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Events such as faults, loss of load or generation may cause unwanted relay operations which initiate cascade tripping leading to system collapse. Security of power system protection is a major concern for utilities. A System Integrated Protection Scheme (SIPS) based approach is proposed for improving security of protection operations. Identification of vulnerable points which may maloperate during...
Digital relays are capable of computing the negative sequence current on both primary and secondary sides of the transformer along with the phase difference between these two negative sequence currents. By using both phase and magnitude information, negative sequence current could be used to detect minor turn-to-turn faults involving 3% of the transformer's windings or more. Turn-to-turn faults may...
With the integration of distributed generation (DG) to meshed distribution systems, the operating time of the protective system becomes a major concern in order to avoid nuisance DG tripping. This paper proposes a new time-current-voltage tripping characteristic for directional overcurrent relays (DOCRs) that can achieve a higher possible reduction of overall relays operating time in meshed distribution...
One of the top reliability concerns in power systems classified by NERC is hidden failures in protection schemes. Such failures are defects that go undetected under normal operating conditions but manifest themselves during faults or transients, which may lead to the false operation of relaying schemes. Specifically, hidden failures typically lead to incorrect input to relays and adversely affect...
This paper presents an algorithm to precisely detect the saturation of Current Transformers (CTs). The algorithm is based on first difference of magnitudes of Lissajous Curve. These Lissajous curves are generated using secondary current signal and its first derivative. PSCAD was used to generate secondary current signals for various practical cases of fault currents and MATLAB was used to implement...
This paper shows how generic protection relay models available in planning tools can be augmented with settings that are based on NERC standards or best engineering practice. Selected generic relay models in Siemens PSS®E have been used in dynamic simulations in the proposed approach. Undervoltage, overvoltage, underfrequency, and overfrequency relays have been modeled for each generating unit. Distance-relay...
Protective relays used in power system today measure external signals to diagnose the internal state of the equipment they protect. Based on measurements of voltage, current, frequency at the bus, the decision is made whether the equipment is healthy or faulty. Due to advances in sensing and computing, it has become possible to use the external measurements to dynamically estimate the internal state...
The encroachment of the measured load impedance into the outer tripping zone was one of the main problems of distance protection relays since their application. Highly loaded transmission lines intensified this issue and caused cascading failures worldwide during the last decades. Restricted zone reach settings or load blinders in the R-X-impedance plane were the common countermeasures until now....
With the integration of wind generators in the distributed network, the power flow and fault current characteristic have been changed. The negative sequence impedance of the doubly fed induction generator (DFIG) is quite different from the positive sequence impedance after the crowbar circuit is activated. This characteristic poses a big challenge on the operation of the protection system. Traditional...
This paper extends the analysis of low frequency AC (LFAC) transmission systems and investigates short-circuit fault characteristics and distance protection considerations. Due to operation at a low frequency, transmission line reactance is reduced and thus the power system transfer capability is increased significantly. The transmission line impedance reduction, however, creates a drawback in LFAC...
As the power distribution grid moves towards actualizing the concept of a smart grid, the dependence of reliable and secure grid operation on the communication architecture and data is increasing rapidly, along with the possible cyber-attack surface. In this paper first an agreement algorithm for a distribution substation with radial topology is presented that leverages the communication capabilities...
In this paper, an innovative agent-based security scheme is proposed for identifying potential impacts of cyber attacks in smart grid protection systems. Smart grids are critical cyber-physical energy systems (CPESs), where potential attacks can manipulate the normal operation of digital relays by injecting malicious control signals. This event could cause the relays to trip at undesired time which...
Large oil-immersed power transformers always have the gas relay equipped between the main tank and conservator. However, due to the inherent defects, the gas relay malfunction caused by external faults happens occasionally all over the world, which jeopardizes the safe operation of bulk power systems. In order to explore the oil flow characteristics inside the pipe during external short circuit faults,...
Several major outages have been traced to the failure of remote backup protection elements in distance relays. Experience has shown that coordination of remote backup zones in stepped-distance protection can be vulnerable during stressed conditions. Furthermore, relay settings are typically biased for high dependability, resulting in lower security especially when several unexpected events coincide...
This paper presents the use of a distributed dynamic state estimation, executed each cycle, to enable simultaneous cyber security and operational security. The basis of the method is: (a) data verification that detects bad data or byzantine type attacks and (b) command interception and fast authentication from the cyber security point of view (reliable detection of cyber intrusions) and from the operational...
Sensitivity of start element impacts the performance of transmission line protection. Normally, start element is affected by data window length. A start element of transmission line relay protection based on current variation sample data of three phases at the same time is proposed in this paper. It includes two criterions. The start element performance is not impacted by data window and frequency...
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