTANU
Mel Electrical Engineering Jabalpur Engineering College Jabalpur
1. INTRODUCTION
In order to achieve commercial application of future Multi Terminal HVDC (MTDC) networks, typically considered an optimum solution for renewable energy transmission and power grid inter- connection, the reliability of HVDC systems must be guaranteed [1], [2].
Conventional point-to-point HVDC systems can be sufficiently protected via mechanical circuit breakers located on the AC side [3]; however, a selective coordination protection scheme that isolates faulted lines should be utilized in MTDC to prevent the blackout of the entire grid system [4]. HVDC circuit breakers (HVDC CB) are widely considered a key technology in the implementation of the MTDC system [5].
Generally, fault current interruption can be easily achieved via zero-current crossing. While AC circuit breakers can interrupt a fault current in natural zero current, artificial current zero should be implemented for DC breakers to enable fault current interruption.
To fulfill the zero-crossing condition of DC fault current, a forced current reduction method should be utilized, and various type of HVDC CB are summarized in [6], some of which have revealed prototypes and successful test results. Nevertheless, an effective and reliable solution considering massive fault energy during DC fault interruption is still lacking. Existing DC current breaking topologies focusing solely on methods to achieve artificial current zero should be somewhat modified [7]. As an alternative, one feasible solution is to combine fault current limiting technologies with DC breaking topologies.
In this work, we investigated application studies of resistive SFCL on the various types of HVDC CB in order to estimate the effects of combining fault
current limiters and conventional DC breakers. Resistive
SFCL have been acknowledged as an effective solution to effectively limit fault current levels by absorbing electrical and thermal energy stresses during fault [8]. In this light, the combined application of SFCL and HVDC CB could be an attractive alternative solution capable of drastically decreasing the dissipated fault energy and improving the performance of HVDC CBs
1.1 High-Voltage Direct Current
A high-voltage, direct current (HVDC) electric power transmission system (also called a power super highway or an electrical super highway)[1][2][3][4] uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems.[5] For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links.
HVDC allows power transmission between unsynchronized AC transmission systems. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz. This improves the stability and economy of each grid, by allowing exchange of power between incompatible networks.
The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden (ASEA) and in Germany. Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, and a 100 kV, 20 MW system
2 between Gotland and mainland Sweden in 1954.[6] The longest HVDC link in the world is the Rio Madeira link in Brazil, which consists of two bipoles of ±600 kV, 3150 MW each, connecting Porto Velho in the state of Rondônia to the São Paulo area. The length of the DC line is 2,375 km (1,476 mi).
1.1.1 High Voltage Transmission
High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current. Since the power lost as heat in the wires is proportional to the square of the current for a given conductor size, or inversely proportional to the square of the voltage, doubling the voltage reduces the line losses per unit of electrical power delivered by a factor of 4.
While power lost in transmission can also be reduced by increasing the conductor size, larger conductors are heavier and more expensive. High voltage cannot readily be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment.
Transformers are used to change the voltage levels in alternating current (AC) transmission circuits. Because transformers made voltage changes practical, and AC generators were more efficient than those using DC, AC became dominant after the introduction of practical systems of distribution in Europe in 1891[8] and the conclusion in 1892 of the War of Currents, a competition being fought on many fronts in the US between the DC system of Thomas Edison and the AC system of George Westinghouse.[9] Practical conversion of power between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, semiconductor devices as thyristors, integrated gate-commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT).
1.2. History of HVDC technology 1.2.1 Electromechanical
Schematic diagram of a Thury HVDC transmission system HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower voltage for transmission to
distant cities from Manitoba Hydro generators. Bipolar system pylons of the Baltic Cable HVDC in Sweden The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted.[11]
This system used eight series- connected generators with dual commutators for a total voltage of 150,000 volts between the positive and negative poles, and operated from c.1906 until 1936. Fifteen Thury systems were in operation by 1913.[15] Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss. Various other electromechanical devices were tested during the first half of the 20th century with little commercial success.[16]
1.3.Voltage-Source Converters (VSC) Voltage-source converters (VSC) Widely used in motor drives since the 1980s, voltage-source converters started to appear in HVDC in 1997 with the experimental Hellsjön–Grängesberg project in Sweden. By the end of 2011, this technology had captured a significant proportion of the HVDC market. The development of higher rated insulated- gate bipolar transistors (IGBTs), gate turn-off thyristors (IGBTs) and integrated gate-commutated thyristors (IGCTs), has made smaller HVDC systems economical.
The manufacturer ABB Group calls this concept HVDC Light, while Siemens calls a similar concept HVDC PLUS (Power Link Universal System) and Alstom call their product based upon this technology HVDC MaxSine. They have extended the use of HVDC down to blocks as small as a few tens of megawatts and lines as short as a few score kilometres of overhead line.
1.4.Disadvantages
The disadvantages of HVDC are in conversion, switching, control, availability and maintenance. HVDC is less reliable and has lower availability than alternating current (AC) systems, mainly due to the extra conversion equipment. Single-pole systems have availability of about 98.5%, with about a third of the downtime unscheduled due to faults. Fault-tolerant bipole systems provide high availability for 50% of the link capacity, but availability of the full capacity is about
3 97% to 98%. The required converter stations are expensive and have limited overload capacity. At smaller transmission distances, the losses in the converter stations may be bigger than in an AC transmission line for the same distance.The cost of the converters may not be offset by reductions in line construction cost and lower line loss.
Operating a HVDC scheme requires many spare parts to be kept, often exclusively for one system, as HVDC systems are less standardized than AC systems and technology changes faster. In contrast to AC systems, realizing multiterminal systems is complex (especially with line commutated converters), as is expanding existing schemes to multiterminal systems.
1.5.High-Voltage DC Circuit Breaker HVDC circuit breakers are difficult to build because some mechanism must be included in the circuit breaker to force current to zero, otherwise arcing and contact wear would be too great to allow reliable switching. In November 2012, ABB announced development of the world's first HVDC circuit breaker. The ABB breaker contains four switching elements, two mechanical (one high-speed and one low-speed) and two semiconductor (one high-voltage and one low-voltage). Normally, power flows through the low-speed mechanical switch, the high-speed mechanical switch and the low-voltage semiconductor switch.
The last two switches are paralleled by the high-voltage semiconductor switch.
Initially, all switches are closed (on).
Because the high-voltage semiconductor switch has much greater resistance than the mechanical switch plus the low- voltage semiconductor switch, current flow through it is low. To disconnect, first the low-voltage semiconductor switch opens. This diverts the current through the high-voltage semiconductor switch.
Because of its relatively high resistance, it begins heating very rapidly
2.CIRCUIT BREAKER
A miniature or molded - case circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent or overload or short circuit.
Its basic function is to interrupt current flow after protective relays detect a fault.
Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.
The generic function of a circuit breaker, RCD or a fuse, as an automatic means of removing power from a faulty system is often abbreviated to ADS (Automatic Disconnection of Supply)
Fig.2.1 Circuit Breakerelectronic Symbol
2.1.Operation
All circuit breaker systems have common features in their operation, but details vary substantially depending on the voltage class, current rating and type of the circuit breaker. The circuit breaker must detect a fault condition; in common mains and low voltage circuit breakers, this is usually done within the breaker itself. Circuit breakers for large currents or high voltages are usually arranged with a protective relay pilot devices to sense a fault condition and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate power source, such as a battery, although some high- voltage circuit breakers are self-contained with current transformers, protective relays, and an internal control power source. Once a fault is detected, the circuit breaker contacts must open to interrupt the circuit; This is commonly done using mechanically stored energy contained within the breaker, such as a spring or compressed air to separate the contacts.
4 Fig.2.2 An Air Circuit Breaker For Low-
Voltage (Less Than 1,000 Volt) Power Distribution Switchgear
2.2 Arc Interruption
Low-voltage miniature circuit breaker (MCB) uses air alone to extinguish the arc. These circuit breakers contain so- called arc chutes, a stack of mutually insulated parallel metal plates which divide and cool the arc. By splitting the arc into smaller arcs the arc is cooled down while the arc voltage is increased and serves as an additional impedance which limits the current through the circuit breaker. The current-carrying parts near the contacts provide easy deflection of the arc into the arc chutes by a magnetic force of a current path, although magnetic blowout coils or permanent magnets could also deflect the arc into the arc chute (used on circuit breakers for higher ratings).
The number of plates in the arc chute is dependent on the short-circuit rating and nominal voltage of the circuit breaker. In larger ratings, oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.[4] Gas (usually sulfur hexafluoride) circuit breakers sometimes stretch the arc using a magnetic field, and then rely upon the dielectric strength of the sulfur hexafluoride (SF6) to quench the stretched arc. Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact material), so the arc quenches when it is stretched a very small amount (less than 2–3 mm (0.079–0.118 in)). Vacuum circuit breakers are frequently used in modern medium-voltage switchgear to 38,000 volts.
2.3.Short-Circuit
Circuit breakers are rated both by the normal current that they are expected to carry, and the maximum short-circuit
current that they can safely interrupt.
This latter figure is the ampere interrupting capacity (AIC) of the breaker.
Under short-circuit conditions, the calculated maximum prospective short circuit current may be many times the normal, rated current of the circuit. When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the current to continue. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further continuation of the arc, or creation of additional short circuits, potentially resulting in the explosion of the circuit breaker and the equipment that it is installed in.
Therefore, circuit breakers must incorporate various features to divide and extinguish the arc. The maximum short- circuit current that a breaker can interrupt is determined by testing.
Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset. Typical domestic panel circuit breakers are rated to interrupt 10 kA (10000 A) short-circuit current. Miniature circuit breakers used to protect control circuits or small appliances may not have sufficient interrupting capacity to use at a panel board; these circuit breakers are called "supplemental circuit protectors" to distinguish them from distribution-type circuit breakers.
2.4.High-Voltage Circuit Breakers High-voltage switchgear Three single phase Russian 110 kV oil circuit breakers 400 kV SF6 live tank circuit breakers 72.5 kV hybrid switchgear module Electrical power transmission networks are protected and controlled by high- voltage breakers. The definition of high voltage varies but in power transmission work is usually thought to be 72.5 kV or higher, according to a recent definition by the International Electrotechnical Commission (IEC). High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers. In substations the protective relay scheme
5 can be complex, protecting equipment and buses from various types of overload or ground/earth fault.
High-voltage breakers are broadly classified by the medium used to extinguish the arc.
Bulk oil Minimum oil
Air blast
Vacuum
SF6
CO2
Due to environmental and cost concerns over insulating oil spills, most new breakers use SF6 gas to quench the arc. Circuit breakers can be classified as live tank, where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential. High-voltage AC circuit breakers are routinely available with ratings up to 765 kV. 1,200 kV breakers were launched by Siemens in November 2011,[8] followed by ABB in April the following year.[9]
High-voltage circuit breakers used on transmission systems may be arranged to allow a single pole of a three-phase line to trip, instead of tripping all three poles;
for some classes of faults this improves the system stability and availability. High- voltage direct current circuit breakers are still a field of research as of 2015. Such breakers would be useful to interconnect HVDC transmission systems.
2.5. Carbon Dioxide (CO2) High-Voltage Circuit Breakers
In 2012 ABB presented a 75 kV high- voltage breaker that uses carbon dioxide as the medium to extinguish the arc. The carbon dioxide breaker works on the same principles as an SF6 breaker and can also be produced as a disconnecting circuit breaker. By switching from SF6 to CO2 it is possible to reduce the CO2 emissions by 10 tons during the product’s life cycle.
Fig.2.3. 72.5 kV carbon dioxide high- voltage circuit breaker
3 INTRODUCTION TO MATLAB
Matlab is a high-performance language for technical computing. The name mat lab stands for matrix laboratory. It integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation. Typical uses include Math and computation Algorithm development Data acquisition Modeling, simulation, and prototyping Data analysis, exploration, and visualization Scientific and engineering graphics Application development, including graphical user interface building.
Matlab is an interactive system whose basic data element is an array that does not require dimensioning. This allows you to solve many technical computing problems, especially those with matrix and vector formulations, in a fraction of the time it would take to write a program in a scalar no interactive language such as C or FORTRAN.
3.2. MATLAB and engineering:
MATLAB was first adopted by researchers and practitioners in control engineering, Little's specialty, but quickly spread to many other domains. It is now also used in education, in particular the teaching of linear algebra and numerical analysis, and is popular amongst scientists involved in image processing. However, many researchers mostly from Computer Science background feel that MATLAB should be used only for mathematical analysis necessary in image processing and not for implementation of image
6 processing software. Moreover, MATLAB should not be used to simulate computer architectures, systems software and computer networks unless while solving some numeric problem.
Toolboxes in Matlab:
Simulink
Fuzzy
Genetic algorithm
Neural network Wavelet
3.3 Simulink:
Introduction:
Simulink is a software add-on to mat lab which is a mathematical tool
developed by The Math
works,(http://www.mathworks.com) a company based in Natick. Mat lab is powered by extensive numerical analysis capability. Simulink is a tool used to visually program a dynamic system (those governed by Differential equations) and look at results. Any logic circuit, or control system for a dynamic system can be built by using standard building blocks available in Simulink Libraries. Various toolboxes for different techniques, such as Fuzzy Logic, Neural Networks, DSP, Statistics etc. are available with Simulink, which enhance the processing power of the tool. The main advantage is the availability of templates / building blocks, which avoid the necessity of typing code for small mathematical processes.
Concept of signal and logic flow:
In Simulink, data/information from various blocks are sent to another block by lines connecting the relevant blocks. Signals can be generated and fed into blocks dynamic / static).Data can be fed into functions. Data can then be dumped into sinks, which could be scopes, displays or could be saved to a file. Data can be connected from one block to another, can be branched, multiplexed etc. In simulation, data is processed and transferred only at discrete times, since all computers are discrete systems. Thus, a simulation time step (otherwise called an integration time step) is essential, and the selection of that step is determined by the fastest dynamics in the simulated system.
Fig 3.1 Simulink library browser 4. MODELLING OF TEST-BED, SFCL AND HVDC CBS
4.1 HVDC Test-bed Model
In order to analyze the impact of SFCL on various types of HVDC CBs, a test-bed model was designed in Matlab /Simulink as illustrated in Fig.5.1. The simple, symmetrical, monopole, point-to-point, 2- level, half-bridge HVDC system was utilized to concentrate the interruption performance of the DC fault current in detail. The AC network adjacent to the HVDC link was substituted by an equivalent RL impedance, which enabled the X/R ratio of the power system to be determined. The converter transformer was a wye-delta connection. A phase reactor, Lp, was added between the converter and transformer to filter the harmonics during conversion. Each type of HVDC CB and SFCL was located at the output of the rectifier. Detailed specifications of the HVDC link are as follows: the rated voltage = ±100 kV, nominal current = 1 kA, nominal power flow = 100 MW, and the transmission line length = 50 km.
Fig. 4.1. 2-level point-to-point HVDC test-bed model (Vac: AC voltage, Rac, Lac: system impedance of AC, Lp:
Phase reactor)
7 4.2. Resistive Superconducting Fault Current Limiter
The resistive SFCL, which is based on the
quenching phenomena of
superconductors, has been an area of great interest for researchers in the last decade [9], and several prototypes have been developed and installed in medium- and high-voltage systems [10].
Focusing on the theoretical approaches for a resistive SFCL [11], the quenching phenomena of SFCL can be expressed as:.
𝑅𝑆𝐹𝐶𝐿 𝑡 =
0 1 < 𝑡𝑞𝑢𝑒𝑛𝑐 ℎ𝑖𝑛𝑔 𝑅𝑚(1 − exp(−𝑡/𝑇𝑆𝐶)) 1𝑞𝑢𝑒𝑛𝑐 ℎ𝑖𝑛𝑔 < 𝑡 (1) whereRm is the maximum quenching resistance, and TSC is the time constant for the transition to the quenching state.
In this work, the SFCL rating was 100 kV DC with a 2 kA of critical current. The maximum quenching resistance, Rm, is 10 Ω. Until now, there is no practical applications of DC SFCL.
4.3.Arc Modeling
The representative HVDC CB topologies are categorized as follows: mechanical CB (MCB), passive resonance CB (PRCB), inverse current injection CB (I-CB) and Hybrid DC CB (HDCCB) [15]. Except for the non-arc type such as inverse current injection and Hybrid DC CB, the implementation of arc dynamics is a major concern in the design for an accurate simulation model. The black-box arc model, which represents the arc dynamics by calculating the differential equation of the arc conductance, was designed.
5.4.Hybrid DC CB (HDCCB):
This scheme is widely considered as the optimal concept for interrupting DC fault current, was designed as illustrated in Fig. 4(d) [21]. The delay times of IGBT was assumed as ΔtIGBT = 6 μs in simulation.
When a DC fault occurs, the auxiliary DC breakers (ADCB) and fast disconnector are opened sequentially, then the current starts to commutate from the main path to secondary path. After commutation, main DC circuit breakers (MDCB) in secondary path are opened, and total current is reduced because the current flows to the snubber circuit of MDCB until the parallel-connected SA trips.
When the voltage across the HDCCB terminals exceed to knee voltage, the SA ignites and forces the DC fault current to zero by absorbing remaining fault energy.
Finally, a RCB opens and isolates the DC fault.
Fig. 4.2. HVDC CB models: the (a) Mechanical CB (MCB), (b) Passive resonance CB (PRCB), (c) Inverse current injection CB (I-CB), and (d)
Hybrid DC CB (HDCCB).
5.SIMULATION ANALYSIS AND DISCUSSION
Transient fault simulations were conducted to analyze the effects of SFCL with additional active and reactive power changes with using the IGBT deviceon various HVDC CB types. Each type of HVDC CB, both with and without SFCLs, was applied at the sending end of the test- bed. The prospective maximum fault current without any protection devices was 14.7 kA in the previous test-bed.
We proposed the model in existing one , with the active and reactive power changes with using the thyrister device like IGBT.
Simulink Model
Fig 6.1 Simulink of MCB and SFCL Model
8 Fig 6.2 MCB and SFCL Inverter Station
2
Result Comparison Table
Paameter WITH MCB
&SFCL Without IGBT
WITH MCB
&SFCL With IGBT
Current Limiter 14.7 KA 4.9 KA Reactive power NA Generating
3.8kVAR
6. CONCLUSION
This thesis is based on the different circuit breakers simulation based on the using and effect SFCL with used rectifier with IGBT device . andfound the active and reactive power changes for the existing system. This paper deals with the impact of SFCL on various types of HVDC CB. We can see the effect of these thing and abou the active and reactive power changes by designed using Matlab/Simulink.
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