transformers!

                                                                transformers:

                 general operating principle of a transformer

Transformateur monophasé:

                           In a simplified manner, a transformer is composed of a magnetic core (soft silicon steel) on which are arranged two copper windings: winding connected to the source of energy is the "primary" and the connected winding to receivers is the "secondary".

                          The two windings have a number of turns (tours) different: the greater the winding "high voltage (HV)" and smaller, winding "low voltage (LV)".

                        The voltage transformation ratio is proportional to the ratio between the number of turns of each winding.

 three-phase transformer:

                           A three-phase transformer comprises a core with three branches which are combined on the primary and secondary windings concentrically or alternately.

Loss of a transformer:

The losses consist of a transformer load losses and load losses.

                          load losses (or losses "iron") occurring within the ferromagnetic core. They are constant regardless of the charge rate of the transformer, that is to say, regardless of the consumption of the building connected thereto.

                          cover the losses (or losses "shorted" or loss "copper") are, they, due to the Joule effect (loss of warm or strapping son carrying a current), plus additional losses (additional losses caused by eddy currents in the windings and structural parts). They vary with the square of the current or power output (if the voltage remains constant).

                       Note: the name "copper losses" dates from the time when all the coils were made of copper. This is still the case for very small powers. For other processors, manufacturers have turned to aluminum. Therefore, there is now talk of "short-circuit losses."

therefore expresses the total loss of a transformer by:

W = Wfe + Wcu x (S/Sn)²

or :

W = total losses of the transformer full load [W]

Wfe = iron losses (constant) [W]

Wcu losses = short circuit at rated load [W]

Sn = rated power of the transformer [VA]

S = load applied to the [VA]

      dry transformers:

                                Cast resin transformers: the LV windings and windings are concentric and embedded in an epoxy resin.

                                Dry transformers are made up of coils wrapped in an epoxy resin.

They may be disposed in a protective envelope (IP 315 or IP 235) which can isolate the transformer from the outside world and to ensure the removal of heat through its walls.

                                   Dry transformers have the best guarantees of security against fire and against pollution (not liquid leakage, no noxious fumes in case of fire).

                                   Dry transformers can be installed in a protective housing (IP 315 and IP 235) or without protection.

In this case, they must be protected against direct contact.

                                                      

  mineral oil transformers:

                                   In this type of equipment, also called immersed transformers, transformer is arranged in an oil bath which provides insulation and cooling.

These processors are less expensive and have lower losses. However, they have a risk of fire and pollution:

An internal failure can cause pressure and deformation of the vessel such as oil leaks may occur. Depending on the circumstances, this can cause inflammation of the oil or explosion.

Oil leaks can also result from a defective joint or a pipe burst. The oils that spread can pollute groundwater. Must therefore be provided under the transformer a drainage pit or an oil holding tank.

                               Burning oil releases toxic products and generates opaque smoke hindering the emergency services.

                               There are still a few years it was selling processors called "askarel". The oil of these transformers contained PCBs. These substances give off noxious fumes during fires and present high concentration of hazards to human health. This is why the European Directive 96/59 / EC is in favor of removing contaminated or PCB-containing equipment.