Parallel operation of transformers - terms of use

Energy – has long been an integral part of civilization. Without it, imagine living it is simply impossible. Indeed, the issue of continuity of power supply is becoming more acute. Parallel operation of transformers – one of such ways. However, is it only for backup use this method, and what are the requirements for the equipment?

Why parallel operation of transformer?

As mentioned above, the initially agreed work was caused by the need to improve the reliability of power supply. However, there are other, no less important, especially when parallel operation of transformers is required. Such moments include:

• The rapid growth of load, which in the near future will exceed (or exceed) the working capacity of one transformer;
• Lack of space (height, width) may not allow you to install a single large transformer, but it is possible to arrange two small and include them in parallel;
• Naturally, the security measures play an important role since the probability of failure of both transformers is very small, however, it is, therefore, in addition to this event as parallel operation of transformers, use other methods of backup.

Commissioning of two transformers

The Inclusion of transformers in parallel operation provides redundancy of critical receivers of electric energy, which implies uninterrupted electricity supply. Most substations have two or more transformers (the exceptions are low-power substations, transmission type). Working in parallel is allowed if both of the transformer correspond to a certain set of requirements, called “the conditions of parallel operation of transformers”

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• Groups of windings must be identical to each other;
• The coefficients of transformation are required to be equal to each other, allowed the insignificant deviation within acceptable specified limits;
• Voltage short circuit must be equal to each other, allowed the insignificant deviation within acceptable specified limits;
• Parallel transformers are required to eat from a single network;
• Secondary cables required to connect the transformers at the point should have approximately equal characteristics and length;
• The phase shift between voltages of primary and secondary windings must be the same.

The Need to pre-calculate

Damage to one of the two transformers is not always possible to pick up exactly the same, which would be entirely consistent with the damaged condition and modes of operation. In these cases, the choice of transformer is grounded in a complex pre-calculations, which show that the windings of both transformers are loaded evenly, and none of them will load to exceed the load capacity of each individual transformer.

Short-circuit Voltage

Parallel operation of transformers is possible when the relative equality of the values of the voltages, short circuits on the windings. If the values of KZ are different, before turning in the work, you must first change the transformation ratio of one transformer with a special switch. Thus it is possible to achieve compensation of redistributed loads, which arise due to the differences of the short-circuit voltages. Occurs due to this mismatch the cross current will not overload the transformer with a lower voltage value of KZ.

Of Course, it is necessary to consider load capacity - how separately from each electrical appliance, and during such events as the parallel operation of power transformers. At idle, however, the difference in the voltage values of the short circuit is absolutely not affected, because the coefficients of transformation are equalized and become the same. Under the same load secondary voltage will be different because of unequal voltage drops can lead to the flow of surge currents in the windings, while in one transformer the equalizing current will be summed with the main and the second to be deducted. The recommended power ratio, the most powerful transformer to the low power should be no more than three to one.

Acceptable

The Possible parallel operation of three-winding transformers, two-winding all the windings. It must be remembered that the appliances included in parallel, the load is distributed inversely proportional to the short-circuit voltage and is directly proportional to the power of each individual transformer. Parallel operation of transformers, if the group of connection of windings of different, possible all odd groups. If the inclusion is not in concert, due to the angle shift between the terminals of the secondary windings, a voltage is applied that causesinvalid surge current.