Parallel operation of transformers - application conditions

Energy - has long been an integral partcivilization. It is simply impossible to imagine life without it. That is why the issue of the continuity of energy supply to consumers is becoming increasingly acute. The parallel operation of transformers is one such way. However, is this method used only for reservation, and what are the requirements for the equipment?

parallel operation of transformers

Why do parallel transformers work?

As already mentioned above, the initially agreedthe work was caused by the need to improve the reliability of electricity supply. However, there are other, no less important features, when parallel operation of transformers is necessary. Such moments include:

  • a rapid increase in the load, which in the near future will exceed (or already exceeds) the power of one operating transformer;
  • The lack of space (height, width) may not allow the installation of one large transformer, but you can arrange two small ones and include them in parallel;
  • of course, security measures play an important rolerole, since the probability of failure of both transformers is extremely small, but it is, therefore, in addition to such an event as the parallel operation of transformers, other methods of redundancy are used.

switching transformers on parallel operation

Commissioning of two transformers

Switching transformers on parallel operationprovides redundancy of especially responsible receivers of electrical energy, which implies the uninterrupted power supply. Most substations use two or more transformers (exceptions are low-power substation type). Work in parallel is allowed if both transformers meet a certain set of requirements, which are called "Transformer Parallel Operation Conditions":

  • groups of windings must be identical to each other;
  • the transformation coefficients must be equal to each other, an insignificant deviation in the allowed normalized limits is allowed;
  • the short-circuit voltage must be equal to each other, an insignificant deviation in the allowed normalized limits is allowed;
  • parallel transformers must be powered from a single network;
  • The secondary cables required to connect the transformers at a point must have approximately the same characteristics and length;
  • The phase shift between the voltages of the primary and secondary windings should be the same.

conditions of parallel operation of transformers

Necessity of preliminary calculation

If one of the two transformers is damagedit is always possible to pick up absolutely the same one, which completely corresponded to the damaged by the conditions and operating modes. In these cases, the choice of the transformer is based on complex preliminary calculations, which show that the windings of both transformers will be loaded evenly, and none of them will not be overloaded by the load capacity of each individual transformer.

parallel operation of power transformers

Short-circuit voltage

Parallel operation of transformers is possible withthe relative equality of the values ​​of the short-circuit voltage on the windings. If the values ​​of the faults are different, then before switching on in the joint operation, it is necessary to first change the transformer ratio of one transformer using a special switch. In this way, it is possible to achieve compensation of the redistributed loads that arise due to differences in short-circuit voltages. Due to this discrepancy, the equalizing currents will not overload the transformer with a lower short-circuit voltage.

Naturally, it is necessary to take into account loadingability - both separately from each electrical appliance, and during such an event as the parallel operation of power transformers. At idle, however, the difference in the values ​​of the short-circuit voltage is not affected at all, because the transformation coefficients are equalized and become the same. Under the load, the secondary voltages will be different, since unequal voltage drops can lead to the flow of equalizing currents along the windings, while in one transformer the equalizing current will be added to the main current, and the second will be subtracted. The recommended ratio of the powers of the most powerful transformer to the lowest power should be no more than three to one.

Admissible conditions

Possible parallel operation of transformersthree-winding, two-winding on all windings. It must be remembered that for electrical appliances connected in parallel, the load is distributed in inverse proportion to the short-circuit voltage and is directly proportional to the power of each individual transformer. The parallel operation of the transformers, if the winding connection groups are different, is possible on all odd groups. If the switching is not coordinated, a voltage arises between the clamps of the secondary windings due to the angle of shear, which causes an unacceptable equalization current.

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