Monitoring DC current for power systems monitoring
November 2004
Electrical Power & Protection
DC power is frequently used in many industrial applications including, petrochemical, telecommunications metals and computers. In these applications batteries are frequently used to provide power back-up to protect against power failure.
Monitoring and measurement of DC current is therefore critical for monitoring and regulating these DC systems. Current transformers cannot be used for these DC systems and shunts require supply disruption for installations and introduce losses to the system (Joule effect), Hall effect transducers are therefore the solution.
With over 30 years experience of current measurement using Hall effect technology, LEM has introduced a product range specifically to meet the requirements of the industrial environment. The products are easy to install and require minimal maintenance.
The DK-B, HTR and HOP series cover a wide range of current measurement (50 A to 2 kA), with a variety of physical sizes designed for fitting to cables and bus bars. Voltage and current output options are available, ensuring compatibility with control systems such as PLCs or DCSs.
Clamp-on design facilitates easy installation to cable or bus bars making it suitable for retrofitting existing installations, allowing modernisation and monitoring without interruption of the supply. Typical applications would include:
Industrial electrical heaters
Electric heaters are used to supply heat to manufactured products, storage systems and recirculating material. If a heater fails, the batch or process may have to be scrapped. A realtime indication of heater status improves product quality and production efficiency. Applying a current transducer to the heater lead and integrating the signal with the DCS will allow the user to monitor the heater's on/off status, alarm the failure and automatically switch on a back-up heater.
Telecommunications
Some 'cells' or substations and transmitters/receivers for mobile phones are in remote locations. To keep these units in good working order, manufacturers use energy management systems that monitor the network power supply and auxiliary batteries and activate an alarm should problems develop. Hall transducers are used for the current measurement.
A transducer for the AC to DC converters is included in each conventional power supply application. The transducer can monitor the output current of the power plant going up to 10 kA. Another monitors the current from the battery banks installed to back up the switches. Currents here fall in the range 200 A to 1 kA. The final stage would be the current measurement in the 48 V power distribution lines - a Hall transducer for each circuit.
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