Load Encroachment Research Articles

Design and Implementation of an Algorithm for Diagnosis of Load Encroachment in EHV Lines

Zone-3 mal-operation of distance relays was one of the important cause for many of blackouts in worldwide. The one of the root cause for the mal-operation is encroachment of load into the Zone-3 characteristics. Such zone-3 mal-operations can be prevented by improvising the zone-3 characteristics which eventually avoids cascaded line tripping. This paper proposes and validates a new algorithm based on the total DC component and Phase angle of the positive sequence impedance to prevent its operation during the load encroachment conditions. Based on the proposed algorithm, improvement in the operation of Zone-3 element can be achieved. The relay can differentiate between actual system faults and load encroachment and thus ensure the security of the system. The proposed algorithm supplements the Zone-3 operation by introducing the ability to identify a load encroachment condition, and thus can avert the possibility of blackouts.

Real‐time monitoring of zone 3 vulnerable distance relays to prevent maloperation under load encroachment condition

Undesired trip operation of zone 3 units of distance relays in power transmission network, during static and dynamic load encroachment can lead to cascading failures and even catastrophic power system blackouts. Stressed conditions such as power flow redistribution and power swing can cause maloperation of the third zone of distance relays. Fast and dependable detection of the symmetrical faults, occurring during these conditions poses an additional challenge. One of the effective methods to avoid the zone 3 contribution in cascading failure propagation is the detection and monitoring of vulnerable relays which are exposed to maloperation in power system stressed conditions. In this study, a new relay ranking index is proposed for real-time identifying the zone 3 of distance relays, most vulnerable to incorrect operation due to load encroachment. A novel synchrophasor data-based monitoring index is also presented for supervision of critical distance relays operation. This index is extracted based on positive-sequence fault component phasors of the current and voltage signals obtained by modern PMUs or GPS based digital relays which have been reconfigured for this application. The proposed monitoring scheme is able to quickly distinguish the fault from load encroachment condition. The performance of the proposed supervisory scheme is evaluated and approved on a nine-bus WSCC system.

Transmission system wide-area back-up protection using current phasor measurements

Zone-3 of distance relays might maloperate during stresses frequently encountered in power systems, such as power swing, load encroachment, and voltage instability. This paper proposes a new protection algorithm for discrimination between short-circuit faults and other stresses in the transmission networks. The proposed method compares the sum of currents at the predetermined buses before and after the disturbance occurrence using synchronized current phasor measurements. The faulted area and line are identified as well. The optimal placement of phasor measurement units (PMUs) is tackled using a mathematical model. One of the main advantages of the proposed algorithm is decreasing the number of required PMUs in comparison with those of existing wide-area back-up protection schemes. In virtue of its computational speed, the proposed method can be exploited as a practical back-up protection cooperating with conventional protection schemes. The extensive simulation studies carried out on the IEEE 57-bus test system verify applicability of the proposed algorithm as a reliable back-up protection scheme for lines.

Simulation of Distance Relay for Load Encroachment Alleviation with Agent Based Supervision of Zone 3

Cascaded tripping of power lines due to mal-operation of zone-3 distance relays has been one of the main causes of many previous blackouts worldwide. Encroachment of load into zone-3 characteristics during stressed system operation conditions is a basic factor for such mal-operation of the relays. By improving the operation of zone-3, it is possible to prevent mal-operations so that cascaded line tripping can be avoided. For proper study of the behavior of distance relay during faults and load encroachment phenomenon, we must build a model of distance relay, so in this paper a modeling study of distance relay is implemented using MATLAB/Simulink program. However, this model is distinguished from previous models that, examines in detail the third zone of distance relay. Many cases are simulated with changing line loading and fault location to ensure the capability of the relay to detect the fault and thus the maximum load ability limit of distance relay is obtained. In order to prevent cascading events caused by hidden failures in zone-3 relays, agent based relay architectures have been suggested in the recent past. In such architectures each zone-3 relay contains agents that require communication with other agents at various relevant relays in order to distinguish a real zone-3 event from a temporary overload. In this paper, a local master agent is consulted by all zone-3 agents before a tripping decision is made. The master agent maintains a rule base which is updated based on the local topology of the network and real time monitoring of the status of other relays and circuit breakers. Cisco Packet Tracer program is used for running communication network simulations. The result of the simulation indicate that the time estimated to send and receive a packet data unit (PDU) message between one relay to anther can satisfy the communication requirement for the proposed scheme with fiber media.

An spatiotemporal information system based wide-area protection fault identification scheme

The paper presents a synchronized phasor measurement based fast and accurate comprehensive wide area back-up protection scheme for transmission lines. The proposed scheme uses Koopman Mode Analysis (KMA) technique on fault current data obtained from Phasor Measurement Units (PMUs) for fault identification in back-up protection. The principal advantage of Koopman operator is that it is based on spatiotemporal information system (STIS). In real world applications, often time and space exists together and hence, dealing with spatial aspect without considering temporal aspect is of limited use. The wide area back-up protection scheme is developed using STIS for fault identification and classification including wide variations in operating conditions of the power network. The New England 39 bus system is used as the test system which is developed on Dig-Silent power factory commercial software (PF4C) platform for evaluating the performance of proposed technique. Further, the efficacy of the proposed scheme is also tested for stressed conditions such as symmetrical fault during power swing and load encroachment and found to work effectively.

Synchrophasor Assisted Adaptive Relaying Methodology to Prevent Zone-3 Mal-operation During Load Encroachment

Phasor measurement unit (PMU) has uniquely blended the contributions of modern information and communication technology in terms of time synchronization and fast data transmission to emerge as the smart sensor for advanced protection methodologies in smart power grids (SPG). The latency issue associated with the functionality of PMUs has made synchrophasors assisted protection algorithms suitable for backup protection, so as to efficiently prevent events, such as mal-operation of relays under load encroachment as well as other stressed situations. This paper proposes a novel methodology to prevent Zone-3 mal-operation of distance relays during load encroachment using the synchrophasor measurements obtained from PMUs installed in a widely-spread power system network. The proposed algorithm is to be implemented in transmission line protection center (TPC), where the synchronized three phase voltage and current phasors acquired from the PMUs are transferred to Phasor data concentrator (PDC) and are used to calculate the impedances seen by the relays in real time. A load encroachment situation and a faulty situation can be distinguished by comparing the impedances seen by primary and backup relays installed at different buses for protecting their respective transmission lines. Numerous case studies have been conducted in WSCC-9 bus system modeled in PSCAD/EMTDC environment to validate the proposed methodology.

Synchrophasor-Based Wide-Area Backup Protection Scheme with Data Requirement Analysis

This paper presents a fast and robust wide-area backup protection scheme to detect the faulty condition and to identify the faulted line in a large power network. The proposed methodology uses positive-sequence synchrophasor data captured by either digital relays with synchronization capability or phasor measurement units dispersed over the network. The basic idea behind the new protection scheme is the comparison of bus voltage values calculated through dissimilar paths. Upon occurrence of a fault, the faulty condition is first detected and the bus(es) connected to the faulted line is(are) determined. Among transmission lines connected to the suspected bus(es), the faulted one is thereafter identified. In addition to two-terminal transmission lines, multiterminal lines are also incorporated. The performance of the proposed method is validated on the IEEE 57-bus test system in different fault conditions (fault type, fault location, and fault resistance). Discrimination of faulty and normal conditions is simulated by examining various stressed conditions, for example, load encroachment, generator outage, and power swing. The data requirement of the proposed technique is analyzed as well. To do so, a mathematical model for the optimal placement of measurement devices is developed and applied to different IEEE standard test systems.

Secured Zone 3 Protection During Stressed Condition

Maloperation of the zone 3 element of distance relays during stressed system conditions, such as power swing, load encroachment, or voltage stressed condition is one of the main reasons for large disturbances in power systems. The improved protection technique for zone 3 can help to prevent such maloperation and, thus, more reliable power systems can be envisaged. This paper proposes an algorithm that utilizes two new criteria: 1) the maximum value of the transient monitoring function obtained from three-phase currents and 2) the phase angle of the positive-sequence impedance to support zone 3 of the distance relay. The technique is tested for various power system events, such as the three-phase fault during the power swing, load encroachment, voltage stressed conditions, and current-transformer saturation during the three-phase fault using data simulated through EMTDC/PSCAD in the IEEE 39-bus New England system. The simulation results show that the zone 3 protection scheme using the proposed technique can correctly discriminate the three-phase fault from stressed system conditions.

Wide-Area Measurement-Based Backup Protection for Power Network With Series Compensation

This paper presents a synchronized phasor measurement-based wide-area backup protection scheme which compares the magnitude of sequence voltages of buses at a system protection center to identify the bus closest to the fault. Then, the sign of cosine of the angle between voltage and current at both ends of all lines connected to this bus are compared to identify the faulted branch. The technique is tested for various faults resulting in voltage/current inversion in a series-compensated line and during load encroachment and power swing conditions using data simulated through EMTDC/PSCAD for a nine-bus, three-machine power system. The scheme is found to be accurate and fast. With today's synchronized phasor measurement technology and communication system, the proposed scheme can overcome the limitations of the conventional backup protection scheme.

Synchrophasor-Assisted Zone 3 Operation

Zone 3 operation of distance relay serves as a remote backup in case of primary failure. Conditions, such as power swing, load encroachment, and voltage and transient instability, cause incorrect zone 3 operation. The detection of faults during such stressed conditions poses a further problem. This paper proposes a synchrophasor data-based technique for correct zone 3 operations by discriminating the fault from different stressed situations. This discrimination is accomplished using impedances calculated from voltage and current signals from synchrophasors placed at strategic locations. The proposed method is tested in the IEEE 39-bus New England system and found to be accurate.

Future Distribution Feeder Protection Using Directional Overcurrent Elements

Distribution feeder protection could soon be complicated by non-radial flows of real and reactive power available from high penetration distributed generation and potentially from microgrids. Non-directional overcurrent protection may not provide necessary security and sensitivity for faults on remote points of the circuit. Directional supervision is necessary to set overcurrent pickups with adequate sensitivity for remote faults. Setting the directional element by traditional means provides a reliability risk at varying VAR flows within reach of specific types of distributed generation. This paper will demonstrate the limitations of non-directional overcurrent protection and the pitfalls of an improperly configured directional element. A unique solution using directional overcurrent elements further secured by a load encroachment function can solve these problems. This approach has been validated in renewable plant collector circuit protection applications over a wide range of operating conditions.

Intelligent coordinated adaptive distance relaying

Malfunctioning of distance relay third zone has been identified as one of the leading factors of power system blackouts in several nations. This inconsistency in operation happens when heavy loads start encroaching the zone 3 settings. In this paper, a novel multi-agent system based methodology for power system protection coordination is proposed. Various system agents are designed to collaborate and adaptively modify the setting of distance relay zone 3 via communication with neighboring substations. The proposed coordination scheme aids in preventing fault misjudgment and possible network breakdown because of load encroachment. Furthermore, it enhances the relay selectivity and loadability. It has been tested using MATLAB®/Simulink™ with the agent programming in Java Agent DEvelopment Framework (JADE) platform. Analysis and test results demonstrate that the proposed method effectively mitigates distance relay malfunction under load encroachment.

Adaptive load blinder for distance protection

This paper proposes a novel adaptive load blinder for distance protection. A distance relay can provide remote backup protection by zones 2 and 3, but it may mal-operate under heavy loading conditions and cause cascading trips in the network, which could further lead to a widespread blackout. To prevent cascading outages, load blinders or load encroachment elements are generally used to block the distance relay when there is heavy load in the system. However, these elements are not always able to discriminate heavy loading conditions from fault conditions, especially for heavy loads with low power factors or faults with fault resistance. This paper presents a novel load blinder scheme for distance protection by using artificial neural network (ANN). Test results show that the proposed ANN-based load blinder scheme is able to discriminate between different heavy loads with a wide range of power factors and different faults with fault resistance.

Phase distance relaying algorithm for unbalanced inter-phase faults

This study presents a new fault impedance estimation algorithm for inter-phase faults for the purpose of phase distance relaying of extra high voltage (EHV) and ultra high voltage (UHV) transmission lines. The principle is based on the assumption that the fault arc path is predominantly resistive, and the phase angles of the unmeasured fault point voltage and fault arc path current are equal. This is used to construct the fault impedance estimation equation, which naturally prevents the effects of fault arc path resistance, load current, power swing and load encroachment. PSCAD (simulation software) simulation shows the validity of the proposed algorithm.

Analysis of overload conditions in distance relay under severe system contingencies

Distance relay protection is widely used worldwide for protection scheme on high voltage transmission lines. This protection tends to be prone to load encroachment condition causing possible undesired tripping condition. Investigations of two system disturbances that occurred in TNB’s (Tenaga Nasional Berhad) Grid in the year 2003 and 2005 have clearly revealed the occurrence of load encroachment condition following line overloads after large number of line tripping. Examination of the impedance locus trajectory during the overload events have enabled a distinction be made between power swing and load encroachment phenomena. This paper presents the analysis and findings of the investigation of the load encroachment phenomena of the two events, including other related transmission line contingencies.

Adaptive load encroachment prevention scheme for distance protection

In this paper, a new adaptive load encroachment prevention scheme based on steady-state security analysis and adaptive anti-encroachment zone (AEZ) is proposed. The new scheme identifies the vulnerable distance relays through real-time security analysis. Selected dual contingencies are included to reflect the influence from the “hidden failures” of protection systems. Effective measures are taken to improve the computational efficiency. The AEZ will be designed online to prevent the undesired tripping if the analysis shows that a distance relay may suffer the load encroachment for a particular scenario. To ensure the dependability of the protection system, the AEZ will be applied only when its introduction is necessary. The effectiveness of the new scheme can be verified through the test cases in this paper.

An enhanced zone 3 algorithm of a distance relay using transient components and state diagram

Zone 3 of a distance relay is used to provide the remote backup protection in case of the failure of the primary protection. However, the risk of maloperation under stressed conditions such as heavy loading, voltage, and transient instability is quite high. Zone 3 is used in combination with the derivatives of the voltage and current, etc. to prevent maloperation. At times, the impedance characteristics that restrict the tripping area of relay are used to avoid maloperation due to load encroachment. This work presents a novel zone 3 scheme based on combining the steady-state components (i.e., 60 Hz) and the transient components (TCs) using a state diagram that visualizes the sequence of studies that emanate from the sequence of events. The simulation results show that the novel zone 3 distance relay elements using the proposed method operate correctly for the various events.

The Egyptian Electricity Authority strategy for distance relay setting: problems and solutions

Abstract This paper presents a study of the problems associated with improper zone settings of a distance relay. These problems include the difficulties of adjusting the setting when a short line follows a long line or visa versa. It deals also with setting problems like high fault impedance, in-feed current and load encroachment. A proposed setting algorithm suitable for digital relays is presented. It helps in improving the dependence and the selectivity of distance relays.