Loss Of Mains Protection Research Articles

Interaction of fault ride through requirements and loss of mains protection

The strongly growing DG capacity is raising concerns related to unintentional islanding. Unintentional islanding is prohibited due to the associated safety risks, and it is therefore mandatory to equip all DG units with some kind of loss of mains (LOM) protection. However, large amounts of unnecessary tripping of DG units cannot be tolerated anymore as the share of DG has already reached a significant share of the total installed power generation in certain regions. Certain grid codes thus require DG units to be able to ride through remote faults and support the power system. It is generally known that grid codes and LOM protection objectives are of somewhat controversial. However, it appears that no papers have studied the relation of LOM protection performance and fault ride through requirements thoroughly with simulations. This paper aims to fill this gap by providing extensive simulations which show how exactly the grid code requirements affect the performance of LOM protection. The studies are performed in a unique simulation environment consisting of two different types of real time simulators and a real LOM relay.

A Novel Hardware-in-the-Loop Approach to Investigate the Impact of Low System Inertia on RoCoF Relay Settings

This paper presents a novel hardware-in-the-loop (HIL) approach as used to investigate the impact of the reduction in inertia on the Great Britain (GB) electrical power system with regard to rate of change of frequency (RoCoF) settings for Loss-of-Mains (LoM) protection. Furthermore, the research as presented in this paper updates, enhances, and validates a reduced model of the Great Britain transmission system, as originally developed in DIgSILENT PowerFactory by the National Grid Electricity System Operator. The enhanced model has been developed for integrated use with the OPAL-RT real-time HIL simulation toolkit and is validated against phasor measurement unit (PMU) data from actual disturbance events using novel automated interfacing between both integrated simulation platforms, PowerFactory from DIgSILENT and ePHASORSIM from OPAL-RT. The corresponding simulations show that the updated reduced model is capable of capturing the dynamic behaviour of the GB transmission system, including both local and inter-area oscillations, with satisfactory accuracy. Finally, the paper presents HIL study results with the reduced model to investigate the influence of decreasing system inertia on the response of LoM protection relays. The studies show that decreasing system inertia may have a significant impact on LoM relays using RoCoF detection, particularly relays using the legacy G59 setting of 0.125 Hz/s. Initial studies have also demonstrated the potential for a previously unrecognised interaction between system oscillations and the 500 ms operating delay, as specified in G59 and G99 Engineering Recommendations. Consequently, faster local oscillations (>1 Hz) reset the relay and decrease the sensitivity, whereas slower inter-area oscillations (<1 Hz) appear to cause the relay to overestimate the average RoCoF.

Impact of inverter-based generation on islanding detection schemes in distribution networks

One of the most frequently used interface protections for Distributed Generators (DGs) is the Loss of Mains (LoM) protection. It detects the formation of an island at the connection point and disconnects the DG to protect the unit, the system and the personnel. The increased penetration of inverter-interfaced DG, in combination with the decommissioning of synchronous generators, reduces the system inertia and leads to faster changing and larger voltage and frequency deviations. Therefore, modern grid-codes require inverter-based DGs to provide support to the grid by modifying their active and reactive power injection based on local measurements. However, this leads to complex inverter-grid interactions and modifies the islanded system behavior, thus disturbing the operation of LoM protections that rely mainly on local voltage and frequency measurements. In this paper, we propose an improved analytical formulation for estimating the Non-Detection Zone (NDZ) of LoM protection devices in the presence of grid-feeding inverters, as well as novel NDZ approximations for grid-supporting and grid-forming inverter-based services. We verify the analytical results with detailed dynamic simulations and comment on the impact that the new inverter requirements have on the performance of LoM protections.

Preventing cascading tripping of distributed generators during non-islanding conditions using thermostatic loads

Integration of large amounts of asynchronous renewable energy sources (RES) would reduce the effective inertia of the future Great Britain (GB) network. As a result, after a large infeed loss, containing the grid frequency and limiting its rate of change (RoCoF) above certain thresholds would be a challenge for the system operator. In particular, large RoCoFs could activate RoCoF-sensitive loss-of-mains (LoM) protections of distributed generators (DGs) and trigger cascading disconnections. In this context, thermostatic loads (TCLs) can be controlled to collectively provide support and contribute to the overall system inertial and frequency response. This paper focuses on the transient response period after a frequency disturbance and the fast protection events occurring in this time frame. In particular, this works evaluates the interplay between the local activation settings of LoM protection of DGs and those used to enable the TCL support. This interaction is analysed through a case study on a 36-bus dynamic equivalent of the GB network which shows how local post-fault frequency dynamics drive the overall system response. Results show that TCLs are able to prevent RoCoF-driven DG tripping and reduce the need to adopt high LoM settings, decreasing the risks of maloperation associated with desensitised protections.

Practical risk assessment of the relaxation of LOM protection settings in NIE Networks' distribution system

This study presents the methodology, experience and practical outcomes of the risk assessment-based revision of loss-of-mains (LOM) protection settings in the NIE Networks' distribution system. An investigative project has been undertaken by the authors to revise the current LOM practice as recommended by the G59/1/NI regulation and to propose the settings which would meet the all-Ireland transmission system stability criteria. It is also important to ensure that any increased personal risk is realistically quantified and satisfies the health and safety requirements. Both aspects (i.e. LOM protection stability and sensitivity) are covered in the study. The results and observations included in the study aim to provide the means and supporting evidence for achieving the best compromise in the revision of LOM protection settings.

Wireless Light-Weight IEC 61850 Based Loss of Mains Protection for Smart Grid

Abstract This paper presents a novel Loss of Mains (LoM) protection method based on IEC 61850 Manufacturing Messages Specification (MMS) protocol over wireless Global System for Mobile Communication (GSM) based access point name (APN) mechanism. LoM or anti islanding protection is a key requirement in modern power distribution grids where there is significant amount of distributed energy resources (DER). The future Smart Grids are based on extensive communication capabilities and thus the communication based LoM approaches will also become dominant. The IEC 61850 standard based systems are gaining ground in the substation communication, and therefore, it is natural to expand this technology deeper into the distribution network. Using this standard for LoM protection, also enables some advanced approaches utilizing large variety of information available in the Smart Grid. There is a specific part of the standard, IEC 61850-7-420, which defines logical nodes (LNs) suitable for this purpose; but, there are no available devices applying this part of the standard yet. In this research, a light-weight implementation of IEDs (Intelligent Electronic Devices) is developed using a low-cost open microcontroller platform, Beagle Bone, and an open source software. Using this platform, a wireless LoM solution based on IEC 61850 MMS protocol has been developed and demonstrated. This paper introduces object modelling according to IEC 61850-7-420 defined LNs and an implementation applying direct client server MMS based communication between lightweight IEDs. The performance of the wireless application using the developed platform is demonstrated by measuring the message latencies. In this paper, a novel LoM protection concept is proposed based on the standardized communication solution brought by IEC 61850 and specific LNs for DERs defined in IEC 61850-7-420. A light-weight implementation of an IEC 61850 based IED is developed in order to reduce large overhead information and complexity of the standard. In addition to LoM function, the developed solution has the ability to monitor DERs status. The available monitoring information can be shared among various distribution management systems (DMS), enabling distributed decision approach for various purposes.

Peak-Ratio Analysis Method for Enhancement of LOM Protection Using M-Class PMUs

A novel technique for loss of mains (LOM) detection using phasor measurement unit (PMU) data is described in this paper. The technique, known as the peak ratio analysis method (PRAM), improves both sensitivity and stability of LOM protection when compared with prevailing techniques. The technique is based on a rate of change of frequency (ROCOF) measurement from M-class PMUs, but the key novelty of the method lies in the fact that it employs a new “peak-ratio” analysis of the measured ROCOF waveform during any frequency disturbance to determine whether the potentially-islanded element of the network is grid connected or not. The proposed technique is described and several examples of its operation are compared with three competing LOM protection methods that have all been widely used by industry and/or reported in the literature: standard ROCOF phase offset relay and phase angle difference methods. It is shown that the PRAM technique exhibits comparable performance to the others, and in many cases improves upon their abilities, in particular for systems where the inertia of the main power system is reduced, which may arise in future systems with increased penetrations of renewable generation and high voltage dc (HVDC) infeeds.

Reducing unnecessary disconnection of renewable generation from the power system

Future power systems with large proportions of embedded generation could be severely affected if several loss of mains (LOM) protection systems maloperate in response to a non-islanding condition, potentially leading to generation shortfall and stability problems. Although many papers discuss methods of sensitively detecting islanded conditions (a short bibliographical survey is included), almost no papers in the literature address the problems associated with the stability of such protection methods during and after perturbations on the network to which they should not react. The aim is to highlight the shortcomings in existing power system protection practices relating to islanding detection with a view to identifying necessary areas of improvement to facilitate the ongoing proliferation of renewable sources in active distribution networks. Existing LOM techniques are described and stability-related shortcomings are demonstrated using the results of rigorous laboratory testing of several commercially available relays. The testing scenarios are developed using a UK Generic Distribution System repository, a public domain database representing typical distribution system architectures. Recommendations relating to the setting of existing LOM protection devices are provided, along with an overview of research and development activities relating to improvements in anti-islanding protection, including a discussion of both technical and economical viability.