Tension Ertzeietako Medioa DC Kiretrukeen Mota eta Aplikazioak

Tensione medioaren DC konputxenak oso egokiak dira itsasontziak, hiriko metroetan, tren elektrikoetan, mikrotxorretan (auto elektrikoetan), banatutako generazioan (energia eguzkiaren bidez) eta bateri-en baseko sistemak (datu-zentroetan) aplikatzeko.

Kontsultarako zirkuituaren impedantzia txikia DC kasuan short circuiten amplitud handiagoak eragiten ditu. Gainera, transformadoreen bobinak ez dutelarik laguntzen denbora konstante orokorrari DC sistemetan, denbora konstante orokorra murrizten da eta short circuitak milisegundo askotan gertatu daitezke. Tensionaren kolapsua ere gertu daiteke, non DC tension nominalaren gutxienez 80% mantentzea voltage source converter (VSC) estazioak normalki funtzionatzeko baldintza prestatua izan behar baita.

Konbertagarrien lanbideen eragin txikiagatik, akatsa milisegundo askotan kendu behar da, bereziki lineaz edo kablearekin ez datorrelako estazioetan.

Mercatuko dagoen tensione medioaren DC konputxen motak:
LVDC eta MVDC merkatuetan garrantzitsuak diren hiru motatako konputxenak daude: solid-state circuit breakers (SSCBs), mechanical circuit breakers (MCBs) eta hybrid circuit breakers (HCBs) SSCB parallelan ultra-fast mechanical switch (UFMS) batekin.

Air eta SF6-based LV eta MV AC MCB arruntak DC irabazi-konplexu bat dute, baina soilik kilovolt eta ampere batzuei mugatuta dagoena.

Solid-state tensione medioaren DC konputxenak:
SSCB-en topologiak tipikoki Integrated Gate Commutated Thyristors (IGCTs), Gate Turn-Off Thyristors (GTOs) edo Insulated Gate Bipolar Transistors (IGBTs) seriean konektatuta dauden arren. Erantzun-denborak oso azkarak izan arren, albo batzuei dagokionez, VSC estazioaren galderen 15-30% ingurukoa da.

Osagaien kostu altuak, galvanik isolamendu falta, eta termika absorbatzaile kapasitatea ados ez dela beste desberdintasunak dira.

Irudi 1-k solid-state tensione medioaren DC konputxen diseinu bat erakusten du:

Irudi 1: a) IGCT-based medium voltage bi-directional solid-state circuit breaker, (b) IGCT-based medium voltage bi-directional solid-state circuit breaker, (c) GTO-based bidirectional solid-state circuit breaker

Proposatutako SSCB-en topologiak desberdinak dira. Hala ere, gehienak ≤ 1 kV tenperaturatan, batez ere ≤ 1000 A korrontean. Kontuan hartu behar da SSCB teknologiaren aspektu trinkoena ondoan dauden galdera altuak direla, eta hainbat artikulu MV SSCB baten MV tenperatura maila betetzen duela esaten dutenak, batez ere ≤ 1000 A rated currenttan, baina beharrezkoa den indarra MWen artean edo hamarrekin bat egin dezakeen kapasitatea izango litzateke 3 paralelo modulutan (3P:3*3.72 MW).

Beraz, etorkizunean MVDC arkitektura baten 10 MWtik behera dagoen DC CB garatzea bakarrik ez da erabilgarria. Uneko semikonduktore teknologiak ezin dituzte horiekin bat etorri; ondorioz, etorkizunean MVDC arkitekturak SSCBek ez dute kostu-ezarpen efiziente eta kompakta emango. Horrek esan nahi du multzu aire handiak eta aktibo urra egokitzea bezalako indarrak behar direla multi-kilowatt mailako ondoan dauden galdera espero direnen korronte altuenentzat.

Hybrid medium voltage DC circuit breakers (HCBs):
Hybrid medium voltage DC circuit breakers include a current conduction path and a current interruption path.

Hybrid breaker combines the exceptionally low forward losses of a pure ultrafast switch with the quick performance of a solid-state breaker in the parallel path. The main breaker is positioned on a parallel path and is made up of a series and parallel solid-state switches that are connected in series.

A developed a modular HCBand one module as shown in Fig. 2 with rated voltage and current, and a current breaking capability of 6.2 kV, and 600 A, respectively.

It’s worth noting that the ultrafast switch’s arc chamber simply needs to generate enough voltage to communicate the current and facilitate the paralleling philosophy of the modules. In all SSCB and HCB designs, a residual current disconnector (RCD) and a shunt resistor to measure the current shown in Fig. 2 is needed. When the current dumps to a low value specified by the leakage current of the metal oxide varistor (MOV), the disconnector opens, isolating the system and preventing any leakage current through the semiconductors and MOV.

Fig 2: Hybrid medium voltage DC circuit breaker

The main path’s UFMS just needs to generate a high enough voltage to commutate the current to the parallel full IGBT breaker. The resistance of the auxiliary DC breaker, Rdson at 2 kA, and the fast mechanical switch need to be less than 20 mW to have similar characteristics as an electromechanical circuit breaker. Utilizing UFMS in the main path results in lower on-state losses and forward voltage than a full SSCB.

The proposed design can be beneficial over the high voltage HCBs manufactured by ABB and Alstom, because (1) there is no on-state semiconductor loss, (2) its control circuit will be simpler, and (3) the expensive “Power Electronic Switch” in the main path, can be avoided. Indeed, only one UFMS can substitute both the “Power Electronic Switch”, and the fast disconnector proposed by ABB for the main path.

However, it needs to ensure that UFMS contact resistance is no more than equivalent electromechanical contacts and has the withstand holding force capability of 4.45×10-7 I2 N (i.e > 178 N for 10x in-rush at 2 kA rated with safety factor 2x or 356 N).

Ultrafast Mechanical Switch in medium voltage hybrid DC circuit breaker:
The challenges for realizing the mentioned philosophy are (1) whether such ultrafast switches can be developed for MV levels, (2) whether the buildup of the arc voltage for commutation is sufficiently high, and (3) whether the same design is possible for RCB. The answer may be YES for all questions as discussed below.

Electromagnetic Thomson coil (TC) actuators operating based on attractive or repulsive forces between current-carrying conductors are very suitable for fast switching because they can achieve high accelerations through precise control. So far, two techniques based on TC have been proposed and well-elaborated for ultra-fast mechanical switches, where the one with series coils outperformed the one based on induction in terms of efficiency.  These two techniques were also compared by Multiphysics finite element modeling.

A single phase 12 kV (nominal voltage) and 2 kA (nominal current) / 20 kA (short circuit) fault-current limiting circuit breaker (FCLCB) and 24 kV, 3 kA / 40 kA FCLCB enabling the arc to be extinguished without any forced arc cooling within 100-300 μs were designed, built.

The induction-based fast switch with a rated current of 7 kA accelerates an HCB contact of ~2 kg with an initial acceleration of ~44,900 m/s2 that results in 4 mm contact separation after ~422 μs, enough to withstand a rated switch voltage of 3 kV .

This fast motion should be damped at the end of travel to prevent over-travel, bounce, fatigue, and other undesirable effects.