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The Story of Electrical Energy, Pt.20 One year after Sydney's Ultimo power station was built, the growing electric tramways had exceeded its capabilities. Massive extensions to the power house together with AC reticulation & AC/DC substations solved the problem. By BRYAN MAHER The Sydney electric tramway system had expanded so quickly by 1900 that voltage drop problems in the 600V DC feeders were acute. Both the Ultimo power station and the 600V feeder system were fast approaching their capacity limits. The 1900 figure of 100 electric tramcars running over the 50km of track 88 SILICO N CHIP was expected to be doubled almost yearly. An additional ten 600V DC feeders laid in 1901, reaching out eight kilometres from the power station, were only a bandaid solution. Massive extensions were called for, including a rethink of the whole system. As electrical technology was ad- vancing fast, it was decided not to build further DC generators but to adopt 3-phase AC. The designers, to their everlasting credit, decided to think big! A new engine room was called for, double in length, width and height compared to the original buildings. Plans were made and, in 1902, foundations were laid for six very large 2-cylinder vertical steam engines. Each was to be direct-coupled to a 1.5-megawatt AC generator. Each 2300 horsepower (1.72MW) engine was designed to supply a 50% overload for the 3-hour peak periods twice a day. By 1904, three of these engines were installed and running. The vertical 2-cylinder steam engines were single expansion cross- Facing page: this view of the Ultimo power house shows the three huge condensing steam engines and their alternators which rotated at 75 revs per minute. It must have been an impressive sight to behold. compounded condensing units. They towered 18.2 metres from top to bottom, although one third of this height was below floor level. That still left the top of the low pressure cylinder reaching 12.2 metres above the engine room floor. The rotors of the alternators were so heavy and so large in diameter that they did double duty as flywheels. The construction of each alternator started with an enormous cast iron flywheel 7.1 metres in diameter, with a rim 915mm wide. Forty DC magnetic field poles were then added around its periphery. These poles were built up of sheet iron punchings, insulated , and wound with 26mm x 3.175mm copper bar, wound on edge on an insulated frame. The 40 fieldpole windings were connected in series, resulting in a total field resistance of just 0.5-ohm. Measured over the field poles, those rotors were 8.85 metres in diameter. Each rotor weighed 98 tonnes without the slipring assembly. Add this to the 20-tonne crankshaft and you had 120 tonnes of machine parts flying around at 75 rpm. In fact, the peripheral speed of the rotors was 125km per hour - incredible figures for 90 years ago! In each machine, the rotor was mounted on the middle of the crankshaft, midway between the enormous cranks of the high and low pressure cylinders. The crankshaft, more than half a metre in diameter and over six metres long, was a massive piece of drop forged and machined steel. The high pressure cylinders were large enough at 813mm in diameter but the low pressure cylinders were enormous, with an inside diameter of over 1.6 metres. Each complete engine-alternator combination was undoubtedly the mightiest machine most Australians had ever laid eyes upon. Each one weighed a total of 450 tonnes. Three of these Allis-Chalmers-ReynoldsGeneral Electric engine generator sets The new alternators at Ultimo power station used up to the minute technology. Previously, all electric generation in Sydney had been 600V DC. Note the size of the low pressure steam cylinder. This had a piston diameter of 1.6 metres. were installed in Ultimo power station. Work had commenced on the building and the machinery foundations in early 1901 and all three machines were running under load just 29 months later, in May 1903, a truly remarkable performance! As the photos show, these machines were truly gigantic - the biggest machines in the southern hemisphere, in fact! Even to this day, the Ultimo engines numbers 5, 7 and 9 hold the record as the biggest reciprocating engines ever installed south of the equator. Interestingly, only three of the planned six machines were in- stalled because reciprocating engines were overtaken by new technology within a decade, New boilers To provide steam for the three new engi nes, 24 extra boilers were installed. These were housed in the boiler house extension, a giant structure which towered over the original buildings. They were Babcock, and Wilcox water tube boilers, each rated at 186kW (250 horsepower) and generating steam at 150psi (1.1 megapascals) and 240°C. These were a great SEPTEMBER1992 89 advance compared with the original units which were just three years older. Coal was fed to the boiler by a new invention, the automatic chain grate stoker. A small steam engine drove the stoker which effectively became the moving firegrate. Continuous movement of the grate finally tipped the spent ash and clinker down via a chute to ash trucks below. High above the boilers, an enormous bunker held 2500 tonnes of coal. Sixty boilers were planned, in two rows of 15 on each of two floors. Extra new pumps provided feed water for the boilers and circulating water for the engine condensers. The boiler house extension was done in two stages so that the old boilers could continue steam supply until half of the new units were installed. When the new southern end structure was completed and operating, the original boilers were demolished and the old boiler house extended vertically so that a complete matching facade was achieved. The extensions used 3-million 90 SILICON CHIP bricks to create a building 54 metres long by 30 metres wide. Near the middle of the south half of the boiler house, two giant new chimneys were erected, 69 metres high. Measuring 7.3 metres square at the base and 3. 7 metres internal diameter at the top, each chimney was capped by a 7-tonne cast iron crown. For the next 70 years, these structures dominated Sydney's western skyline. Coal brought from five different areas by tail way was crushed and then lifted by a chain elevator with 288 steel buckets to the storage hopper above the boiler room. Driven by a large DC motor through a reduction gear train, the elevator had a capacity of 40-tonnes per hour. High voltage alternators Not only were the alternators very large, they also produced very high voltages for the day - 6600 volts AC. The stationary armature coils were wound with square insulated copper (10.2 x 10.2mm), then insulated overall by nine layers of half-lapped 178 microns thick linen tape. Each layer This view of the Ultimo power station shows the alternators which were installed at a later date. Even so, the size the of the three original alternators and their condensing steam engines was never to be challenged. was baked, varnished and baked again, six times in succession. The 6kV insulation made by this simple method was reliable and long lived. Lead-sheathed oiled paper insulated cables of 3-core construction carried the current from the alternators to the 13-metre long switchboard. Sixteen panels of blue Vermont marble served the three generators, exciters and the original ten 6.6kV outgoing feeders. The high voltage circuit breakers were something new in Australia. A series of brick compartments lined with opalite had cast iron doors at front and soapstone slabs on top. Each such chamber contained one pole of a 6.6kV circuit breaker. Each pole consisted of two isolated sets of sprung copper contacts, arranged in pairs (like your thumb touching your first finger). To close the switch, a moveable copper bar of triangular cross section was raised to bridge all the contacts. The live moving copper bar was actuated by an impregnated wooden rod , connected by other rods and bell cranks to a grounded metal handle on the front panel. The whole contact assembly was immersed in a tank of heavy mineral oil which extinguished the arc as the current passed through the AC zero voltage point. AC to DC substations The 6.6kV AC from Ultimo power station allowed longer transmission distances but it then had to be transformed down to a lower AC voltage and converted to DC to supply the trams. For this purpose, five tramway substations were built at Macquarie St (City), Newtown, Waverley, Randwick and North Sydney. Two underground high voltage cables were laid to each substation by the British Insulated Wire Company. These oiled paper insulated cables were lead-sheathed and the lead sheathing was grounded to earth electrodes at both ends and at intervals of about 800 metres along their length. The shortest run was tci the city substation (2.9km) and the longest to North Sydney (6.4km). A 732-metre section to North Sydney was laid on The Ultimo power station had Gothic proportions, with the men in this photo giving some idea of the scale. The massive switchboard is situated at the far end of the building. the floor of Sydney Harbour and is thought to be the first high voltage submarine cable laid in Australia. This underwat er section , from Dawes Point to Blue's point, had extra steel armouring but also contained three submerged joins. This was because the technology of the day in England could not produce cable lengths greater than 185 metres. Arc-gap voltage surge arresters were fitted to .the cables, to flash over if a switching surge or lightning ground The chimney stacks of the Ultimo power station dominated Sydney's skyline for many years but they are now long since demolished. The main building still survives however and now houses the Powerhouse Museum. current elevated the voltage momentarily above 15kV. At each of the five substations , the 6.6kV supply was transformed down by air-blast cooled delta-delta transformers to 375V. This was fed to rotary converters which produced 600V DC to supply all trams in the section. Initially, 450kW and Z00kW converters were installed. But so fast did the system grow that within a few years larger units had to be provided. The largest were the 1.8MW machines installed at the new city substation at Jamieson Street. A rotary converter looks somewhat like a big DC generator with commutator and brush gear but without any mechanical drive. Instead, the AC electrical input is conducted by sliprings and brushes to connections on the back of the armature winding. Readers are probably aware that in any DC machine the armature winding always carries AC , this "being mechanically rectified by the rotating commutator and stationary brushes. This fact is used in rotary converters, the armature rotating at a speed in synchronism with the AC supply. The 600V DC output taken from the comSEPTEMBER 1992 91 This photo shows the interior of North Sydney substation as it was in 1902. It included three rotary converters, each rated at 1200A. In the left foreground are the three switchboard sections controlling the DC side of the converters. At the top are the automatic overcurrent circuit breakers, below that the dynamic ammeters and below them the two open blade knife switches for each machine. mutator by the brushes then fed the tramway system. With the incoming AC at a frequency of 25Hz, the 6-pole rotary converters ran at 500 rpm. Mounted on the back end of the shaft of each converter was a 30kW 4-pole induction motor intended for starting the converter and bringing it up to synchronous speed. Later, these pony motors were dispensed with and the converter started as an induction motor from low voltage taps on the transformer, through limiting inductances. A third method was to start the converter from the substation battery. Dynamic ammeters The large ammeters of the day, with a scale up to 400mm long, demanded strong field magnets. Lacking powerful permanent magnets, manufacturers used 600V DC electromagnets instead. To desensitize the meter against voltage fluctuations, the iron cores were driven hard into magnetic saturation. This was ingenious! Should a machine circuit breaker trip on overcurrent, the operator would stand on a rubber mat and: (a) open the blades of the knife switches; (b) close the circuit breaker; and (c) slam the bare knife switches closed by the handle, at the same time being 92 SILICON CHIP prepared to duck and jump sideways quickly should that closure cause the circuit breaker to trip again. Any circuit breaker opening on over-current could rain down red hot globules of the copper or carbon contacts. Also, the breaking of a high current arc made a thunderclap noise loud enough to scare the living daylights out of the unfortunate operator. 600V batteries Most of the substations were fitted with one or two 600V batteries, each consisting of 280 lead-acid cells. Constructed of lead lined timber and containing nine positive and 10 negative plates, each cell contained 125kg of sulphuric acid electrolyte. Heavily coated timber bearers and glass insulators supported the batteries. Rated at 500 ampere-hours, these batteries could supply up to 1000 amperes for short periods. They were used to supplement the converter output to the trams during peak periods, as well as for far-off-peak supply when the converters could be shut down. Charging and discharging of the 600V battery was controlled by a clever differential booster generator. This machine had its shunt fields separately excited by the 600V bus bar and was driven at a constant speed by a separate DC motor. When there was no tramway load on the substation converters, the booster armature generated 100V. This was added to the 600V bus bar supply to give 700V and charged the battery at 500A. The booster series field was connected in series with the rotary converter, so that series field opposed the booster's shunt field. This meant that when the rotary converters were supplying heavy tramway load, the booster generated less voltage, and so the battery charging current pulled from the rotary converters was correspondingly reduced. During peak hours, heavy tramway loads would occur, often of 3000A to 4000A, such as when 30 trams started simultaneously. Under such a condition, the booster's differential series field would completely overcome its shunt field so that the voltage generated by the booster would reverse. Thus, the charged battery, in parallel with the rotary converter, would share the tramway load. In this way, the load fluctuations on the rotary converters were reduced. Despite the expense of providing substations, rotating conversion machinery and the trained staff to tend them, the new AC/DC system proved economical. The interest paid on loans raised to finance the project was less than the calculated cost of power which would have been lost in feeder voltage drop had the DC transmission system been simply extended. Sydney continued to have an insatiable need for more and more electric traction. Between 1900 and July 1904, electrified track mileage had quadrupled to 192 kilometres, while the number of trams had grown to 500. This rate of expansion continued for years and at the same time Sydney people wanted electric appliances and lights in their homes and streets. Many more power stations had to be built in the years to come. Acknowledgements Grateful thanks for photographs domi,ted by SRA Archives, the Trustees of the Sydney Museum of Applied Arts and Sciences, and the Public Works Department of NSW. Acknowledgements to Don Godden et al in "Ultimo Power House; Report on its History and Technology"; also to Victor Poljanski, Arthur Perry, P. Smythe, P. Tweedie, T. P. Strickland and W. Upton. SC