Telephone Central Office Power System Availability

Switching systems are specified as having a downtime of 2 hours in 40 years. Part of this downtime is attributable to the power system. If the power system contributes 10% of the allowed downtime, then the total power system must meet a downtime requirement of 1 hour in 200 years. This paper will look at the various parts of a telephone power system and determine a reasonable downtime based on failure and repair rates of the various components: 1) ac mains 2) ac standby 3) rectifiers 4) lead acid storage batteries The paper will consider several unusual complications of the power system over other systems with regard to availability as follows: 1) the batteries which provide a limited time reserve redundancy for other failures; 2) the repair rate for ac main recoveries and rectifier and ac standby equipment is not constant - an important factor when coupled with the limited reserve time of the battery; 3) a common fault could conceivably damage more than one rectifier at one time, resulting in a multiple failure; 4) ac standby and battery may fail and not be detected until it is needed.