Incipient fault detection in transformers can provide early warning of electrical failure and could prevent catastrophic losses. To develop the transformer incipient fault detection technique, a transformer model is required, to simulate internal incipient faults. This paper presents a methodology to model internal incipient winding faults in distribution transformers. These models were implemented by combining deteriorating insulation models with an internal short-circuit fault model. The internal short-circuit fault model was developed using finite element analysis. The deteriorating insulation model, including an aging model and an arcing model connected in parallel, was developed based on the physical behavior of aging insulation and the arcing phenomena occurring when the insulation was severely damaged. The characteristics of the incipient faults from the simulation were compared with those from some potential experimental incipient fault cases. The comparison showed that the experimentally obtained characteristics of terminal behaviors of the faulted transformer were similar to the simulation results from the incipient fault models.

Modeling Transformers with Internal Incipient Faults

Arcing Fault Protection for Low-Voltage Power Distribution System - Nature of the Problem

An arcing fault is a dangerous form of short circuit that may have a low current magnitude. In the case of such faults, the magnitude of the current is limited by the resistance of the arc and may also be limited by the impedance of a ground path. This lower level fault current is often insufficient to immediately trip phase overcurrent devices, resulting in the escalation of the arcing fault, increased system damage, tremendous release of energy, and threat to human life. Despite modern advances in system protection and the adoption of National Electrical Code Section 230-95, people continue to be injured or killed from arcing faults, initiated by accidental physical contact or through a glow-to-arc transition. The initial phase of an arcing-fault research project was to review the historical evolution of arc modeling for low-voltage systems. A summary of the electrical aspects and the physics involved in arcing faults appeared in previous work. Today's better analytical tools facilitated the development of new instantaneous arc models with current-dependent arc voltages, which better represent the arcing phenomenon than the assumed arc voltage associated with previous instantaneous arc models. The arc currents in a typical medium-size building system are determined and harmonic analysis is performed.

Instantaneous arcing-fault models developed for building system analysis

An arcing fault is a dangerous form of short-circuit that may have a low current magnitude. In the case of such faults, the magnitude of the current is limited by the resistance of the arc and may also be limited by the impedance of a ground path. This lower level of fault current is often insufficient to immediately trip overcurrent devices, resulting in the escalation of the arcing fault, increased system damage, tremendous release of energy and threat to human life. Despite modern advances in system protection, many people are critically injured or killed each year as a result of such faults. The initial phase of an ongoing arcing-fault research project was to review the pioneering work, dating back to the 1920s. After a comprehensive literature search was completed, today's sophisticated analytical tools are aiding development of a new arc model. An improved arc model will more accurately calculate the arc currents in an actual arcing event. This paper summarizes the physics involved and describes the historical evolution of arc modeling. The condensed review presented in this paper facilitates a better understanding of arcing faults in low-voltage power systems; in addition, it serves as a foundation for current and future research.

The historical evolution of arcing-fault models for low-voltage systems

An arcing fault is a dangerous form of short circuit that may have a low current magnitude. In the case of such faults, the magnitude of the current is limited by the resistance of the arc and may also be limited by the impedance of a ground path. This lower level fault current is often insufficient to immediately trip overcurrent devices, resulting in the escalation of the arcing fault, increased system damage, tremendous release of energy, and threat to human life. Despite modern advances in system protection, people are critically injured or killed each year when they are in the vicinity of an arcing fault that is either accidentally physically initiated or initiated through a glow-to-arc transition. The initial phase of an ongoing arcing-fault research project was to review the pioneering work, dating back to the 1920s. The historical evolution of arc modeling for low-voltage systems and a summary of the electrical aspects and the physics involved in arcing faults were reviewed in a companion paper (1999). After a comprehensive literature search was completed, today's better analytical tools facilitated the development of new arc models with current-dependent arc voltages. A current-dependent arc voltage better represents the arcing phenomenon than the assumed arc voltage associated with previous instantaneous arc models.

Schurig

Papers

Fault Voltage Drop and Impedance at Short-Circuit Currents in Low-Voltage Circuits