0 items

No products in the basket.

Share this page

A design, consultancy and manufacturing service

Following the privatisation of the Central Electricity Generating Board (CEGB) in 1991, Dr David Ward founded Rocoil Limited to continue his work with Rogowski coils. David understood well the versatility of Rogowski coil transducers, having spent many years studying and working with them whilst in the CEGB, and still explores today the very wide range of applications that they have. His interest in understanding these applications has led to them being used in a wide range of applications across many industries. From a small beginning, the company has expanded and now exports specialised current-measuring equipment to more than 40 countries worldwide.

Case Studies

  • Measuring the earth resistance of a transmission tower

    Location: UK
    Industry: Power Transmission

    The Challenge

    To measure the current in each of the four legs of a transmission tower to determine the total current to earth so that the earth resistance can be determined.

    Our Solution

    We injected a voltage from a power supply. We configured a Rogowski coil measuring system so that four current measurements could be summed algebraically giving the total current and this enabled the resistance to earth to be calculated. The earth resistance measurement was made at several frequencies.

  • Precision calibration of current transformers

    Location: Finland / UK
    Industry: Electrical Installations

    The Challenge

    To check the calibration of current transformers on site without the need to remove them to a calibration laboratory.

    To provide a portable precision current-measurement standard which can be clipped on to the CT wiring without disconnecting any conductors.

    Our Solution

    Rocoil rigid coil systems can be calibrated to an uncertainty of 0.1%. They can also be produced in a clip-on version without loss of accuracy. These can be used as reference standards for calibration.

  • Measuring both leakage and fault currents in a semi-conductor device

    Location: Brazil
    Industry: Petroleum

    The Challenge

    To measure the leakage current of a few mA in an SCR when it is turned off. The measurement should survive the current surge of about 60kA when the device is turned on. The same coil to be used for measuring both currents.

    Measuring the leakage current requires a sensitive system. The input stages of the sensitive integrator must be designed to withstand the large coil voltage caused by the current surge.

    Our Solution

    Rocoil engineers produced a solution with two integrators connected to the same rigid coil. The 'leakage current' integrator was designed using resistors that had the watt rating to withstand the coil output at 60kA. During the current surge the integrator would overload and saturate but recover as soon as the current was reduced. The 'current surge' integrator was designed to make accurate measurements at the larger current. This application illustrates the linearity of a Rogowski coil where the same coil can be used to measure a very wide range of currents.

  • Sudden short circuit testing of large generators

    Location: Wales
    Industry: Generator Manufacture

    The Challenge

    To measure a very large current transient with an asymmetric waveform.

    Transients are difficult to measure with a conventional current transformer and the usual method is to use a resistive shunt which can be difficult to install and may require modification of the generator output connections.

    Our Solution

    We designed a Rogowski coil to measure very large transient currents. It was compact and was installed on the output connections with no significant disruption to other work on the generator. It was left in position until it was convenient to make the short-circuit measurements.

  • Shaft current measurement

    Location: Germany / Australia / Tasmania
    Industry: Power Station

    The Challenge

    Currents flowing along the shaft of a generator or motor can cause damage to the bearings. There is a need to monitor these currents.

    To measure a low current, less than 1A, in a very large conductor which could be 1m or more in diameter.

    Our Solution

    Rocoil flexible Rogowski coils can be made in lengths up to at least 12m. A flexible coil round the shaft used with a sensitive integrator can measure currents with a sensitivity of a few mA. The success of these measurements depends on very careful screening of the coil and integrator.

  • Protection system for slip-ring induction motors

    Location: UK
    Industry: Power Station

    The Challenge

    To measure large currents at a low frequency (~1Hz) to check the performance of the regulator which was controlling a boiler feed pump motor at a power station.

    Motor problems, such as excessive vibration, can be difficult to investigate because they can have both electrical and mechanical causes. Accurate measurement of the slip-frequency currents can help with the diagnosis.

    Our Solution

    The slip-frequency currents can be measured accurately using Rocoil rigid coils which have very good low-frequency response. The measurements can be used with a protection system to monitor phase imbalance and earth faults.

  • Arc furnace currents

    Location: Germany / Austria / Spain / Turkey / India / China / Indonesia / USA
    Industry: Steel Industry

    The Challenge

    To measure the current into an arc furnace which can be of the order of 100kA or more. These measurements are used to ensure efficient operation of the furnace.

    To measure the actual electrode current where there is limited space and not sufficient room for a current transformer.

    Our Solution

    Rocoil flexible coils can be installed where there is limited space. Special techniques developed by Rocoil ensure that measuring systems can be calibrated accurately even for the largest currents.

  • High-current testing of switchgear and fuses

    Location: China
    Industry: High-Current Test Laboratory

    The Challenge

    Testing switchgear and fuses to check their correct operation under high-current fault conditions.

    To measure large current transients at mains frequency which last only a few cycles. These transients frequently have large 'DC offsets' which need to be measured accurately.

    Our Solution

    High-current measurements can be made with both flexible and rigid Rogowski coils. Special calibration techniques developed by Rocoil ensure that measuring systems are accurate. Rigid coils are calibrated with an uncertainty of 0.1% even for large currents. The integrators are designed to have very good low-frequency response so that the DC offsets can be measured correctly.

  • Monitoring the current in railway lines to check signalling currents

    Location: UK / India / Brazil
    Industry: Rail

    The Challenge

    Currents of a few amps in the range 1 - 2 kHz are an essential part of the railway signalling system for determining where the trains are. When there is a fault the trains cannot run and it is important to find the fault with a minimum of delay.

    Provide a current transducer to measure signalling currents in a railway line that can be moved around easily to trace the currents.

    Our Solution

    A U-shaped Rogowski coil was developed which could be simply dropped over the rail to make a measurement. This was a battery-powered unit and the integrator incorporated a high-pass filter that would allow measurement of the higher-frequency signalling currents but reject 50Hz signals which could cause interference.

  • Measurements with lightning test equipment

    Location: UK / USA
    Industry: Aircraft Test Facility

    The Challenge

    Certain components, notably aircraft parts, are tested using artificial lightning to check their integrity.

    To measure a current pulse of the order of 20kA lasting about 10µs.

    Our Solution

    For measuring large, fast currents Rocoil has developed special low-output coils. These coils have been used with suitable integrators to provide an accurate and effective measuring system.

Our company philosophy is that a customer should be able to purchase the coils and integrators that meet the needs of their applications. If we can work out how to make it, then we should and we do. We build the products that a customer actually needs, to meet their specific measuring requirements.

David Ward

Founder and Director

About us - quote 1

Our goods are manufactured by hand, thoroughly checked and calibrated to ensure they are of the highest quality.

David Ward

Founder and Director

About us - quote 2

We pride ourselves on offering excellent customer service and are frequently described by our customers as being responsive to enquiries and offering high quality advice and guidance that helps them select the coils and integrators that best meet their needs.

David Ward

Founder and Director

About us - quote 3

We have over 400 active customers based in over 47 countries

Our products are used in a wide variety of industries including, nuclear power, electricity generation, transport, steel manufacture, research and development, calibration and product testing.

Our history...

Rogowski coils take their name from W. Rogowski who, in 1912, co-authoured a paper with W. Steinhaus entitled 'Die Messung der Magnetischen Spannung' (Messung des Linienintegrals der Magnetischen Fieldstärke). This describes a coil wound on a flexible strip of material and a number of experiments to measure electric currents and other magnetic quantities as well as the ability of such a coil to reject external magnetic fields that do not originate from currents flowing through the coil.

An earlier account of the use of a coil wound on a flexible former is the paper written in 1887 by A. P. Chattock 'On a Magnetic Potentiometer' Which describes the use of a long flexible coil for measuring magnetic potentials (magnetomotive force). Chattock's name is now associated with the Chattock Potentiometer which is used for testing the cores of generators and motors for defects.

Rogowski Coils have been used subsequently by several laboratories for specialised electronic current measurements in a wide range of applications.

In 1977 The Central Electricity Generating Board (CEGB) Scientific Services Department in Harrogate began to explore the use of Rogowski Coils to investigate problems in power station electrical plant. The team responsible for this work consisted of John Exon, David Ellison, and David Ward. Problems investigated ranged from the monitoring of rotor currents in slip-ring induction motors, sudden short circuit tests, the investigation of unwanted currents flowing in the support frameworks in large turbogenerators, The latter measurements were part of a much larger investigation into overheating in generator cores. See Applications for many other applications in the Power Industry.

During this time the technical experience with Rogowski coils was licenced to Robinson Instruments who marketed a 'Linear Current Transducer' consisting of an integrator (Type 543) with a Worm Coil (Type 545) or a Solid Coil.

Following the privatisation of the CEGB in 1991, Rocoil
Limited was founded to continue the work with Rogowski coils.

Some of our clients