Alternating current power measuring apparatus

Patent metadata

Field	Value
Publication number	US-9529024-B2
Application number	US-201213405650-A
Country	US
Kind code	B2
Filing date	Feb 27, 2012
Priority date	Apr 6, 2011
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

An alternating current power measuring apparatus includes a first capacitance element having one end connected to a conductor wire of a first electrical cable of a set of electrical cables for supplying alternating current to a load and having the other end capacitively coupled to a conductor wire of a second electrical cable, a first voltage measuring part which measures a first voltage which is a voltage of both ends of the first capacitance element, a first current measuring part which measures a first current flowing in the first electrical cable, and a processing part which computes a power to be supplied to the load by the set of electrical cables by the multiplication among a proportion between a specified voltage value of a voltage applied to the set of electrical cables and an effective value of the first voltage, the first voltage and the first current.

First claim

What is claimed is:

1. An alternating current power measuring apparatus comprising:
a first capacitance element having one end capacitively coupled to a conductor wire of a first electrical cable of a set of electrical cables for supplying alternating current to a load and having the other end capacitively coupled to a conductor wire of a second electrical cable of the set of electrical cables;
a first voltage measuring part for measuring a first voltage V which is a voltage of both ends of the first capacitance element;
a first current measuring part for measuring a first current I flowing in the first electrical cable; and
a processing part which accepts a value of E eff being a standard voltage, accumulates N measurements of first voltage V and first current I over a predetermined period, and then computes a power P to be supplied to the load by the set of electrical cables according to the following formula:
P=P 0 ×E eff /V eff

wherein P 0 is given by the following formula:
P 0 =(1/ N )Σ( V×I )

Σ being the summation sign representing accumulation of the N measurements, and
V eff being the effective value of the first voltage V for the predetermined period.

2. An alternating current power measuring apparatus comprising:
a first capacitance element having one end capacitively coupled to a conductor wire of a first electrical cable of a set of three electrical cables for supplying three-phase alternating current to a load and having the other end capacitively coupled to a conductor wire of a second electrical cable of the set of electrical cables;
a second capacitance element having one end capacitively coupled to a conductor wire of a third electrical cable of the set of electrical cables and having the other end capacitively coupled to the conductor wire of the second electrical cable;
a first voltage measuring part for measuring a first voltage V ac which is a voltage of both ends of the first capacitance element;
a second voltage measuring part for measuring a second voltage V bc which is a voltage of both ends of the second capacitance element;
a first current measuring part for measuring a first current I a flowing in the first electrical cable;
a second current measuring part for measuring a second current I b flowing in the second electrical cable;
a switching part for capacitively coupling selectively either of said the other end of the first capacitance element and said the other end of the second capacitance element to the second electrical cable; and
a processing part which accepts values of E ac,eff and E bc,eff being a standard voltage, accumulates N measurements of V ac , V bc , I a and I b over a predetermined period, and then computes a power to be supplied to the load by the set of electrical cables by summation of a first value P ac and a second value P bc , which are determined according to the following formulas:
P 0,ac =(1/ N )Σ( V ac ×I a )

Σ being the summation sign representing accumulation of the N measurements,
P ac =P 0,ac ×E ac,eff /V ac,eff

V ac,eff being the effective value of the first voltage V ac for the predetermined period
P 0,bc =(1/ N )Σ( V bd ×I b )

Σ being the summation sign representing accumulation of the N measurements, and P bc =P 0,bc ×E bc,eff /V bc,eff
V bc,eff being the effective value of the first voltage V bc for the predetermined period.

3. An alternating current power measuring apparatus according to claim 1 , further comprising:
a first clamp part including a first electrode, a first magnetic core and a first coil wound around the first magnetic core and bringing the first electrode adjacent to an insulator of the first electrical cable; and
a second clamp part including a second electrode, a second magnetic core and a second coil wound around the second magnetic core and brining the second electrode adjacent to an insulator of the second electrical cable,
said one end of the first capacitance element being capacitively coupled to the conductor wire of the first electrical cable via the first electrode,
said the other end of the first capacitance element being capacitively coupled to the conductor wire of the second electrical cable via the second electrode, and
the first current measuring part detecting a current flowing in the first electrical cable or in the second electrical cable, based on a signal detected by the first coil or the second coil.

4. An alternating current power measuring apparatus according to claim 2 , further comprising:
a first clamp part including a first electrode, a first magnetic core and a first coil wound around the first magnetic core and bringing the first electrode adjacent to an insulator of the first electrical cable; and
a second clamp part including a second electrode, a second magnetic core and a second coil wound around the second magnetic core and brining the second electrode adjacent to an insulator of the second electrical cable,
said one end of the first capacitance element being capacitively coupled to the conductor wire of the first electrical cable via the first electrode,
said the other end of the first capacitance element being capacitively coupled to the conductor wire of the second electrical cable via the second electrode, and
the first current measuring part detecting a current flowing in the first electrical cable or in the second electrical cable, based on a signal detected by the first coil or the second coil.

5. An alternating current power measuring apparatus according to claim 4 , further comprising
a third clamp part including a third electrode, a third magnetic core and a third coil wound around the third magnetic core and bring the third electrode adjacent to the insulator of the third electrical cable,
said one end of the second capacitance element being capacitively coupled to the conductor wire of the third electrical cable via the third electrode, and
the second current measuring part detecting a current flowing in the second electrical cable or in the third electrical cable, based on a signal detected by the second coil or the third coil.

6. An alternating current power measuring apparatus according to claim 1 , wherein
an input impedance of the first voltage measuring part is twice or more of an impedance of the first capacitance element.

7. An alternating current power measuring apparatus according to claim 2 , wherein
an input impedance of the first voltage measuring part is twice or more of an impedance of the first capacitance element.

8. An alternating current power measuring apparatus according to claim 6 , wherein
an input impedance of the first voltage measuring part is five times or more of an impedance of the first capacitance element.

9. An alternating current power measuring apparatus according to claim 7 , wherein
an input impedance of the first voltage measuring part is five times or more of an impedance of the first capacitance element.

Assignees

• Oshima Hirotaka
• Ambe Takayuki
• Ito Akio
• Fujitsu Ltd

Inventors

• Oshima Hirotaka
• Ambe Takayuki
• Ito Akio

Classifications

• G01R21/06 Primary

  by measuring current and voltage (G01R21/08 - G01R21/133 take precedence) · CPC title

• G01R21/1331

  Measuring real or reactive component, measuring apparent energy · CPC title