Electro-Magnetic Field Analysis Electro-Magnetic Field Analysis andand

Faraday Cage DesignFaraday Cage Design

Faraday cage design process

Identifying and characterizing the magnetic and electric field sources through measurements

Calculating the cage aperture based on frequency composition of the EMI and shield thickness based on field strength

Simulating the test setup (source, measuring equipment and faraday cage) and evaluating shielding effectiveness

Selection of the most cost effective and least disruptive field reduction method

Magnetic Field Magnetic Field AnalysisAnalysis

Faraday Cage Model Enclosing PD Measuring Equipment

Current Cycling Test Equipment (1200A)

Faraday Cage

PD Measuring Equipment

B-Field In Actual Lab Conditions

The B-Field is very low and any thin cage can give the required shielding. Considering the worst scenario, wherein the current cycling loop is in proximity (10 cm) of PD equipment further evaluation is carried out

The current cycling loop is about 6m away from PD measuring equipment

Flux density on PD measuring equipment

Case A: Without faraday cage Case B: With faraday cage

Case A Case B[Cage shown for reference]

Flux density on the impinging phase of measuring equipment

Case A

Case B

[Cage shown for reference]

Flux density along the cross -section of faraday cage enclosing PD measuring equipment

Case A

Case B

Case A

Case BOuter Surface

Flux density on the nearest face of faraday cage

Case BInner Surface

Flux density (Tesla)

Case A Case B

On Measuring Equipment

0.5 0.003

On Faraday cage (Outer face)

0.12 0.48

Magnetic Field Analysis

Inferences

Considering maximum radio or PD discharge interference frequency of 3 GHz the mesh size shall be smaller than 5cm

Considering the worst scenario the flux density on faraday cage for Case1 is 0.5 Tesla. The use of steel mesh (µr-1000 and thickness 2mm) as in Case2 brought down the B-value from 0.5 Tesla to less than 3mTesla (required limit 7-50 mTesla)

The skin depth evaluation is not considered as the field is static and hence flux distribution is based on ratio of air to mesh permeability alone

Theoretical calculations are in agreement with simulation results

Ref. Std: IEEE Std C95.6™-2002

Electric Field AnalysisElectric Field Analysis

Faraday Cage Model Enclosing PD Measuring Equipment

Current Cycling Test Equipment 1 kV

Faraday Cage

PD Measuring Equipment

Case A Case B

Electric stress on PD measuring equipment

Case A: Without faraday cage Case B: With faraday cage

Emax- 0.15 kV/m Emax- 0.00004 kV/m

Case A

Case B

Electric field distribution

Electric Stress (kV/m)

Case A Case B

On measuring Equipment

0.15 0.00004

On Faraday cage 0.02 0.08

Electric Field Analysis

Inferences

The maximum electric field is 0.08 kV/m on faraday cage (worst scenario case) which is well with in the required limit (5 kV/m)

The electric and magnetic fields in the laboratory are low. The effect of electric field is much lower than magnetic field. Hence, the proposed shield design is based on minimum requirements and magnetic field.

The steel mesh of µr-1000 and thickness 2mm shall provide the required shielding

Ref. Std: IEEE Std C95.6™

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