Machine transformer
A machine transformer , also block transformer or Maschinenumspanner called ( English generator Transformer ), in which electrical energy technology , a power transformer , which as part of a power plant in the electric generator generated electrical voltage in high voltage transformed to those in the power network feed.
General
The synchronous generators used in medium-sized to larger power plant blocks to convert the mechanical power supplied by the turbine , such as the turbo generators, can only be designed for generator voltages of a few kilovolts due to their design: For a block output of up to 40 MVA , 6.3 kV is common, and for large power plant blocks of over 1000 MVA up to 27 kV are achieved. The very high generator currents of a few 10 kA that occur with these powers can not be distributed economically, since the losses along a line due to the electrical resistance increase squarely with the current.
The machine transformer therefore converts the generator voltage to the significantly higher voltages customary in the high-voltage network, for example 220 kV or 380 kV, with the current being reduced by the same factor by which the voltage is increased. Due to their high performance and a weight of over 500 tons, machine transformers are among the largest technically used transformers.
In power plants that cannot be black-started , such as some coal-fired power plants , the energy required to start up is taken from the power grid via the machine transformer. In this operating mode, the machine transformer is operated briefly "backwards" and supplies the power for the power plant's own requirements.
Control devices
In addition to the necessary cooling and control devices, most machine transformers are equipped with a step switch for setting the reactive power (indirectly via the generator voltage regulator), which regulates the power supply voltage during start-up. There is also a generator circuit breaker between the generator and the machine transformer , with which the generator can be disconnected from the machine transformer.
safety
Due to their high performance, machine transformers are designed as oil-filled and usually as three-phase transformers. Single-phase machine transformers are also used in power plants in special areas of application such as traction current . The mineral oil used in the transformer is used for electrical insulation and heat dissipation to the outside. Insulation faults in the transformer can be detected using special safety devices (such as the Buchholz relay ). In the event of serious insulation faults, overheating leads to excessive gas formation in the oil, resulting in a transformer fire.
In the case of a fire that is difficult to extinguish, the transformer is usually destroyed, since the fire fighting must be limited to cooling the outer wall. In order to avoid consequential damage to the rest of the infrastructure, power transformers are therefore structurally separated and positioned in the outer area of the power plant and separated from the machine house or other parts of the plant by fire protection walls. When planning a power plant, attention is also paid to quick interchangeability, for example the transformers are mounted on rollers and guided in rail systems.
Literature sources
- René Flosdorff , Günther Hilgarth: Electrical energy distribution . 8th edition. Teubner, 2003, ISBN 3-519-26424-2 .
- DIN EN 50464-1: 2007 (VDE 0532-221): Oil-filled three-phase distribution transformers 50 Hz, 50 kVA to 2500 kVA