Patent ID: 11892488
Assignee: HITACHI ENERGY LTD
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 0:
1. A method, for monitoring N number of transformer bushings operating in substantially the same environment at least regarding temperature, N being any number more than 1, the method comprises:
estimating an absolute value for the capacitances of each of the bushings, the absolute values for the capacitances being denoted Cx,
estimating an absolute value for the loss factor or the power factor of each of the bushings, the absolute values for the loss factors or the power factors being denoted Fx,
wherein estimating the absolute value for the capacitances and the absolute value for the loss factor or the power factor of each of the bushings includes obtaining measurements of a terminal voltage and a bushing tap current of each of the bushings using a voltage transformer,
wherein X is a number representing which bushing the value is associated to and X larger than 1,
calculating Δ-values for all C values and Δ-values for all F values, according to:

ΔCX=CX−CX+1, for all values up to, and including, ΔCN−1,

ΔCN=CN−C1, for ΔCN,

ΔFX=FX−FX+1, for all values up to, and including, ΔFN−1,

ΔFN=FN−F1, for ΔFN, and

determining whether the Δ-values are within predefined ranges.