Type of DC Network: Network with one terminal grounded

 

DC Network with one terminal grounded | Source: ABB

This type of network is obtained by connecting one terminal to the ground. This connection type allows the overvoltages due to static electricity to be discharged to the ground.


Grounding Solution | Source: ABB 


Fault types in a network with one terminal grounded. 

In the following examples, the grounded terminal is the negative one.


Fault A

The fault between the two terminals is a short-circuit current fed by the full voltage V. The breaking capacity of the circuit breaker shall be sized according to the short-circuit current relevant to such fault.

Sample Fault: Fault at A


Related Article: 


Fault B

The fault on the non-grounded terminal sets up a current involving the overcurrent protections as a function of the soil resistance.

Sample Fault: Fault at B

Fault C

The fault on the grounded terminal sets up a current which affects the overcurrent protections as a function of the soil resistance. This current presents an extremely low value because it depends on the impedance of the soil and the V is next to zero because the voltage drop on the load further reduces its value.

Sample Fault: Fault at C

With this type of network, the fault type which affects the version of the circuit breaker and the connection of the poles is fault A (between the two terminals). However, it is also necessary to take into consideration the fault between the non-grounded terminal and the ground itself (fault B) because as described above, a current could flow at full voltage. For this reason, all the circuit breaker poles necessary for protection must be connected in series on the non-grounded terminal.

Source: 

  • ABB Circuit Breakers for Direct Current Applications | pp. 16-17
  • Publisher: ABB
  • Download Here

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