EATON 25RBA4-100E Type RBA4 Class E Standard Speed Expulsion Fuse Refill Unit, 100 A, 25.5 kV, Glass Epoxy

EATON renewable RBA or RDB fuse unit is not totally discarded after it interrupts a fault. This makes the RBA quite economical to use over time. Normally, only the fuse refill is discarded with the RBA design. The RBA power fuse provides performance characteristics especially intended for power system protection up to an operational voltage of 34.5 kV. Because RBA fuses are available in a wide range of continuous current ratings and time current characteristics, close fusing can be achieved, maximizing the protection and overall coordination. The quality and accuracy of the RBA design and manufacturing process ensures accurate initial and ongoing melting time current characteristics. Proven RBA power fuses perform as intended and operate exactly when and how they should, and do not operate when they should not operate. This is a subtle but important point. Each individual RBA fuse component is discussed individually. Its makeup and unique role in the protection process are also discussed. The internal parts of an RBA refill Unit are a calibrated current responsive fuse element and a parallel high strength strain element, an arcing rod, an auxiliary arcing rod assembly, and a solid boric acid liner which assists with the interruption. The lower end of the fuse element is attached to an end cap which is securely crimped onto the lower end of a glass epoxy refill tube and the upper end is brazed or securely crimped to the main arcing rod. The upper end of the tube permits the upper end of the arcing rod to exit the refill tube through a molded plug. At the upper end of the refill Unit, the plug is sealed around the arcing rod where it exits from the refill tube. The lower end of the refill Unit is sealed with a blowout disc to maintain the integrity of the seal in RDB outdoor applications. The seal must be removed before an exhaust control device is fitted to a fuse holder for indoor applications, to prevent clogging the exhaust control device. The calibrated fuse element assembly determines the operational time current characteristics of the RBA fuse. It is sensitive to the heat produced by the amount of current flowing. How, when or if it melts for different magnitudes of current and amounts of time, a particular current magnitude experienced by the fuse is indicated on the specific time current characteristic curve for a particular fuse. RBA fuse elements are available in standard and time-lag configurations. The standard element assemblies are made of pure silver with a parallel Nichrome strain wire, and the time-lag elements have a calibrated tin alloy joint. The Nichrome wire relieves the fuse element of any strain put on it by the spring loaded arcing rod. This parallel high resistance vaporizes immediately after the fuse element melts. The heavy copper cylindrical arcing rod is contained within the main bore of the boric acid liner and performs two functions. Under normal operating conditions, it carries the continuous rated current of the fuse. when the fuse element melts during a fault interruption, the acing rod lengthens the arc as it is pulled through the boric acid liner. This backward movement occurs because the arcing rod is under spring tension from the outside of the refill. An auxiliary arcing rod is contained within the small bore of the boric acid liner. It plays a role in the proper operation of the fuse under low intensity fault conditions. No load current is carried by the auxiliary wire.