A fault protection and location method for a dc bus microgrid system is presented in this paper. Unlike traditional ac systems, dc bus systems cannot survive or sustain high-magnitude fault currents. And if a fault causes the dc bus to de-energize completely, it makes locating faults very difficult. The main goal of the proposed scheme is to detect and isolate faults in the dc bus without de-energizing the entire system and identifying the fault location. In order to achieve this, a ring-type bus was used in this paper. The bus was segmented into overlapping nodes and links with circuit breakers (CBs) to isolate the segment in the event of a fault. Backup protection is implemented for circuit breaker failures to improve system reliability. A noniterative fault-location technique using a probe power is also presented in this paper. This probe power can also be used for a pilot test before main CB reclosing to avoid system issues that can be expected when the reclosing fails due to a permanent fault. The proposed algorithm can be implemented and executed by an intelligent electrical device for individual node. The proposed concepts have been verified with computer simulations and hardware experiments.

DC Ring-Bus Microgrid Fault Protection and Identification of Fault Location

Lightning is a significant cause of faults and outages in many electric power systems and is one of the major causes of poor system reliability. Predictive assessment of distribution reliability indices can be used to identify areas that have poor reliability so that appropriate changes in system design can be implemented. The assessment of distribution system performance under lightning conditions requires modeling of storm characteristics and system response. In this paper, a Monte Carlo simulation for evaluating distribution system reliability under lightning storm conditions is presented. The results from a practical distribution system show the importance of detailed modeling of storm characteristics and simulation of the system response in assessing distribution system reliability during lightning storms.

Distribution system reliability assessment due to lightning storms

The implementation of smart grids will fundamentally change the approach of assessing and mitigating system voltage deficiencies on an electric distribution system. Many distribution companies have historically identified customer level voltage deficiencies utilizing a reactive approach that relies upon customer complaints. The monitoring capabilities of a smart grid will allow utilities to proactively identify events that exceed the voltage threshold limitations set forth by ANSI Std. C84.1 before they become a concern to end-users. This proactive approach can reduce customer complaints and possibly operational costs. This paper describes an approach for determining voltage threshold limits as a function of duration for proactive voltage investigations utilizing smart grid monitoring equipment. The described approach was applied to a smart grid located in Boulder, Colorado. This paper also describes the results of this two-year study.

Utilizing a Smart Grid Monitoring System to Improve Voltage Quality of Customers

The results of a study undertaken to characterize lightning-caused surges and damage occurring in distribution systems are reported. Seventy five lightning transient recorders were installed on operating 15 kV class overhead distribution lines to measure lightning-caused surge arrester discharge voltage and currents. During the study period, 1309 lightning surge waveshapes were measured at four utility field sites. These waveshapes were carefully analyzed to obtain characteristic distributions of their rates-of-rise, risetimes, decay times, and other relevant parameters. In addition, the portion of damage and faults caused by lightning was assessed at one of the four field sites. >

Characteristics of lightning surges measured at metal oxide distribution arresters

Electricity grid resilience amid various natural disasters: Challenges and solutions

As a part of EPRI Research Project 2542-1, Characteristics of Lightning Surges on Distribution Lines, a coincident lightning events detector (CLED) was developed, tested, and installed in a test area on the Florida Power Company distribution system in St. Petersburg, Florida. The CLED provided the data to determine the number of lightning-caused circuit breaker operations for the first time. During the 3-year recording period, a total of 546 faults causing circuit breaker operations occurred on the seven circuits in the test area. Of these faults, 415 (or 76%) were temporary faults. A lightning strike was coincident with 42% of the temporary faults. Improper operation of line fuses was traced to the absence of lightning arresters at line fuse locations. >

D.E. Parrish

Papers

Lightning-caused distribution circuit breaker operations