| The Arc Guard system can detect an arc flash in less than one millisecond, and depending on the disconnecting device it can disconnect the power to the switchgear within 30 to 50 milliseconds. This will not prevent the accident, but it will significantly reduce the damage. |
The ABB LOW VOLTAGE PRODUCTS division has released TVOC-2, an update to its proprietary Arc Guard System™ for protecting electrical equipment from electrical arc flashes. TVOC-2 features numerous upgrades and new functions to provide arc-flash protection, detect faults in low- and medium-voltage switchgear, and disconnect the power provided to the arc within 30 to 50 milliseconds, preventing serious injury to personnel and damage to expensive equipment. Without the Arc Guard System an arc flash will typically trip a circuit breaker in approximately one second, enough time for the arc to destroy the switchgear and kill or seriously injure a person.
TVOC-2 is UL listed, and carries a functional safety rating of SIL-2 (certified by TÜV Rheinland) for protecting human and equipment), when installed with ABB’s Emax circuit breakers.
An arc flash is a strong electric current, and often a major explosion, that passes through air when insulation between electrical conductors is no longer sufficient to contain the voltage within them, creating a short that allows electricity to race from conductor-to-conductor1. Arc flashes can emit heat up to 35,000°F. It is estimated that five to ten arc flashes occur in the U.S. every day, causing one to two daily fatalities. Despite attempts to design systems that inherently reduce risk, mechanical measures often fail because most accidents occur with the switchgear door open, and electrical breaker protection is solely based on delayed over-current stoppages. The main cause of arc flashes is human error and 65% occur when an operator is working on the switchgear.
The Arc Guard system can detect an arc flash in less than one millisecond, and depending on the disconnecting device, it will typically disconnect the power to the switchgear within 30 to 50 milliseconds. This will not prevent the accident, but it will significantly reduce the damage. It uses light as the main condition to instantaneously trip the incoming circuit breaker, responding in milliseconds and overriding slower protection elements.
The system acts in three phases:
• Detection - on optical sensor senses when light (an arc flash) is inside the equipment
• Recognition - the arc monitor determines the intensity of the light
• Action - the TVOC-2 sends a signal to trip the breaker(s).
Short-circuit protection alone is not enough to provide the necessary response time because power distribution systems often include a required selectivity designed to achieve desired plant efficiencies and ensure power availability. This selectivity delays the breakers tripping in the necessary time. The Arc Guard System, along with properly specified circuit breakers, overrides the protection delays within the necessary timeframes to minimize injuries and equipment damage.
In addition to achieving the functional safety design as approved through third-party testing and certification, the feature upgrades of TVOC-2 provide significant system enhancements, including:
• Reliability: Pre-calibrated optical sensors and fiber optic point sensors; Hardware-based self-monitoring system for critical functions; the software is used only for supervision and information processing; Wide-ranging input voltage ratings (100 to 240 V AC and 100 to 250 V DC); Selective tripping of only the affected circuit breaker, not all breakers within a system.
• Flexibility: The HMI can be mounted on the TVOC-2 or panel door; Standard system has 10 sensor inputs, expandable to 30; The system can be configured according to specification.
• Simplicity: User-friendly start-up menu; Mounting options on DIN-Rail or directly on a panel wall; Easy to expand as the switchgear grows.
The Arc Guard System is compatible with a range of applications, including new or OEM installations, and old equipment soon to be out-of-date without a safety upgrade.