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© FRS Consulting-Messerstrom  2014

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A good faith effort has been made to make the information contained in this site accurate and complete.  However, there is the possibility of misstatements and misinterpretations.  If errors are found, they will be corrected immediately.  The information contained in this site is only the first step toward a formal agreement. Please see our terms and conditions for more information.

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Please Contact Us to buy, lease or invest in the technology to measure current as described in this site.  Additional development is required and the amount of time and cost involved depends on the expertise and resources devoted to accomplishing that goal.  Please see our request for proposal for more information.

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Beta Ver 4/19/2014

Current Measurement Technologies

Several instruments that measure electrical currents are available but most or all of them have deficiencies.  Current transformers are the most widely used AC (only) instruments but they major limitations and significant power losses that have prompted several other current sensors designs to be developed.  The Rogowski coil was one of the first alternatives to gain a spot in power system measurements but it also only measures AC current and none of the countless design variations despite claims to the contrary have overcome that flaw.   After decades of development, fiber optic systems based on the magneto-optic effect are being sold but seem best suited to measure high DC currents used in aluminum smelting and arc furnaces.

This website introduces another method of measuring current based on the Bio- Savart law of magnetic's.   The magnetic flux surrounding a conductor is concentrated by very high permeability Nickel-Iron alloy to a density that can be accurately measured by Hall Effect Devices.   The flux density is proportional to the conductor current and the relationship is linear for AC, DC , and transients including the important asymmetrical currents cause by power system faults.  This arrangement is called a magnetic field current sensor or MFCS.

Measuring Transformer Losses



transformer power lost test equipment

Transformer Loss Measuring System


Power transformers load and no load loss tests require high precision instrumentation and frequent calibration checks to insure accurate measurements.  Current transformers with electronic flux compensation can be used to measure current accurately but the cost is very high.  A cost effective alternative is used in the above installation.

Magnetic field currents sensors (MFCS) are installed around the inside end of the bushings (see arrow).  The accuracy depends on the calibration which can be done in situ and portable calibrators are available that can inject know currents with no disassembly.  Accuracy can be demonstrated and testing resumed in a few hours.

transformer power loss system components


1 - Terminal - Output
2 - Bushing - Wall
3 - Copper Cylinder - MFCT
4 - Magnetic Sensor - Hall
5 - Switch - Signal Level
6 - Switch - Voltage Sel.
7 - HV Fuse
8 - Potential Trans.
9 - Terminal - Input