1. Technical Field
The present invention relates to detecting high impedance faults (HIFs), and more particularly, to detecting HIFs by analyzing a local deviation from a regularization.
2. Discussion of the Related Art
In the electrical power generation and distribution industry, monitoring transmission and distribution networks for fault conditions is very important. The term distribution network is used herein to refer to any electrical power transmission or distribution facility. Moreover, a fault condition is any abnormal (unexpected) current-conducting path in a distribution network. Fault conditions often present danger to people and property. They also waste electrical energy.
One type of fault is a bolted (short circuit) fault of one or more legs of a distribution network to another leg thereof or ground. This type of low-impedance (low-Z) fault condition is easily detected by conventional circuit overcurrent protective devices such as fuses or circuit breakers. In other words, a complete short circuit (a low-impedance path) usually trips a circuit breaker or blows a fuse. A circuit of the distribution network experiencing such a fault condition is quickly removed from service until such time as repairs can be effected (i.e., until the fault is cleared).
Another type of fault condition occurs when an unintended high impedance (high-Z) conductive path occurs between transmission line legs or between one leg and ground. Such high-Z paths may occur when a tree limb or the like falls across a transmission line or when a single leg of the transmission line breaks (due to ice or wind, for example). Generally, a single conductor of the distribution network dropping to the ground will not create a short circuit, but will continue to allow current flow at a relatively low rate. Such current flow often causes arcing. This condition presents a great danger of electrocution to people or animals happening across the downed conductor. This arcing can also result in fire.
A problem in the electrical industry is finding an effective way to differentiate between a high-Z fault (HIF) condition and similar effects caused by changes in the loads attached to the distribution network. In addition to load switching events, power factor correcting capacitor banks are frequently switched on and off the network and transformer taps are automatically changed to keep the network performance constant. Both of these events also create conditions on the network which may appear similar to a HIF condition.
An effective system for detecting HIFs should be able to distinguish fault conditions from normal load switching events. A system which ignores legitimate HIF conditions risks the aforementioned dangers while a system which falsely trips in response to normal load switching events can wreak havoc with consumers relying on uninterrupted electrical service. Interruption of electrical service to certain manufacturing processes, for example, may destroy work-in-process and result in large expense to the manufacturer. An interruption of medical apparatus can be inconvenient at best, and disastrous at worst.
Accordingly, there exists a need for a technique of distinguishing HIF conditions from normal load, capacitor bank or transformer tap conditions with high accuracy.