Apparatus and Method for High Frequency Low Pressure Arc Flash Sensor
Air around high power electric arcs is rapidly heated to over 10,000 degrees. This heat causes the air to expand rapidly. The expanding air creates shock waves of pressure that emanates from the arc. As a high powered arc moves it pushes plasma and air at velocities measured at over 800 miles per hour which exceeds the speed of sound. It is desirable that the pressure wave be detected on its leading edge while the pressure is still at a low level, as these pressures are known to reach levels that have knocked down cement walls.
While the pressures from the arc can be quite high, the pressure oscillates up and down quite rapidly due to the rapid motion of the arc. Detection of this pressure wave can be used to identify the presence of the arc.
Some of the arc fault detection systems presently on the market open breakers based solely on the light from the arc. Unfortunately, flashlights and strobe lights can also set off photo detectors. An arc flash pressure sensor used in conjunction with arc light sensors provides a more robust arc detection system preventing false alarms from opening breakers and the loss of power at inopportune times.
The APL pressure sensor is an innovative approach to measurement of the pressure shock wave from the arc. The entire housing is made from plastic, removing the need to worry about installing metallic components in close proximity to bare copper bus bar conductors. Most low pressure sensors require large sensing elements to achieve the needed sensitivity. The APL senor uses a unique pressure switch with the sensitivity to detect the leading edge of the pressure wave within a few milliseconds and yet the unit is immune to mechanically induced shock. While the gain on small semiconductor pressure sensors can be adjusted to achieve the needed sensitivity, semiconductor based units require periodic recalibration to compensate for drift. The APL solution requires no recalibration to achieve stability over a period of years. The pressure sensor signal can be combined with the response from a photo sensor to produce an arc detection signal which is immune to false alarms. The quick response of the pressure sensor results in the ability to open breakers rapidly enough to prevent the explosive ejection of covers from a switchboard. The APL pressure sensor contains dual independent pressure detectors to insure a long trouble free lifespan. The arc pressure signal is a very dynamic alternating pressure signal. The APL sensor includes pneumatic components to smooth the pressure yielding a steadier pressure signal, while simplifying the electronics necessary to process the signal. The APL pressure signal could also be combined with conventional over current signals to produce more robust detection of switchboard than use of the over current signal alone.
Patent Status: U.S. patent(s) 8091429 issued.CONTACT:
Mr. J. E. Dietz
Phone: (443) 778-8782