ABB’s Low Voltage Products division has released TVOC-2, a new generation of its proprietary Arc Guard System that has been protecting electrical equipment from dangerous electrical arc flashes for over 35 years.
According to the company, TVOC-2 features numerous upgrades and new functions to provide superior arch flash protection, detecting faults in low- and medium-voltage switchgear and disconnecting 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 1 second, enough time for the arc to destroy the switchgear and kill or seriously injure a person.
TVOC-2 is now UL listed, and when installed along with ABB’s Emax circuit breakers, carries a functional safety rating of SIL-2 as certified by TÜV Rheinland, an independent global provider of safety analysis. The SIL-2 certification, said ABB, confirms the TVOC-2 has achieved the standard required to protect both humans and equipment.
“The SIL-2 rating is especially important because it allows the TVOC-2 Arc Guard system to be used where an engineered safety solution is required,” said Steve Zbytowski, product manager of control gear at ABB. “The rating makes the TVOC-2 a unique product in today’s market.”
Hotter Than the Sun
An arc flash is a strong electric current, often taking the form of 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-conductor. Arc flashes can emit heat up to 35,000°F, four times the surface temperature of the sun. In the U.S. alone, it is estimated that five to 10 arc flash incidents occur every day, causing one to two daily fatalities.
Despite conscientious 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 1 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.
Detection, Recognition, Action
The Arc Guard System 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—an optical sensor senses light—an arc flash—inside the equipment;
- Recognition—the arc monitor determines the intensity of the light; and
- 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.
“ABB has over 35 years of experience detecting arc faults with the predecessors to the TVOC-2,” said Zbytowski. “While we are proud of that history, we weren’t satisfied with only protecting equipment. Our goal, which is now realized, was to gain the TÜV certified SIL-2 rating allowing the TVOC-2 to be used in engineered safety solutions.”
ABB said that, in addition to achieving the functional safety design as approved through rigorous third party testing and certification, the feature upgrades of TVOC-2 provide significant system enhancements, including:
- 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.
- 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.
- User-friendly start-up menu, easy to install.
- Mounting options on DIN-Rail or directly on a panel wall.
- Easy to expand as the switchgear grows.
The Arc Guard System is claimed to be compatible with a wide range of applications, including new or OEM installations, as well as older equipment lacking a safety upgrade.
(See related article, “Minimizing Arc Flash Danger in Mining Operations.” p. 40.)