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The last three decades have seen significant improvements in power system protection. With the rise of digital relays, recalibration during maintenance tests became obsolete. The model of one IEEE element per electromechanical relay is not the case anymore. Digital relays build a system of elements freely combinable with programmable logic conditions. Additionally, to be able to protect the increasingly...
This paper describes several commonly applied line protection schemes, including distance schemes, directional comparison schemes using distance and directional elements, and line current differential schemes. Using analysis tools like fault trees, power system studies, and event analysis, we evaluate and compare these protection schemes in terms of speed, sensitivity, dependability, security, and...
Modern microprocessor-based relays are designed to provide robust and reliable protection even with disruptions in the dc supply, dc control circuits, or interconnected communications system. Noisy battery voltage supplies, interruptions in the dc supply, and communications interference are just a few of the challenges that relays encounter. This paper provides field cases that investigate protection...
Several classic papers explain the fundamentals of capacitive voltage transformer (CVT) design, operation, and transient response. Distance elements can overreach, particularly in high source-to-line impedance ratio (SIR) applications, which can result in undesired Zone 1 operations. Because this continues to be a problem in real applications, this paper revisits documented field cases using event...
How stable is the frequency of the power system on a given day? How does a microprocessor-based relay track power system frequency? Why is frequency tracking important? This paper reviews the fundamentals of frequency tracking and explains, in practical terms, how and why this is done in digital relays. The performance of protective elements at off-nominal frequencies is of key interest. As with all...
Phase and ground directional elements are relied on for fast and secure protection throughout the power system. Although directional relays have been applied successfully for many years, several new and unique applications and power system disturbances present challenges. Using field and laboratory data, this paper reviews fundamentals, discusses the limits to sensitivity, and shows how and why directional...
In August 1999, a lightning strike caused a misoperation of a relay installed in the late 1980s. The relay misoperation caused a two-minute outage at a petrochemical plant and led to an exhaustive root-cause analysis. The misoperation can be attributed to incorrect fault type selection in a distance element-based, 1980s-era relay. Two separate events in different locations, one in December 2007 and...
Substance P (SP) is an important neurotransmitter in the control of intestinal motility and is found in both the enteric and sympathetic nervous systems. This study examined the effect of celiac ganglionectomy on (1) mechanical properties of the circular muscles of the duodenum, ileum and proximal colon, (2) circular muscle responses to SP and neurokinin A, (3) distribution of substance P-like immunoreactive...
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