Transformers for Washington

The util­i­ty PEPCO in Wash­ing­ton DC, USA has award­ed Siemens Ener­gy Aus­tria with the deliv­ery of three 220/138/13.8kV, 280MVA trans­form­ers. A chal­lenge here is that, accord­ing to state­ments by estab­lished tap-chang­er sup­pli­ers, con­ven­tion­al tap-chang­er solu­tions for switch­ing from volt­age-ratio con­trol (VRC) to phase-angle con­trol (PAC) can­not cope with the high volt­ages which occur dur­ing the oper­a­tion and test­ing of these trans­form­ers.

There­fore, a spe­cial sin­gle-col­umn rotat­ing design DEETAP® DU with mod­i­fi­ca­tions between the switch­ing con­tact lev­els was ini­tial­ly con­sid­ered to be the best tap-chang­er solu­tion. A below-tank-cov­er recon­nect­ing sys­tem was also con­sid­ered as an alter­na­tive. Final­ly, engi­neers from MR and Siemens Ener­gy Aus­tria were able to iden­ti­fy the lin­ear de-ener­gized tap-chang­er CAPT SPT 030 K B 2 170.KC800 with 12 columns as the first choice since this solu­tion allowed the team to keep the dimen­sions with­in the customer’s needs.

Not only the com­pact size was a con­tribut­ing fac­tor in favor of the CAPT SPT 030, but also the more secure and safer oper­a­tion pro­vid­ed by the inte­gra­tion of two CAPT motor dri­ves which are syn­chro­nized and inter­locked when in ser­vice. In the end, a safe and sound solu­tion for the life­time of the units was achieved thanks to the good col­lab­o­ra­tion between PEPCO, Siemens, MR and CAPT.