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Entry type: FAQ, Entry ID: 21826790, Entry date: 07/12/2005

3VF with DI module in a grounded system (IT-network) - principle function

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3VF with DI module in a grounded system (IT-network) - principle function

3VF with DI module in a grounded system (IT-network) - principle function(Extract from operation Instruction for DI-module)Function
All conductors, including the neutral conductor N (if provided) are passed through the window of a summation current transformer in the same direction. In non-disturbed the sum of the operating currents equals zero.
If this equilibrium is disturbed, for example, by an earth fault (current flows back to earth to the grounded conductor of the transformer), the DI module trips the circuit-breaker after expiry of the set delay time td. Take note, if you have only 100V operation voltage:
Proper functioning of the DI module is guaranteed from a voltage difference of > = 50V onwards two phases or between one phase and the neutral conductor.
The functional test of the DI module with the "Test" button requires a voltage difference of > = 110V between terminals L1 and N(operation of test button causes instantaneous tripping of circuit breaker).
The attached diagram shows an ungrounded Transformer (IT-system)In IT system networks the capacity of network to ground must be sufficient to allow a fault current to flow which has the same level as the rated fault current.

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