Bushing sensors and their role in reliable on-line bushing monitoring

On-line monitoring has proven to be an effective technology to detect deteriorating high voltage bushings and prevent failures. While there is much focus placed on the monitor and the data it provides, the sensors used to transmit the signals are often overlooked. An on-line bushing monitoring program is only as good as the quality and reliability of the sensors used to provide the signals. Many problems and false alarms can be avoided by using a properly designed sensor and making sure it is correctly installed. This article will discuss what to consider when selecting a bushing sensor and how to install the sensor properly

Characterization of Power Transformer Frequency Response Signature using Finite Element Analysis

Power transformers are a vital link in electrical transmission and distribution networks. Monitoring and diagnostic techniques are essential to decrease maintenance and improve the reliability of the equipment.This research has developed a novel, versatile, reliable and robust technique for modelling high frequency power transformers. The purpose of this modelling is to enable engineers to conduct sensitivity analyses of FRA in the course of evaluating mechanical defects of power transformer windings. The importance of this new development is that it can be applied successfully to industry transformers of real geometries

Insulation assessment of high voltage oil impregnated paper bushing and resin impregnated paper bushing

Transformer diagnostic testing is perform to reveal the condition of the transformer. Early detection of problems can minimize the repairs involved and mitigate catastrophic failures. CIGRE findings show that bushings are common reason for power transformer failures. There are few research development conducted over the years to improvise construction of condenser bushings. One of the first technologies was the Resin Bonded Paper (RBP), but not manufactured anymore due to many technical & environmental reason. Secondly and the most widely used is Oil Impregnated Paper (OIP) technology apparently because of its low primary cost. In the circumstances? whenever there is problem with the insulation or internal degradation, it can accumulate high internal pressure inside bushing which can cause explosion of OIP bushing. That why migration from Oil Type to Dry Type Bushing Technology chosen to reduce risk of explosion /caught in fire during bushing failures .The new safer alternative considered is the Resin Impregnated Paper (RIP) technology which offer better technical performance over OIP bushings. This study presents comparison on insulation assessment of both types of bushing through power factor measurement and dielectric frequency response (DFR) analysis that contributing to assessment of failure characteristics of OIP and RIP bushings. Field testing was implemented to capture data for comparison purpose focusing on selection power transformer in grid division installation. The measurement of bushing insulator capacitances and measurement of the dissipation factor is to determine bushing health condition while DFR measurements as a supporting diagnostic tool for bushing condition assessment on paper inside the bushing. Commonly, both OIP & RIP constructions are that they are subject to very high mechanical, electrical and thermal stresses during operation. With result of this study, it may become possible to identify failure characteristic of insulating material between Oil Impregnated Paper Bushings (OIP) and Resin Impregnated Paper Bushings (RIP) and explain that moisture content in oil and paper has significantly contributed to the degradation of bushing. This methodology can be utilize for effective way to monitor moisture content at site and as a tool to decide condition of insulation bushing

Dielectric Analysis of High Voltage Power Transformers

Dielectric tests have been used for decades for diagnosis of power transformers and bushings. In addition to the traditional tests at line frequency, modern types of dielectric tests using different frequencies and voltages have evolved. The article considers the scope of this principle, explaining the most common test procedures and describing what information can be derived from the measured values

Electrical stress monitoring of distribution transformers using smart grid techniques

Electrical stresses that distribution transformers rated 16 kVA up to 2 MVA are subjected to can often cause premature transformer failures. In this study, research related to the development of cost effective bushing embedded sensors that can measure the electrical stresses on the MV side of distribution transformers has been conducted. An embedded screen in a specially designed 24 kV bushing was used for both power frequency and transient voltage measurements. Observed results showed that the screen-based bushing capacitive voltage divider offered results that are consistent with those of a commercial capacitive voltage divider for power frequency voltages as low as 1 kV up to 24 kV. Impulse voltage measurements were consistent with those of a wideband resistive divider for voltages lower than 60 kV. Voltages higher than 60 kV revealed non-linear behaviour which increases as the 150 kV BIL rating of a 22 kV transformer is reached. A nonlinear resistor added to ATPdraw simulations was able to compensate for the observed nonlinearity. PD tests conducted on the prototype bushing showed that the designed prototype had surface discharges which are affected by the positioning of the bushing screen. A Rogowski coil embedded in the same bushing was used for the measurement of both power frequency and transient currents. Measured coil parameters used in ATPdraw simulations produced results that were consistent with the output of the Rogowski coils when measuring 8/20 s current impulses. Numerical integration of the Rogowski coil output voltages was successfully used in the recovery of both power frequency and measured impulse currents. The Rogowski coil sensitivity is affected by both coil dimensions and terminating resistance. The designed prototype bushing opens up opportunities for performing stress monitoring on the MV side of distribution transformers