Understanding the moisture temperature and ageing dependency of power transformer winding clamping pressure

Abstract

Progressive loss of winding clamping pressure is a failure mode that reduces the short circuit withstand capability of power transformers. Short circuit faults exert strong electromagnetic forces on the transformer winding structure, which could deform and displace its conductors. Failure to maintain the structural integrity of the winding structure during short circuit faults often leads to a catastrophic transformer failure, which could cause a disastrous network failure.

Investigation of overall and local vibration characteristics of disk‐type windings

“…In core-type power transformers, windings are wound coaxially around each core limb. Their top and bottom clamping supports are joined by flitch plates (tie plates or rods) which pass along the core to ensure stability [18]. Acting on clamping rings, the CP has a significant effect on windings' overall responses, which can be estimated as follows:…”

“…The sharp increased CP curve is due to the non-linear stress-strain characteristics of insulations. After assembly, the windings' height is almost kept constant throughout the transformer's service life [18].…”

“…Mechanical properties of pressboards in the in-plane direction are determined by the strength of cellulose chains. In out-of-plane direction(thickness direction), mechanical properties of pressboards are affected by the weak bonds between layers [18,20]. Hence, elastic modulus of the in-plane direction is much higher than that of the thickness direction.…”

“…Owing to ageing, long cellulose chains of pressboards gradually break into short chains leading to a reduction of pressboards' mechanical strength [18].…”

Application of operational modal analysis to investigate transformer vibration patterns

“…To obtain the modal parameters, two techniques can be carried out, namely experiment modal analysis (EMA) [8,16] and operational modal analysis (OMA) [8,14,[17][18][19]. Both methods require a broadband excitation applied to the transformer in order to excite all modes within the transformer.…”