Reliable Generator Islanding Detection for Industrial Power Consumers With On-Site Generation

Large power consumers often have on-site generation. If the utility tie opens, it is essential to isolate the on-site generators to prevent generator equipment damage before the utility attempts to reclose in a possible out-of-synchronism condition. Typically, islanding detection schemes are used to detect this condition and disconnect on-site generation quickly, thereby allowing successful utility reclose. This paper introduces a reliable islanding detection solution that was proposed, implemented, and tested at a refinery in Texas. The facility houses two on-site generators and is interconnected to the utility via a looped system. A topology-based islanding detection scheme was originally installed at this facility but was later decommissioned because of difficulties in adapting to evolving topology changes. Following an undesirable event in the utility system that could have resulted in damage to the refinery on-site generator equipment, the refinery decided to implement an islanding detection scheme that is independent of system topology changes and only relies on local-area measurements. However, the dependability of a traditional local measurement-based scheme is vulnerable to the dynamic generation-load mismatch, making it possibly unreliable. This paper describes a solution using a redundant high-speed multiprinciple islanding detection scheme that incorporates a unique voting supervision logic to achieve security.

I. Introduction

Large industrial power consumers, particularly those in continuous process industries, often have on-site generation capabilities in order to meet their essential power requirements. Islanding is defined as a condition where a portion of the power system that contains loads and on-site generation remains energized but is electrically isolated from the rest of the utility system [1]. Typically, islanding is caused by a disturbance in the utility system due to faults or wide fluctuations in frequency and/or voltage caused by real and reactive power mismatch. Fig. 1 shows a simplified one-line diagram of an industrial plant interconnected to a utility. Under normal operating conditions, the on-site generators operate in parallel with the utility to feed the total plant load. The local generation (P _G) plus the imported power (P _I) together meet the entire plant load (P _L). For a fault on the line supplying power to the plant, line protective relaying will detect the fault and open Breakers 2 and 3, thus resulting in a loss of utility supply to the plant and leaving it islanded.