Electronics Protection - March/April 2012 - (Page 8)

Feature A Case for Safety - AC Arc Fault Circuit Interruption for PV Systems with Microinverters or AC Modules damaged during installation, aged wiring, and loose connections. In homes, examples of non-operational arc events would include outlets with mechanical motion due to numerous plug insertions Alternating current (AC) arc fault circuit interruption (AFCI) over time, the incidental piercing of wires due to nails or screws has been an area of advancement across various industries for being inserted in to walls, or damaged/pinched cords. many years. However, specifically in regard to solar installations, it Additionally, the exposed wiring and connectors of exterior remains a relatively new concept. branch circuits with PV microinverters or AC modules is suscepToday we still rely primarily on fuses for fault protection in solar arrays, although our counterparts in commercial and industrial tible to damage from weather, aging and the environment – all of which can contribute over time to the increased potential for facilities have continued to progress and utilizing thermal magAC arcing. netic circuit breakers for overIn fact, wire and connector current protection. We’ve also degradation is one of the main seen the addition of ground drivers and concerns of these fault and arc fault protection dangerous, non-operational arc in buildings, which can detect faults. Because factors includother types of faults at lower ing high temperatures, humidcurrents than would typically ity, corrosion, mechanical and be capable with an overcurrent voltage stress and aging (among protection device. many others) are major catalysts AC arc fault circuit interrupof wire degradation, and betion has been in the National cause all of these attributes are Electrical Code (NEC) for intehighly-prevalent on roofs, the rior residential branch circuits likelihood of wire degradation since 2002, and since that time, and non-operational arc faults is over 50 million AC arc fault circuit interruption devices have Photovoltaic systems are being installed not only on residential and com- amplified by the environment of been installed. With a vast num- mercial buildings, but also on other ground mounted structures such as most PV systems. It should also be noted that ber of manufacturers supplying the carports. under normal circumstances, PV these devices, you can expect branch circuits have the power being sourced from the PV mito see these numbers increase as states continue to update and croinverters or AC modules back into the load center and onto enforce their code requirements. the grid, but under certain fault conditions, you can also have Extensive progress has also been made in the area of direct the utility service feeding through the breaker in the direction of current (DC) arc fault protection in industries including vehicular, the fault. aerospace, datacom and telecom. The 2011 NEC code introduced So in terms of arc faults, one of the greatest potentials for fire is the requirement for DC arc fault protection on PV systems. Howunintentional arc conditions, which create a very high temperature ever, we have not yet seen a similar requirement to protect AC when an arc is formed, igniting any materials in close proximity. branch circuits on solar installations. In fact, AC arc faults have zero voltage crossings 120 times Although microinverters and AC photovoltaic (PV) modules a second that repeatedly extinguish the arc. While these cycles limit the DC voltage present within the PV system, the potential do not always result in a restrike of an arc for every half cycle, for an AC arc fault is still present on the 240 VAC split-phase 15 to each short time interval creates additional heat and arc energy to 20 amp branch circuits and associated AC PV wiring exposed on potentially start a fire. And the current may not be sufficient to roof installations. heat the bimetal in a thermal magnetic circuit breaker and cause In addition, if you calculate the current produced from half a it to trip. dozen microinverters on a branch circuit (typically one amp per microvinverter), you will find more than enough current to cause an arc fault. Mitigating AC Arc Faults Understanding the two types of AC arc faults, series (in-circuit) AC Arc Faults arc faults and parallel (short-circuit) arc faults, is the first step in Classifying arc fault events is a good place to start in order to mitigation and safety assurance. Series arc faults are most often due to a loose connection, determine what type of protection is needed for these events. Operational arcs occur in a properly functioning electrical system, corrosion or a broken wire. In the case of a series arc fault on a branch circuit containing PV microinverters or AC modules, an AC and are perfectly normal occurrences. An example of an operational arc would be a switch contact closing or opening to turn arc fault protection device within the load center would detect an a load on and off, or similar events commonly observed with fan AC arc fault and interrupt current flow, thereby causing the arc fault to extinguish. Note that the PV microinverters, because of controls or dimmer lights. These arcs are normal, operational events and can be ignored. In PV applications, what we need to anti-islanding requirements, will also shut down because of lost address are the non-operational arcs, which can present severe connection to the grid. fire hazards. Similarly, parallel arc faults would also be mitigated using an AC Non-operational arcs most often occur due to cable insulation arc fault protection device, but the subtle difference would be that 8 March/April 2012 www.ElectronicsProtectionMagazine.com Charles J. Luebke, Chief Engineer, Eaton Corp. ’s Milwaukee Innovation Center http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - March/April 2012

Electronics Protection - March/April 2012
Surge Stopper Shields Electronics From Transients Beyond 100 V
The Lowdown on IP Codes – Ingress Protection of Electrical Products
A Case for Safety - AC Arc Fault Circuit Interruption for PV Systems with Microinverters or AC Modules
Enclosure Design: IVC’s new Lightweight Explosion-Proof Camera Enclosure System
Portable Shock and Vibration Protection
Polycase Offers New Options for NEMA 4X Plastic Enclosures
New Circuit Board Shielding from Leader Tech
Laird Technologies Releases new Liquid Cooling Systems Product Line
ASI Releases New UL489 Hydraulic Magnetic Circuit Breakers
PEM C.A.P.S. Captive Panel Screws Offered in Three Mounting Styles26
SolarFocus Releases new SolarKindle Case
Indsutry News
Coherent Integrates Marway’s Power Distribution Solution into Energy Efficient, Direct-Diode Laser System Design

Electronics Protection - March/April 2012