Patent ID: 7656149

Claim:
A current transformer to detect a sine-wave alternating current having a maximum effective current value I max (A rms ) and a frequency f(Hz), and a half-sine-wave rectified current having a maximum peak value I peak (A op ) and a frequency f(Hz) in a primary winding, comprising: at least one magnetic core having one turn of primary winding and multiple turns of secondary winding to which a detecting resistor is connected in parallel, and having an effective cross section A e of the magnetic core being determined by A e ≥ A e ⁡ ( min ) * ⁢ ⁢ ( m 2 ) A e ⁡ ( min ) * = I max · ( R Cu + R b ) 4.44 · f · N s 2 · B s ⁢ ⁢ ( m 2 ) , where B s is a saturation magnetic flux density of the magnetic core (T), N s is a number of turns of the secondary winding, R Cu is a resistance of the secondary winding (Ω), R b is a resistance of the detecting resistor (Ω), and A e ≥ A e ⁡ ( min ) ** ⁢ ⁢ ( m 2 ) A e ⁡ ( min ) ** = ( R Cu + R b ) ⁢ ( D i ⁡ ( min ) + 1.5 × 10 - 3 ) 2 ⁢ ⁢ f ⁢ ⁢ μ r ⁢ μ 0 ⁢ N s 2 ⁢ tan ⁢ ⁢ ϕ ⁢ ⁢ ( m 2 ) D i ⁡ ( min ) = a ⁢ I max + b ⁢ ⁢ ( m ) 0.75 × 10 - 3 ≤ a ≤ 1.25 × 10 - 3 ⁢ ⁢ ( m ⁢ / ⁢ A 0.5 ) 8.0 × 10 - 3 ≤ b ≤ 12.0 × 10 - 3 ⁢ ⁢ ( m ) , where D i(min) is a minimum value of an inner diameter of the magnetic core (m), μ r is an incremental relative permeability of the magnetic core, μ 0 is a permeability of a vacuum, 4π×10 −7 (H/m), and φ is a phase error of current transformer (rad), and the mean magnetic path length l e satisfies ⁢ l e ≥ l e ⁡ ( min ) * ⁢ ⁢ ( m ) l e ⁡ ( min ) * = I peak π ⁢ 〈 H s - N p · I peak ⁡ ( R Cu + R b ) 2 ⁢ ⁢ π ⁢ ⁢ μ r ⁢ μ 0 ⁢ N s 2 · A e ⁢ { T 2 ⁡ [ cos ⁢ ( 2 ⁢ ⁢ π ⁢ ⁢ T Vs ⁢ ⁢ 0 T ) - cos ⁡ ( 2 ⁢ ⁢ π ⁡ [ ( T / 2 ) - T Vs ⁢ ⁢ 0 ] T ) ] + 2 ⁢ T Vs ⁢ ⁢ 0 - ( T / 2 ) } 〉 ⁢ ⁢ ( m ) ⁢ ⁢ ⁢ H s = Bs μ r ⁢ μ 0 ⁢ ⁢ ( A ⁢ / ⁢ m ) ⁢ ⁢ ⁢ T Vs ⁢ ⁢ 0 = T 2 ⁢ ⁢ π ⁢ sin - 1 ⁡ ( 1 π ) ⁢ ⁢ ( s ) , where ⁢ ⁢ ⁢ T = 1 ⁢ / ⁢ f ⁢ : ⁢ ⁢ period ⁢ ⁢ ( s ) , ⁢ ⁢ and ⁢ l e ≥ l e ⁡ ( min ) ** ⁢ ⁢ ( m ) ⁢ ⁢ ⁢ l e ⁡ ( min ) ** = π ⁡ ( D i ⁡ ( min ) + 1.5 × 10 - 3 ) ⁢ ⁢ ( m ) .