Tom Papallo

Zone Based Protection for Low Voltage Systems; Zone Selective Interlocking, Bus Differential and the Single Processor Concept

Time based coordination and protection is the normal basis for coordinating low voltage power distribution systems. Enhancements, such as zone selective interlocking and bus differential protection, may be used to accelerate protective devices. However, these improvements may be costly, difficult to implement, and may not function as expected using commonly available technology. Nevertheless, the potential benefit of fault clearing speed and selectivity are more valued in todaypsilas arc-flash and reliability conscious environment than ever before. The writers shall discuss some issues associated with these traditional improvements, pitfalls to avoid and, more effective ways to implement zone-based protection to achieve fast fault protection while maintaining complete selectivity for a broad range of fault magnitudes, system configurations and load types.

Arc-flash energy mitigation by fast energy capture

The predominant technologies for reducing arc-flash incident energy today rely on the speed of protective devices, remote operation, encapsulating arc-flash energy in arc-resistant enclosures, which channel energy where it is less dangerous, and on crowbars to divert the arc energy into a bolted fault. Though more thoughtfully applied than they may have been in the past, none of these methods has provided a solution for all situations, particularly in existing installations. This paper will describe a method and include test results of an arc-flash energy sequestration that is able to divert an arcing faults energy into a specific environment within a half-cycle after initiation of the arc. This is achieved without the need to introduce bolted fault current like a crowbar or for fast current interruption, such as a current-limiting fuse. The system protection provided has the benefits of arc-resistant switchgear without reliance on equipment sheathing and can be added after normal equipment is installed. Further advantages include the protection system and switchgears ability for reuse after an arcing event, as well as the ability to easily test without the need for cumbersome high-current test equipment.

The single-processor concept for protection and control of circuit breakers in low-voltage switchgear

Protection of low-voltage circuits has been a key area of research and continuous improvement since the invention of electricity. In the current state of the art, fuses and circuit breakers protect individual circuits. These devices, in turn, use many different kinds of trip mechanisms, operating in various modes that require sensing the current that travels through the circuits. Communication networks and external relays are sometimes used to enhance selectivity and provide better protection. In this paper, the authors explore a protection-and-control architecture based on a single processor that provides all the protection and control functions for a lineup of low-voltage switchgear. We demonstrate how this method of protection changes the paradigm from individual circuit protection to system protection, while cost-effectively and significantly increasing system reliability and protection.

Predicting Let-Through Arc-Flash Energy for Current-Limiting Circuit Breakers

IEEE 1584, “Guide For Performing Arc Flash Incident Energy Calculations,” provides a method to conservatively predict the incident energy let-through by over-current devices based on the devices time-current-curve or tested transfer functions. Additional testing by various manufacturers shows that current-limiting circuit breakers operating in their instantaneous current-limiting range perform significantly better than the IEEE Time-Current Curve-based model predicts. The authors will present an analytical method to estimate incident energy from published circuit breaker let-through curves. The method will provide a conservative, yet better estimate of the actual performance compared to test data. This method can be used as part of hazard risk planning rather than the method described in IEEE 1584 or when the manufacturer does not provide an incident-energy transfer function based on tests.

Method for determining selective capability of current-limiting overcurrent devices using peak-let-through current

Time-Current-Curves are the accepted industry standard for predicting overcurrent device operation and analyzing selective behavior under overload or fault conditions. A conservative interpretation of drawn curves has sufficed for many years and provided acceptable performance. However, recent emphasis on better selectivity while still trying to provide optimal protection increases the demand for more accurate selectivity predictions. Currently, manufacturers are publishing tables and other guidelines to facilitate the selection of optimally coordinated devices by systems designers. However, no standard or single methodology exists for the creation of these tables. The writers shall present three methods of device interaction analysis based on peak let-through current, suitable for predicting selective behavior of protective devices above what time current curves may indicate. The method may be applied with published information or manufacturers internal test information.

Method for determining selective capability of current-limiting overcurrent devices using peak-let-through current “What traditional time current curves will not tell you”

Time-Current-Curves are the accepted industry standard for predicting overcurrent device operation and analyzing selective behavior under overload or fault conditions. A conservative interpretation of drawn curves has sufficed for many years and provided acceptable performance. However, recent emphasis on better selectivity while still trying to provide optimal protection increases the demand for more accurate selectivity predictions. Currently, manufacturers are publishing tables and other guidelines to facilitate the selection of optimally coordinated devices by systems designers. However, no standard or single methodology exists for the creation of these tables. The writers shall present three methods of device interaction analysis based on peak let-through current, suitable for predicting selective behavior of protective devices above what time current curves may indicate. The method may be applied with published information or manufacturers internal test information.

Finding fault - Locating a ground fault in low-voltage, high-resistance grounded systems via the single-processor concept for circuit protection

High-resistance grounded systems have distinct advantages over solidly grounded systems in facilities where very reliable delivery of power to the loads is desirable. Unlike solidly grounded systems, resistance- grounded systems are able to operate continuously with one unintentional ground. However, this is true for only the first ground fault. A second ground fault on another phase and circuit breaker allows a phase-to-phase fault that may be of significant magnitude.

Method for Determining Selective Capability of Current-Limiting Overcurrent Devices Using Peak Let-Through Current—What Traditional Time–Current Curves Will Not Tell You

Time-current curves are the accepted industry standard for predicting overcurrent device operation and analyzing selective behavior under overload or fault conditions. A conservative interpretation of drawn curves has sufficed for many years and provided acceptable performance. However, recent emphasis on better selectivity while still trying to provide optimal protection increases the demand for more accurate selectivity predictions. Currently, manufacturers are publishing tables and other guidelines to facilitate the selection of optimally coordinated devices by systems designers. However, no standard or single methodology exists for the creation of these tables. The writers shall present three methods of device interaction analysis based on peak let-through current, suitable for predicting selective behavior of protective devices above what time current curves may indicate. The method may be applied with published information or manufacturers internal test information.

Fast Energy Capture

Tests on the arc-containment device have confirmed that fast energy capture by transferring an arcing current from an open-air arc to an enclosed, controlled chamber provides a high degree of protection to LV switchgear. Tests confirmed the ability of the device to perform within the requirements of applicable IEEE standards for LV and arc resistant switchgear, without relying on special enclosures or blast-pressure conduction methods. Tests also confirmed the ability to reduce incident energy levels to less than 1 cal/cm at an 18-in working distance with no barriers between the arc source and the measurement devices. Furthermore, testing at low and high-available fault current, with larger and small arcing-fault gaps, confirmed the ability of the device to reliably function within a range of LV power-distribution fault currents and equipment arrangements that may be found in many industrial facilities.

Predicting let-through arc-flash energy for current-limiting circuit breakers

IEEE 1584, “Guide For Performing Arc Flash Incident Energy Calculations,” provides a method to conservatively predict the incident energy let-through by over-current devices based on the devices time-current-curve or tested transfer functions. Additional testing by various manufacturers shows that current-limiting circuit breakers operating in their instantaneous current-limiting range perform significantly better than the IEEE Time-Current Curve-based model predicts. The authors will present an analytical method to estimate incident energy from published circuit breaker let-through curves. The method will provide a conservative, yet better estimate of the actual performance compared to test data. This method can be used as part of hazard risk planning rather than the method described in IEEE 1584 or when the manufacturer does not provide an incident-energy transfer function based on tests.