Get Involved with Low Cost Rogowski Coil Current Sensor Development. RevA

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1 Get Involved with Low Cost Rogowski Coil Current Sensor Development. RevA Contents 1 The Project The Patent The Offer The Appendix What is a Rogowski Coil InnovateUK assessment of the project LCR009 Datasheet The Project Cox-Smith Consultants Ltd have been awarded a grant by InnovateUK to develop a Low Cost Rogowski Coil AC Current Sensor. The award is described by InnovateUK as follows: Innovate UK is to invest up to 2m in feasibility studies to stimulate innovation across four enabling technology areas: advanced materials; biosciences; electronics, sensors and photonics; and information and communications. This competition is especially suited for innovative businesses looking to explore new technological opportunities, expand their business sectors and refresh their R&D strategy. Innovate UK has a wide range of tools and competitions to support such businesses. Part of the process is to present the results at InnovateUK s Collaboration Nation event. They say: Innovate UK runs regular Collaboration Nation events which enable companies that have been successful in feasibility studies competitions to showcase the results of their projects to their peers and others, with a view to finding new partners to collaborate with and new sources of funding. For more information see the Feasibility Studies pages at innovateuk.org. Successful applicants to this competition will be required to present their feasibility studies at a Collaboration Nation event in the autumn of Further details of the Collaboration Nation event will be announced nearer the time. This introduction is an advance invitation to get involved in the exploitation of the results of the feasibility study. This is our description of the project: Many technologies are needed to keep the electrical network running and current measurement is one of them. It is employed for measuring power consumption, for billing users, for control of the network and for efficiency controls that lead to savings of cash and carbon. Cox-Smith Consultants Ltd have worked on Low Cost Rogowski Coil Current Sensors for efficiency projects, for example in data centres and machines in factories. The requirement is for a low cost current sensor, of small size, 2% accuracy and one that can be applied quickly at many points in a local electrical network. We have patented a Low Cost 1

2 Rogowski Current Sensor but the accuracy of our prototype is 20% at 5A, which is not good enough to make it saleable. This project aims to optimise the coil design and method of manufacture to make it both low cost and 2% accurate to supply the market for current measurement in electrical networks. The LCR009 prototype was designed to be compatible with a National Instruments data acquisition module and can be powered directly by it. This is what the prototype looks like: Low Cost Rogowski Coil Current Sensor LCR009 designed by Cox-Smith Consultants Ltd attached to a National Instruments USB-6008 data logger. It is powered from the logger s 5V rail and is referenced to the 2.5V rail with a signal range of ±2V. The LCR009 is built on a single PCB and incorporates an amplifier and an integrator to scale the output in amps. The scaling is determined by the gain of the amplifier this coil design has been used at 150A (gain 800) and 25A (gain 5000) full-scale, but it could be used up to 60000A with a gain of x1. The coil is insulated from the conductor by the outer layer of the PCB. It is worth clarifying the above statements about accuracy. The LCR009 prototype was designed to operate at very low current for a Rogowski coil as well as to be low cost. The brief was to achieve a 25A sensor with an error at 5A of ±2% (error at 1/5 full-scale). In this configuration, the gain is 5000, and the ±20% error occurs at 5A when the conductor passes through the sensor at ±10 to the plane of the coil. The 150A configuration with a gain of 800 performs within specification at 1/5 full-scale see datasheet. During the project, for which we have the grant, we will use electromagnetic modelling software to investigate the errors and to optimise the design of the coil tracking. 2

3 2 The Patent Cox-Smith Consultants Ltd have applied for a patent to protect the construction of the sensor and the means of attachment to a conductor. The PCB has a gap that can be opened up to put the sensor over the conductor as can be seen here: The gap opens up to slip the sensor over the conductor. This is a useful feature as there is no need to either turn off the conductor or disconnect it from the equipment. The gap closes when the sensor is in position to start the measurement. 3

4 The sensor is installed on a 500A bus-bar and is ready to measure current. The outer layer of the PCB provides insulation. This is a prototype device, the amplifier needs protection depending on the application. 4

5 3 The Offer To exploit this product, Cox-Smith Consultants Ltd will need to find business partners. While we have the ability to do the R&D work and we can get the product made by subcontractors, we will not set up a production line or a sales and marketing organisation. Therefore our client or clients will be companies that can offer production and most importantly sales and we will licence the patent and the results of the project described in this document. At this stage we are looking for potential partners and we would offer for sale a copy of the final report once any further patent protection is in place. The offer is to share the results but on a licence basis. 4 The Appendix 4.1 What is a Rogowski Coil The Wikipedia entry about the Rogowski coil is a simple introduction to the technology: and this is an extract: A Rogowski coil, named after Walter Rogowski, is an electrical device for measuring alternating current (AC) or high speed current pulses. It consists of a helical coil of wire with the lead from one end returning through the centre of the coil to the other end, so that both terminals are at the same end of the coil. The whole assembly is then wrapped around the straight conductor whose current is to be measured. There is no metal (iron) core. The winding density, the diameter of the coil and the rigidity of the winding are critical for preserving immunity to external fields and low sensitivity to the positioning of the measured conductor. Since the voltage that is induced in the coil is proportional to the rate of change (derivative) of current in the straight conductor, the output of the Rogowski coil is usually connected to an electrical (or electronic) integrator circuit to provide an output signal that is proportional to the current. 4.2 InnovateUK assessment of the project These are quotes from the assessment of the project carried out by independent consultants: The proposal explains well the motivation for the improved sensor design the applicants wish to prove. The market demand is substantiated. The technology challenges are clear and quantitative detail is provided on claimed benefits. The competition is well understood.. Clear objectives in terms of technical specification and commercial requirements. Very good description of current limitations of the technology and the potential if technical challenges can be addressed. Clear plan and approach described. Valid work plan leading to tangible outputs. Clear explanation of partner work / contributions. The application clearly states what will be delivered at different points during the study. Meaningful targets for accuracy have been set. Good understanding of technical risk and reasons for funding. Good arguments for funding and added value. Proposal could have been improved with more information with respect to exploitation, supply chain partners required and route to market, including potential size of market. 5

6 4.3 LCR009 Datasheet The LCR009 current sensor is an air cored coil manufactured as part of a PCB with an integral amplifier. The sensor is made on a split ring to allow easy application to a conductor, especially useful when the conductor is carrying current and/or cannot be disconnected. The dimensions are: Outer diameter 80mm Inner diameter 37mm Thickness 1.70mm Tab dimensions 35x30mm Power supply, 5V, 2.5V and 0V Output ±2.0V referred to 2.5V rail (compatible with DAQ module) (Other voltage rails are possible such as ±5V with a 0V reference for the output.) Current range (depends on the amplifier gain) from 150A full scale to 5000A full scale and is AC only. The coil track is insulated by a surface film. The sensor is readily compatible with DAQ modules, for example National Instruments USB The sensor is in development and the accuracy will depend on the environment in which it is used. As it is based on a PCB it can be readily customised to a specific application. To discuss a customised sensor in detail a Non-Disclosure Agreement must be signed. A patent application has been made. 6

7 Gain x800, 150A full-scale, conductor at 90 to plane of sensor. Typical errors at locations shown relative to location 0, measured at 24Arms. Location Error relative to location % % % % Gain x800, 150A full-scale, conductor at location 0 and various angles to the plane of the sensor. Typical errors at angles shown relative to location 90, measured at 24Arms. Angle Error at location % % % % % % 7