Failure analysis of a low-cost domestic permanent fault indicator and its solution

Abstract

The concept of Permanent Fault Indicator (PFI) is that when a fault occurs in the circuit, the indicator will light up and continue to light up until the fault is rectified. A low-cost PFI using the neon bulb in series with a current limiting resistor is within the scope of the study. The research is about analyzing the operation of PFI based on the neon bulb, in a real scenario. Simulation, as well as laboratory experiments, were conducted for testing the response of Permanent Fault Indicator on a real scenario. The loophole (false indication when loads are connected) was identified and solved through the development of a low-cost prototype. Falstad online and Multisim™ software were used for simulation/modeling. Circuit voltage and current were monitored for analysis. In case of normal condition (load connected and no short circuit), although the neon indicator is energized, there are some millivolts (depending on load type) across the load. So these few volts are sensed by a comparator circuit (dual comparator configuration) to de-energize it's Light Emitting Diode (LED), thus enabling the user to discriminate between a short circuit and a normal condition, which was not possible with existing PFI. The developed prototype was tested on resistive as well as inductive loads, which allows the user to test whether a short circuit exists or the tripping of breaker is due to some other problem. Both indicators (Neon and LED) are energized only in case of short circuit. Deployment of a low-cost prototype integrated with PFI on distribution boards would increase the life span of the protective device by reducing their operation cycles on high fault current, as well as safety for personnel. Lastly, it would reduce unwanted power interruptions, due to long-duration unwanted tripping of circuit breakers, by resetting them after checking the status of indicators.