THE EFFECT OF DC OFFSET ON CURRENT OPERATED RELAY

IEEE Transactions on Power Delivery, 2011

A current transformer (CT) is accurately modeled for representation of the CT saturation effects on digital protective relays. Simulation studies performed in the PSCAD/EMTDC platform are used to investigate the impacts of CT saturation on the current phasor estimation. A new algorithm is also proposed for detection and compensation of CT saturation effects, based on: a least error squares (LES) filter which estimates the phasor parameters of the CT secondary current; a novel saturation detection method which uses the output of the LES filter for saturation detection; and a new minimum estimation error tracking approach which enhances the precision of the phasor estimation. The proposed saturation detection/compensation algorithm is independent of the parameters of the CT, the burden, and the power system. The study results show that the proposed algorithm: 1) reconstructs the distorted current waveform, under dc and ac saturation conditions, with the required precision and speed and 2) performs satisfactorily under inductive burden and under deep and slight saturation conditions.

IEE Proceedings - Generation, Transmission and Distribution, 2004

Protective current transformers (CTs) are integrated into electrical power systems for assessment of the health of the system. They are intended to provide a scaled-down value of the line current. During major faults, excessive fault currents with decaying DC components could flow through the primary of the CT, causing core saturation and a consequent malfunction of the protection system. This problem is addressed in the paper, and a signal-processing scheme is proposed for fast predetermination of the peak value of the steady-state AC component, instant of occurrence of fault and the time constant of the decaying direct current. Samples of the CT secondary current are collected until the onset of saturation, and are operated upon using a covariance-Prony algorithm to estimate the aforementioned critical parameters. Simulation results in support of the proposed technique are also presented.

This paper presents the results of an investigation about current transformers (CTs) transient behavior and the factors that can lead its core to saturate. For this study, two methodologies are used: CT model implemented in MATLAB and CT modeling using ATP. The results of this analysis are compared in order to validate the models and the main conclusions are presented.

2012 65th Annual Conference for Protective Relay Engineers, 2012

Current transformers (CT) normally have excellent performance when applied correctly under conditions for which they were designed. While the common operating conditions affecting CT performance are usually recognized and properly considered, there is one factor, the importance of which is sometimes underestimated or even overlooked entirely. This is the effect of external stray flux produced by: • abrupt bends of the CT primary conductor at very close distance from the CT location; • high-current busses adjacent to the CT; and • other sources of magnetic fields near the CT (e.g. CTs installed within power transformer or shunt reactor tank). If a CT is applied incorrectly (e.g. without considering the existence of stray fluxes) the secondary CT current can be, under certain circumstances, entirely different from the primary CT current which then can easily cause unwanted operations of sensitive protection relays like for example differential protection.

IEEE Transactions on Power Delivery, 2015

Current transformer (CT) saturation threatens accurate discrimination between internal fault current and magnetizing inrush current of a transformer and endangers the proper operation of differential relay. Thus, compensation of CT saturation could substantially improve the performance and security of transformer differential relays. So far, almost all of the technical literatures in this field have focused exclusively on the fault current compensation. However, this paper proposes an efficient compensation algorithm to reconstruct both of the fault and inrush currents which are distorted by CT saturation. Some of the attractive features of the proposed method are its accuracy, fast response time, desired sample-by-sample output, no dependency on power system topology, immunity against noise and harmonics, and its simplicity. These features are extracted through the application of numerous test cases reflecting a wide range of variations in fault and inrush currents. The proposed algorithm is proved to be fast, accurate, and reliable.

2006

In presenting this thesis in partial fulfillment of the requirements for a Master's degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis work was done. It is understood that any copying, publication, or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in my thesis.

2009

This paper presents an analysis of possibility of detection of a fault position with respect to the compensating bank in a series compensating transmission line. The algorithm designed for this purpose is based on determining the contents of dc components in the distance relay input currents. Fuzzy logic technique is applied for making the decision whether a fault is in front of the compensating bank or behind it. The delivered algorithm has been tested and evaluated with use of the fault data obtained from versatile ATP-EMTP simulations of faults in the test power network containing the 400 kV, 300 km transmission line, compensated with the aid of the compensating bank installed at midpoint. The sample results of the evaluation are reported and discussed.

2007

This paper presents a novel algorithm (patented) for detecting the early CT saturation in bus differential protection, which, combing with the late CT saturation block zone and other security enhancement features provides great securities to the bus differential relay on external faults, and also maintains the relay with high sensitivity and fast operation for internal faults. Index Terms – CT saturation, Bus protection, 87B Differential Protection

IPST Conference, 2001

Modern protective systems require a faithful reproduction of primary short circuit current. Often, specially in high power installations, an important part of the current, during a few cycles at least, is the d.c. component, which causes severe saturation conditions, if the current transformer is not correctly selected and employed.

This paper presents an analysis of possibility of detection of a fault position with respect to the compensating bank in a series compensating transmission line. The algorithm designed for this purpose is based on determining the contents of dc components in the distance relay input currents. Fuzzy logic technique is applied for making the decision whether a fault is in front of the compensating bank or behind it. The delivered algorithm has been tested and evaluated with use of the fault data obtained from versatile ATP-EMTP simulations of faults in the test power network containing the 400 kV, 300 km transmission line, compensated with the aid of TCSC (Thyristor Controlled Series Capacitor) bank installed at mid-line. The results of the evaluation are reported and discussed.