FBG-based fibre-optic current sensors for power systems protection : laboratory evaluation

Conventional differential current unit protection schemes rely on a pair of electronic protection relays that measure current phasors separately at the boundaries of the protected zone. The scheme requires a separate, often optical, communications channel for the sharing of measurement information to enable the timely identification of and reaction to internal faults. The high voltage environment that the transducers must operate in poses a number of engineering problems stemming from the need for electrical isolation and requirement for transformation of high primary system current magnitudes. Additionally, when either the number of relays or distance between relays is increased, timing problems can arise due to the limited bandwidth, speed and changeable latencies of the communication channels and the increased computation requirements. Fibre-optical sensor systems are maturing as a technology and offer a number of advantages over conventional electronic sensor regimes, including the possession of inherent electrical isolation, chemical inertness, immunity to electromagnetic interference, and their small size and serial multiplexing capability. Fibre sensor systems are therefore experiencing increased uptake in industries that operate in harsh environments, such as oil and gas, or where specific requirements such as large step-out distances or resistance to radiation prohibit the use of electronic sensors. The Advanced Sensors Team within the Institute for Energy and Environment has developed fibre-optic point sensors for voltage and electrical current, based on fibre Bragg grating (FBG) technology, that have been applied successfully to power systems diagnostics. With the photonic systems capability to interrogate up to 100 km from source at kHz sample rates with up to 30 sensors in series, it is possible and highly desirable to adapt this technology for use in power systems protection, where immediate applications in unit and distance protection are clear. In this paper, the application of the FBG-based hybrid current sensor system to power systems protection is presented for the first time. Experimental tests of the response of an optical unit protection system to a range of internal and external fault scenarios are also reported. Secondary current inputs to the system are modelled using ATP and injected into the prototype test system via an APTS3 (Advanced Protection Testing System) unit. Fibre sensors, separated optically by 24 km of fibre, provide all measurement information via a single interrogation system situated at one end of the protected zone. Experimental results confirm high performance of the optical unit protection both in terms of sensitivity to internal faults and stability under external fault conditions. Therefore, the systems ability to overcome problems experienced in electronic relaying systems using conventional current sensing technologies is demonstrated. No separate communications channel is required in this configuration, with fault algorithms being deployed only at one location that need not be close to the protected zone. The fibre-optic current sensor systems capacity for long-distance interrogation and high sensor count qualify it for further applications in more complex protection schemes, or over larger distances, where a single fibre could form the basis of highly novel distributed protection schemes. This potential will also be discussed in detail in the paper

Investigating gait adaptations to split belt treadmill walking in healthy adults

Disability as a result of stroke is a major issue. Gait is a priority in rehabilitation, where asymmetry is a common and detrimental feature. Conventional treadmills are not able to treat this asymmetry. Recently the use of split belt (SB) treadmills has been suggested as a novel approach, SB allows each leg to travel at independent speeds. This study seeks to investigate the effects of SB gait on healthy young adults as a model for stroke patients. The study carried out motion analysis using the Motek CAREN. Subjects (n=10) were exposed to a total of 15 minutes SB in 5 and 10 minute blocks with a period of normal walking either side. Step length asymmetry and accommodation strategy was analysed. SB resulted in initial negative asymmetry, inferring a shortening of step of the leg on the fast belt (n=6) with some subjects showed a mirrored response (n=4). The asymmetry returns to baseline as subjects accommodate the novel condition. A distinct strategy was characterised, in which step length on fast belt was increased by delaying heel strike. When returned to normal walking conditions the initial asymmetry is reversed with a longer step on the fast leg. This is transient, after a short period normal walking there is a return to baseline asymmetry. Upon subsequent exposure to SB the adaption process is more rapid in adopting heel hang strategy (1st exposure 13 strides, 2nd exposure 3 strides), with significantly reduced asymmetry (p<0.001). The results show that young healthy adults can adapt to SB with distinct strategies. The improved adaption as a result of subsequent exposure suggests that there is some level of learned adaption. If applied to stroke patients, long term SB exposure may improve asymmetry and may be encouraged to adopt specific strategies to accommodate an increase in step length.Disability as a result of stroke is a major issue. Gait is a priority in rehabilitation, where asymmetry is a common and detrimental feature. Conventional treadmills are not able to treat this asymmetry. Recently the use of split belt (SB) treadmills has been suggested as a novel approach, SB allows each leg to travel at independent speeds. This study seeks to investigate the effects of SB gait on healthy young adults as a model for stroke patients. The study carried out motion analysis using the Motek CAREN. Subjects (n=10) were exposed to a total of 15 minutes SB in 5 and 10 minute blocks with a period of normal walking either side. Step length asymmetry and accommodation strategy was analysed. SB resulted in initial negative asymmetry, inferring a shortening of step of the leg on the fast belt (n=6) with some subjects showed a mirrored response (n=4). The asymmetry returns to baseline as subjects accommodate the novel condition. A distinct strategy was characterised, in which step length on fast belt was increased by delaying heel strike. When returned to normal walking conditions the initial asymmetry is reversed with a longer step on the fast leg. This is transient, after a short period normal walking there is a return to baseline asymmetry. Upon subsequent exposure to SB the adaption process is more rapid in adopting heel hang strategy (1st exposure 13 strides, 2nd exposure 3 strides), with significantly reduced asymmetry (p<0.001). The results show that young healthy adults can adapt to SB with distinct strategies. The improved adaption as a result of subsequent exposure suggests that there is some level of learned adaption. If applied to stroke patients, long term SB exposure may improve asymmetry and may be encouraged to adopt specific strategies to accommodate an increase in step length

Inertia emulation control of VSC-HVDC transmission system

The increasing penetration of power electronics interfaced renewable generation (e.g. offshore wind) has been leading to a reduction in conventional synchronous-machine based generation. Most converter-interfaced energy sources do not contribute to the overall power system inertia; and therefore cannot support the system during system transients and disturbances. It is therefore desirable that voltage-source-converter (VSC) based high voltage direct current (HVDC) interfaces, which play an important role in delivery of renewable power to AC systems, could contribute a virtual inertia and provide AC grid frequency support. In this paper, an inertia emulation control (IEC) system is proposed that allows VSC-HVDC system to perform an inertial response in a similar fashion to synchronous machines (SM), by exercising the electro-static energy stored in DC shunt capacitors of the HVDC system. The proposed IEC scheme has been implemented in simulations and its performance is evaluated using Matlab/Simulink

Moral distress and moral residue among nurses working in the surgical intensive care unit: a descriptive qualitative approach.

Introduction: Approximately one in five Americans will die in the intensive care unit (ICU). Nurses spend more time with chronically ill and end-of-life patients than any other healthcare professional, and may perceive some actions in the ICU as immoral. Moral distress is defined as knowing the right course of action to take but being hindered by institutional constraints. Development of the Moral Distress Scale-Revised revealed that 31% of ICU nurses left a prior position or considered leaving their current nursing job because of moral distress. The purpose of this descriptive qualitative study is to explore surgical ICU (SICU) nurses’ perceptions and experiences of moral distress and moral residue, coping, and perceived quality of care. Methods: A descriptive qualitative approach used in-depth, semi-structured individual interviews with SICU nurses. Purposive sampling methods of maximum likelihood variation and snowball sampling recruited a heterogeneous sample of 21 SICU nurses from two SICUs in a university hospital until theoretical saturation occurred. Essential themes were identified through reflective writing, rewriting, memoing, and content and thematic analysis. Verbatim transcription of interviews and an audit trail ensured rigor and trustworthiness of the data in order to highlight descriptions, patterns, uniqueness, and interpretations of firsthand accounts. Conclusion: Moral issues were highlighted to explore root causes of moral distress at the individual-level for SICU nurses with a deeper understanding of moral distress and moral residue, particularly how nurses cope with the stress involved and their perceptions of the influence of moral distress on quality patient care. Understanding nurses’ experiences is essential to addressing ethical issues of moral distress and moral residue before they negatively impact patient outcomes

What I believe about leadership and education

Every administrator at every school is different and every administrator has a different vision for their future. It is our job as educators to lead each student down the correct path. If one student\u27s goal is to go straight to the work force after graduation, we as educators need to do everything we can for him/her to make sure he/she has the skills to be prepared. The same is true for the college bound student. Successful leaders are those who have a vision of where their school needs to go. If a school did not have a vision, it would be no surprise to anyone if that school got lost on the way. A successful leader will get faculty, staff, parents, and members of the community together to talk, discuss, and collaborate to figure out what identity the school will want in the future. It is important that the vision be communicated to all stakeholders. A successful leader will support and sustain the vision of the school in good and bad times

Inertia emulation control strategy for VSC-HVDC transmission systems

There is concern that the levels of inertia in power systems may decrease in the future, due to increased levels of energy being provided from renewable sources, which typically have little or no inertia. Voltage source converters (VSC) used in high voltage direct current (HVDC) transmission applications are often deliberately controlled in order to de-couple transients to prevent propagation of instability between interconnected systems. However, this can deny much needed support during transients that would otherwise be available from system inertia provided by rotating plant

Translating proprietary protection setting data into standardized IEC 61850 format for protection setting validation

For smart grid development, one of the key expectations is that the data should be accessible to and readily interpreted by different applications. Presently, protection settings are represented using proprietary parameters and stored in various file formats. This makes it very difficult for computer applications to manipulate such data directly. This paper introduces a process that translates the proprietary protection setting data into IEC 61850 standardised format and saves the data as System Configuration description Language (SCL) files. A code generation process that allows rapid implementation of the translation process is proposed. Among various applications, the paper demonstrates how such a translation process and generated SCL files can facilitate the development of an intelligent system for protection setting error detection and validation

Standardization of power system protection settings using IEC 61850 for improved interoperability

One of the potential benefits of smart grid development is that data becomes more open and available for use by multiple applications. Many existing protection relays use proprietary formats for storing protection settings. This paper proposes to apply the IEC 61850 data model and System Configuration description Language (SCL), which are formally defined, to represent protection settings. Protection setting files in proprietary formats are parsed using rule-based reasoning, mapped to the IEC 61850 data model, and exported as SCL files. An important application of using SCL-based protection setting files is to achieve protection setting interoperability, which could bring multiple compelling benefits, such as significantly streamlining the IED configuration process and releasing utilities from being “locked in” to one particular vendor. For this purpose, this paper proposes a uniform configuration process for future IEDs. The challenges involved in the implementation of the proposed approach are discussed and possible solutions are presented

Distributed photonic instrumentation for smart grids

Photonic sensor networks possess the unique potential to provide the instrumentation infrastructure required in future smart grids by simultaneously addressing the issues of metrology and communications. In contrast to established optical CT/VT technology, recent developments at the University of Strathclyde in distributed point sensors for electrical and mechanical parameters demonstrate an enormous potential for realizing novel and effective monitoring and protection strategies for intelligent electrical networks and systems. In this paper, we review this technology and its capabilities, and describe recent work in power system monitoring and protection using hybrid electro-optical sensors. We show that wide-area visibility of multiple electrical and mechanical parameters from a single central location may be achieved using this technology, and discuss the implications for smart grid instrumentation

Performance of loss-of-mains detection in multi-generator power islands

This paper presents an investigation of the impact of multi-generator power islands on the performance of the most-commonly used anti-islanding protection method, Rate of Change of Frequency (ROCOF). In particular, various generating technology mixes including Photovoltaic panels (PV), Doubly Fed Induction Generators (DFIGs) and Synchronous Generators (SG) are considered. The Non-Detection Zone (NDZ) for a range of ROCOF setting options is assessed systematically and expressed as a percentage of generator MVA rating. It was discovered that ROCOF protection becomes very ineffective when protection time delay is applied. In the majority of islanding situations the generator is disconnected by frequency-based G59 protection