When a de-energized tap-changer has to maintain a huge test voltage of 1,000 kilovolts and switch 112 kilovolts in a single step, size really does matter. The experts at Maschinenfabrik Reinhausen (MR) have built three of these giants for the Canadian transformer manufacturer PTI Transformers.
The largest de-energized tap-changers in MR’s portfolio measure three meters in length and one meter in diameter. No other supplier includes tap changers of this size as standard in its portfolio or has so much experience in highly specialized areas of application. However, at the outset, it wasn’t clear if the de-energized tap-changers PTI Transformers needed would be technically feasible even for MR.
Switching step of 112 KV
PTI Transformers had been commissioned by a Canadian energy provider to replace a transformer for a hydroelectric power plant that had reached the end of its service life. The new transformer had to be able to switch between one transmission line at 250 kilovolts and another at 143 kilovolts. The test voltage required was a massive 1,000 kilovolts. “From our point of view, the huge challenge of having to bridge a switching step of 112 kilovolts while maintaining a test voltage of this magnitude meant that there was only one supplier we wanted to work with—and that was MR,” states George Partyka Jr., Vice President of PTI Transformers. There was no doubt at all in the mind of the Canadian manager that MR could bring its technical know-how and its expertise to bear in building a de-energized tap-changer (DETC) to this specification. But it was obvious that it wouldn’t be easy.
Karl-Heinz Sperger, MR project manager, said: “Historically, we have always relied upon rotary de-energized tap-changers with a head design. De-energized tap-changers of this magnitude can only be produced using this type of design. A straight-line de-energized tap-changer would need to be more than ten meters long to achieve the kind of performance values we were looking for.” One of the challenges that arose during the development stage was that MR’s design was only able to accommodate test voltages up to a maximum of 750 kilovolts. Mr. Sperger explains: “While these de-energized tap-changers are huge, there are still certain restrictions on the space we have to work with and we can’t just increase the distance between the contacts as much as we want. That made the physics of this project a real test. But true to our motto “If something is doable, we’ll do it” we worked together with PTI Transformers to find the right solution.”
Another significant factor contributing to the complexity of the project was the transmission ratio of 1:1.78. Switching 143 kilovolts to 250 kilovolts in a single step requires six high-voltage winding strands — for every phase. For PTI Transformers, this meant housing 18 windings and three of the massive tap changers within the transformer, something which, as PTI Transformers’ Mr. Partyka explained, was only possible with MR’s support: “The transformer power is highly dependent on the tap-changer capacity, so the development departments working on the tap-changer design and the transformer design had to work together very closely. Only as a team was it possible for us to coordinate the winding configuration with the special design of the tap changer.” The PTI Transformers and MR experts completed this complex development task in a mere three months, resulting in the order being placed in February 2019 and allowing the de-energized tap-changers to go into production. The technicians were then able to construct the three special pieces of equipment in just five days.
Maschinenfabrik Reinhausen GmbH (MR) consists of 42 subsidiaries and 7 affiliated companies globally. Our core business is the regulation of power transformers. This is done above all with the aid of tap changers, which adapt the transmission ratio of the primary to secondary winding to changing load ratios and, together with additional, innovative products and services, ensure an interruption-free power supply. Through increasing integration of renewable energies into the power network, this regulation also has an ever-increasing importance on the distribution network level. Here, we likewise provide innovative system solutions. Together with conceptual design of systems for reactive power compensation and accompanying services, such as network analysis and calculation, we round out our network regulation offerings.