Modern Lighting
A Phase of Workshop Re-organisation

(By C. A. Mackersey, A.C.S.E., Assistant Electrical Engineer, S. and E. Branch)

The main changeover at Petone Workshops to the Public Works Supply at 11,000 volts from the Khandallah Sub-station, was carried out during last Easter, and the installation of motors to dispense with the old suction gas plant having been practically completed, some description of this installation, which was designed and carried out by the Signal and Electrical Branch, may be of interest.

Before dealing with Petone Shops themselves it is interesting to go back to the source of the power supplied, and trace it step by step until it reaches the various machines in the Shops and does useful work in the form of locomotive, car and wagon building and repairs.

Energy is never lost, but merely transformed from one state to another. Interesting, however, as is the early history of Petone's electrical energy, in the forms of sunheat, rain, brook and river, it must be passed over and taken up at the stage when it is in the form of water flowing apparently idly, though in reality stored with energy, along the bed of the Mangahao River. On reaching the Mangahao Dam this water is diverted from its natural course through approximately a mile of tunnel into the Arapete Dam. From this Dam it again flows through approximately a mile of tunnel into the surge chamber 900 feet above the power house at Mangaore. After its fall of 900 feet and entry into the various Pelton wheels of the power house the water is of no further interest.

Electric Lighting in Locomotive Erecting Shop. Note absence of shadows and glare.

Some of its energy is given up to the revolving Pelton wheels, which in turn transmit it to their respective alternators, thus transforming water energy into electrical energy. This electrical energy is developed at a pressure of 11,000 volts, and by means of step-up transformers the pressure is raised to 110,000 volts, at which it is transmitted over the wooden pole and steel tower transmission lines to Khandallah substation, a distance of 61½ miles. At Khandallah the pressure is again reduced to the original value of 11,000 volts and transmitted by a transmission line along the Hutt Road to the Petone Railway Shops sub-station. The sub-stations measures 43 ft. by 17 ft. and is situated practically at the electrical centre of gravity of the works. It is divided into two, the smaller part being a workshop and store for materials, and the larger section accommodating the transformers and switchgear. The whole of the electrical gear is ironclad and totally enclosed, and the connections between the switchgear and transformers, by means of lead-covered cable, are laid in concrete ducts in the floor. The switchgear is of the most modern type, and this, in conjunction with the design of the sub-station, gives complete protection to the operator against fire, explosions, etc.

The apparatus of the sub-station consists of the High Tension 11,000 volt switch, controlling the supply to the transformers, and the 400 volt switchgear, controlling the supply of power to the various shops. The switchgear is arranged along one side and the transformers page 11 placed on the other side of the sub-station. The 11,000 volt switch is in line with, but separate from, the rest of the switchgear. Above the switchgear are placed the necessary

Oil passing through purifier, before being used in 11,000 volt transformer.

instruments, consisting of voltmeters, power factor meters, ammeters and watt hour meters, to enable the necessary measurements to be made of the energy consumed. All the switches are provided with safety trips, so that in event of faults developing, or power being cut off, the line affected is immediately disconnected. The three transformers, which are of 350 k.v.a. each (about 470 h.p.) transform the power from 11,000 volts to power at 400 volts, which is suitable for operating the motors on the machines. The path of the power from the transmission line to the machines is first from the line to the High Tension switch, from the High Tension switch to the transformers, and from these to the main 400 volt switch, capable of dealing with 2,000 amps per phase, and from this to the switches controlling supply to the various shops, of which there are the following:—

Machine Shop panel—800 amps per phase. Car and wagon shop panel, 600 amps per phase.

One spare panel.

Boiler and Blacksmith's shop panel—200 amps per phase.

One panel for the lighting.

From these shop switches, or panels, armoured cables go underground to a series of switches in each shop controlling the various supply circuits to the machines. These switches are again completely ironclad and totally enclosed and arranged so as to switch power on to any sub-circuit as required.

Transformer Core being lowered.

They also confine any shut down to a faulty circuit and the faulty circuit only, as they are provided with the necessary trip gear to operate in event of page 12 faults or failure of power. The sub-circuits are run from these switches in piping to the roof trusses and from there are carried on insulators. The mains to each machine are connected to these sub-circuits and carried in piping to the switches controlling each individual motor. All the motor starters or switches are again provided with overload trips so as to localise any fault on an individual machine without affecting the rest of the circuit. Various types of motors are used at Petone for different purposes, but space will permit of the description of only one or two of the most interesting.

Of the machines driven by the A.C. 400 volt supply direct, probably the most interesting are the air compressors, for supplying air for pneumatic tool and many other purposes. There are two of these machines, each driven by a 125 b.h.p. auto-synchronous motor.

Motor Generator Set for 500 volts D.C. supply.

The operation of the compressors is automatic so that, after pumping air in the reservoir up to a pressure of 100 lb. per square inch, they automatically cut out, and, although the motor continues running, no more pumping takes place until the pressure drops to about 80 lbs. per square inch. The cranes, and some of the older machinery at Petone, operate on 550 volt D.C. power. Previous to the changeover they were supplied by a 550 volt dynamo driven by the gas engines. During the changeover the dynamo drive was disconnected, the machine swung round and coupled to an auto-synchronous motor.

The next machine of interest is the rotary converter set. This consists of a three-phase transformer, rotary converter, and starting and control switchgear. The power supplied to the transformer is three-phase at 400 volts. The transformer reduces this to about 140 volts which is supplied to the rotary, emerging as direct current at 220 volts. The direct current power is used for driving the D.C. variable speed motors in the works. For electric welding there are two small motor generator sets—one portable and one fixed. These transform the alternating current at 400 volts to direct current at a sufficiently low pressure for welding operations to be carried out. One extreme advantage of the electric drive over the former gas engine drive, from the production point of view, is the complete check that can be kept on the daily power consumption in each individual shop, thus the allocation of the annual power bill to the various shops ceases to be a matter of conjecture and becomes a matter of absolute certainty. In addition to the installation of electric power in the shops, an extensive scheme of artificial lighting has been carried out and is now nearing completion.

Rotary Converter Set for 220 volts D.C. supply.

The lighting has been arranged to give just the correct luminous intensity required for the particular work which is carried out under it and, in every case, attention has been paid to the question of glare, the light being directed on to the work and away from the workers' eyes. All the reflectors used are so fitted that, while performing his normal duties, the workman's eyes never come into direct vision of the electric globes.

The whole undertaking is of interest both on account of its size and the fact that the most modern appliances, in the way of ironclad apparatus, have been used throughout.

The time of high wages and mass production has definitely come to stay.—Dr. Herbert Schofield, Principal of Loughborough College.