+44 (0) 1580 891521

High Metering accuracy (HMA) Current Transformer Cores

Tape Wound MuMetal Toroidal Cores      



High permeability 80% nickel-iron MuMetal alloys are commonly used in the manufacture of high metering accuracy (HMA) current transformer cores. Close control of the magnetic properties over a wide flux density range permits the most economic design of the transformer for requirements in both ratio and phase angle error.

 Core Magnetic Properties 

Guaranteed relative permeability at 0.4m 1rms 

Guaranteed relative permeability at 0.4m 1rms

 *Other guarantees may be given to meet specific customer requirements

Dimensional Specification

 Range of limiting core sizes 

Range of limiting core sizes

Cores fabricated using 0.1mm thick strip can be supplied by prior arrangement.

Core maximum outside diameter is 900mm. However, cores may be supplied up to 1200mm diameter with reduced magnetic guarantees, subject to a minimum build-up limitation of 5% of the diameter.

Where cores are required with greater height they can be supplied in two or more sections. 

 Dimensional Tolerances 

Dimensional tolerances






 Material Properties 

 Typical Magnetic Properties 

Saturation Induction 0.77 (T)
Remanence from saturation 0.40 (T)
Cure temperature 350 °C

 Typical Physical Properties 

Density 8,800 (kg m-3)
Resistivity 0.6 (µΩ m)
Coefficient of linear expansion 13 (x10-6 °C-1)
Thermal conductivity 33 (W m-1 °C-1)
Specific heat capacity 0.46 (kJ kg-1 °C-1)



Headcorn Road  |  Staplehurst  |  Tonbridge  |  Kent  |  TN12 0DS  |  UK

Tel : +44 (0) 1580 891521  Fax : +44 (0) 1580 893345

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