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DB400 solid current transformers are used with EM72 and other suitable electricity meters. A suitable size current transformer is selected according to the power measurement requirements. |
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| Application Note: |
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When using CT’s with an aperture, it is possible to reduce primary ratio by passing multiple turns of the primary conductor cable through the aperture. The resultant ratio will be CT primary divided by the number of turns, e.g. a 200/5A CT with the primary conductor passed through the aperture twice will produce a CT ratio of 100/5A.
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| Secondary Lead Burden: |
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When selecting a current transformer, it is important to consider the power absorbed by the cables connected between the CT secondary terminals and the measuring instrument. The resultant cable burden should be added to the equipment burden, and the total should not exceed the available VA of the CT. Where the current transformer is to be mounted remotely, a -/1A secondary is recommended.
For every 10°C variation in temperature, the VA absorbed by the cables will increase by 4% (Ambient Reference Temp °C). |
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| An example: Cable size from CT to meter 2.5 mm2. Length of cable 5m. Burden with 5A CTs is about 2.5VA. With 150A CT the maximum burden to reach accuracy class 1 is 3VA, hence the installation would achieve accuracy class 1 for the 150A CT. If the CT primary current were above 300A accuracy class 0.5 would be achieved. |
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