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DESIGNED IN THE EARLY 1970s, the Amtrak E60CP is the most recent but possibly the last all-American electric loco. Later American electric locos have used Swedish technology. THE EVOLUTION OF ELECTRIC RAILWAYS In this episode, we compare a very large electric loco designed in the early 1970s for Amtrak with a much smaller loco designed 10 years later by the Swiss. The Swiss loco is less than half the weight hut is more powerful than Amtrak's monster. By BRYAN MAHER Right from the start, electric locos have used series DC motors for traction. These are controlled by inserting resistances in series and/or switching the motors in series for starting, then connecting the motors in parallel when up to speed. So naturally, early electric locos ran on a DC supply. There was some use of 3-phase AC induction motors but this practice did not become widespread (see SILICON CHIP, June 1988). For 50 years then, most electric traction was based on DC systems using voltages around 650 volts, 1.5kV or 3kV. These voltages are nominal, of course, and vary with time and different track sections. For example, a 1.5kV DC system may fall to as low as 1.2kV during heavy starting conditions and may rise to as high as 1.95kV on regenerative downhill running. For longer main lines in Europe, single phase 15kV 16.6Hz AC overhead supply established a firm hold, with a 15kV to 500V transformer carried in each locomotive. The traction motors were the familiar DC series type modified to work on low frequency AC. Speed control via taps on the transformer secondary windings was simple and effective. Yf.20: AMTRAK'S MONSTER VS. A SWISS TIIOROUGHBRED 80 SILICON CHIP Equivalent locos in the USA used 11kV single phase 25Hz AC, also with series motors running on AC. (The AC/DC system of the Great Northern Railroad of USA described last month was the exception rather than the rule). Eventually, electronics finally became incorporated into railway traction. The 1950-70 period saw the introduction in Europe of static rectifiers in loco traction circuits to supply the motors with DC. France was first, using mercury arc rectifiers, but later changed to silicon rectifiers which became the universal practice. Speed control. was still via taps on the transformer secondary windings while later designs used taps on the high voltage primary, Overhead supply was 15kV 16.6Hz AC in most European countries except France where 25kV 50Hz was tried. With the motors fed from rectifiers to give DC there was no longer any reason for the continued use of a low frequency AC supply. France has been the pioneer user of the 50Hz 25kV AC system. Thyristors The 1970-80 period saw a great leap forward with the introduction of thyristors (also known as silicon controlled rectifiers or SCRs) rated at thousands of volts and thousands of amps. As well as rectifying the AC supply from the transformer, thyristors allowed more precise control of the voltage and current. The method used was the familiar "phase control" system, as applied in today's light dimmers. Early thyristors rated at thousands of amps could not switch on and off much faster than 120Hz, so series DC motors on a controlled rectified AC supply remained the norm for many years and many such locomotives were built. During the 1970s, to ease the high voltage/high current design problems, a combination of thyristor control with transformer tap changing became popular. The Amtrak E60CP An American example of this approach is the Amtrak class E60CP. In all, 26 of these electric locos ONE OF THE LATEST EXAMPLES of Swiss design, the Re 4/4 IV is a Bo-Bo type loco weighing only 80 tonnes but it is very powerful with a rating of 4960 kilowatts (6650 bhp). That's more than 1650 horsepower per axle. were purchased from General Electric on an $18m contract begun in 1973. It was this locomotive which was to be Amtrak's ultimate replacement for the GG 1 locomotives which served for more than 50 years: Ultimately though, it does not seem to have worked out that way but the General Electric designed and built loco is a massive piece of machinery. The E60CP has a high voltage transformer with two tapped primary windings which are switched in series or parallel to cope with an overhead supply of 1 lkV at 25Hz, or 12.5kV or 25kV at 60Hz. This allows the loco to run without stopping from the old 1 lkV 25Hz American lines onto a transition section of track wired at 12.5kV 60Hz, then straight onto new track sections wired at 25kV 60Hz. This technique has allowed Amtrak to electrify new ·sections of track at 25kV AC, which is fast becoming a world standard. Because DC motors running on DC (supplied by rectifiers) are used, the supply frequency change from 25Hz to 60Hz has no effect at all. Eventually all 25Hz systems can be replaced by 25kV 60Hz AC, removing the need for special power stations or frequency changing substations with their extra losses. Traction motors Each of the 6 axles of the E60CP is driven by a GE traction motor JUNE 1989 81 ANOTHER VIEW OF THE AMTRAK E60CP electric loco: weighing 176 tonnes, they are capable of travelling at speeds of up to 190km/h. These locomotives are now being rebuilt and repainted for use on secondary lines. rated at 746kW (lO00hpJ. Total power is 4476kW (6000hp). The drive to the loco axles is via a 38/68 ratio single reduction gear. The motor is axle-hung, meaning the weight of the motor hangs on roller bearings mounted on the loco axle, so the motor and train axle rise and fall together, following the track undulations. The other side of the motor, the so-called ''nose'', is suspended in a spring arrangement from the bogie chassis. With this gear ratio and 1016mm diameter driving wheels, the E60CP can exert a short term tractive effort of 34 tonnes at any speed from zero to 80km/h or 15.42 tonnes continuously up to 95km/h, reducing to 7.26 tonnes at 193km/h. The main high voltage transformer has seven secondary windings, with two groups of three windings each for traction, plus a seventh secondary for auxiliaries. As noted above, traction motor speed control is achieved by a combination of secondary taps and 82 SILICON CHIP thyristor bridges. The three motors of each bogie are connected in parallel and reversing is achieved by reversing the connections to all series fields. cars' brakes are activated. This is prevented by a WABCO braking unit which sends electrical signals to operate the air brakes simultaneously on all cars. Braking Wheel slip/slide control Blended dynamic and air brakes are used for smooth slowing from high speed and for stopping. The application of up to 50% braking by the driver is brought about by dynamic braking alone (where the traction motor fields are separately supplied and the armatures switched to braking dissipation resistors). When more than 50% braking effort is required, the dynamic braking is supplemented by compressed air brakes on both the locomotive and the train. When hauling long trains, the time taken for brake air pressure changes to travel the length of the train air line is important and could result in "concertina" effects if the front cars slow before the back Each axle of the loco carries a small alternator which generates a voltage proportional to that axle's rotational speed. The 6 voltages so generated are fed to a comparator to detect and correct wheel slip under acceleration or wheel slide under braking conditions. Auxiliaries Readers may wonder why many electric locos are as large or even larger than equivalent diesel electric units. The E60CP is a perfect example of this, being very large at 21.72 metres long, 4.46 metres high and 2.97 metres wide. It weighs no less than 176 tonnes, giving a high track loading of 30 tonnes per axle. So why are they so big and heavy? After all, they don't have a diesel engine or alternator even though those running from high voltage do carry a big step-down transformer. What more is needed? Wouldn't you expect the inside of the loco body to be virtually empty? One big requirement for passenger locos is for train heating and air-conditioning. In the E60CP that takes a lot of power in the form of a large 940kW single phase AC motor driving a 750kW 3-phase 60Hz 480V alternator. This supplies all train heating (in winter), air conditioning and cooling, lighting, cooking in the buffet and restaurant cars and other train electrical loads. Australian readers may be surprised at the sheer size of the auxiliary power supply, known as "head end power", which with the other auxiliary systems add up to more than one megawatt. This is about 117th of the main transformer capacity. But heating alone in the American sub-zero winter temperatures demands large quantities of power for a whole train. Australian trains are not faced with such severe environmental conditions. Rarely do Australian trains see snow and almost never a blizzard! Then there are essential functions that the passengers never see. In the E60CP locomotive, one 74V 15kW static rectifier supplies regulated DC power for train control and the loco's lights. These functions also have to be provided by a large battery and it too needs its own transformer and rectified supply. In an emergency, either bogie can drive the locomotive and train, as auxiliary circuit breakers are provided to allow one parallel set of three traction motors to be cut out of service. Of course the electricals must be kept cool and you need compressed air for the brakes. The air blower (for equipment cooling) and the single stage rotary air compressor with air cooler are driven by a large DC motor. Even the transformer oil must be circulated by a pump to dissipate the internally generated heat. Communications Safety demands that train dri- THIS MAIN HIGH VOLT AGE TRANSFORMER is the heaviest component in the Swiss Re 4/4 IV loco, apart from the fabricated steel chassis. Weighing about 13 tonnes, it is rated at 5.9MV A. vers keep in communication with other trains and ground staff. Therefore each driver's cab is equipped with a Motorola train intercommunication radio and a system for communication with crew and passengers. The driver is also automatically warned of train overspeed and trains can be stopped automatically if necessary by signals and ground control. Though geared for 192km/h (120mph) running, today these locomotives are often used on the short-haul trains at 144km/h (90 mph). New loco designs When it was designed in the early 70s, the E60CP would have been regarded as having the latest technology but compared with locos designed just a few years later in Europe, it is a dinosaur. Admittedly these later designs have the advantage of much improved thyristors which can operate at higher frequencies but a comparison is still startling. Swiss comparison Though Switzerland is a small country the Government railway system is second to none in the world in locomotive and coach design. Because there are three official languages - German, French and Italian - they write the name "Swiss Federal Railway" in those three languages as: Schweizerische Bundesbahen or SSB; Chemins de Fer Federaux Suisses or CFF; and Ferrovi Federali Svizzere or FSS. Hence Swiss locos may be labelled by any or all of those three sets of initials. Electric-powered since 1914, Swiss loco designs have included most possible types but their latest effort designed in 1981, the Re 4/4-IV, is remarkable in its power to size ratio. Rated at 4.960MW (6650hp), they JUN E 1989 83 3950 3950 15800 Achsfahrmasse + 201 2187 • + 201 201 • 201 2187 10700 THIS LINE DRAWING EMPHASISES just how tiny the Swiss Re 4/4 IV really is. It is only 15.8 metres long. are only 15.8 metres long and weigh a mere 80 tonnes. They are a Bo-Bo design (four powered axles) so the power per axle is extremely high at 1.24MW (1663hp). But with advanced all-thyristor motor control, radar track speed sensing and 5 % forward continuous slip control, sufficient traction is _achieved with only 20 tonnes per axle. In fact , maximum tractive effort is 30 tonnes. The designers took note of the speed and power of three earlier classes: (1). Bo-Bo-Bo class Re 6/6 rated at 7.832MW (10,500hp), weighing 120 tonnes and capable of 140km/h. 89 of these were built between 1972 and 1980. (2). The Bo-Bo class Re 4/4-II, the most numerous in Switzerland, rated at 4.7MW (6300hp), weighing 80 tonnes and capable of 140km/h. 84 SILICON CHIP 273 of this class were built up to 1985. (3). The Bo-Bo class Re 4/4-III, an 80 tonne 4.650MW (6233hp) loco of which 17 were built in 1971. For the next model, Re 4/4-IV, the designers opted for a lightweight Bo-Bo locomotive but with a top speed of 160km/h in mind. This speed is quite high considering the mountainous terrain of Switzerland. Design outline Swiss locos use a 15kV 16Hz overhead supply and so the designers chose a simple basic design. This uses a high voltage main transformer with separate secondaries and thyristors for the front and rear bogies, each with two separately excited DC traction motors. A third secondary with thyristors feeds the field windings of all motors. Speed control is therefore entirely by thyristors. Busbar connections from the transformer feed the fore and aft traction thyristor groups. These consist of two banks of thyristor assemblies, each bank fed by a 686V 1880A secondary winding. Field excitation for all four traction motors comes from a separate secondary and associated thyristors. Yet another secondary winding supplies auxiliaries. Each of the four traction motors is an 8-pole DC type with -series fields for greater starting effort, and with separately excited (shunt) fields for precise speed control. Braking Electric dynamic braking is automatically blended with the train air brakes, although the ANOTHER VIEW OF THE SWISS Re 4/4 IV which is tiny by comparison with the Amtrak E60CP but somewhat more powerful. Designed in 1981, it has full microprocessor control of all the thyristor traction circuitry. dynamic brake does most of the work, except at near stop or in emergencies. For dynamic braking, the traction thyristors are switched off and other thyristors connect the motor armatures to air-cooled braking resistors mounted within the loco ea bin alongside the traction thyristor assembly. During braking, the motor field windings are supplied as before from the separate circuit by a braking regulator. Microprocessor control Full microprocessor control is employed over the motors at all times. The microprocessor continually measures armature currents, rate of change of a rmature current and the integral of the armature current. Up to a limit, the control algorithm allows overcurrent for starting, but with safe limiting to keep the armature temperatures under control. Auxiliaries From the 990V transformer secondary (which also supplies the motor fields), supply is also taken via an harmonic filter and rectifier to a DC/ AC inverter giving 3-phase AC output at 500V, up to 65Hz, for control and auxiliary loads. Other train loads and locomotive circuits operate from a 230V supply or a smaller 36V, 60A control current circuit. An additional secondary winding on the main transformer provides for a 600kW train heating load very necessary for trains in high mountain country. Comparison with E60CP Comparisons between the Re 4/4-IV locomotive and the American E60CP show that the Swiss loco is far superior in power/weight ratio. It is also much smaller in physical size. The greatly reduced size and weight of the Re 4/4-IV compared with the American E60CP is due partly to the Swiss loco's much more modern traction control system. The American E60CP uses a bulkier transformer and busbar assembly (because its secondaries are multi-tapped), together with many large electropneumatic high current contactors. In addition, the E60CP employs a large 940kW AC motor and 750kW 3-phase alternator for train heating and airconditioning. It also ha s 6 axles and 6 traction motors in longer and heavier bogies . Overall though, the E60CP is completely overshadowed by the Swiss design. These days it is very much confined to secondary service in the USA with primary Amtrak services being provided by the Swedish designed AEM7. ~ Acknowledgements: thanks to M. Gerber et al of SBB Motive Power Works, Bern, Switzerland; to ASEA of Sweden ; to R. Clifford Black IV and K. M. Watkins of Amtrak, USA; and to General Electric USA for data, photos and drawings. JUNE 1989 85