Current ratio device
First Claim
1. A device for use in constructing an alternating current, current transformer, said device comprising(a) a first magnetic core,(b) a second magnetic core,(c) a measuring winding having Nm turns electromagnetically coupled with the first core but not with the second core,(d) a compensating winding having Nc turns electromagnetically coupled with both cores,(e) an amplifier having an input and an output,(f) said input being connected to receive the waveform across the measuring winding,(g) said output being connected to the compensating winding to provide a compensating currect Ic through the conpensating winding equal to a magnetizing current Iμ
- required to magnetize the second core, and(h) said output being connected to the measuring winding to provide a measuring current Im through the measuring winding in a direction opposite to that of the compensating current and equal to ##EQU5## whereby, when primary and secondary windings are electromagnetically coupled with the cores to form an alternating current, current transformer and the secondary winding is connected to a burden, the magnetizing current Iμ
for such transformer is provided by the device.
2 Assignments
0 Petitions
Accused Products
Abstract
A current ratio device for use in constructing a current transformer comprises a first magnetic core, a second magnetic core, a measuring winding electromagnetically coupled with the first core but not with the second core, and a compensating winding electromagnetically coupled with both cores. An externally powered amplifier has its input connected to receive the voltage waveform across the measuring winding. Its output provides a compensating current through the compensating winding equal to a magnetizing current required to magnetize the second core. The amplifier output also provides a measuring current through the measuring winding in the direction opposite that of the compensating current and equal to the compensating current multiplied by the ratio of turns in the compensating and measuring windings. This device is a self-contained article of commerce that, when electromagnetically coupled (without electrical connection) to conventional primary and secondary windings and a burden, provides a current transformer with improved qualities. In particular, the magnetizing current needed by the transformer is provided by the separate current ratio device, thus avoiding the error inherent in current transformers that arises from the need to supply the magnetizing current from the primary circuit. Another disclosed feature is the ability to examine the waveform of the magnetizing current and in particular to detect the presence of even harmonics and hence a probability of direct current in the primary circuit.
-
Citations
21 Claims
-
1. A device for use in constructing an alternating current, current transformer, said device comprising
(a) a first magnetic core, (b) a second magnetic core, (c) a measuring winding having Nm turns electromagnetically coupled with the first core but not with the second core, (d) a compensating winding having Nc turns electromagnetically coupled with both cores, (e) an amplifier having an input and an output, (f) said input being connected to receive the waveform across the measuring winding, (g) said output being connected to the compensating winding to provide a compensating currect Ic through the conpensating winding equal to a magnetizing current Iμ - required to magnetize the second core, and
(h) said output being connected to the measuring winding to provide a measuring current Im through the measuring winding in a direction opposite to that of the compensating current and equal to ##EQU5## whereby, when primary and secondary windings are electromagnetically coupled with the cores to form an alternating current, current transformer and the secondary winding is connected to a burden, the magnetizing current Iμ
for such transformer is provided by the device. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
- required to magnetize the second core, and
-
19. A current transformer comprising:
-
(a) a first magnetic core, (b) a second magnetic core, (c) a measuring winding electromagnetically coupled with the first core but not the second core, (d) a primary winding electromagnetically coupled with both cores, (e) a secondary winding electromagnetically coupled with both cores to provide a secondary current Is when connected to a burden, (f) an amplifier having an input and an output, (g) said input being connected to receive the waveform across the measuring winding, (h) said output being connected to provide a current in the measuring winding equal to a magnetizing current Iμ
required to magnetize the second core,(i) the measuring and secondary windings being connected in parallel across the burden, and (j) means for observing the waveform of the current in the measuring winding. - View Dependent Claims (20, 21)
-
Specification