BEHIND THE SWITCH

Hauraki Plains Gazette, Volume VLI, Issue 3416, 4 December 1935, Page 7

BEHIND THE SWITCH

TIRELESS WATCHERS OF THE: ELECTRIC SERVICE.

The control of the modern electric power transmission lines embodies many features which are little known or appreciated by the general public, which is concerned more with the continuity of the electric supply than with the means taken to maintain efficient service. The control of the power station at the Waitaki hydro electric works represents the most modern and up-to-date methods of power distribution, the ideas and inventions of men during the past century. The automatic cutting out of faulty lines to prevent line trouble from affecting good lines is usually carried out by small instruments called “line protective relays” which are constantly in service, and act as sentinels to give the alarm when wrong conditions appear. These relays set in operation the mechanism which opens the main switches and cuts the line affected out of service. In the case of the main transmission lines from the Waitaki Hydro power-house to Glenavy, these lines are protected by relays, so that correct switching is done automatically and accurately under varying conditions. These relays are fitted on switchboards in the control room at the power-house and work in conjunction with supplementary relays at the IGlenavy sub-station. Externally these important instruments appear as a number of small black boxes mounted together on vertical polished slate-panels. Whilst at first glance apparently not very important, they represent the result of many years’ experience and developments by electrical engineers in many parts of the world. Some of the functions of these line relays are as follows:—They prevent excessive load on the transmission lines from causing damage either to the lines themselves or the transformers arid other equipment connected to such

lines. The relays are adjustable so that they can be set to operate on a predetermined amount of load, and will allow an overload to continue only for a limited time. If the fixed period is exceeded the relays immediately cause the main switches to open, and thus clear the line for investigation. Other abnormal conditions will be cleared instantaneously by the relays, for instance, in the event of a line breaking and connecting to the ground, or when the flow of power in the line is reversed. It is possible to have indications of faulty conditions appear on a “healthy line” due to trouble at another part

of the transmission system, and in such a case the relays will instantly discriminate between the apparent and the real faulty section and bring about the necessary switching operations to clear the fault. The required action is produced in a small fraction of the time which would be taken by any person, as such a person would naturally need a short period of time in order to deduce the actual position of the trouble. The action of the relays can be adjusted to meet the requirements of a number of different types of faults, and hence keep a constant watch on the maintenance of efficient electrical service. In a somewhat similar manner the generating

machines and transformers are protected by these “relays” of a different type which cause faulty conditions to be brought to the notice of the men in charge in the control room and also cause operation of the necessary switches to take place and protect the plant from serious damage.

We wonder how many realise the ideas, inventions, and time expended in thinking out these masterpieces of human machinery to bring an ample supply of power to every home, every minute, every hour, day in and day out. These tireless watchers of a faithful service give warnings, and prevent serious accidents to ensure a constant supply of power for every user from “behind the switch.”