TECHNOLOGY I SAFETY
Safety in your
hands
Photovoltaic modules convert sunlight into electricity into direct current (DC) and must convert that to alternating current (AC) for general usage. One of the major concerns with this is the potential for electrical arcing that can create potential problems for any PV installation. Chris Oberhauser, Applications Engineer at Texas Instruments discusses why PV needs arc detection and when a fuse isn’t enough.
FUSES ARE A CRITICAL SAFETY ELEMENT in almost every electrical system. By limiting current from reaching dangerous levels, they reduce the risk of fire or other hazardous conditions. However, a fuse cannot handle all of the significant hazards alone. One such hazard that it cannot protect against is electrical arcing.
Electrical arcing occurs when an insulator ceases to function as an insulator and, instead, starts conducting current. Most commonly, the insulator breaking down is air. Compared to the equivalent volume of copper, an arc is a poor conductor of current. As a result, a large amount of energy dissipates, mostly as heat. Electrically, arcs can be modeled as a variable negative resistor. This is valid since an arc does not store electrical or magnetic energy like a capacitor or inductor. It is a negative resistor since there are more air molecules available to ionize and act as charge carriers to sustain the arc, if higher current is available.
With a focus on photovoltaic (PV) applications, this article provides detail into the different aspects of designing a dedicated
Figure 2: RD-195 detection interval
arc detect unit (ADU) to address the hazardous conditions created by arcs. The needs and challenges of such a system design are highlighted. This includes an assessment of arcing signatures, different system implementation techniques, self- testing and system handling of false-detect events. This article also summarizes the real-world performance of an extensible system design.
Arcing hazards Figure 1: RD-195 system block diagram 32
www.solar-uk.net I Issue III 2013
Characteristics of PV systems introduce additional risks of arcing. These include high DC voltages in the range of 600–1000 V, degradation and insulation wear due to constant exposure to the
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