Mahesh Edirisinghe

Power system switching transients in passenger automobiles

Design of automobiles has already reached to a level that many uses highly complex and sophisticated computing applications with associated electronics. These high-ended car electronic automation systems require very accurate and steady supply and most of these sensitive car electronics like multimedia systems, navigation units, etc., prone to fail in the presence of transient over voltages through the DC supply lines. Therefore a measurement of transients in automobiles and analysis has been done in order to identify the characteristics and risk levels of such transients for the vehicular control and attendant systems. In evaluating, an extensive survey of the transients carried out at a constant location within the electrical system of many late model automobiles. Transients were measured, rise times ranging from 0.3 us to 700 us and pulse durations from few microseconds to hundreds. There are bursts spread over milliseconds while number of transients have rise and fall times (<; 5 ns) in the RF range (> 200 MHz). Thus the transient waveforms were first categorized to arrive at a compact set of common types of waveforms and analyzed. The measured transient parameters were compared with the sensitivity of several standard car electronic devices to identify their immunity to the conducted transients. Providing an overview of how to mitigate or reduce the effect of transients in automobiles in order to increase the power system efficiency and reliability, also expected while addressing the sensitivity of devices.

Behavior of low voltage varistors under very fast oscillatory type current impulse environment

In this study, the behavior of low voltage varistors under very fast oscillatory type non standard current impulses were analyzed. The experiment was performed on 20 mm disk varistors with different nominal operating voltages of 14V, 30 V, 40 V, 75 V, 150 V, 250 V and 275 V. Non standard current impulses were generated using a Van De Graaff generator. The shape of the impulse was like a double exponential oscillatory type wave which has the oscillation frequency of 14.53 MHz. The rise time of the impulse was 8 ns with a maximum peak current rate-of-rise is of 2.41 × 1011 A/s. According to the results, under vary fast non standard current impulse environment, clamping voltage could be depend on both nominal voltage of varistors as well as its disk diameter. Another important feature of the voltage signatures observed was the DC offset voltage causes between terminals of varistor immediately after it triggered due injected fast current impulses.

Critical electric field needed for the propagation of surface discharges on water

The core objective of this study was to investigate the behavior of electric discharge exited in air over water and to study the way in which the lightning impulse is conducted into a water body. During the experiments, standard lightning impulses from -550 kV to 350 kV have been directed on water surfaces and surface discharges has been photographed using two cameras. The conductivity of the water has been varied from 41.5 μS/cm to 51.5 mS/cm. Analysis carried out in the study revealed that the current rather travels along the water surface than into the water when the conductivity of the water is low. A logarithmic variation was observed between the calculated electric field and the conductivity. For this variation a saturating trend could be observed and it appeared as if there is a critical value for the electric field below which no penetration will occur at any level of conductivity. Based on the experimental results of this study it can be estimated that to be less than 1.5×105 V/m for the positive breakdown and -5.0×105 V/m for the negative breakdown.

Transients in low voltage power systems (LVPS) in Sri Lanka under modern domestic environment

A life in modern society without safe and reliable supply of electricity is almost unimaginable, as it plays an indispensable role in human life. This reliability, essentially the balance is very important for safe operation of electronic appliances, but failures by transients become more prevalent due to their higher susceptibility of control circuits. Therefore either it should be reduced or eliminated in order to keep the mains safe and clean for other electrical appliances. Even though time duration that the electrical transients are present in the system is short, the components in the system are subjected to high-current and high-voltage peaks that can cause catastrophic damage. In order to identify this formidable menace, 1148 transient waveforms were recorded in LVPS in Sri Lanka under modern domestic environment. These recorded transients were due to induce over-voltages under lightning, switching, loading, energizing, etc. Through an empirical analyses carried out to extract the parameters of transients in LVPS in Sri Lanka, the highest positive peak of 472 V, negative peak of 448 V and the highest amplitude of 815 V were recorded. Burst width as high as 1.338 ms is also reported. Rise times are as short as 15 ns for impulsive transients and 0.1 us for oscillatory transients calculated. Results may be used to identify and understand the behavior of transients by correlating the major components in transients to the operated electrical appliance and to develop proper transient protection systems.