AFCI Reaction to Utility Events

CenterPoint Energy 35 KV Distribution Capacitor Bank – Switched through an automated system

New breaker box built to 2008 NEC requirements with AFCI breakers

Failing vacuum switches on CNP capacitor banks were causing customer AFCI breakers to trip

There are 40,000 fires a year caused by problems with house wiring

Changes in the 2005 and 2008 National Electric Code call for installation of AFCI breakers on almost all branch circuits

Arcing faults can generate temperatures in excess of 9,000 degrees

Arcing Fault Circuit Interrupters can sense a downstream arc and trip before starting a fire.

AFCIs serve a dual purpose by tripping from an arc or from overload.

Arcing faults can occur in series or parallel to the load. Parallel faults involve the greatest amount of energy and are more likely to create a fire hazard.

Some loads have arcing inherent in their normal, safe operation.

The AFCI is designed to prevent electrical fires that may result from normal wear and tear or aged connections.

GFCI prevent electrocution, AFCI prevent fires.

Some loads produce arcing during normal use, the AFCI must distinguish between the load arc and an arcing fault.

AFCI and GFCI breakers are similar in appearance but much different in design and function

Early designs of AFCI breakers would trip when a TVSS would discharge a transient to ground.

Centerpoint Energy serves 5000 square miles in and around the greater Houston metropolitan area.

Residential load growth within the service area tends to be grouped by time and location.

Builders will consolidate construction activity to achieve efficiencies in all steps of the construction.

The end result is a grouping of new homes, all built with similar equipment and components manufactured at or near the same time.

The end result is a grouping of loads, with similar characteristics. And, if located near distribution equipment there is potential for interaction.

Centerpoint Energy electrical design criteria requires multiple capacitor bank installations on every distribution circuit. Which results in many capacitor bank located in and around residential developments.

Newer homes should be wired to the 2008 NEC, which requires the installation of AFCI breakers.

The interaction of the AFCI with events on the distribution system depends on the design of the AFCI. Its response times and sensitivity.

The load served through the AFCI is just as important as the characteristics and design of the AFCI in determining response.

Eventually, over time all distribution equipment will be damaged or fail.

System maintenance and repair is essential to keep voltages within design criteria specifications.

Communication of events, trends and results is essential to insure that all field, dispatch and engineering support are aware of a situation.

One failed component does not make a crisis, but is the first step in identifying a root cause which could eventually impact thousands of customers.

Advice for the future – learn to listen to your system.