E-T-A joins the high flyers

Citation

(1999), "E-T-A joins the high flyers", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 4. https://doi.org/10.1108/aeat.1999.12771daf.002

E-T-A joins the high flyers

E-T-A joins the high flyers

Keywords: E-T-A, Circuit breakers

Combat aircraft in operation can put great demands on their on-board equipment as well as on the pilots flying them. The stresses which can be experienced during acrobatic-style manoeuvres, or when particular systems are activated or de-activated can present a particular challenge for components, especially those with moving parts. Circuit breakers for the protection of electrical power distribution systems are one such item.

Circuit breakers specially designed for this purpose are widely used by aircraft manufacturers to operate at very precise conditions of overcurrent. This prevents the destruction of wiring and components in the protected circuit and minimises the smoke and fire risks that overheating can cause. Such overcurrents may be due to intermittent faults. By resetting the circuit breaker button the circuit can be immediately re-powered if desired.

The manufacturing consortium comprising British Aerospace, and its German, Italian and Spanish partners, looked to E-T-A to provide the reliability, quality and performance needed for the circuit protection requirements for the Eurofighter -- or Typhoon (Plate 1) as it will be marketed in some territories - which is one of the world's most advanced combat aircraft. Two circuit breaker models in particular, the E-T-A 483 and the E-T-A 583, have reportedly already stood the test of time in service with the Panavia Tornado as well as British Aeorospace Hawk and Sea Harrier aircraft (Plate 2). These products now have proven in-service reliability extending over 20 years. Since their introduction these circuit breakers have been subject to continuous development to provide significant performance improvements over the earlier versions. For example life expectancy is double the original figure, which in turn was double the life expectancy of earlier circuit breaker designs on the market. The ability to withstand random vibration, be unaffected by temperature variations and still operate within the stated specifications were crucial to BAe design engineers when selecting E-T-A products to protect the vital power distribution systems within the aircraft.

Plate 1 Eurofighter/Typhoon

Plate 2 E-T-A 483 and 583 circuit breakers for equipment (CBEs)

The 483 and 583 CBEs are single pole and three-pole temperature compensated aircraft circuit breakers respectively. With the addition of the latest version, the 483 range now extends from 1A up to 35A offering the smallest package on the market for higher ratings. A high tolerance to sudden current surges is in-built, reducing the risk of nuisance operation, and enabling an optimum match of cable size to circuit breaker rating with weight and cost saving benefits.

Both circuit breaker models have a tease-free operating mechanism ensuring that the contacts open and close with a snap action. This reduces arcing between the contacts, minimises the feed-back of power spikes into the circuit, and reduces contact surface damage and contact resistance problems which can occur with other circuit breakers which may be teased closed. This feature is particularly relevant at 28V DC and significantly reduces the risk of contact welding.

The E-T-A circuit breakers also feature a two-chamber construction which physically separates the active and compensating bimetals from the switching contacts. This avoids any danger of cross-contamination. Without this separation, heat from the contacts could influence the bimetals leading to performance fluctuations, and any soot or deposits from operation of the contacts (particularly at high overcurrents) could contaminate the bimetals. Furthermore, heat transfer from the bimetals to the contacts is also avoided.

The springs, which provide the contact pressure, are thermally isolated from the contact by an insulating barrier. Heat produced by the contacts will not be conducted to the springs thereby ensuring stable contact pressure. This feature avoids a potentially dangerous thermal cycling problem caused by heating of the contacts which results in a loss of spring pressure, leading to increased contact resistance, in turn leading to further build up of contact heat. In this event the cycle can continue until the contact resistance becomes so high that the circuit breaker loses continuity. This phenomenon may be aggravated by contact surface irregularities such as pitting which can develop over a period of time. However, in the 483 and 583 this effect is itself reduced by the tease free design.

The significant performance advantages of the E-T-A aircraft circuit breakers, which these design features provide, include a particularly high resistance to physical shock and vibrations, especially the random vibration which can occur in high performance aircraft. They also possess the ability to withstand the effects of a wide temperature variation between -55úC and +125úC. Their electrical short circuit and overcurrent protection capability will also meet the more demanding requirements of state of the art aircraft such as the Eurofighter/Typhoon.

The World Wide Web site www.etacbe. com offers further information on E-T-A and its products.

Details from: E-T-A Circuit Breakers Ltd, Tel: +44 (0)1296 420336; Fax: +44 (0)1296 488497.