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The New Zealand Railways Magazine, Volume 13, Issue 5 (August 1, 1938)

Remote Control of … — Substations on the Wellington Electrification

page 60

Remote Control of …
Substations on the Wellington Electrification.

The ground equipment of the Johnsonville electrification forms an integral part of the major electrification scheme which will extend to Paekakariki through the Tawa Flat tunnels.

To supply power to the overhead contact wire between Wellington and Johnsonville—8 3/4 miles of contact wire being made alive for the Johnsonville service—two substations are in operation, one at Khandallah just north of the railway station, and the other at Kaiwarra.

Both these substations are breaking down and rectifying stations and draw power at 11,000 v. from the Public Works Dept.'s substation at Khandallah, the feed to Kaiwarra being via the Tawa Flat line.

The electrical energy is received from the Public Works Dept. as alternating current and it is rectified to direct current in the two railway substations, and thence fed through circuit-breakers to the overhead system for propelling the trains. The two substations are designed to operate unattended and a feature known as automatic load control is installed at both places. In simple language automatic load control causes extra rectifier units to be brought into service when the power consumption increases beyond the capacity of the rectifiers actually working at the time. This happens in peak traffic periods, mainly in the mornings and evenings when extra trains are running to convey people to and from their places of employment. As the demand for power decreases with the passing of a peak period, the reserve rectifier units are automatically switched out of use.

In addition to the switching done by the automatic load control a system of supervisory control of all substations is provided, whereby the whole of the Wellington electrification system will be managed from a control room in the railway main substation on Waterloo Quay. In the meantime the operator requires to manage only the Khandallah and Kaiwarra substations, both of which are rectifier substations equipped with automatic load control. Later on, when the whole system is in use there will be rectifier substations at Porirua, Plimmerton, Pukerua and Paekakariki, and a transformer substation at Glenside, all under the supervision of the Wellington operator. All these substations will be unattended and the one at Pukerua will have the automatic load control feature, similar to Khandallah and Kaiwarra.

In the control room at Wellington—which is staffed whenever there are electric trains running, that will be continuously when the whole scheme is in use—is a mimic diagram of the main connections at all of the substations, and corresponding to every circuit breaker is a small key switch on this diagram. The illustration shows the control desk bearing the diagram on the top.

The supervisory system—or “Centrovisory,” as the manufacturers, Messrs. A. Reyrolle, call it—has two functions, (a) It indicates to the operator in the control room the state of all circuit breakers—closed or open. Associated with each circuit breaker on the control diagram is a red and a green lamp and when illuminated the red means “closed” and the green means “open.” If a circuit-breaker at any substation opens or closes through any cause then the diagram immediately shows this. In addition, if the control operator did not cause the change to take place—that is to say, if a circuit breaker opens due to a fault, or is operated by hand, then an audible alarm is sounded and the operator must acknowledge this by depressing a key-switch, which stops the alarm.
The control desk bearing the diagram.

The control desk bearing the diagram.

(b) The second function is that the operator may open or close any circuit-breaker. The equipment functions on a principle similar to an automatic telephone exchange, each switch or unit of equipment being treated as a subscriber. If the operator wishes to close a circuit-breaker at Khandallah he presses the selection key on the mimic diagram corresponding to this circuit-breaker. This causes the equipment to select the circuit-breaker required just as dialling a number selects a wanted subscriber on the telephone. As the operation is required to be very reliable the equipment then automatically checks the selection of the unit required and if correct a white lamp alongside the selection key lights up and tells the operator that a connection has been established with the circuit-breaker required. He is then free to either close or trip the circuit-breaker with another key and when it changes the indication given by the red and green lamps changes as already described.

When any additional rectifier units are brought into operation or shut down by the automatic load control the operator receives notice of these changes by the indications of the red and green lights on the mimic diagram and is therefore kept advised of what is going on.

Ample protection is provided whereby any faults, short-circuits or other dangerous conditions which may arise, automatically cause the circuit-breakers concerned to trip, or open, thus cutting off the power and the remote control system in no way qualifies or otherwise affects this feature.