Motor–generator

A transducer is in electrical power engineering a mechanical combination of rotating electrical machines, a current type to another, for example, dc to ac converted. Also, a conversion between alternating current with different frequencies is possible to frequency converter can be used.

A similar scope have the drive and in particular frequency, but unlike transformers representing a power electronic device without mechanically moving components.

Basics

Converters of the AC network, which is then used transformers and semiconductor rectifiers and inverters were also common for low power before the introduction. Today units for large services are only operated. A large-scale application is still in Bahnstromumformerwerken. The Bundeswehr still uses converters to supply aircraft for maintenance work with power.

Construction

A rotary transformer composed of an electric motor which drives a generator for the desired type of current. Both can be implemented or they consist of only one machine ( so-called rotary converters ), in which is both a converter set, that is, as a single, coupled with its wave machine. Such rotary converters have no outwardly projecting shaft.

Applications

Having an input coupled to a mains-powered asynchronous motor, an externally excited direct current generator can be produced, for example, by controlling the excitation of a variable DC voltage.

If, with a constant drive speed, the output frequency to be variable, you can:

• A synchronous generator is energized with an alternating voltage of variable frequency
• A variable DC voltage (see above) is connected, a further transformer set consisting of the DC motor and a synchronous generator.

Further applications of transformers and machine sets are in the interception of load surges as they occur for example in rolling drives in steel mills or in the supply of high voltage laboratory. Due to the inertia and mechanical decoupling so abrupt load fluctuations can be avoided in the electrical supply network.

The Leonardsatz, a machine set to a variable speed drive large machines not heard, actually to the converters, due to the similar components used and principles he is here but also described.

Rotary converters

Rotary converters were used for low power, for example, to generate low voltages from the original DC power. Another application of small rotary converters for example, was the generation of the 400 - Hz three-phase current ( 36 V ) for operation of centrifugal engines in gyros or the artificial horizon from the 28- volt DC electrical system of aircraft. Such small converters had a permanent magnet excitation, their output voltage could therefore only be influenced by the input voltage.

Traction power

The frequency of long-distance train current in Germany and other European countries is 16.7 Hz or 25 Hz These low frequencies were chosen as a compromise in order to operate a hand in the locomotive a variable transformer can ( the wide transmission also requires a high voltage, with that can not be directly operated the engines) and on the other hand effectively to feed the series-wound DC motors of the drive ( these work best but at least better than at 50 Hz) with direct current at a low frequency. The frequencies used arise specifically from the divider ratio of 1:2 or 1:3 of the mains frequency 50 Hz, so that they could be produced with different pole pair converters in motor and generator on a common shaft from this. Traction power converters phrases have a separate excitation so that the voltage output can be controlled. They are capable of regenerative feedback.

Leonardsatz

The Leonardsatz is named after its inventor, the American electrical engineer Harry Ward Leonard, also Ward-Leonard converters. It consists of a converter ( formed of three-phase current into a variable DC voltage ) and a connected d.c. motor. The Leonardsatz used to be the only way for the realization of large variable speed drives, which were fed with AC.

The illustrated portion of a transducer is used to supply and control Leonardsatzes a reciprocating engine of a motor test bed and consists of:

• Said drive (1), an induction motor
• The generator ( 2), an externally excited direct current machine
• The excitation generator (3 ), a small auxiliary DC power generator for generating the excitation voltage for (2)

A Leonardsatz consists of a transducer, the first generated using an induction motor and a mechanically coupled thereto via a DC generator whose excitation controllable DC voltage ( voltage conversion ). The primary drive is usually a directly connected to the AC power induction motor, but could also be a DC motor or an internal combustion engine to be. The information provided by this converter variable DC voltage feeds a DC motor whose excitation is partially also varied. The engine can also be accommodated spatially separated from the transformer set, namely the driven machine ( mill, elevator, spinning machine, etc.). Loading devices of engine test benches use the fact that a Leonardsatz is capable of regenerative feedback, that is, it can supply power back into the network when the output of the DC motor is driven - this then acts as a generator, the DC machine of Umformersatzes as a motor and the induction motor as an induction. See also pendulum machine.

Usually a Leonardsatz also includes an exciter generator ( shunt machine ) to provide the DC machines an excitation voltage. This exciter generator is also driven by the prime mover. The small excitation power can be controlled with a variable resistor. The armature of the direct current generator is directly connected to the armature of the DC motor; this DC voltage intermediate circuit transmits the power, the large current flowing therein must not be connected - one of the advantages of Leonardsatzes. The excitation current of the motor is not normally changed in order to have the maximum torque at all speeds available. Field weakening means may, however, the rotational speed to be increased at the expense of torque about the rated speed.

The Ward-Leonard set enables low-loss variable speed drives and also the energy recovery during braking. In addition, the DC motor can also be intermittently loaded without that transfer the load surges on the power ( inertia of the machine set ). The starting of the DC motor and the driven machine is carried out by ramping up the voltage of the generator is zero, by the excitation current of the DC generator is gradually increased. A high inrush occurs therefore only at the start of the induction motor.

Ilgner converter

The Ilgner converter based on the same principle as the Leonardumformer. Its special feature is simply a large flywheel which is coupled to the AC motor. This flywheel stores kinetic energy which can be used differently:

• It may thus drive failures are bridged
• It can be intercepted load surges as they occur in steel mills, for example, in rolling drives.

Leonardsätze found their application from the early 1920s and run in part to this day. Good alternatives arose only through thyristor and inverter. In this case, however, electric storage are required to replace the mechanical energy storage device of Ilgner converter.

An intermittent network load of rolling mills, electric steel furnaces or other arc furnaces leads today to problematic mains voltage fluctuations, so often you build it near power plants whose generators and turbines load fluctuations can compensate because of their inertia.