Old transformer like new again

New tap chang­ers from Rein­hausen make old trans­form­ers ready for the future. This was the case for grid oper­a­tor Elia in the Bel­gian town of Zaven­tem.

Apow­er trans­former that has been in use for many years is like a per­son: It ages and needs more fre­quent health checks. Over time, the costs add up—especially if the trans­former requires replace­ment parts that are no longer avail­able or dif­fi­cult to come by.Belgian grid oper­a­tor Elia was fac­ing this exact prob­lem in its pri-mary sub­sta­tion in Zaven­tem, in the exurbs of Brus­sels. A trans­former had got­ten old­er and the tap chang­er inside was worn out. Since the man­u­fac­tur­er had ceased pro­duc­tion back in 1989, replace­ment parts were increas­ing­ly scarce and expen­sive.

How­ev­er, a new trans­former was out of the ques­tion for Elia. After all, all oth­er com­po­nents were still func­tion­ing with­out prob­lems. So the grid oper­a­tor com­mis­sioned ser­vice provider Main­te­nance Part­ners, togeth­er with the Rein­hausen Lux­em­burg (RLU) sub­sidiary, to replace the old tap chang­er with a new one in ear­ly May, thus future-proof­ing the trans­former.

The entire con­ver­sion took only ten busi­ness days, despite the added com­pli­ca­tions of the coro­n­avirus pan­dem­ic. Sebas­t­ian Hölz­er, Man­ag­ing Direc­tor of RLU, explains how the team got it done in six steps:

1 Getting to know the transformer

Every pow­er trans­former is dif­fer­ent. For that rea­son, we first com­piled all the infor­ma­tion from the trans­former book and name­plates. This includ­ed the pow­er of the trans­former, the line and insu­la­tion volt­ages and the sup­ply volt­age for the motor-dri­ve unit. Fur­ther­more, we were able to use this data to deter­mine how much cur­rent was sup­posed to flow through the new tap chang­er and how the elec­tri­cal wiring should look.

2 Selecting components

With this pre­lim­i­nary knowl­edge, it was clear that only a three­p­hase VACUTAP VM 500 with Y con­nec­tion would be a pos­si­ble tap chang­er, which requires almost no main­te­nance in com­par­i­son to the old OILTAP OLTC. Fur­ther­more, our experts in Regens­burg explained how the adapter flange need­ed to look for the switch head, so that we could insert the new tap chang­er into the open­ing of the old one. We also spec­i­fied the equip­ment of the motor-dri­ve unit togeth­er with Elia. We then pro­duced the tap chang­er and dri­ve in-house. A third-par­ty steel man­u­fac­tur­er pro­duced the adapter flange.

3 Preparing the transformer

Before replac­ing the tap chang­er, the ser­vice provider Main­te­nance Part­ners pre­pared the trans­former for two days. The trans­former first need­ed to be switched off and ground­ed. Oil was then drained from the trans­former tank and man­holes were cut in the 15-mil­lime­ter thick trans­former wall. This allowed our tech­ni­cians to climb into the inside of the cramped trans­former tank, in full-body suits, and start the replace­ment work.

4 Replacing old with new

First, the old tap chang­er need­ed to be removed. To do so, we cut open the cov­er using a blow torch and lift­ed the tap chang­er out of the trans­former tank by crane.

We were then able to bring in the oil com­part­ment of the new tap chang­er, along with the divert­er switch insert, and posi­tion the selec­tor. Then we con­nect­ed the selec­tor in the trans­former with the tap wind­ing and to the old sup­ply lines via indi­vid­u­al­ly adjust­ed cables. Final­ly, the motor-dri­ve unit and the link­age from the tap chang­er to the dri­ve were attached.

5 Testing and measuring

Test­ing was done in the next step. For this pur­pose, experts from Main­te­nance Part­ners mea­sured the trans­mis­sion ratio at low volt­age to see whether the tap chang­er stepped down the volt­age prop­er­ly. In this way we were able to ensure that all sup­ply lines were attached to the cor­rect points on the selec­tor. Mea­sure­ments of the resis­tance and iso­la­tion took place lat­er.

6 Back on line

This con­clud­ed the work onsite. Main­te­nance Part­ners closed the trans­former tank again and filled it with oil. The oil was then treat­ed — in oth­er words, dried, degassed and cleaned to remove con­t­a­m­i­na­tion par­ti­cles. For this pur­pose, the filled trans­former need­ed to be con­nect­ed to a pro­cess­ing sys­tem for sev­er­al days. After­wards, we hand­ed the trans­former over to Elia and, after a two-day no-load test, it was back on line.

“Next to the qual­i­ty of the OLTC itself, the qual­i­ty of the replace­ment work is also cru­cial to guar­an­tee a high reli­a­bil­i­ty of our trans­form­ers. There­fore Elia was hap­py to count on the part­ner­ship between one of its local trans­former main­te­nance sup­pli­ers and MR to real­ize this chal­leng­ing replace­ment pro­gram.” Ben­jamin Pierre, Oper­a­tional & Safe­ty Excel­lence Man­ag­er at Elia

Reinhausen inside

Reinhausen’s ser­vice range includes much more than replac­ing on-load tap-chang­ers.
It also includes:
• Attach­ment and instal­la­tion of ETOS®
• Mount­ing sen­sors, such as those of the MSENSE® sen­sor fam­i­ly
• Safe­ty devices

Find out more about ser­vice at:


Do you have more ques­tions about the project in Bel­gium?
Then please con­tact Sebas­t­ian Hölz­er:

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