The traditional reliability of telecommunication systems that users have come to expect and rely upon is based in part on the systems'operation on redundant equipment and power systems. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to either equipment breakdown or loss of power, is unacceptable since it would result in a loss of millions of telephone calls and a corresponding loss of revenue.
Power distribution systems such as battery plants address the power loss problem by providing the telecommunication system with a secondary source of power, a battery, in the event of the loss of a primary source of power. Battery plants operate generally as follows. Each battery plant includes batteries, rectifiers, protection devices (e.g., circuit breakers or fuses), and other power distribution equipment (e.g., cabling). Due to the enormous size of the equipment, the batteries are generally located in a battery room, while the rectifiers are located in a power center, some distance away. The primary power source is produced by the rectifiers, which convert an AC line voltage into a DC voltage, to power the load and to charge the batteries. The primary power source may become unavailable due to the loss of the AC line voltage or the failure of the rectifiers. In either case, the batteries then supply power to the load. The protection devices provide protection from excessive current conditions caused by short circuits or other malfunctions, either in the load or in the battery plant.
Protection devices, such as fuses, are typically placed in the power center to protect the rectifiers from high current conditions. The failure of a particular rectifier due to an internal short circuit, for instance, trips the fuse, effectively isolating the failed rectifier from the system. The batteries, however, are not similarly protected. Failures in the distribution system, due to cable damage, for instance, may result in a short circuit across the batteries. Internal failures within the batteries may also result in a short circuit condition. Since the batteries are not protected, the high currents resulting from the short circuit may cause the batteries to become a fire hazard.
Accordingly, what is needed in the art is a protection device employable to protect the batteries in a power distribution system. Further, what is needed is an apparatus for detecting high current fault conditions (e.g., short circuits) in the batteries.