On the intrinsic thermal stability in HVDC cables

Abstract

The paper deals with some important aspects of steady state thermal stability in the insulation of HVDC cables. The resistively graded electric field distribution and the temperature distribution, under steady state, in dc cables, are interrelated. The dc conductivity is known to be a function of stress as well as of temperature. Reasonably convincing theories of electric stress and temperature distribution are now available in the literature. Until recently, the thermal runaway was believed, primarily, to be a consequence of an inordinate run away in the sheath temperature due to dynamic interaction with the ambient. While this premise is partly true, there are other overriding factors controlling the stability. This paper presents a detailed investigation on this aspect and it is shown that the multi-factor dependent dc conductivity alone causes the thermal instability, boundary conditions at sheath having a marginal role.

Some investigations on temperature dependent breakdown of electric cables under no load

“…9). The dashed line represents the theoretically estimated values of breakdown voltages as plotted against temperature, calculated using [4], [6]. The obtained experimental results are in reasonable agreement with the theoretical estimation proving the mechanism of breakdown in PVC cables as of thermal origin.…”

“…Theoretical formulations relating the maximum thermal voltage to the physical and geometrical parameters of the HVDC cable insulation have been proposed in [5]. Much literature is also available detailing causes of thermal instability and runaway [6]. Also, proposals have been made to improve the thermal performance of cable insulation by using polymer nanocomposites to improve dielectric volume resistivity and breakdown strength [7].…”

“…rise of conductor prior to breakdown as defined in[6] Experimental breakdown voltage with Weibull 95 % confidence bounds and theoretical estimation.…”

Thermal accumulation and tracking failure process of BN-filler epoxy-matrix composite

“…These articles have mainly considered the influence factors of electrical breakdown from view of adding the nano or micro particles. Some researchers also have studied the phenomenon of thermal breakdown [9][10][11][12][13][14][15]. T. Mizutani et al have concluded that a filamentary thermal breakdown occurs in polyimide at high temperature [12].…”

Defects and interfaces at DC voltage

“…The other mechanisms do not necessarily need the presence of macroscopic defects. Insulation degradation can however lead to increased losses and possibly hot spots, eventually leading to thermal instability [2], [3]. In section IV, space charge accumulation, a mechanism that does not require the presence of a macroscopic defect is further explored.…”