270-VOLT DC CONTACTOR Solves Cost vs Performance Problems Aircraft requiring greater electrical power for an increasing num­ ber of critical electri.cal loads are employing 270Vdc power. But to make, break or change the connection of elec­ tric circuits for the high voltage poses а signifi­ cant challenge for the manufacturers of relays and contactors. Various solutions exist, but one contactor technology succeeds in resolving ail of the obstacles: weight, high heat, safety, cost and performance. ID]Access lntelligen(e he "more electric aircraft" is rapidly evolving. New aircraft designs are increasingly forsak­ ing heavy, maintenance-intensive and T (in combat} vulneraЫe hydraulic and pneumatic subsystems in favor of elec­ trohydrostat ic actuators (EHAs). EHAs, which comblne electric and hydratIlic power, are control systems designed to enhance aircraft performance while reducing weight Ьу eliminating miles of tuЬing, pumps and valves required for aircraft with traditional controls. Тhese subsystems generally have built-in test capabllity and require much less maintenance than hydraulics and pneumatics. For commercial carriers that means less aircraft downtime, and for military aircraft, а shorter logistics tail. Electrics for control surfaces, such (alternating cu rrent). But АС power has appl ications, which are not weight- or its own limitations. For example, mul­ size- sensi tive. For instance, scaling tiengine aircraft wotIld require mtIltiple up АС techno logy to accommodate power generators, and this posed the electrohydrostatic acttJators in place proЫem of either coordinating frequen ­ of hydratJlics and pneumatics isn't а cies, or tJsing t:he alternating current viaЫe option. On, say, а Boeing 737, from the generators for separate and converting to EHAs and sufficiently isolated busbars-not an elegant soltJ­ enhancing the existing 60-kilo-volt ­ tion! DC power, which is constant, does ampere (kVA) fixed frequency per not require devices that synchronize channel would рrоЬаЫу cause power power sources, which is why applica­ , generati on and distribution to Ье tions such as fuel cells, solar power heavier and much more costly. The systems, and electric & hybrid vehicles viaЫe option is to employ 270 volts DC other than in aviation also are turning power derived f rom variaЫe frequency more and more to high -voltage DC. АС generators. АС voltage in its raw form still is used for nonessential systems оп board aircraft; however, it doesn't meet the requirements of EHAs, etc., which demand sufficient power delivery that is consistent and highly controlled. The as flaps and ailerons, are the most demanding and critical, but Previous Sealing Technology other subsystems require greater electrical power, as well. Forexample, air condi­ tioning in the caЬin and rotor Ыаdе deicing оп а helicopter. lt all adds up to а much greate demand forelectrical power: 270 volts DC (direct current), electrical power is more effi ­ cient in achieving this greater electrical demand. With this, less total energy is required from the aircraft engines. Add to this the fact that this greater power at 270Vdc results in smaller wires, and it becomes readily apparent how high- High-voltage 270Vdccontactors were first used оп the lnternational Space Station. High-vo ltage DC is now employed in the F-22 combat aircraft and will Ье used increasingly in the Joint Strike Fighter. Тhе Airbus External Coil Economizer Magnels Weid Metal Сап Green indictates area within the ernclosure Green in,d ctates агеа withinlhe endosure Left dr·awing Ceram1c envelope- Costly, large, ancl li ard to shape. All o1,s1 tor higl1 pressu-r e 1nternal gases tог optimal SN ' itching. Auxiliary contacts are not оп main armature and coil economizer must Ье outside voltage DC contributes to opti- thes ea le d enc ols u r e _ mizing the power-to-weight Right Drawing 1:роху Seal- Large, less rugged, lo\ er temperature rated, ar1d caлnot use hydrogengas ratio of an aircraft. tог optimal s1,it1ch1ng. Aux1l1 ary cont acts are not оп ma1 n arn1ature and co1l econorn 1zer 1s outs1de tl1e sealed enclosure_ Growing Demand for Power Applications of high -voltage DC power at 270 volts and higher are not new and go back as far as Тhomas Edison , himself. Trains and industrial facilities have long used high-voltage DC. Air­ craft have used DC power since World War 11, but the onboard generation and distribution has been limited to 28 volts for mалу years. When larger, commercial airliners entered the skies in the early 1960s, the demand for power became greater, and to avoid the consideraЬle weight of larger 28Vdc generat ors and саЫеs, air­ craft began using 115volts, 400Hz АС more electric aircraft, therefore, relies more and more on high-vo ltage DC. DC power also provides an addi­ tional advantage for aircraft that have onboard batteries, which are employed as redundant power sources, should the primary source fa il. DC powercan Ье used to charge the batteries, with no need to convert the voltage from АС to DC, as was required in the past. Corn:actor Applications The challenge, however, has been to adapt to aircraft the high-voltage DC power long enjoyed for ground-based АЗВО is intr oducing high-voltage DC to the commercial marketplace and the Boeing 787 makes much greater use of this power source. Future aircraft on the drawing board will take the use of 270 volts DC to an even higher level. The trend is obvious. Challenge in Contactors However, this trend posesa challenge to the manuf'acturers of contactors that must switch the power. (Contac­ tors аге similar to electrical relays but are larger and have the higher over­ load rating needed for most critical aircraft components.) Any агс that occurs when switch­ produce an impervi- ing DC current must somehow Ье extinguished. The higher the voltage, chamber. Ceramic mate­ rial, used to produce contactors for the lnter­ national Space Station, the more difficult this is to achieve. (The proЫem does not exist when switching АС because the voltage passes through zero volts every cycle; hence any агс is quickly extin­ guished automatically.) Most ground-based applications of high-voltage DC haven't had to face the challenge because, in managing the higher voltage, they do not have tors, which аге not sealed and allow the heat generated from the discharge of an electric arc. Тhese contac tors аге large and heavy, employing агс chutes, ог baffles, that split the elec­ tric агс into metal plates to reduce the voltage. (Тhе агс in а contactor is an electrical discharge through а gas producing the voltage drop required to EPICm Ceramic Header Weld Coil Economizer (Optional) сап seal off all types of gases accompanying the arc, including hydro­ gen, which is the best gas to break а high­ voltage DC current (see cha rt). But ceramics also сап Ье cost prohiЬi­ tive; it initial ly takes on to Ье concerned about the contactor's weight and size. Light rail systems, therefore, сап use open-air contac ­ New Higher-Performance EPIC Technology ous ce ramic, switching Magnets Metal Сап Green indictates area within the enclosure а semi-liquid f orm, so making an exact -shaped EPIC Ceramic Header Lo1•1 cost. rugged, h1gh temperature chamber to manage the rated ceramic header allo10/s high pres.sure internal gases tor opt1 mal s>N1 tching Aux1l iary coпtacts аге оп maIn armatureand arccan Ье tricky. The coil economizer is l'riH1inthe sealed enclosure. chambers don't always plastics. lt allows the use of high ­ come out as planned. An alternate solution is with an ероху sealed contactor аnd use of high-temperature plastics in the агеа pressure gases and remains small in size and weight. Called ЕР1стм (Extended Performance lmpervious interrupt t he cu rrent.) Contactors f or aircraft must closely maлage and seal the агс to prevent that manages the arc. While much less expensive, this type of con tactor has its own limitations. The seal is not as good as ceramic, so the contactor Ceramic), this new technology has been applied to а high-voltage con­ tactor design over the past two years interference, yet also provide DC switching at an ассерtаЫе heat level and Ье small, lightweight and reason­ cannot use hydrogen gas, which pro­ vides the best switching environment for 270 volts DC power management. aЫy priced. ln an attempt to provide these features, various technologies have been employed. AII have limita­ tions-except one. And the ероху seal is temperature­ limited (to about 150 degrees С) and susceptiЫe to failure in severe over­ current situations . ture plastics inside for the arc man­ agement . No thick layer of ероху is Other Desigrns The EPIC™ Solution Contactors for aircraft must Ье sealed to prevent electrical leakage and interference, and the electric arc must А new sealing technology exists that produces а contactor comЬin ing the required, yet the EPIC contactor has а seal sufficient to contain high-p res­ sure gases such as hydrogen. Ье isolated, as well as the magnets that move the arc. One solution is to benefits of high -temperature sealing quality 0·1ceramics with the low cost arc management of high-temperature Gas and Contact Material Performance Comparisons for Switching Applicati ons Н2 N2 Application (Нydroge11) (Nitrogeп) Copper Moly/Gopper Copper Moly/Copper Contacts Better Fair Сапу Only BEST Good But IIU1il guud " 11ll ЩJl) I But 1юt11 guud ,Ш::i ct ll w pp t: 1 Make Only Life Make& Br eak Life Verv High Overload Make& Br eak Good Вut not as good as Moly/ Co pper Good Вut not asgood as Moly/ Copper Good В111 11ut 1lli uud as Muly/ Cupµei BEST Fair Fair Fair But 1юt нs youd as Moly/Cupp• 1 EPIС Вenefits Тhе EPIC high-voltage DC contactor provides all the benefits of an all-ceramic c ontactor but at less than ha the weight and about one-tenth the cost. Specifi­ cally, it offers the following advantages over other high -voltage contactors: • The inert gas in the controlled environment of а sealed switching Better Better contactor therefore сап Ье made smaller and lighter and аЫе to oper­ ate with less coil powerthan with But not as good as Moly/Copper BEST high-voltage relays. The EPIC high-voltage DC contac­ t or includes а ceramic header t hat is welded to а can with high-tempera­ chamber will not cause oxidation, and this allows the use о! low resis­ tance copper contacts. With the excellent conductivity of copper, the Better But not as good as Moly/Coppe1 BEST Ьу aircraft electrical component and equipment manufacturer Leach lnter­ nati onal and GIGAVAC, а maker of other metals. • The low leakage of the contactor's ceramic seal, compared to ероху, means all types of gases, includ­ ing highly desiraЫe hydrogen, can Ье used for high-current int.em1p ts. lt also allows various comЬina­ tions of different gases and contact materials, to accommodate difficult switching app lications . • The new contactor has а higher temperature rating than contactors sealed with ероху. lnitial EPIC tech­ nology products are rated at 175 degrees С, but а header can reach well over 250 degrees С with out damage to the seal or risk of fail ure. • With а higher temperature rating, there is much less risk of а contac­ tor failure or а fire, should а down­ stream circuit breaker fail in an abnormal over-current situation. • The thinner seal leaves room in the contactor for built-in, dou Ые-t hrow, auxiliary contacts that are driven off the same armature as the main con­ tacts, and for а cutthroat, dual-coil economizerwhen required. (With the epoxy-seal contactor, the auxiliary contact is а secondary activated micro switch and the economizer is located outside the chamber.) ЕР/С11• 1 is а regbl ered trademar!r o f GIGAVAC . А Collaborative Effort This ncxl geneг11tioп o'l lнgl1-,·ol tagc DC co вt ac tors ,\11\s joiпt l y de \'elopcd Ьу Le11 11 l11 te1ш 11 ioпn l. c oнsidcгe,i tl1e ··1'a tl1eг" о( a rospc1c c гciays. 11 B11e na r aгk. Cali J:-based di,·1sio п ol' E steг line. a11 d GI GA\' AC. co пside гed toda·y s е, ре гt 111 l1iglн ollн ge rela ys. b11scd ш S11ntп Ва1· Ьп п1. Calit: А long гelп lioпs h ip lн1s o.,1sted ,1111ong 0ГГ1с ш ls ш t hc rwo co111 p«nie s. L.ea 11 1 пt e rп пt юn n l 1s п mпт 1Гас t11 ге r or elcc t гica l ро\\'с1· d1stг' 1b11 Lion а ·se111Ь11es a nd c o n1pon cn l s. s1.1c l1 пs relп ys a nd co11t <1c tors. a11d or Г:0111l1 с штс пt dctec­ to rs. 1 t ma nt1 (,1ct11 гсs co m pone n ts tо г Yп r1011 s пpp licn t юпs. 1 пcl11d1 пg lo,Yc1· ­ c u гrcn t _70\"dc so l1d st.1L c 1-c lays а nd роv. с г con t rollc r:; Го1· 270Ydc switc hin g. То pl'Odt1cr п п a lTo гd r1Ыe. l igh1wc-ig1Jt. l11gl1-\'ol t,1gc co11t r1c t ш Гог n1il1 ta гy пnd пе rоs рпсс пpp l1Cп tio11s tl1 пl с а п ,11,; onш юci a tc 0Уе1· 1 0 t1111t' S g1· cпl cr а111 рсгп gе. Le11c l1 tеп111е,1 \vith GI GAYAC. Tl1e tеп1н th eп de, ·elopr d th c E.,tcnded Pcгro r­ n1п nc e I m peп 'io11 s Ccm111 ic 1E Pl C r" ) tec h 11ology llн н сн n Ьс 11scd witl1 t11gh­ Yol1п ge DC р о1\I СГ tlн ll res ol, ·c-s tl1 e р гоЫсп 1s оГ ,,·eigh t. sп Гсt у. l11gl1 h e11t п nd c ost wh1 lc 1111 pг,o, in g peгГol'llш ncc . 1 • l n addition to increased coil effi­ ciency, the cutthroat, dual-coil economizer сап Ье used to increase coпtact pressure s in order to gain additional contact current -carrying capabllities. They also сап Ье used to offset larger returп springs to handle higher coпtact current, make or break, fault conditions. ogy coпtactors for 270 volts DC. The contactors meet all military and aero­ space standa rds. Accord ing to the companies that jointly developed the EPIC techпol­ ogy contactor, the first airvehicle to use the new contactors will Ье Early Uses an unmanned air vehicle (UAV). ln addition to use in aircraft, potential applications forthe 270 volts DC contactors range from missiles to Extensive qualification testing has been completed on the EPIC technol- naval ships to а hybr id Humvee for the U.S. Army.
