Busbar Differential Protection Research Articles

A Blocking Method for Bus Protection of CT Disconnection and Opening Method of HIF Based on Current Characteristics

Current transformer (CT) disconnection in busbar can lead to erroneous operation of busbar differential protection. The existing methods for handling CT disconnection have not taken into account how to re-enable the protection in the case of high-impedance faults (HIFs). If the two types of faults cannot be distinguished in a timely manner, it can adversely affect the safe operation of the power grid. This paper provides a theoretical analysis of the differences between differential current and restraining current in the case of busbar CT disconnection faults and HIFs. Based on these characteristics, this paper proposes a criterion for CT disconnection fault blocking and a criterion for HIFs opening. Simulation results demonstrate that this method can effectively and accurately identify HIFs even in the presence of CT disconnection faults.

Sampled Value Attack Detection for Busbar Differential Protection Based on a Negative Selection Immune System

Considering a variety of sampled value (SV) attacks on busbar differential protection (BDP) which poses challenges to conventional learning algorithms, an algorithm to detect SV attacks based on the immune system of negative selection is developed in this paper. The healthy SV data of BDP are defined as self-data composed of spheres of the same size, whereas the SV attack data, i.e., the nonself data, are preserved in the nonself space covered by spherical detectors of different sizes. To avoid the confusion between busbar faults and SV attacks, a self-shape optimization algorithm is introduced, and the improved self-data are verified through a power-frequency fault-component-based differential protection criterion to avoid false negatives. Based on the difficulty of boundary coverage in traditional negative selection algorithms, a self-data-driven detector generation algorithm is proposed to enhance the detector coverage. A testbed of differential protection for a 110 kV double busbar system is then established. Typical SV attacks of BDP such as amplitude and current phase tampering, fault replays, and the disconnection of the secondary circuits of current transformers are considered, and the delays of differential relay operation caused by detection algorithms are investigated.

Review of Bus Differential Protection Using IEC 61850

The electrical power system is susceptible to several faults, which can cause the system to malfunction. Among these, the ones that occur in the busbars of substations stand out. The main bus of a substation can concentrate a large amount of power and many derivations to service electrical loads, making it an element of high importance for the reliability of the system. Although the buses have a low incidence of faults, they are considered critical elements of the electrical power system, as their operating output can cause a large number of forced outages. This situation makes the protection of this component of paramount importance. There are currently two widely used bus differential protection techniques: high-impedance and low-impedance bus differential protection. The second technique is more commonly used due to the possibility of sharing current transformers (CTs). However, the high cost and greater requirements for maintenance makes the differential protection of busbars in distribution or sub-transmission substations unfeasible. With the advent and implementation of the IEC 61850 standard, modern protection systems based on this standard offer significant advantages, such as lower expenses with installation, wiring, commissioning and maintenance; adaptable bus configuration; use of different CT ratios; considerably minimized susceptibility to CT saturation; lower risks of open secondary CT circuits and viability of implantation in distribution substations. The objective of this review is to present an overview of the works found in the literature on substation busbar differential protection, considering classical methods and those based on the IEC 61850 standard.

Bus protection in systems with inverter interfaced renewables using composite sequence currents

Power systems are experiencing noticeable changes in operation with the integration of a large number renewable sources, which are generally connected to the grid through inverters. With significant modulation in voltage and current during fault by the embedded controllers in the inverters, available grid protection schemes are vulnerable. The theoretical analysis and simulated case studies reveal the influencing factors on the malfunction of the conventional busbar differential protection while connected to an inverter based resource. This paper proposes a differential protection method for the busbar, connecting inverter based resources to the grid, based on composite sequence currents. The performance of the proposed method is immune to the variations due to control action in the inverter based resource and change in grid codes. The IEEE 9-bus system interconnecting a PV plant is used to evaluate the proposed method where the comparative assessment reveals its superiority.

Busbar Differential Protection Using an Alternative Generalized Alpha Plane

This paper describes an alternative busbar differential protection function based on the generalized alpha plane. This approach faithfully maps several currents in two equivalent currents such that it preserves the original restraint and operation signals. The original formulation was applied to multi-terminal transmission lines protection but the number of terminals can be small if compared with the number of bays connected to busbars. For this reason, this first method is initially assessed in order to verify its suitability for busbar protection purposes. After that, an alternative algorithm to map the currents in the same plane is described and tested by using a double-bus-single-breaker 220 kV busbar configuration, modeled in ATPdraw. The simulations of internal and severe external faults, as well as evolving faults, are performed for a wide variety of scenarios including fault times, fault resistances and fault types. The results bring up a greater robustness and shorter response time if compared with original alpha plane approach, thus it represents an alternative as a busbar protection function which provides high reliability and it can be easily implemented in a commercial relay due to its mathematical simplicity.

Formation of Instantaneous Differential and Restraining Cur-rents for Differential Protection of Busbar Assemblies

The methods of forming differential and restraining currents for busbar differential protection are reviewed; their advantages and disadvantages are considered. It is noted that differential protection according to instantaneous values has a shorter proper response time than for current ones, since it does not use digital filters. The response characteristic and principles of setting selection are studied. The effect of sampling on the operation of differential protection according to instantaneous values is analyzed. It was found that without the use of special measures, depending on the sampling step and the frequency of the signal, the response current would fluctuate within the mathematical error caused by sampling. A solution to this problem has been proposed. The method consists in applying piecewise quadratic interpolation and determining the values of inflection points of instantaneous differential and restraining current signals. The efficiency of the proposed method has been evaluated. It was found that its use reduces the error in determining the response current. For a sinusoidal signal, the maximum possible error was 0.02 %. The trajectories of operating point s of differential protection in case of external fault with saturation of current transformers have been analyzed. In this mode, protection for instantaneous values is more susceptible to false positives than for active ones. The method of exponential smoothing of the restraining current was considered and investigated. An exponential smoothing algorithm has been proposed and analyzed. It is concluded that exponential smoothing increases the stability of the differential protection according to instantaneous values to external faults. Exponential smoothing does not exclude the possibility of false positive of differential protection in case of external fault.

IEC 61850-Based Centralized Busbar Differential Protection with Data Desynchronization Compensation

This paper proposes an IEC 61850-based centralized busbar differential protection scheme, in which data desynchronization between intelligent electronic devices (IEDs) leads to differential current errors. As the differential current errors could result in erroneous operation of the centralized busbar differential protection, data desynchronization should be compensated for. The main causes of data desynchronization are subdivided into measurement timing and time synchronization errors. In this paper, the first-order Lagrange interpolation polynomial is used to compensate for measurement timing errors and the voltage angle differences between IEDs are used to compensate for time synchronization errors. The centralized busbar differential protection is tested using a real-time digital simulator and IEC 61850-based IEDs, which are implemented with the MMS-EASE Lite library and Smart Grid Infrastructure Evaluation Module. The test results show that the data desynchronization compensation can significantly reduce differential current errors, and thus prevent erroneous operation of the IEC 61850-based centralized busbar differential protection.

Initial travelling wavefront‐based bus zone protection scheme

A high-speed busbar protection scheme based on initial travelling wavefronts is presented in this study. The aerial mode current travelling waves (TWs) across all lines connected to the busbar are calculated using Karenbauer transformation. Thereafter, the polarity and magnitude of wavelet transform modulus maximas of line current appearing after fault inception are analysed for fault zone and faulty phase identification. Its performance has been evaluated by modelling an existing 750 kV Indian substation in PSCAD/EMTDC software package. The simulation results reveal that the proposed scheme provides better stability for external faults and higher reliability in case of internal faults in comparison with conventional low-impedance busbar differential protection scheme (87B). Moreover, it remains immune to the current transformer saturation problems. In the end, comparative evaluation of the proposed scheme with the existing busbar protection schemes proves its superiority in terms of stability against external faults, sensitivity for internal faults, computational obligations, and communication requirements.

Instantaneous-Power-Based Busbar Numerical Differential Protection

This paper presents a new method for busbar differential protection based on the instantaneous power concept. In order to do so, the instantaneous power per phase of each network element connected to the busbar is computed by using the instantaneous current values and a voltage memory action strategy. The performance of the proposed technique is compared to one of the traditional instantaneous-current-based differential protection algorithms, which is widely used by manufacturers of commercial relays. Both internal and external faults, as well as evolving external-to-internal faults, were simulated in a power substation with double-bus single-breaker configuration using the software ATPDraw. The obtained results reveal that the proposed algorithm is twice or more faster than the traditional instantaneous-current-based algorithm for most of the internal and evolving external-to-internal faults, while ensuring secure operation for external ones even when severe current transformer (CT) saturation takes place, through a new harmonic power restraint strategy. Also, since the proposed method provides faster fault detection time, the requirements for CT time to saturate may be alleviated, guaranteeing correct operation even in the case of early CT saturation.

A Wavelet-Based Busbar Differential Protection

This paper presents a new wavelet-based busbar differential protection algorithm, named as 87BW function. The instantaneous current-based differential protection fundamentals are taken into account and the well-known 1-out-of-1 and 2-out-of-2 tripping logics are mapped into the wavelet domain. Operating and restraint wavelet coefficients energy of currents are computed, regarding station configuration and bus zones boundaries. Thereby, the proposed 87BW function can be properly used in both static and dynamic busbar configuration. Its performance was evaluated through EMTP-based simulations of faults in a 230 kV power substation with double bus single breaker configuration. The obtained results reveal it provides ultra-high-fast trip for internal and evolving external-to-internal faults, guaranteeing security for normal through-load and external faults as well, even in the case of early and severe current transformer saturation.

Intelligent busbar protection scheme based on combination of support vector machine and S‐transform

Differential protection is the main protective scheme of busbar in power systems but its operation degrades during current transformer (CT) saturation conditions. In this study, the busbar differential protection scheme is improved by the addition of a new feature extracted from differential current using S-transform analysis. S-transform as a powerful signal processing technique gives a complete visualisation of the signal in both time and frequency domains. The new extracted feature as well as the magnitude of the differential and restraint currents are utilised to increase the security of traditional busbar differential protection scheme. With the addition of this new feature, distinctive regions are created in the feature space which can be separated by an appropriate classifier. In this study, the well-known classifier, i.e. support vector machine is employed to effectively discriminate internal faults from external faults. To evaluate the performance of the proposed method, a part of Iranian 400-kV power system grid is simulated in the PSCAD/EMTDC environment. The transient behaviour of CTs during saturation conditions is simulated based on the precise Jiles–Atherton model. The obtained results justify the superiority of the proposed method in terms of speed and security even in noisy conditions.

Bus Differential Protection in Industrial Systems With Generators Connected Directly to the Main Distribution Bus

In industrial facilities with on-site generation, there are two major approaches to connect generators to the main distribution busbar. One is to connect generators through step-up delta-wye transformers with low-resistance grounded wye on the busbar side. The second common method is to connect generators directly to the main distribution busbar and use low-resistance grounding or hybrid grounding in the generator neutral. A grounding resistor in the step-up transformer’s wye side neutral or in the generator neutral will limit the ground fault in the main distribution system. When busbar differential protection is used on the main busbar, sensitivity for bus ground faults has to be evaluated to ensure detection of limited low-level ground faults. While step-up transformer grounding resistors can be selected to allow ground faults of higher magnitudes detectable by bus differential protection, the choice of grounding resistor is more complex when generators are connected directly to the main busbar. In such systems, a grounding resistor in the generator neutral limits the generator fault to protect the alternator core from excessive damage. At the same time, busbar differential protection needs to detect a limited low-magnitude ground fault on the bus. This paper discusses considerations to select the main distribution busbar differential protection type, CTs, and relaying scheme to enable detection of busbar ground faults limited by the generator low-resistance grounding resistor.

Implementation of noise-immune Rogowski coils for busbar differential protection modernization

Although a wide variety of different types of electrically protective devices is used nowadays, industrial facilities witness constant growth in the number of failures of power station and substation switchgear components due to various reasons. Many specialists working in the power-engineering sphere express opinions that the facilities should be equipped with protection that operates in case of busbar faults. The given article investigates peculiarities in the design of the busbar differential current protection instrument that employs Rogowski coils as primary current transducers. A design of a noise-immune sectionalized Rogowski coil with double-layer winding is suggested, which makes it possible to significantly improve operational performance of busbar differential protection. Main attention is paid to methods of mathematical modeling of transient processes in busbar differential protection, based on designs of such coils developed in the Far Eastern Federal University. The article dwells upon theoretical research and technical features to be taken into account while developing modeling schemes of longitudinal differential protection of a three-phase busbar system based on Rogowski coils. Results of protection modeling in Micro-Cap software are described. Based on the analysis of data acquired during modeling; a valid conclusion is made about advantages of using Rogowski coils in busbar differential protection, which provides improvement of sensitivity and speed of response of such protective devices.

Analysis and discussion of a dead-zone protection mal-operation case in Brazil

A mal-operation case of busbar protection caused by a dead-zone protection abnormality in the Brazilian Midwest Grid on September 19th, 2012, is briefly described. The operation process of pilot distance, automatic re-closure, busbar differential and dead-zone protection, and the emphasis on the logic scheme of dead-zone protection are analyzed. The time delay between the breaker’s main pole and auxiliary contact during re-closure was the main cause in this case, and a defect in the logic allowed it to occur. The differences in dead-zone protection logic between Brazil and China are discussed. A test platform was constructed in the laboratory, and a site simulated experiment was also performed. Possible causes are suggested and test activities are carried out to verify them. Results show the values of practical engineering approaches to the solution. Experience also contributed to avoiding future mal-operations and strengthening the reliability of the protection system, and thus of the power supply in Brazil.

Busbar Differential Relaying Method Based on Combined Amplitude and Phase Information of High Frequency Transient Currents

Busbar differential relaying method based on combined amplitude and phase information of high frequency transient currents is put forward in this paper for the speed and reliability problems of busbar protection based on fundamental frequency. Under the analysis of features of bus high frequency differential currents, complex wavelet analysis is used to extract the amplitude and phase features of 1/4 period high frequency differential currents, and amplitude and phase information are used to form the polar coordinates. Bus fault is identified intuitively and precisely according to polar locus differences. This polar coordinates represented busbar differential protection scheme based on high frequency transient signals can not only avoid TA saturation, realizing quick protection, lots of PSCAD/EMTDC simulations also show that this busbar differential protection scheme works well under different fault conditions.

Busbar differential protection in conjunction with a current transformer compensating algorithm

The design, evaluation and implementation of a busbar differential protection relay that operates in conjunction with a current transformer (CT) compensating algorithm are described. Prior to saturation, the secondary current of a CT is not compensated. The compensating algorithm detects the start of first saturation on the basis of the third-difference function of the current and estimates the core flux at the first saturation start by inserting the negative value of the third-difference function of the current into the magnetisation curve of a CT. Thereafter, it calculates the core flux and then the corresponding magnetising current in conjunction with the magnetisation curve. The calculated magnetising current is added to the measured secondary current to obtain the correct secondary current. The algorithm can estimate the correct current irrespective of the level of the remanent flux. In the proposed busbar protection scheme, a current differential relay with the single-slope operating characteristic is used on the basis of the compensated current of the saturated CT. Test results indicate that the relay shows satisfactory performance for the various external and internal faults with CT saturation, particularly in the case of a progressive fault from a feeder fault to a busbar fault. The algorithm is implemented in a prototype relay based on a digital signal processor. The relay achieves greater stability on external faults, enhanced sensitivity on internal faults and fast operation on internal faults with CT saturation.

A Busbar Differential Protection Relay Suitable for Use With Measurement Type Current Transformers

The design, evaluation and implementation of a busbar current differential protection relay suitable for use with measurement type current transformers (CTs) is described in the paper. The relay operates in conjunction with a saturation detection algorithm, which effectively detects the start and end of each saturation period using a technique based on the third-difference function applied to the current signal. A blocking signal is activated immediately after the onset of saturation and is maintained active until the saturation period plus an additional delay of one cycle has expired. For internal faults that result in CT saturation, the relay issues a trip command before the blocking signal is activated. For external faults, that result in CT saturation, the blocking signal arrives first and the trip command remains inactive. Test results indicate that the relay successfully discriminates between internal and external faults, even when the remanent flux in a CT is high and the fault capabilities of the measurement CTs are severely limited. The paper concludes by describing how the relay was implemented on a prototype relay based on a digital signal processor. Compared to a conventional busbar differential protection scheme, the new relay achieves greater stability on external faults and enhanced sensitivity for internal faults.

Design, evaluation and implementation of a busbar differential protection relay immune to the effects of current transformer saturation

The design, evaluation and implementation of a busbar current differential protection relay that operates in conjunction with a current transformer (CT) saturation detection algorithm is described. The detection algorithm detects the start and end of each saturation period based on the third-difference function of the current. A blocking signal is activated during saturation and for one cycle after it ends. For internal faults that cause CT saturation, the relay operates before activation of the blocking signal and consequently, a trip signal is issued. For external faults that cause saturation, the blocking signal arrives first and the trip signal remains inactive. The technique does not delay the operating time of the delay. Test results indicate that the relay can discriminate between internal and external faults even when a CT is severely saturated due to the effect of remanent flux. The relay is implemented in a protection scheme based on a digital signal processor. The new relay achieves a high level of stability on external faults and a major improvement in sensitivity for internal faults.

An impedance-based CT saturation detection algorithm for busbar differential protection

An impedance-based CT saturation detection algorithm for busbar differential protection

Isotope effect on intramolecular vibration of C 80

Although a wide variety of different types of electrically protective devices is used nowadays, industrial facilities witness constant growth in the number of failures of power station and substation switchgear components due to various reasons. Many specialists working in the power-engineering sphere express opinions that the facilities should be equipped with protection that operates in case of busbar faults. The given article investigates peculiarities in the design of the busbar differential current protection instrument that employs Rogowski coils as primary current transducers. A design of a noise-immune sectionalized Rogowski coil with double-layer winding is suggested, which makes it possible to significantly improve operational performance of busbar differential protection. Main attention is paid to methods of mathematical modeling of transient processes in busbar differential protection, based on designs of such coils developed in the Far Eastern Federal University. The article dwells upon theoretical research and technical features to be taken into account while developing modeling schemes of longitudinal differential protection of a three-phase busbar system based on Rogowski coils. Results of protection modeling in Micro-Cap software are described. Based on the analysis of data acquired during modeling; a valid conclusion is made about advantages of using Rogowski coils in busbar differential protection, which provides improvement of sensitivity and speed of response of such protective devices.