Parallel Operation of Transformers

Parallel Operation of Transformers

Many developments such as that of technology in recent years, and the rapid population growth have led to the growth of cities. Due to these growths, humanity’s need for energy has increased more than ever before. In order to meet this need, new energy production facilities are established and different ways are sought. It is a reality that developments in energy needs and supply are expected to increase in the future. It is possible to easily foresee that the problem of energy needs will not be removed in the near future, while a considerable part of humanity still have problems in reaching this need. Energy continuity is as important as energy production today, especially in strategic centers, hospitals, factories and many places; it is very critical that energy be continuous.

When electrical energy is mentioned, transformers are the most basic Electrical Machine that comes to minds. Transformers; have been used for many years in many fields such as energy generation, transmission and distribution. They are produced in different power and voltage levels according to the system needs. With developing technologies, the increase in the energy needed in systems has brought the issue of parallel connection of transformers to the agenda. This article focuses on the parallel operation of transformers.

In many systems, the load demand increases over time and the existing transformers are not enough to meet them after a point. In order to meet the increasing load demand, it is necessary to increase the transformer capacity. There are two methods for doing this

Instead of the existing transformer, another high-power transformer is placed.

Another transformer is connected in parallel with the existing transformer.

This article seeks, to examine the parallel connection of transformers.

Parallel Connection Of Transformers

In case of an increase in load demand in existing systems, although the existing transformer is usually replaced with a transformer with a higher power level, the most economical solution is to connect 2nd or more transformers in parallel to the system. Thus, the total current to be drawn from the transformers will increase and the system will continue to be fed uninterruptedly. Parallel connection of transformers is in many ways an economical and reasonable solution. There are some special conditions for connecting transformers in parallel.

The conditions required for parallel connection of transformers are as follows.

The power of the transformers should be equal to each other or close to each other in a way that does not exceed 3/1 ratio. (The most ideal is equal power)

The short circuit voltages (%Uk) of the transformers should be equal to each other.

Frequencies of transformers should be equal to each other.

The difference between the short-circuit impedances of the transformers should be at most 10%.

Phase differences between HV-LV should be equal.

The polarities of the transformers must be equal to each other.

The conversion ratio of the transformers should be equal to each other.

Parallel Connection of Transformer Ideal Operation

Currents shared by transformers should be proportional to MVA.

No current should flow between the primary and secondary windings of the transformers.

No short circuit between phases should be allowed. Therefore, the phase sequences must be the same when connecting transformers.

The conversion steps of the transformers must be equal. If this is not the case, failures will occur in the relay, which is exposed to different current levels from the two transformers.

Transformer, cell and panel distances should be positioned considering very high short-circuit currents.

Advantages of Parallel Operation of Transformers

• High efficiency is achieved at much lower costs.
• It provides a great advantage in maintenance and energy continuity. In case of maintenance and failure, the system continues to be fed from the backup transformer and does not remain without energy. In this way, system security is ensured.
• It provides a flexible solution opportunity.
• It has benefits such as ensuring system continuity and energy security in critical centers, as there is a possibility of redundancy.

Disadvantages of Parallel Operation of Transformers.

• Risk of very high short-circuit currents.
• High probability of error due to technical confusion in the system.
• Since it is a complex system, a lot of auxiliary equipment is needed.
• Risk of formation of circulating currents between transformers.
• Due to high current, it can cause big errors in cases where it is not used correctly.

In summary, parallel connection of transformers has some risks but it provides benefits in many respects. A system that is planned to operate in parallel with transformers should be commissioned after examining in detail and making sure that all calculations are made correctly. After the correct design of the system, it provides many benefits in terms of economy and flexibility.

VEKMAR supplies all these range of transformers as official distributor of ABB, Legrand, Eaton, Astor and Eltaş brands. We can help you for your medium voltage transformer projects with our expert engineering team.