After the possibility of handling reactive power with these circuits was introduced by Steenbeck and then by Petersen Fig.
Table 2 again presents some aspects of this development. From the preceding paragraph and from figure 19a it may be gathered that by connecting the discharge tube in series with a mechanical switch he was able to obtain the characteristic of a controlled rectifier. This is the more remarkable, because at that stage the controlled mercuryarc rectifier still belonged to the future. The high voltages in the reverse direction and the actual commutation were the responsibilities of the rectifier. This indicates that Bolliger had already fully realised the necessity for a static electronic commutator but did not yet have the necessary circuit elements.
Van der Bijl described control systems for DC generator current and voltage in , attributing the origin of the ideas to Wold.
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In these systems a vacuum triode 'audion' was connected either in series or in parallel with the field winding of the generator, the essential control element Fig. Before Voorhoeve in the Netherlands investigated the possibilities of controlling generator voltages by electronic means. Contrary to the work reported by Van der Bijl, he employed vacuum diodes, the heating current being the variable Fig.
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This was done in the conviction that gas discharge tubes did not yet have the constant characteristics essential for achieving accurate control. Later work by the same group included the use of vacuum triodes, but was overshadowed by the fast developing control schemes with grid controlled mercury-arc rectifiers [64, 65]. One of the initial ideas that sprung from the availability of the controlled mercury-arc rectifier was to build an electronic commutator. This idea grew gradually. It is worth mentioning that in two steel tank mercury-arc rectifiers were installed in a traction unit of the Pennsylvania Railroad in the USA.
This unit, with four HP V motors completed approximately km in normal traction service by . In this case two frequency conversion processes are to be observed, one of which is still mechanical. The first machine to use a true electronic commutator was the machine of Kern — a now famous example . In fact, Kern suggested various configurations, one being shown in Fig. The first locomotive with this system was built by Brown Boveri around Before , these types of machines were studied by many workers, and were originally primarily intended for traction purposes .
Although it was applied in Europe and in the USA to a certain extent , the thyratron or controlled mercury-arc commutator motor never attained true widespread practical application, despite considerable enthusiasm see, for instance, discussion of Alexanderson to Marti . One of the ideas being applied at present is the use of thyristor frequency changers in conjunction with squirrelcage induction machines for electric traction purposes [69, 70].
This idea is not new, it has been considered in the A direct voltage chopper circuit, or DC to DC transformer, necessitates the forced commutation of direct current through the electronic switch. Although this art was well understood before , as introduced by Prince  and Hull , and treated explicitly by Tompkins  it was apparently not applied to the control of electromechanical transducers until recently. On the other hand efficient phase control circuits were developed much earlier and applied with success to the control of DC machines and other DC loads, and to the control of AC loads.
Using the idea of control of the discharge of Cooper-Hewitt, Dunoyer and Toulon  effectively demonstrated how to obtain regulation at the output of an electronic convertor in Modifying this idea for current flow in both directions, Lenz  proposed and tested the antiparallel naturally commutated switch configuration in This configuration and the previous one were used extensively in the control of welding equipment . The reason for the rejection of this proposal in was the enormous volume of equipment needed, as it was impossible to transport it aboard an ordinary locomotive.
Thyristors are relatively small in size and eliminated this problem, as has been illustrated by the present developments see discussion in Section 6. The interest in electronic commutators, stimulated anew by the thyristor, has apparently stimulated the use of transistors for the same function in small machines. This is the inevitable conclusion, as it was not until that this type of electronically commutated machine received serious attention [72, 73], although switching transistors were available years before.
The consideration that mercury-arc controlled rectifiers are expensive and have a voltage drop of V during forward conduction confined these investigations to larger machines. Alexanderson proposed an electronic Scherbius cascade in . Working independently, Stohr reported investigations comparing machines with an electronic commutator to the mentioned cascade in . Later the operation of the electronic Scherbius cascade was extended to the oversynchronous region of operation .
Subsequently Holters  also investigated this type of system. The development of silicon rectifiers renewed the interest in systems consisting of wound-rotor induction machines and frequency convenors in the rotor , while thyristors held the promise of making this drive economic and compact — also for smaller machines.
The magnetic amplifier was applied with good results to stator and rotor control , but it is only after the development of the thyristor that this type of control has received increasing attention in the form of electronic switching of the rotor current, notably in Germany see, for instance, Reference Although the idea of using antiparallel switches to regulate voltage had been around for a long time, it does not seem to have been worked out for the stator control of induction machines.
About , the idea of applying phase control to the rotor and stator circuits of induction machines by magnetic amplifiers found wide application [79, 81]. Only after did interest arise in employing this type of control to advantage on the stator of squirrel-cage motors by using electronic switches . It was realised that this offers the possibility to regulate the main current in the motor , and was apparently first extensively investigated by Schilling , see Fig.
Later, attention was devoted to constructing static Ward-Leonard drives in this way see for instance Reference Semiconductor switches increased the possibilities, and it may be expected that the present popularity of this type of semiconductor controlled drive will still continue for some time. In the same way that the thyristor revived the interest in convertor locomotives in countries with AC traction systems, the controlled mercury-arc rectifier originally initiated the design of the convertor locomotive, one of the first examples being that of Reichel .
The problem was to obtain a mechanical or electronic switch that could be operated reliably and fast enough to achieve this control. Many years elapsed before the idea of Blaufuss was taken up again. The first practical realisation of this scheme by electronic means appears to be due to Jones  in the USA and to Abraham, Heumann and Koppelmann  in Germany, the two groups working independently, and employing thyristors as switches. It is interesting to note that the electronic chopper as employed by these groups was discussed in by Hull in relation to the parallel inverter .
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These types of power-electronic systems have since developed rapidly, especially with respect to the circuit improvements possible. Electronic choppers regulating series, parallel and separately excited direct voltage machines are one of the most successful machineelectronics systems at present, finding widespread applications in low-loss control in traction circuits. Some of the important developments in machine electronics are summarised in Table 3.
Table 3: Some important developments in machine electronics Semi-electronic commutator machine Field-regulation of generators by vacuum triodes Field-regulation of generators by vacuum diodes All-electronic commutator machine Electronic Scherbius cascade Electronic Ward-Leonard Control Electronic chopper control Bolliger Van der Bijl, Wold Voorhoeve Kern Alexanderson Schilling Bayha Jones Abraham, Heumann, Koppelman         6 Growth of power electronics in rail drives as an example of application in the control of electric machines From the early attempts outlined in the preceding sections, a tremendous growth has resulted in all fields where power electronics have been applied to condition power flow.
As only one example of this, the applications to the field of electric traction will be traced in some detail in the subsequent paragraphs. With power electronic convertors it is possible to achieve appreciable technical improvements in drives for electric rail vehicles. In this part of the paper the following developments will be discussed: i Replacement of the unfavourable single-phase series commutator motor with DC or pulsating current commutator machines in conjunction with rectifiers ii The control of tractive effort with controlled rectifiers instead of transformer tap changing or with DC choppers instead of resistance variation iii Favourable control of electric braking both for resistive braking and regenerative braking iv Replacement of commutator machines with lighter multiphase AC machines with more favourable maintenance characteristics v Reduction of supply reaction caused by traction drives with line side power electronic convertors.
This solved the problem of energy supply to railways. The price that had to be paid for this was the use of the single-phase AC commutator machine which was unfavourable from the viewpoint of machine construction.bridgegaptraining.com/par-honor-30-smartphone.php
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It is consequently not surprising that with the development of mercury-arc rectifiers, attempts were made to install these elements in traction vehicles to convert the AC to DC, so that normal DC machines with more favourable construction characteristics could be employed. In there were attempts in the USA at using mercury-arc rectifiers in a traction vehicle .
In the following years, General Electric and Westinghouse built experimental railway equipment with mercury-arc rectifiers [92, 93]. Five series E 80 locomotives of the German Federal Railways were put into service in These locomotives used two parallel 6-anode mercury-arc rectifiers in glass enclosures in single-way connection. The control was obtained by means of transformer tap changing and resistors. The Westinghouse Corporation in the USA developed mercury-arc rectifiers in steel tanks with igniters called ignitrons.
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These robust elements without vacuum pumps were well suited for use in traction vehicles. The first experimental vehicle consisted of a multiple unit changed to this system for the Pennsylvania Railroad by the Westinghouse Corporation in [93, 95]. The ignitrons were used in a single-phase bridge connection and the tractive effort was controlled with series resistors. Once this technology proved itself, several American railroad companies ordered series of units using this method.
Between and , 66 rectifier locomotives of the Series 44 are also an example of this technology. The last locomotives of this series were not supplied with ignitrons but with silicon diodes, as these were at that stage already available with a sufficient power capability . In this case a smooth transition from convertor technology with mercury-arc rectifier systems to convertor technology with the much simpler and more robust semiconductor diodes may be observed. The new development was extensively used all over the world.
In France, the Societe Nationale des Chemin de Fers SNCF used ignitron-type rectifier locomotives [, ], as well as excitron type rectifier locomotives [, ].
With the arrival of semiconductor diodes in , the SNCF also used these devices. Multisystem locomotives is a particular problem of the European Railway System. After the Second World War, railway traffic across the borders increased continuously, causing a demand for 2-, 3- and 4-system locomotives.
Several electric circuits were used for these locomotives. Most often the locomotives used circuits with resistive control and motor rearangement in the DC drive mode, where the motor rearrangement was also used as a means of transferring between the DC voltage systems for 1. When the locomotives were fed from AC systems, the supply was via a transformer and a rectifier to supply the DC busbar in the locomotive. From onwards, the mercury-arc rectifiers were replaced with silicon diodes .
A similar development occurred with British Railways BR. After experiments with mercury-arc rectifiers, the first locomotives with multi-anode mercury-arc rectifiers were equipped in With British Rail the transition to semiconductor technology took place by using germanium diodes. After , silicon diodes were used instead. Also in this case, several hundreds of multiple units were equipped with these diodes and tractive control with transformer tap changing [, ]. Many more examples of the transition from mercuryarc rectifiers to silicon-diode rectifiers on railway drives are described in the literature.
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As examples papers about the Swiss [, ], the Swedish , the German , the Indian , and the USSR  development can be found in our Reference list. Soon after the construction of the first mercury-arc rectifier locomotive, suggestions were made to obtain tractive effort control with grid control of the mercury-arc rectifier . In , a locomotive with a grid controlled mercury-arc rectifier for experimental use on a 50 Hz system by the German Federal Railways on the Hollental part of the network was equipped .
During these experiments a locomotive with single phase series field commutator machines, a machine-convertor locomotive with uncontrolled rectifiers , as well as a locomotive with grid controlled mercury arc rectifier  were tested. This last locomotive, representing a very important state in the development, was equipped by the AEG Company.