27/35 9.5 Current and Power Measurement Most other current-sensing schemes depend on the magnetic field that surrounds any current-carrying conductor. The classical approach uses a current transformer and is restricted to AC current. Current transformers have the primary winding connected in series with the conductor carrying the current to be measured or controlled.The secondary winding is thus insulated from the high voltage and can then be connected to low-voltage metering circuits. Current transformers are also used for street lighting circuits to provide constant current to prevent flickering lights. 2If currents of general waveform(including DC)are to be measured, sensors based on the Hall effect,or the magnetoresistance (effect, are available. -A Hall generator is a magnetosensitive semiconductor that provide an output voltage proportional to the product of its current (which is held constant)and the component of magnetic field that is perpendicular to its surface. high voftage canen tansfo menUSD 2006pc /p6720hz Most other current-sensing schemes depend on the magnetic field that surrounds any current-carrying conductor. ①The classical approach uses a current transformer and is restricted to AC current. − Current transformers have the primary winding connected in series with the conductor carrying the current to be measured or controlled. The secondary winding is thus insulated from the high voltage and can then be connected to low-voltage metering circuits. − Current transformers are also used for street lighting circuits to provide constant current to prevent flickering lights. ②If currents of general waveform(including DC) are to be measured, sensors based on the Hall effect, or the magnetoresistance (磁阻) effect, are available. − A Hall generator is a magnetosensitive semiconductor that provide an output voltage proportional to the product of its current (which is held constant) and the component of magnetic field that is perpendicular to its surface. 9.5 Current and Power Measurement 27/35 9.5 Current and Power Measurement high voltage current transformer, USD $ 2000/pc http://www.diytrade.com/china/pd/6762036/high_voltage_current_transformer.html#normal_img 28/35