The strategies and recommended practices that apply to protection schemes for commercial and industrial facilities have evolved in the past decade. It is important that facilities managers and protection practitioners understand and embrace these developments. Read more
Category Archives: Electrical Protection
Monitoring circuit breakers: Reviewing current testing methodologies
BY FINLEY LEDBETTER, Group CBS
Circuit breakers, from low-voltage molded case to high-voltage SF6 (sulfur hexafluoride) circuit breakers, all connect and isolate electrical loads from downstream machinery. While some breakers are used as disconnect switches, they are not designed for this purpose. Most breakers are used sparingly, giving technicians few opportunities to test the breaker’s operation without removing the breaker and downstream equipment from service.
To minimize downtime, maintain productivity, and improve personnel safety, electricians are constantly looking for faster, easier ways to verify that circuit breakers will perform to original equipment manufacturer (OEM) specifications. Today, electrical testing technicians have a multitude of available test methods and sets available to them. Industry Essentials will look at those testing methods with a focus on the trend towards testing methodologies that are capable of providing frequent, operational data on the breaker without the need to remove the breaker from service.
Addressing relay challenges with the modern technology
BY MARK STEPHENS & ALDEN WRIGHT, Electric Power Research Institute
In 2009, the Electric Power Research Institute (EPRI) began an effort to create improved alternating current (AC) “ice cube” relays that could withstand voltage sags without dropping out.
Their white paper entitled “AC Ice Cube Relays Applied for Improved Power Quality” outlined the basic design and vulnerability of these common devices that often appear in modern industrial control circuits. These are called “ice cube” because they are housed in clear plastic having the appearance of an ice cube (see photo).
Similar appearing relays with direct current (DC) coils are generally robust to common power quality problems as long as their corresponding DC power supplies are robust as well. However, “ice cube” relays with AC coils have shown extreme sensitivity to voltage sags.
With an average dropout at or near 70 percent of nominal for a cycle or less (as short as one-quarter of the cycle—four milliseconds), these devices can lead to as many as 13 equipment shutdowns per year in a distribution-fed commercial or industrial facility.
10 suggestions to optimize equipment life and enhance reliability
BY HAL THEOBALD, Schneider Electric
With increasing dependence on computers and automated processes, most modern facilities cannot afford downtime. According to studies published by the Hartford Steam Boiler Insurance Company and FM Global, “Electrical equipment failures account for millions of dollars in damage and lost business every year.”
Performing proper maintenance on a facilities’ electrical equipment can reduce the risk of an unplanned outage and help extend useful life of the asset. In today’s economy, budget constraints on capital improvement projects will mean more reliance on existing equipment maintenance.
Electrical switchgear is composed of passive and active components. The passive components include the horizontal and vertical bus structures while the active components are the power circuit breakers and fusible switching devices.
The main function of the active components is to protect the electrical assets downstream, to disconnect the circuit, and to protect personnel in case of an arc flash event. Both the passive and active components require regular maintenance to ensure equipment integrity and proper mechanical and electrical functionality, as well as to optimize the equipment’s useful life.
A regularly scheduled electrical system preventive maintenance program is intended to detect, repair, or replace affected electrical components, parts, or equipment before they lead to catastrophic damages, significant power interruptions, and loss of business functions.
Most of this feature will focus on circuit breakers, as they are the most commonly utilized active component in low and medium-voltage switchgear and switchboards. Medium-voltage switchgear can consist of one of three types of circuit breakers; air, vacuum or oil.
These circuit breakers are typically draw-out type, a design which facilitates removal from the power source, simplifying maintenance. The three types require similar maintenance; however each has unique characteristics and testing procedures.