Electrical Supply.

Arrangements were made to obtain supply from the Public Works Department's substation at Khandallah at 11,000 volts, in order to feed the Railway substation at Khandallah, the balance of the supply for the line being supplied from the Kaiwarra substation, which is fed by an alternative 11,000 volt line via the Tawa Flat tunnels.

The substation equipment consists of 11,000 volt armour-clad switchgear, supplied by Messrs. Reyrolle and Company, for the purpose of connecting the 11,000 volt supply to the transformers and rectifiers. The supervisory and remote control equipment was also supplied by Messrs. Reyrolle and Company.

For the purpose of converting the 11,000 volt alternating current supply into 1,500 volt direct current to drive the multiple units, converting apparatus consisting of transformers and glass-bulb rectifiers was installed. The glass-bulb rectifiers were supplied by the Alliance Electrical Company, Ltd., Wellington, on behalf of their principals, the Hewittic Electric Company, Ltd. These rectifiers work in pairs, each bulb being capable of supplying continuously 300 k.w., so that a pair of rectifiers can continuously supply approximately 800 h.p. These bulbs, which are capable of supplying four times this amount for short periods, are of the largest size made for 1,500 volt traction work.

After the power has been rectified to 1,500 volts it is connected to the overhead line through high-speed circuit breakers. The breakers are capable of disconnecting the supply on the occurrence of any fault in .02 of a second. They are provided not only to form a connecting link between the substation and the overhead, but also to prevent the substation being damaged in event of a fault occurring on the overhead.