Abdulaziz A. El-Sulaiman

Effect of sub-atmospheric pressure on the conduction current in transformer oil

The effect of subatmospheric pressure on the quasi-steady-state and burst currents in transformer oil is investigated. Nonuniform high DC field is applied to aged and fresh transformer oil samples. The applied pressure is reduced from 10/sup 3/ torr to 50 torr and then increased correspondingly for each applied voltage inside a controlled vacuum chamber. Generally, it is found that at a fixed-field voltage the quasi-steady-state current remains almost unchanged with pressure variation. At a certain critical low subatmospheric pressure, the current increases sharply. The value of this critical pressure increases as the applied voltage is increased. Variation of pressure has similar effects on burst current. The results reveal that the gas bubble mechanism is the dominant factor affecting the conduction current and breakdown in insulating liquid at low pressure. A critical pressure initiates the formation of a stream of gas bubbles after which the current increases sharply, leading to a breakdown.<<ETX>>

High Field DC Conduction Current and Spectroscopy of Aged Transformer Oil

This paper studies the experimental results of the quasi-state high field dc conduction current, and changes occuring in the molecular structure of aged transformer oil, sampled from EHV transformer operating for the last five years. Aged oil was compared with fresh transformer oil and liquid paraffin. It was found that aged oil exhibits higher conduction than both of the other oils through 600 seconds of field application. However, no molecular changes were detected using different techniques of spectroscopy such as GC; UV; IR and NMR. Metallic impurities were found to be of the same order but the acidity increased manifolds to that of fresh oil.

EFFECT OF ADDITIVES ON THE PERFORMANCE OF CABLE OIL AND KRAFT PAPER OIL COMPOSITE

This study investigates the effect of 1-Methylenaphthalene and Benzophenon as additives in cable oil used in extra high voltage paper insulated underground cable in service in Riyadh area. Samples containing different concentrations of these additives were used. Impact of variation of temperature and additive concentrations was evaluated for conduction current and burst current. Virgin samples of the dielectric paper used in this cable were impregnated in these oil samples for the investigation of power factor and breakdown voltage. The results indicate that an optimum concentration of the additives improves the performance of paper-liquid composite.

STABILITY OF LARGE INDUCTION MOTORS AS INFLUENCED BY VOLTAGE DISTURBANCES

ABSTRACT The stability of large induction motors as influenced by supply voltage disturbances has been studied, using a simple approach. The load angle in this type of motors is taken as an indicator for motor stability rather than motor speed. This resulted in an appreciable saving in computation time with a reasonable accuracy compared with the exact simulation Various modes of voltage disturbances have been applied and the critical clearing time and its associated clearing angle are predicted. Comparison with exact simulation results showed very good correlations with good accuracy Some useful. conclusions regarding stability studies of large induction motors are presented showing a promising approach for direct evaluation of critical angle and clearing time.

Effect of temperature on burst phenomena in aged mineral oil under non-uniform fields

Presents the experimental results of high field conduction current burst phenomena in aged transformer oil using point-plane configuration. The effect of temperature and field strength variations on burst parameters are emphasized. It was found that bursts can be classified according to their direction. Generally, the amplitude of bursts increases with the increase in temperature, up to a certain value, after which the trend reverses. The total number of bursts per minute peaks at about 60-70°C. This observation suggests that bursts may be attributed to the electrode-film-liquid interface and not to micro bubble mechanisms.

Effect of point cathode and point anode on conduction and burst current in an inhomogeneous field for inservice transformer oil

This paper presents a study on the effect of point cathode and point anode on conduction and burst currents in transformer oil under high field. It has been found that the current in point cathode is higher than in point anode. Field emission satisfies the Fowler-Nordheim relationship in both cases within a range of applied voltage, and above which space charge contribution becomes dominant. The rate of current decrease in point anode is faster than point cathode. The amplitude of UDI-Burst in point cathode is larger than point anode. The total number of burst per minute is larger for point anode than the point cathode. The condition mechanism is discussed and the role of liquid/metal interface is emphasized.

Study of DC conduction in aged transformer oil under non-uniform high fields

This paper emphasises experimental results of DC conduction current in aged transformer oil using point-plane configuration. The effects of oil dehydration and filtration, anode material and field strength are investigated and discussed. It is found that i-t and i-E characteristics display exponential “behaviour and tunneling phenomenon, respectively. Moreover, sample preparation and anode/liquid interface play an important role in explaining the mechanism of DC conduction under non-uniform high field.