{"id":3070,"date":"2026-07-10T08:57:19","date_gmt":"2026-07-10T00:57:19","guid":{"rendered":"http:\/\/www.lire-en-serie.com\/blog\/?p=3070"},"modified":"2026-07-10T08:57:19","modified_gmt":"2026-07-10T00:57:19","slug":"what-are-the-requirements-for-parallel-operation-of-substation-transformers-4e61-f774b1","status":"publish","type":"post","link":"http:\/\/www.lire-en-serie.com\/blog\/2026\/07\/10\/what-are-the-requirements-for-parallel-operation-of-substation-transformers-4e61-f774b1\/","title":{"rendered":"What are the requirements for parallel operation of substation transformers?"},"content":{"rendered":"

Hey there! I’m a supplier of substation transformers, and today I wanna chat about the requirements for the parallel operation of these transformers. It’s a topic that’s super important in the power industry, and I’ve seen firsthand how getting it right can make a huge difference. Substation Transformer<\/a><\/p>\n

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First off, let’s talk about what parallel operation of substation transformers actually means. When we run transformers in parallel, we’re basically connecting two or more transformers to the same busbars. This setup allows us to increase the total capacity of the power system, share the load more evenly, and improve the reliability of the supply. But to make this work smoothly, there are a few key requirements we gotta meet.<\/p>\n

Voltage Ratio<\/h3>\n

One of the most crucial requirements is that the voltage ratios of the transformers must be the same. The voltage ratio is the ratio of the primary voltage to the secondary voltage. If the voltage ratios of the transformers in parallel are different, it’ll create a circulating current between them. This circulating current doesn’t do any useful work and can cause overheating in the transformers, which is a big no – no.<\/p>\n

For example, if we have two transformers, and one has a voltage ratio of 10:1 and the other has a ratio of 10.5:1, there’ll be a potential difference between their secondary windings. This potential difference will drive a current to flow between the transformers, even when there’s no load connected to the secondary side. So, before we connect transformers in parallel, we need to make sure their voltage ratios match as closely as possible.<\/p>\n

Percentage Impedance<\/h3>\n

The percentage impedance of the transformers also needs to be similar. The percentage impedance is a measure of the transformer’s internal resistance and reactance. It affects how the transformers share the load. If the percentage impedances of the transformers are too different, the transformer with the lower impedance will take a larger share of the load, while the one with the higher impedance will take a smaller share.<\/p>\n

Let’s say we have two transformers with different percentage impedances. The one with the lower impedance will act like a more "eager" load – taker. It’ll draw more current, and this can lead to overloading of that transformer. On the other hand, the transformer with the higher impedance might not be fully utilized. To ensure a proper load – sharing between the transformers, we usually aim for the percentage impedance to be within a certain tolerance, typically around 10%.<\/p>\n

Phase Sequence<\/h3>\n

The phase sequence of the transformers must be the same. Phase sequence refers to the order in which the voltages in a three – phase system reach their maximum values. If the phase sequences of the transformers are different, it’ll result in a short – circuit condition when they’re connected in parallel.<\/p>\n

Imagine a three – phase system with phases A, B, and C. If one transformer has a phase sequence of ABC and the other has a sequence of ACB, when we try to connect them in parallel, there’ll be a large current flowing between the phases due to the phase difference. This can cause serious damage to the transformers and the entire power system. So, before connecting transformers in parallel, we need to double – check the phase sequence using appropriate testing equipment.<\/p>\n

Polarity<\/h3>\n

Polarity is another important factor. In single – phase transformers, the polarity indicates the direction of the induced voltage in the secondary winding with respect to the primary winding. In three – phase transformers, it’s a bit more complex, but the principle is the same. If the polarities of the transformers are not the same, it’ll lead to a short – circuit when they’re connected in parallel.<\/p>\n

For single – phase transformers, we can use a simple test to check the polarity. We connect the primary windings of the transformers to the same source and then measure the voltage across the secondary windings. If the polarities are correct, the measured voltage will be the sum or difference of the individual secondary voltages, depending on how we connect the windings. For three – phase transformers, more sophisticated testing methods are required to ensure the correct polarity.<\/p>\n

Vector Group<\/h3>\n

In three – phase transformers, the vector group is a key parameter. It describes the phase relationship between the primary and secondary voltages. Transformers with different vector groups cannot be connected in parallel. Each vector group has a specific angular displacement between the primary and secondary voltages.<\/p>\n

For example, a transformer with a vector group of Dyn11 has a 30 – degree angular displacement between the primary and secondary line voltages, while a transformer with a vector group of Yyn0 has no angular displacement. If we try to connect these two transformers in parallel, there’ll be a large circulating current due to the phase difference. So, when selecting transformers for parallel operation, we need to make sure they have the same vector group.<\/p>\n

Why Meeting These Requirements Matters<\/h3>\n

Meeting these requirements is not just about following some technical rules. It has real – world implications for the power system. When transformers are operated in parallel correctly, it improves the overall efficiency of the power system. The load is shared evenly among the transformers, which means that each transformer can operate at its optimal efficiency point.<\/p>\n

It also enhances the reliability of the power supply. If one transformer fails, the other transformers can continue to supply power to the load, reducing the risk of a blackout. And from a cost – perspective, parallel operation allows us to increase the capacity of the power system without having to install a single large – capacity transformer, which can be more expensive.<\/p>\n

Our Role as a Supplier<\/h3>\n

As a substation transformer supplier, we play a crucial role in ensuring that these requirements are met. We provide transformers with accurate voltage ratios, well – matched percentage impedances, and the correct phase sequence, polarity, and vector group. We also offer technical support to our customers to help them with the installation and parallel operation of the transformers.<\/p>\n

We understand that every power system is unique, and our team of experts can work with you to select the right transformers for your specific needs. Whether you’re looking to upgrade an existing substation or build a new one, we can provide you with the best solutions.<\/p>\n

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If you’re in the market for substation transformers and want to learn more about parallel operation or discuss your requirements, don’t hesitate to get in touch. We’re here to answer your questions and help you make the right choices for your power system.<\/p>\n

References<\/h3>\n