Advances in power relay design

Power relays have come a long way in the past 30 years, writes Ian Purcell of Matsushita.

In electrical terminology a "power relay" can cover a wide range of products.

At one end of the spectrum it may describe a 3A simple contact device, and at the other cover a major power breaker used to isolate a complete substation output.

Some 30 years ago the ubiquitous "Modern relay technology" handbook written by Hans Sauer of SDS Relais, described a power relay as one that was "for use with contact loads equal to, or greater than, 10A", and this is probably as accurate a definition as any other that has been made.

Power relays have a number of salient areas where technology has made inroads during the past few decades.

A typical power relay in the 1970s would have taken a fairly large amount of space to house.

Typically designed around an octal terminal base (similar in style to a thermionic valve base) such relays were, by today's standards, very inefficient.

Coil operation wattage's were expressed in high figures, generally mains voltage driven and emitting tens of degrees of heat into the surrounding ambient temperature.

Contacts were usually silver based and prone to unreliable switching action and wear.

Through the work of pioneering figures in the relay industry, such as the aforementioned Hans Sauer, the power relay has evolved through a number of stages to become a technically advanced component of modern electrical circuits.

Alongside these technical advances are the benefits of more cost effective product both in initial cost and the ongoing benefits of high reliability produ