Transient Effect in Telephone Switching Circuits When Relay Windings are Disconnected

The disconnection of a relay in a switching circuit involves a number of time-variant design problems for which a quantitative treatment is needed. These mainly concern (/) the release time of the structure, or (ii) the transient current and voltage surges which are a potential cause of oscillations and breakdowns in the circuitry. The subject of release time is chiefly related to a change in the core's magnetization from its operated to its residual value, i.e., a very substantial change in core flux occurring over a comparatively long time, typically several milliseconds. The transient circuit surges tend to develop much earlier in the interval after disconnection, often in times from about 10-1' to 10~4 second during which the core's magnetization has not yet had time to change appreciably. Thus, while both phenomena are related to the core's demagnetization curve, their performance tends to be controlled by different features of this nonlinear characteristic. The subject of release time, including the design of slow release relays, has been on a firm quantitative basis for many years, 1 - 4 based on relationships involving the whole demagnetization curve. However, only qualitative or empirical treatments have so far been available to describe the transient surges of current and voltage. An analytical 2997