Energy has long been an integral part of civilization. Without it, it is simply impossible to imagine life. That is why the issue of uninterrupted energy supply to consumers is being raised more and more sharply. Parallel operation of transformers is one such method. However, is this method used only for redundancy, and what are the requirements for equipment?
Why is parallel operation of transformers necessary?
As mentioned above, the initially agreed work was caused by the need to improve the reliability of power supply. However, there are other, equally important features, when parallel operation of transformers is necessary. These moments include:
- rapid increase in load, which in the near future will exceed (or already exceed) the power of one working transformer;
- lack of space (height, width) may not allow you to install one large transformer, however, you can arrange two small ones and include them in parallel;
- Naturally, safety measures play an important role, since the probability of failure of both transformers at once is extremely small, but there is one, therefore, in addition to such an event as parallel operation of transformers, other backup methods are also used.
Commissioning of two transformers
The inclusion of transformers for parallel operation provides redundancy of critical receivers of electrical energy, which implies uninterrupted power supply. Most substations use two or more transformers (exceptions are low-power through-type substations). Work in parallel is allowed if both transformers meet a certain set of requirements, which are called "Conditions for parallel operation of transformers":
- winding groups should be identical to each other;
- transformation coefficients must be equal to each other, an insignificant deviation is allowed within the permissible normalized limits;
- short-circuit voltages must be equal to each other, an insignificant deviation within the permissible normalized limits is allowed;
- parallel transformers must be powered from a single network;
- the secondary cables needed to connect the transformers at the point should have approximately equal characteristics and length;
- the phase shift between the voltages of the primary and secondary windings should be the same.
The need for preliminary calculation
If one of the two transformers is damaged, it is not always possible to select exactly the same one that would fully correspond to the damaged one according to the conditions and operating modes. In these cases, the choice of a transformer is justified by complex preliminary calculations, which show that the windings of both transformers will be loaded uniformly, and none of them will exceed the load capacity of each individual transformer in terms of load.
Short circuit voltage
Parallel operation of transformers is possible with relative equality of the values of short-circuit voltages on the windings. If the short circuit values are different, then before switching on to joint work, it is necessary to first change the transformation coefficient of one transformer using a special switch. In this way, compensation for redistributed loads that arise due to differences in short circuit voltages can be achieved. The surge currents arising due to such a mismatch will not overload the transformer with a lower short-circuit voltage.
Naturally, it is necessary to take into account the load capacity - both separately for each electrical appliance, and during such an event as the parallel operation of power transformers. At idle mode, however, the difference in the values of the short circuit voltage does not affect at all, because the transformation coefficients are equalized and become the same. Under load, the secondary voltages will be different, since unequal voltage drops can lead to the flow of equalizing currents through the windings, while at one transformer the equalizing current will be summed with the main one, and subtracted from the second. The recommended power ratio of the most powerful transformer to the most low-power should be no more than three to one.
Allowed Conditions
Parallel operation of three-winding transformers, two-winding transformers on all windings is possible. It must be remembered that for electrical appliances connected in parallel, the load is distributed inversely proportional to the short circuit voltage and in direct proportion to the power of each individual transformer. Parallel operation of transformers, if the connection groups of the windings are different, is possible on all odd groups. If the switching is not consistent, then due to the angle of shift between the terminals of the secondary windings, a voltage appears that causes an unacceptable surge current.