| 摘要 |
PURPOSE:To surely detect speed even though an output current is large by applying a current in the reverse direction of the output current by providing a control winding in a current transformer in the control where a control section detects the drive speed of a motor in response to the output of the current transformer. CONSTITUTION:A current transformer 4 has a control winding 8 in addition to a primary winding 6 and a secondary winding 7, and a control power supply 13 is provided for applying a current to the control winding 8 in the reverse direction of that of the output current flowing through the primary winding 6. By doing this, the current transformer 4 can be used in the region where the magnetic flux density has a great fluctuation in response to the fluctuation in the intensity of the magnetic field. Therefore, any decrease in the amplitude of the output of the secondary winding 7 can be suppressed against a large current so that the speed detection of a motor 1 can be reliably performed by a control section 3. |
