BACKGROUND

Field

The present disclosure relates generally to a control scheme for sectionalizing switches in an electrical grid feeder. More particularly, it relates to a system and method enabling automated sectionalizing switches equipped with only three-phase current sensing to isolate faults when upstream interrupter/reclosers are testing for continued fault presence.

Discussion of the Related Art

An electrical power transmission/distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each including a number of power generator units, such as gas turbine engines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The grid may also include wind and/or solar energy generation farms. Not only are there many different types of energy generators on the grid, but there are many different types of loads, and the generators and loads are distributed over large geographic areas. The transmission grid carries electricity from the power plants over long distances at high voltages. The distribution grid, separated from the transmission grid by voltage-reducing transformers in a variety of substations, provides electricity to the consumers/loads.

Many portions of the distribution grid, commonly known as feeders, are arranged between two or more different sources (i.e., substations, or adjacent feeders), where one source is a main or primary source which is normally connected to and provides the preferred source of power to the feeder, and the other sources are alternates which are normally disconnected from the feeder by an open switching device. Additional switches, known as sectionalizing switches, are also typically placed along the length of a feeder, thereby creating multiple feeder sections each separated by a switch, where each feeder section typically serves multiple customers. If a fault occurs in the feeder, the fault can be isolated by opening one or more of the normally-closed sectionalizing switches.

Control of the sectionalizing switches has been largely automated in recent years, using a strategy known as fault location, isolation and service restoration (FLISR). FLISR applications can reduce the number of customers impacted by a fault by automatically isolating the trouble area and restoring service to remaining customers by transferring them to adjacent circuits. In addition, the fault isolation feature of the technology can help crews locate the trouble spots more quickly, resulting in shorter outage durations for the customers impacted by the faulted section.

One known FLISR technique is a centralized FLISR system, where real-time communications between switches and a controller are required to locate and isolate a fault in a feeder. Centralized FLISR systems, based on real-time communications, are effective when the communication channels are operable, but are completely defeated when communication is interrupted for any reason. The communication system equipment requirements also add cost and complexity to the switches. Another known FLISR technique involves pre-defined, static behavior characteristics for each sectionalizing switch. In this approach, each switch is pre-programmed to open if it experiences a certain number of fault current or voltage events, where the pre-programmed number is based on each switch's proximity to the feeder source. However, if the feeder source changes to an alternate, the pre-programmed sectionalizing switch behavior will result in incomplete or suboptimal fault isolation.

Pulse-testing interrupter/reclosers are known in the industry, where these interrupter/reclosers operate as a smart source interrupter which, after a fault is initially detected, deliver a series of test pulses to the feeder. The low energy test pulses are designed to detect the continued presence of a fault, and are recognized by the sectionalizing switches as fault current events or load current events, where the sectionalizing switches open if they experience a number of events exceeding a threshold. However, it can be difficult in some situations for a sectionalizing switch to distinguish between a fault current pulse and a load current pulse during the testing process.

In view of the circumstances described above, there is need for a sectionalizing switch control methodology which does not rely on an additional real-time communications infrastructure between switches and controllers in distribution grid feeders, yet controls switch opening behavior properly to isolate faults while still accruing the benefits of using low-energy test pulses.

SUMMARY

The present disclosure describes a control system and method for sectionalizing switches and pulse-testing interrupter/reclosers in a feeder, or portion of the distribution grid, which enables fault location, isolation and service restoration without requiring a separate communications infrastructure between the switches and/or a central controller. The method includes switches entering an armed state when they experience a high fault current during an initial fault event. Then, when the interrupter/recloser runs its test pulse sequence, any armed switch counts all test pulses as fault pulse events, while non-armed switches count the test pulses as load pulse events. Switches open to isolate the fault based on threshold values of fault count and load count events. When an initially active interrupter/recloser completes its test pulse sequence, another interrupter/recloser may begin its sequence, and all switches reconfigure their threshold values based on the new interrupter/recloser. After the interrupter/recloser has completed its test pulse sequence other related interrupter/reclosers use a fast close-open event if necessary to arm remaining switches for proper fault-count opening.

Additional features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

