Nuisance Tripping Research Articles

Data Center Air-cooled Chiller Broadband and Tonal Noise Control

Data centers require vast amounts of cooling using large farms of air-cooled chillers as the primary equipment of choice. The amount and nature of noise generated by these chiller farms to the surrounding area can create complaints and the noise control solutions require an understanding and knowledge of both broadband and tonal noise. The dominant noise sources on air-cooled chillers are compressors and condenser fans, each of which produce both broadband and tonal noise spectrums. Therefore, noise control solutions should address both the broadband and tonal aspects of the source. A common noise control solution for chillers serving data centers is a sound barrier wall and while effective at providing overall broadband noise control, does little in targeting tonal issues. However, a sound barrier wall can be supplemented to address these tonal issues by applying source treatments to the chiller, such as a sound cover treatment for the compressors and associated refrigerant piping and sound stacks and intakes for the condenser fans. In addition, barrier walls an create a "pit" application impeding chiller condenser fan discharge air resulting in recirulation and nuisance trips. Using a sound stack source treatment with a barrier wall can help mitigate this issue while providing attenuation.

Transient Stability of Synchronous Generator Connected to Micro Combined Heat and Power

Micro Combined Heat and Power (Micro CHP) refers to small-scale installations that generate heat, electricity or both connected to the low voltage distribution network at the customer side. Although the connection of the Micro CHP to the low-voltage distribution networks improves security of supply, there are many operational challenges such as stability and control. This paper study the stability of synchronous generator connected to reciprocating engine as one type of Micro CHP. Also, a several studies have been done to investigate the response of Small scale embedded generation (SSEG) to a range of network faults and thereby ascertain the range of conditions under which SSEG might be expected to trip. Many of these may be regarded as nuisance trips when the action of network protection does not isolate the SSEG from a mains supply. Any protection associated with the SSEG has not been included in order to demonstrate inherent capability and response. The critical clearing time (CCT) is used to indicate the stability of the SSEG. In this investigation the CCT of the SSEG is calculated and simulated using Power Systems Computer Aided Design PSCAD/EMTDC as well as from the mathematical calculations.

OPTIMAL LOCATION AND SIZING OF DG IN DISTRIBUTION NETWORK: IMPACT ON OVERCURRENT DISTRIBUTION PROTECTION SCHEME

The integration of distributed generation (DG) into the existing distribution networks minimizes active power losses and improves the voltage profile. The recent improvement in the development of DG technology has caused increase in the penetration of DG from different sources. The optimal location and sizing of DG is very challenging and introduces different protection issues. This is caused by penetration of current flow from different source which is contrary to the principles of operation of the conventional overcurrent scheme. This paper presents optimal method of DG placement and sizing using firefly algorithm and its impact of DG penetration on overcurrent protection scheme. Low voltage distribution network is modelled and simulated in PSCAD/EMTDC and DigSilent power factory software using IEEE 33 and Ayepe 34 standard bus. False tripping of feeders, Nuisance tripping, blinding of the protection scheme and unintentional islanding caused as result of Photovoltaic penetration into the distribution network were simulated. Coordination of overcurrent relays with and without DG penetration were analyzed and possible mitigation algorithm were proposed. The simulation result obtained showed that the proposed methods significantly improve the protection scheme coordination..

A flexible islanding identification technique for PV based grid-tied systems

The phenomenon of islanding, which occurs in grid integrated distributed generators (DGs), poses significant challenges and potential risks for customers, utility providers, and operational personnel. Detecting islanding quickly and accurately is crucial. The issues related to the conventional islanding methods paved the way in developing a hybrid islanding identification scheme. The developed method achieves accurate results within a reduced time span of 30 ms. The hybrid technique combines the passive method of sliding window based moving average (SWMA) for faster detection and the active method of asymmetrical bilateral reactive power perturbation (ABRPP) for improved precision. The developed hybrid method is simulated and tested using MATLAB/Simulink 2023a. It undergoes testing under various load conditions, including small and large power mismatches between DG generation and local load demand, as well as different load quality factors (QF). Additionally, the hybrid algorithm demonstrates no nuisance tripping when subjected to different load switching conditions such as capacitor switching, motor load switching, and nonlinear load switching. A comparison with existing islanding detection methods confirms the accuracy and speed of the proposed method in identifying islanding conditions.

Nonisolated Three-Phase Current DC-Link Buck–Boost EV Charger With Virtual Output Midpoint Grounding and Ground Current Control

Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

Simulation model of a protection scheme for active distribution networks

The growing trend of installed power from Distributed Generators (DG) in distribution networks is giving rise to new issues in grid operations. In particular, the interaction between DG and grid protections can cause nuisance trips, unwanted island operations and, in general, worsening of power quality. The paper discusses a possible protection scheme suited for active networks and implementing logic selectivity. The proposed approach is based on directional protections coordinated through communications. Simulation models of an urban Medium Voltage (MV) distribution grid, of distributed generators and of the employed types of protections have been developed in the DIgSILENT Power Factory environment. Digital simulations confirms the effectiveness of the proposed approach.

Voltage Disturbances and Inrush Current of DC Power Supplies

The potential damaging effects of high inrush currents occurring after power quality disturbances on switch-mode dc power supplies (SMPS’) have been reported, but have not been studied in detail. This paper presents a new analytical model for the accurate representation and calculation of inrush currents of low-power SMPS devices. This model is verified against previously developed circuit-based simulation model and compared with the only other analytical model available in existing literature. The developed analytical model is also used to investigate device protection co-ordination, in order to demonstrate two important effects of high-inrush current: nuisance tripping of protection and damage of internal SMPS components. Key words. Inrush current, load modelling, analytical representation, switch-mode dc power supply (SMPS), power quality disturbance, short interruption, voltage sag

Empowered Virtual Synchronous Generator Based Control Scheme for Improved Transient Response and Reduced Nuisance Tripping in Stable Microgrids

Empowered Virtual Synchronous Generator Based Control Scheme for Improved Transient Response and Reduced Nuisance Tripping in Stable Microgrids

Lightning and Grounding Issues Impacting Safety and Performance of Liquified Natural Gas-Supplied Power Generation Plants: Lessons Learned to Correct Commonplace Misunderstandings of Requirements

This article covers the lessons learned from performing multiple liquified natural gas (LNG) power plant audits following nuisance tripping, personnel safety issues, and potential equipment failure. This article focuses on a specific facility but includes aspects of three other sites, as well. These investigations started out as forensic investigations but quickly moved into lightning and power system grounding audits based on evidence encountered. These audits covered improvement opportunities in lightning protection, transferred earth potentials, personnel step and touch potentials, safety, electronic grounding of generation controls, and related LNG gas supply. It was clear that there were several commonplace misunderstandings of the correct site lightning and grounding installation requirements to ensure a safe and reliable electrical system. Based on the professional experience of the authors, the documented improvement opportunities identified are not unique to this site and are very similar in nature at other locations.

Multicharacteristics Arc Model and Autocorrelation-Algorithm Based Arc Fault Detector for DC Microgrid

DC microgrids contribute to the increasing penetration of renewable energies. However, a DC arc fault will lead to malfunctions and even fire hazards in a DC microgrid. To ensure the safe and efficient operation of a DC microgrid, the characteristics of DC arc faults should be determined, and a reliable arc-fault detection technique is required. Nevertheless, it is difficult to investigate the DC arc faults in a practical system. Thus, an accurate and reliable arc model for simulation research of arc faults is significant. Since a DC microgrid has numerous branches, the existing arc models cannot express the complex and random characteristics of potential arc faults. Besides, the detection points need to be determined for the appropriate installation of arc fault detectors. Furthermore, the arc features may be ambiguous and affected by the environmental noise and power electronics noise leading to nuisance tripping to arc detectors. In this paper, a multi-characteristics arc model is established based on the volt-ampere, current sag, and power spectral characteristics of arc faults. According to the frequency domain features of arc faults and interaction effects between different branches, the arc-detection-point selection principle is formed. A non-invasive arc fault detector based on magnetic-field sensing and autocorrelation algorithm is developed. It can avoid the effects of periodic environmental noise and power electronics noise by comparing the correlation between arc features in periods. The experimental results verify that the arc faults can be detected with high accuracy by installing the autocorrelation-algorithm-based arc detector at detection points selected by the arc-detection-point selection principle in a DC microgrid.

Detection and classification of DC and feeder faults in DC microgrid using new morphological operators with multi class AdaBoost algorithm

DC microgrids with energy storage systems based on photovoltaic (PV) and wind energy are gaining popularity as a means to offer users with reliable supply in either a stand-alone or grid connected mode. However, because DC and AC side faults have similar current–voltage profiles, developing a viable safety strategy for the proposed integrated DC microgrid is difficult. Traditional protection techniques based on pre-defined thresholds are unable to discriminate between DC and AC side faults, and so fail to offer independent control actions in both circumstances. In this context, new morphological operators with improved AdaBoost algorithm is proposed for detecting and classifying the AC and DC side faults in the proposed DC microgrid. To explore this, current signals are captured at the DC bus of the proposed integrated DC microgrid. The captured signals comprise background noise which is eliminated by dilation erosion difference operator (DEDO) and opening closing difference (OCDO) operators. The two operators work together to meet the accurate fault detection to avoid nuisance tripping by multiscale operation of structuring element (SE). For effective outcomes the multiple scales are optimized by sparse kurtosis (SK) index. The optimized scales are passes through target features to retrieve the data. The acquired data is sent into the multi-class AdaBoost approach, which recognizes faults by modifying the distribution of data and iteratively adjusting the weight of each instance. The proposed system's efficacy is tested using the MATLAB/Simulink platform under various operating situations such as load variation, irradiation and fault resistance changes. The proposed algorithm's superiority is demonstrated by comparing it to existing approaches using confusion matrix (CM) parameters.

Improving resilience of islanding protection - implementation of a Q-f droop for inverter-based generation

As the prevalence of distributed generation (DG) continues to increase in the GB network, anti-islanding protection has been the subject of industry focus, with work done to alter the existing Rate of Change of Frequency (ROCOF) settings. However, there are still concerns regarding the resilience and security of this method based upon non-detection zones (NDZ), and the potential of system-wide events and network faults leading to nuisance tripping. This paper provides a review of the theory and literature, exploring the issues with power system islanding and the current anti-islanding protection methods. A novel protection method, based on a reactive power - frequency (Q-f) droop, is developed and implemented into a Simulink inverter-connected DG model, to test under various distribution network scenarios including islanding and system-wide frequency excursions. This new method was compared to the existing ROCOF method and showed improved performance in all network scenarios studies. The Q-f droop method had no NDZ and was developed to be customisable for a range of network regulation requirements. Finally, aspects of the method such as multi-DG operation, financial and practical implications have been explored.

Assessment of Low-Voltage Motor Ride Through: A Comparison of Solutions for Critical Processes in the Oil and Gas Industry

Voltage sags initiated by utility transmission system faults cause nuisance trips of low-voltage (LV) motors, due to contactors dropping off as a result of the undervoltage condition. Since voltage disturbances by utility systems cannot be prevented, it is essential to mitigate the impact of LV motors trips on critical process systems in the oil and gas industry, such as lubrication and shaft-sealing systems. To address this challenge, there is a tendency in the industry to modify standard LV motor control schemes to hold contactors closed during voltage sags to maintain process continuity. This approach will be evaluated against restarting schemes and sag correction devices in terms of their impact on motor performance and motor controller design. A simulation model was developed using Power Systems CAD to assess motor performance and subsequent current and torque profiles associated with various ride-through solutions. The reliability and safety aspects of modifications associated with different ride-through solutions were evaluated and benchmarked against relevant international standards and industrial practices.

A DC Arc Fault Detection Method Based on AR Model for Photovoltaic Systems

DC arc faults are dangerous to photovoltaic (PV) systems and can cause serious electric fire hazards and property damage. Because the PV inverter works in a high−frequency pulse width modulation (PWM) control mode, the arc fault detection is prone to nuisance tripping due to PV inverter noises. An arc fault detection method based on the autoregressive (AR) model is proposed. A test platform collects the database of this research according to the UL1699B standard, in which three different types of PV inverters are taken into consideration to make it more generalized. The arc current can be considered a nonstationary random signal while the noise of the PV inverter is not. According to the difference in randomness features between an arc and the noise, a detection method based on the AR model is proposed. The Burg algorithm is used to determine model coefficients, while the Akaike Information Criterion (AIC) is applied to explore the best order of the proposed model. The correlation coefficient difference of the model coefficients plays a role as a criterion to identify if there is an arc fault. Moreover, a prototype circuit based on the TMS320F28033 MCU is built for algorithm verification. Test results show that the proposed algorithm can identify an arc fault without a false positive under different PV inverter conditions. The fault clearing time is between 60 ms to 80 ms, which can meet the requirement of 200 ms specified by the standard.

Analysis of Passive Islanding Detection Techniques for Double Line Fault in Three Phase Microgrid System

Microgrids are able to dispatch power to distribution systems with the advancement of power electronics-based inverters. As per IEEE-1547-2018 standards, Microgrid has to maintain voltage of 0.88 < V < 1.1 p.u (per unit) and frequency of 58.8< f_0 < 61.2 Hz and detect un-intentional faults in less than 2 seconds to bring Microgrid into islanding mode seamlessly. Unless these faults are detected and Microgrid is islanded, the system stability cannot be maintained and Microgrid cannot feed the connected loads. To detect these unsymmetrical faults, to bring the Microgrid to islanding mode and to be stable during non-islanding cases like loads switch on and throw off at Point of Common Coupling (PCC), a passive islanding detection method, Rate Of Change Of Voltage Phase Angle (ROCOVPA) is proposed. The methodology is simple. First, the voltage phase angle of generator bus and the grid is monitored. Then, absolute value is found and finally differentiated to get ROCOVPA and detect islanding. Also, this technique is compared with the widely used method of Rate Of Change Of Frequency (ROCOF) at different percentage active and reactive power mismatches. It also avoids nuisance tripping so that Microgrid's stability is maintained. This method is tested for un-symmetrical double line fault, for islanding cases and switch on or throw off, for non-islanding cases with linear and non-linear loads. In this method, the power quality is also not affected because of no perturbations during testing and the Non-Detection Zone (NDZ) is almost zero. The proposed method is verified by simulating islanding and non-islanding conditions in MATLAB/Simulink and by comparing with ROCOF method and found effective.

Measurements and modeling of the frequency behavior of residual current devices- from 4 Hz to 40 kHz

Residual current devices (RCDs) are a common means of protection against shock due to indirect contact in low voltage (LV) systems. Due to the increasing penetration of power electronics equipment in LV systems, higher amounts of waveform distortion at a broad range of frequencies, from dc, subharmonics up to hundreds of kHz (supraharmonics), are expected to be present both during normal operation and during faults. The standardization committees and manufacturers have responded to this challenge by proposing different types of RCDs that are expected to function under given conditions of fault current waveform. However, subharmonic and supraharmonic frequency components are not considered in the standards for most of the RCD types. This article studies the effect of these frequency components on RCDs type AC, A, B and F. An assessment is made in terms of two types of RCD failure: blinding and nuisance tripping, for which both magnitude of the current and breaking time is considered. A frequency mapping of the RCDs is performed, and an assessment of these results based on the frequency-dependent response of the human body to currents is performed. Finally, a frequency model for RCDs type A, F and B is developed.

Improvement of the impedance-based loss-of-field protection scheme based on the dynamic behavior of the synchronous generators

This paper deals with an innovative Loss of Field Protection Scheme (LoFPS), in which, some key supplementary features are provided to avoid spurious trip of the Conventional Impedance-Based Relay (CIBR) during Stable Power Swing (SPS). The proposed algorithm is developed for two conditions of the multiple-parallel-synchronous generator (SG) and single-SG in service. Entrance time (ti) of Z-trajectory to the CIBR zones is utilized for single-SG in service owing to the different dynamic responses of the SG to the LoF/SPS events. Meanwhile, for the multiple-parallel-SGs condition, the average value of the variation of the output reactive current of SG (ΔIRSG¯) is selected to analyze the dynamic behavior of the faulty- and healthy-parallel-SGs. The ΔIRSG¯ for all the parallel-SGs during both normal and SPS conditions has a similar polarity, whereas during LoF incidence in one SG, its polarity is different for the faulty and healthy-parallel SGs. Therefore, the nuisance trip of the CIBR can be easily avoided by implementing the selected features. Widespread simulation studies in MATLAB/Simulink environment on the IEEE 9-bus test system affirm the superiority, higher reliability, and easy implementation of the developed LoFPS than other schemes, especially the CIBR ones.

An Investigative Analysis of the Protection Performance of Unbalanced Distribution Networks With Higher Concentration of Distributed Energy Resources

Despite the substantial reliability and power quality improvements, the proliferation of distributed energy resources can introduce many protection complexities in distribution networks (DNs). This research article presents a comprehensive investigative analysis of the distributed generation (DG) impacts on the protection performance of the DN. Various protection coordination case studies have been analyzed under different operating conditions by varying the DG penetration level or the fault conditions to highlight the potential risks of the protection networks. The severity of the risks is evaluated by considering the DG locations, protection settings, and fault types/impedance parameters on a standardized IEEE 13 node test feeder in DIgSILENT Power Factory/MATLAB softwares. The subsequent protection hazards are examined for the mutual coordination of the overcurrent relays, auto-reclosers, and series fuses in DNs along with the differential protection issues for dc bus system. Furthermore, the impacts of DGs/PDs types are assessed on the nuisance tripping of the protection networks and results are reported.

Battery Storage-Based Novel Hybrid Islanding Detection Technique Using Lissajous Pattern Estimation

The reliability, uncertainty, and sensitivity of local islanding detection method for distributed generation (DG) system under diversified real-time scenarios and nonlinear loading conditions are not greatly explored. In this article, a new type hybrid islanding detection technique (IDT) is suggested, which reduces uncertainty and simultaneously improves reliability and sensitivity under different situations. In the technique, one detection parameter is defined, which is calculated from estimation of major and minor axes of Lissajous pattern (LP). Here, the evaluation of the parameter is done in two stages to avoid erroneous detection. In the first stage, the initiation of voltage transient is detected by LP. In the second stage, the active control via battery energy storage system (BESS) distinguishes nuisance tripping case from the islanding state. The extra active power injection/absorption via BESS also helps to identify islanding state at very near to zero power condition, i.e., sensitivity is enhanced. The detection time is found within 160 ms for different test cases, which is well below that of the acceptable upper value (2 s) specified in standard. The uncertainties in detection and threshold setting due to variations of harmonics and other operating conditions are removed in the proposed case, which is a distinct advantage. The Typhoon-HIL tool is used to carry out various case studies in real-time. Here, superior performances of proposed approach are observed in comparison with other state of the arts reported in the literature.

A reliable and straightforward index to avoid nuisance trip of the conventional Z‐based loss‐of‐field relay in synchronous generators

The conventional impedance (Z)-based relay which is the well-known relay to preserve the power plant's synchronous generator (PPSG) against loss of field (LOF) accident may fail during some stable power swing (SPS); on the other hand, most of the previously introduced schemes may fail during the happening of hybrid events. In this paper to overcome the raised problems, a straightforward index is developed for reliable detection of the hybrid events, and it is combined with an AND-logic cluster with the Z-relay to avoid its spurious trip during SPS events. The reactive power (QSG) of the faulty PPSG is continuously decreased during LOF, while it oscillates under both SPS and hybrid events, leading to non-detection of the hybrid event. Hence, using the integral operator and arithmetic mean value are suggested to eliminate the swinging variations of QSG as a Z-relay blocking function (ZRBF). Thus, QSG decreases during both LOF and hybrid events and does not decrease under SPS events. Therefore, by combination of ZRBF with the Z-relay, the PPSG is properly tripped out during the both LOF and hybrid events, and wrong tripping under SPS is reliably hindered. The reliable performance of developed scheme is completely approved thorough performed simulation studies.