Current Differential Principle Research Articles

Current differential protection of double-circuit transmission lines in modal domain

In this paper, we present a new approach to protection of double-circuit transmission lines using modal transformation. The current differential principle is applied in the modal domain, and the relay characteristics are plotted in the alpha plane for numerical differential protection applications. Synchronized voltages and currents from both the ends are transformed to modal values. The transmission lines are modeled as equivalent $$\pi $$ model in modal domain, and line charging current is compensated. Electromagnetic transient program EMTP-ATP is used to simulate the double-circuit transmission systems, and the algorithm is implemented in MATLAB. The extensive case studies demonstrate the utility and the superiority of the proposed current differential scheme.

Adaptive differential protection scheme for wind farm integrated power network

In this paper, an adaptive differential protection scheme is proposed for wind farm integrated power network. Any fixed threshold setting based protection scheme is not always suitable for the different operating conditions of power system. Considering the possible modulations in the fault signal, a particle swarm optimization (PSO) based differential relay algorithm is proposed in this paper. The positive sequence current differential principle is used. For different operating conditions, fault conditions and configurations of the system, the threshold value can be calculated online. So, practically the method can be applied to any power system model and the impact of dynamic operation of wind farm on the protection function is negligible. The threshold setting is designed considering the fault location and fault inception angle. Initially, the most effective faults among all the possible faults are identified with a single variable (fault location) objective function. Later, only single-phase-to-ground fault is considered for threshold setting with all possible parameters. The method is tested using a standard power system model integrated with wind farm and simulated using MATLAB R2016a software. Results prove the efficacy of the method.

Development of a Substation-Area Backup Protective Relay for Smart Substation

A substation-area protective relay is proposed to overcome the inherent defects of the traditional backup protection system. The relay performs local backup protective functions for the whole substation and its connected transmission lines. The setting coordination of backup protections will be simplified by this relay with a shorter fixed time-delay. The algorithm of locating the faulted component employs the current differential principle with a self-adaptive restraint characteristic. The current sampled values are obtained by process-level networks inside the smart substation and by wide-area Ethernet between adjacent substations. The relay also works with the breaker states and the tripping generic object oriented substation event (GOOSE) from primary protections. A prototype based on the proposed scheme and IEC61850 standards has been developed by digital signal processor / field programmable gate array. The performance of the prototype was evaluated through the complete digital testing system using real time digital simulator / gigabit transceiver network and a communication simulator. Tests were carried out under different typical scenarios, such as fault transition resistances, inrush currents, current transformer saturations, and abnormal communications.

Enhancing Power Transformer Differential Protection to Improve Security and Dependability

Current differential principle is a well-known principle used for protection of transformers, motors, generators, buses, and any other type of power equipment with input and output current measurements. Further the principle is used in developing percent differential protection which can be programmed to the desired sensitivity for detecting in-zone faults, and security during external faults. This protection dependability is usually achieved by modeling a differential-retraining characteristic with two regions, operating and non-operating, and tracking the real differential restraint ratio during faults. Some external faults with high DC offset and high X/R system time constant would easily saturate the installed current transformers (CTs), which in return would cause high differential/restraint ratio above the preset characteristic into the operating region. In such cases the differential protection would operate and cause unwanted transformer trip. This paper focuses on a number of enhancements applied to the differential principle of the main differential protection, and defines guidance on how to setup the protection for better sensitivity and security. The paper is supported by fault cases, showing the improved security and dependability during internal/external faults with and without CT saturation.

Current Differential Protection for Distributed Transmission Lines using Low Sampling Frequency

Current differential protection has been affected negatively by the distributed capacitive current of transmission lines. In order to solve the problem of distributed capacitance current of transmission line, the current differential protection in this paper is based on distributed parameters model of the transmission line. The current formula along with the transmission line is derived under this distributed parameter line model. The differential criterion is constructed with the current calculated from both ends to the set point. In order to improve the practicality of the criterion, the implementation of the differential protection is given under low sampling frequency. By adding a cubic spline data interpolation point at each sampling interval, the calculation of the set point distributed current under low sampling frequency is achieved. In order to improve the operating speed of current differential protection, the point is set at the midpoint of the line, and the magnitude of the current is calculated with a half data window absolute value integrals. The results show that the proposed novel current differential principle is not affected by the distributed capacitance current. It has obvious advantages compared with traditional current differential protection principle for the low sampling frequency requirement, fast action speed and the small amount of computation.

Extra high speed hybrid protection scheme for high voltage transmission line

To improve the reliability of traveling wave protection, this paper proposes a hybrid protection scheme based on the traveling wave polarity comparison principle and current differential principle. In this scheme, the traveling wave relay is primary and the current differential relay is supplementary. Two complementary relays simultaneously operate to ensure that the hybrid protection has a good performance. For the general faults, the traveling wave relay can fast discriminate internal faults from external faults using the polarity characteristics of initial current traveling wave. For some special fault conditions, the identification result for fault is determined by the current differential relay. Therefore, the sensitivity and reliability of traditional traveling wave protection may be greatly improved. Using the same hardware platform and only requiring current signal, the hybrid scheme is easily achieved. Simulation results verify that the hybrid protection has fast speed and high reliability level.

Protection of standard-delta phase shifting transformer using terminal currents and voltages

This paper presents a new standard-delta phase shifting transformer (PST) protection technique based on the normal operating voltage–current (v–i) relationships of the PST equivalent circuit. These voltage–current relations are used to define the v–i differential equations, which are further used to detect and discriminate the internal and external faults. Using the v–i differential relationships, the proposed protection relay computes small or zero (ideally) differential quantity during normal and external fault conditions. However, in the event of an internal fault, the v–i relationships become invalid and the proposed differential relay therefore computes significantly large differential quantity. A comparative performance analysis of the proposed protection technique and the former methods, that make use of the current differential principle, suggest that the proposed technique offers a more secure protection solution of the standard-delta PST. It successfully detects and discriminates the internal/external faults, while remaining stable during a magnetizing inrush current and the saturation of the series winding, and offers a high degree of tolerance against external faults with current transformer saturation. A real representation of a standard-delta PST has been modeled in PSCAD/EMTDC to simulate various normal and faulted conditions to test and validate the performance of the proposed protection technique. Implementation of the proposed protection algorithm requires currents, voltages and tracking of the tap-changer position.