Fullscreen HTML5Med Res (??MB)HTML4

The Story Of Electrical Energy, Pt.21 Electric lighting came to Sydney's streets on 8th July, 1904. Suddenly, at 5.16pm, the city streets were a blaze of light from Circular Quay to Redfern & from Hyde Park to Darling Harbour. By BRYAN MAHER Back in the new Pyrmont power station, the Lady Mayoress, Mrs. S. E. Lees, had turned a gold presentation key. That simple act had closed the exciter field circuit of a 5.2kV alternator. This supplied 3-phase AC to new substations at Town Hall and Lang Park. At each site, a high-voltage induction motor began to spin, driving two direct-coupled 240V DC genera- tars. With the generators in series, 240/480V DC 3-wire circuits buried under the city's footpaths supplied 231 arc lamps to illuminate the streets. These 2000 candlepower electric lamps so overpowered the old gas lamps that the future of electricity was assured. Each set of 10 carbon arc lamps was connected into a series group which was supplied by the 480V DC mains. The grounded centre neutral wire was used to provide odd sets of five series arc lamps with a 240V DC supply. The carbon rods had a burning life of only 16 hours and then had to be replaced. But we have begun our story in the middle. Though practical electric lighting became possible from 1831 followfng the discoveries made by Michael Faraday in England, Sydney was then only a struggling convict Top of page: this photo shows the interior of Pyrmont power station as it was originally built, with Ferranti high speed twin-cylinder steam engines. NOVEMBER 1992 79 dangerous, that the electricity leaked away in the ground, and that it could cause fires and/or electrocution. These companies made no mention of their own dubious installations, where cables were sometimes just flung over the roofs of buildings. As well, there were numerous new entrants to the field, like the Empire Electric Company Ltd, whose advertised rate per kilowatt hour (kWh) forced the council to reduce its tariffs. And this was before the said company had even commenced operations. Commercial/domestic supply Manufactured by Belliss and Morcom, this 300 horsepower twin-cylinder steam engine measures about four metres long. The engine with its 4-tonne flywheel is direct-coupled to a Bruce Peebles alternator which once supplied 210kVA at 420V 3-phase to drive the machinery in a biscuit factory. The small generator at the righthand end is the exciter, which can produce up to 90V DC at 61A to supply the rotor field coils of the alternator. This 14-pole machine ran at 428.57 RPM & generated a 50Hz AC supply. However, the frequency would not have been all that stable, regulated as it was by a simple but fairly effective steam valve governor. The unit is today a working exhibit at the Power House Museum in Sydney. village. And even though Sir Humphrey Davy's arc light invention had illuminated the Paris Opera House in 1846, practical electric illumination had a long gestation period. The illumination of Sydney's streets was by oil lamps in 1843, then by gas three years later. But the city fathers were slow to adopt electric light. Other towns were more progressive. On 8th November, 1888, Tamworth had the honour of being the first town in the Southern Hemisphere to have electrically lit streets. The town of Young was soon to follow and then the towns ofLambton, Moss Vale, Broken Hill and Redfern got into the act. The electricity bill Moving slowly, the NSW government took 10 years.to pass a bill au~ thorising the Sydney Municipal Council (SMC) to acquire generating plant. Finally, the council appointed one Major Cardew as its consultant. He advised the building of a power station in Kent street to supply an 8km radius with illumination. The Kent Street site was resumed 80 SILICON CI-IJP by the Government due to an outbreak of bubonic plague, so Pyrmont became the second choice. With incredible foresight, the Council anticipated the coming demand from homes and private factories. However in entering the electricity supply business, the City Council faced competition from five well established private DC generating enterprises. At the forefront of this competition were th_e Oxford Street Electric Light Company, the Imperial Arcade Electric Light Company, and the Strand Electric Company whose 100-volt DC system spread like a spider's web around the Strand Arcade and adjacent shops. In the long run, the City Council's greatest competitor was the implacable Australian Gaslight Company. Well entrenched for over 60 years before the advent of electricity, the gas company was a formidable adversary. A lot of quite unethical propaganda emanated from the Council's competitors . The private electric companies spread false tales to the effect that the council's underground supply was The Council power also supplied city buildings and homes where the new incandescent filament lamps, invented by Swan in England and Edison in the USA, were a great boon. These globes were more suitable for indoor lighting than arc lamps which generated lots of heat and copious quantities of carbon dioxide and other noxious gases. City building owners immediately saw the advantages of lifts powered by DC motors. These were much cheaper than the steam powered hydraulic elevators previously used by the largest companies. Some big city stores retained their hydraulic lifts for 50 years or more, simply replacing the steam engine with a DC motor. However most new buildings went straight to electric elevators, many later changing to the Ward Leonard control system for more accurate positioning. Little did those people realise that their DC lifts would dominate electrical supply policy for the next 80 years. Home owners and tenants in city apartments quickly saw the advantages of electric appliances. After lighting, there was a big demand for electric irons and European hair curlers, as in this field gas had no equivalent. Slowly, electric heating and cooking replaced gas appliances. Sydney Municipal Council charged lighting either at a flat rate of five pence per kWh or a two-part rate which cost more for primary units and two pence for each subsequent kWh. Power for all motors, lifts, cooking and heating was charged at the lower rate. One year's operation saw 86 private and government consumers connected to the DC mains supply, in Sydney Council linesmen used to do all the work without any heavy machinery. This photo shows how the heavy cable reels were grappled off the horse-drawn drays prior to the cable being laid in the trenches. addition to the street lighting, with a total loading of just over 1MW. Generating and distribution costs were 1. 99 pence per kWh. Pyrmont power station The original Pyrmont station was equipped with three Ferranti twincylinder high speed steam engines. Each was direct coupled to a Ferranti 5200-volt 50Hz alternator. Two of these units were rated at 1000 horsepower (746kW) each, while the third was rated at 500hp (373kW). Five Babcock and Wilcocks boilers supplied steam at 160 psi (1.1 MPa) to drive the engines. Coal was brought in by rail (or ship in emergencies), while cooling water came straight from Darling Harbour. This installation was state of the art in its day, with economisers and feed water heaters to increase thermal efficiency. So fast was electricity accepted in Sydney town that within 12 months of Pyrmont opening, additional machinery was ordered to almost double the original capacity. The 45km of underground cabling around the city was extended and the existing DC substations enlarged. Today, we can only marvel at the speed at which such work progressed without the aid of heavy machinery. All trenching was done by pick and shovel and all carting by horse and dray. While the City Council was busy wiring up the city and close surrounds, a few industries further out set up their own plants. Some of these were state-of-the-art AC systems. One notable engineering effort was installed in a biscuit factory. AC/DC system True to the preferences of Thomas Edison, and with lift motors in mind, Sydney Council supplied all the in- ner city with a 240/480V 3-wire DC system. But the AC/DC rotary substations were expensive to install and operate. Therefore, the outer city areas were supplied by 240/415V AC mains from transformer substations at Darlinghurst, Athlone Place and the power station itself. This was the first normal AC supply for Sydney horn:es. In outer city regions, streets were lit by the same arc lamps as in the city, except that groups of nine lamps were arranged in series across the 415V AC mains. Thus electricity was ushered into Sydney as two incompatible systems : DC and AC. This dichotomy was to persist for more than 80 years, until 1986, often to the despair of city shopkeepers. As late as the 1950-1960 period, some business establishments in York and Clarence Streets still operated on the 240V DC supply. The custom was for electrical businesses to provide their own motor generator set to provide 240VAC 50Hz, so that radios and NOVEMBER 1992 81 DC in the inner city caused Sydney Municipal Council to upgrade its biggest and longest lasting DC substation in Clarence Street. Originally installed in 1904, this substation used high volt. age induction motors driving series connected pairs of DC generators. Later, rotary converters generating 240 volts DC were connected in pairs to give the 240/480 volt 3-wire supply. The first mercury arc rectifiers were installed in 1933. Mercury arc rectifiers This photo shows three of the 36 600kW mercury arc rectifiers installed in the Clarence Street substation in 1959. These mercury rectifiers used six anodes, for 3-phase full wave rectification. The cubicles underneath them house auxiliary equipment and the cooling fans. appliances could be demonstrated. Problems came with television, because the in-house AC supply was usually of uncertain frequency. Any deviation from the nominal 50Hz caused drifting hum bars on the screens of early TV receivers, to the consternation of shop owners and prospective customers. So fast was the electrical growth in 1904 that within three years an extension was added to Pyrmont to house new more efficient machinery, thus reducing the cost per kWh. The City Council then shocked its competitors by dropping the council's rate from 2 pence to 1.5 pence per kWh. Subsequently, each private electric company asked the council to buy it out as they could no longer compete. The goodwill of four companies was eventually purchased by the Council for a total of 110,375 pounds, each in proportion to its yearly unit sales. The largest was the Strand Electric Lighting Company which had been selling 1.24 million kWh units annually. The Council then refurbished those customers' installations to bring them up to 240V standards. Legal tussle A legal tussle, previously unheard of in Australia, ensued in 1905. The new Royal Hospital for Women, in Oxford and Young Streets, Padding82 SILICON CHIP ton, was designed and built assuming an electricity supply. It was four storeys high and electric lifts and lights were essential for safety reasons. But Paddington Council wanted to charge Sydney Municipal Council rates for the narrow land corridor occupied by the high voltage power line to the hospital. Further argument raged over a substation site. Sanity eventually prevailed; the substation was built within the hosp.ital and agreement between the councils was reached. Sydney Council mounted an intensive campaign to electrify the city. Arc lamps were hired out to commercial users who could not afford the purchase price. Similarly, businesses could rent DC motors in any size from 375 watts to 22.5 kilowatts. The small units were 240V types, while the larger units ran off the 480V supply. The conservative rates charged encouraged businesses to hire a total of 361 motors in the first two years of the scheme. More than 50 different types of factories and stores took advantage of this facility. Three years after its commencement, the Council undertaking had 1600 customers using 6 million kWh units annually. And the system was growing daily, taxing the power stations' 6.7MW installed capacity. The increased use of 240/480 volt On 1st June 1959, the substation was changed over to mercury arc rectifiers exclusively. Six sets of six 600kW glass bulb mercury arc rectifiers with main and interphase transformers and accessories were provided. When placed on load, the mercury arcs bathed the interior of the cabinets in a beautiful (but dangerous) violet glow. Together, the 36 mercury rectifiers could deliver 7300 amperes DC. The large glass bulbs came by sea from Hersham in England, the final shipment arriving in early 1959. During shipment, the bulbs were suspended in a large timber crate using ropes and steel springs. The bulbs were shipped upside down with the large quantity of mercury sloshing about in the head of the condensing chamber. In Sydney, each glass vessel was mounted within a steel cabinet, its mercury cathode at the bottom and the condensation void at the top. Each glass vessel had anode arms with external copper plated molybdenumiron alloy contacts. These connected via the glass/metal weld to join the dense graphite anodes inside. The glass arms each provided a separate pathway for the mercury arc from the cathodic pool at the bottom to each graphite anode. This isolation prevented any chance of a flashover between the AC anodes of any two adjacent phases. The auxiliaries consisted of a cooling fan and starter electrodes for each glass bulb. The fan was automatically speed controlled by passing its AC supply through a saturable reactor. These were commonly used to control AC currents before the days of gas thyratrons or Triacs and SCRs. A saturable reactor is an iron-cored inductor with two AC windings and a DC winding. The AC windings car- ried the current to the fan while the DC winding carried the output current from the mercury arc rectifier. When the rectifier was supplying little output current, the inductance of the AC windings was so high that the fan would not run. As the rectifi er was called upon to supply more current, that current passed through the DC winding of the saturable reactor. This increased the magnetising force in the iron core and so reduced the reactance of the AC windings. This in turn increased the AC voltage to let the fan run. At full DC load current in the rectifier circuit, the reactor core would be completely saturated, cancelling all the inductance of the AC windings and allowing the fan to run at full speed. Thus, the fan speed was automati cally varied to give the right amount of cooling at all times. Exciter circuit When first switched on, the rectifier bulb contained cold mercury. To initiate an arc and thus ionise the liquid metal, a magnet pulled down a spring arm within the bulb to make contact with the mercury. That passed a current into the mercury. A second magnet would then attract the spring arm upwards , drawing an arc sufficient to initiate ionisation. To maintain ionisation, even with no load current, two subsidiary electrodes continually maintained a sma 11 arc to the mercury surface. Because the cathode mercury pool must be the positive output terminal, there is no such thing as a negative output 6-phase glass rectifier. Therefore, in a 3-wire positive/zero/negative DC system, the negative 240V DC bus must originate at the transformer secondary star point. To obtain balance in the 480V /240V system, the council linesmen would connect some lighting circuits between positive 240V DC and zero. Other circuits would be connected between zero and negative 240V DC . With roughly equal loads on both sides , only a small difference current would flow in the zero line returning to the substation. Motors and other heavy loads were made for a 480V DC supply and were thus connected between the +240V and -240V lines. Because th e major lo ad current flowed out on the +240V line and returne_d via the -240V line, four recti- This photo shows smaller mercury arc rectifiers than were used in the Clarence Street substation. These units have only three anodes and a somewhat lower current rating. fiers out of the six were used in parallel to supply this current. The fifth and sixth rectifiers of a set provided a zero centre line potential. Each set of six rectifiers could supply 1215 amps continuously, or 1520 amps for a 2-hour peak period. In addition, heavy loads of up to 2430 amperes mulrl be supplied for up to 15 seconds , allowing the starting of large motors anywhere in the city. Out-of-balance current in the zero line could be as high as ·1 20 amperes indefinitely. As late as 1986, Sydney City still drew just over 4000 amperes from the last remaining three sets of glass rectifiers. Apart from their high efficiency, these mercury arc rectifiers were designed for zero maintenance. They had no moving parts, the critical components were sealed under vacuum , and neither the mercury nor the graphite anodes deteriorated during full load operation. These rectifiers thus had a very long working life. You might ask why so much DC load still existed in Sydney as late as 1986? In truth , much of that load exists to this day but it is now hidden. The advent of the AC supply in later years saw the replacement of most DC machinery with 3-phase squirrel cage induction motors. But from the very first days, DC motors were found to be superior for controlling city lifts and indeed this is still the case. Many buildings in York, Clarence, George and Pitt Streets, as well as around the waterfront area, date from early days before modern building standards were in force. Any attempt to rebuild the lifts in these buildings to modern design using AC motors would be very costly. Therefore, the DC driven lifts remain to this day, and will probably continue for years to come. By the mid 1980s, the advent of high current solid state rectifiers allowed building owners to install their own rectifier systems to run from 415V AC mains. But until 1986, the supply authority, Sydney County Council, was obliged to maintain the 480/240V DC reticulation throughout the city. Thus Clarence Street substation remained a_s a supplier of DC for 82 years. Acknowledgement Special thanks to Phil Parsonage and Des Barrett, and grateful acknowledgement to the staffs of Sydney El ectricity, Pacific Power and the Museum of Applied Arts and Sciences, and to Gordon Anderson. SC NovEMB EH 1992 83