Design of prototype non directional overcurrent relay micro-controller-based

Directional overcurrent and earth-fault protections for a biomass microgrid system in Malaysia

Non-standard characteristic of overcurrent relay for minimum operating time and maximum protection level

Protecting transmission lines frequently involves adopting distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of interest. Accuracy and convergent speed of the filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily erase harmonics using simple calculation. However, the voltage and current signals contain large harmonics and DC offset during the fault interval. The DC offset heavily influences the precision and convergence speed of the fundamental frequency signal from DFT. In this investigation, the authors present a novel Fourier algorithm to remove the DC offset in a voltage or current signal. Applying a full-cycle DFT (FCDFT) requires one cycle plus two samples to calculate and compensate for the DC offset. Half-cycle DFT (HCDFT) only requires half of a cycle plus two or three samples to accomplish the algorithm when the input signal has no even order harmonics. Adopting the proposed algorithm in distance relays effectively suppresses the DC offset and quickly decomposes the accurate fundamental frequency components.

Effect of non standard characteristics of overcurrent relay on protection coordination and maximizing overcurrent protection level in distribution network

An overcurrent relay is designed to measure the current flowing into a short-circuit fault and after an appropriate time trip its circuit breaker. Current transformers may saturate and distort the current measured by the relay. This distortion may affect the operating time and cause the maloperation of a time graded protection scheme operating with inverse overcurrent relays. The paper describes the design and evaluation of a directional overcurrent relay suitable for the protection of a distribution feeder. The relay is designed to operate with signals derived from iron-core measuring current transformers (CTs). This type of CT will saturate during a fault and the secondary current signals used to energise the relay will be severely distorted. The relay will use the information contained in the distorted current signal to predict the magnitude and phase of the primary current signal. A superposition algorithm and cross-correlation processing techniques are used to evaluate the direction to the fault and the amplitude of the fault current. These techniques were developed using MATLAB and tested using transient data generated by the EMTDC simulator. The design features of the directional and overcurrent algorithms and the results obtained during their evaluation are described in the paper.

The coordination of overcurrent relay protection in the power framework is crucial for preserving electrical distribution systems. It ensures that both primary and backup protection are provided to the system. It is essential to maintain a minimal level of coordination between these relays in order to reduce the overall running time and guarantee that power outages and damage are kept to a minimum under fault conditions. Proper coordination between the primary and back-up relays can minimize the operation duration of overcurrent with instantaneous and earth fault relays by selecting the optimum TMS (Time Multiplier Setting) and PS (Plug Setting). The present study investigates the difficulty associated with determining the TMS and PS values of earth-fault and overcurrent relays at the 33/11 kV power distribution substation in Basra using the instantaneous setting element. Overcurrent and earth fault relays were simulated in two scenarios: one with a time delay setting and one with an immediate setting. This procedure was carried out to generate Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay took place in the Nathran substation, which has a capacity of 2×31.5 MVA and operates at a voltage level of 33/11 kV. The substation is a part of the Basrah distribution network. The short circuit current is estimated at each circuit breaker (CB), followed by the simulation of protection coordination for the Nathran substation using the DIgSILENT Power Factory software. This research is based on real data collection, and the setting considers the short-circuit current at the farthest point of the longest feeders. The results show the effectiveness of the proposed coordination scheme, which reduced trip operation time by 20% compared to the presented case study while maintaining coordination between primary and backup protection.

The use of earthing in electrical power reticulation has an interesting history. Initial power distribution systems did not deliberately reference the phase conductors to earth. Later, depending on the application, there was a bifurcation of earthing practices, with some systems solidly earthed through low impedance resistors and some loosely earthed through high impedance resistors. The coal mining industry in Australia has converged to high resistance earthing. The supply is removed on the first earth fault to ensure that the fault is not escalated on the occurrence of a second earth fault. While this has safety benefits, there are challenges for the design of sensitive earth leakage protection. This is further complicated with the introduction of Variable Speed Drives (VSDs). This paper charts the history of earthing and how it has influenced the way that earth fault protection is implemented in coal mines, both in Australia and overseas.

Distance protection is not utilized in distribution networks, unlike the transmission systems, due to the inherent characteristic of the distribution networks and the additional required facilities of distance protection, compared with over-current protection, which is in use in the distribution systems. This paper discusses the measured impedance by six elements of distance relay first zone applied on a distribution feeder in the case of a single phase to ground (AG) fault. This is done by presenting the measured impedance at the source node the distance relay ideal tripping characteristic for each element. The variation of the ideal tripping characteristic due to the changes in the system parameters is investigated.

Development and hardware implementation of a reliable protective relay data acquisition system

Detection and isolation of faulty line in an active distribution network using intelligent numerical relay

Generalized distance-based protection design for DG integrated MV radial distribution networks — Part II: Application to an actual distribution line

Some clients request the stability study of a protection system in designing power system to evaluate whether protection relays properly operate in case of an internal fault and if they do not function in the events of severe external fault. High fault currents could cause Current Transformers (CTs) to be saturated. A critical concern is the performance of fast protective relay (instantaneous or differential elements) during severe saturation of CTs. Time domain transient simulation software is widely used for the study of these types of works. In this paper, a relay stability study of 115 kV and 34.5 kV transmission and distribution systems was carried out and evaluated utilizing the PSCAD software, which provides several modeling methodologies for various electrical equipment such as transmission line, power transformer, current transformer and protective relays. For the purpose of this study, the modeling method of CT is the most important factor because it influences heavily on the protection relay operation. It is very important to model CT as close as the real characteristics of the CT. Two types of CT models provided by the PSCAD were discussed and compared with each other and an appropriate CT modeling methods were covered in this study. This study is mainly based on digital relays, which prevail recently in the relay market. Digital relay characteristics like anti-aliasing filter, digital filter and various setting function are embedded into PSCAD.

This paper describes the design and testing of a digital distance relay for high voltage systems. It shows how a prototype has been built using two single board computers in a multiprocessor configuration. This design allows simultaneous real-time filtering of the voltage and current signals and computation of the apparent impedances "in parallel". The paper presents the results of the tests carried out on a prototype of the relay using a transient signal generator test circuit. A trip signal is produced by the relay in less than one 60 Hz cycle after fault occurrence for all faults.

Overcurrent protection for distribution feeders with renewable generation

Design and implementation of a versatile digital directional overcurrent relay