Charging current 1

[vennivivi]

Hi,

I`m looking for guidelines on how to measure the capacitive charging current on a 400 V 3500 kVA system.The intention is to limit the ground fault current close to the capacitive charging current.

Thanks.

Grundig

 

[waross]

After checking that the system is free of grounds, ground one phase and measure the current with an ammeter to estimate the capacitive current to ground. Measure phase currents with no load on the system to estimate combined phase to phase and phase to ground charging currents. How will you discriminate a ground fault from capacitive charging current if they are similar values? The charging current may change as motors and motor feeders are connected and disconnected. Depending on the type of cable, the ratio of phase to phase and phase to ground charging current may change. You may want to consider a higher current limit for your system.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

What location is this for? LV systems in most (all?) of Western Europe are required to be solidly earthed, and what you are proposing sounds like a high impedance earth of some form.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[tem1234]

http://www.i-gard.com/pdf/application guides/HRG Application Guide.pdf

 

[vennivivi]

Thanks all for the prompt replies. The intention of using high impedance grounding is to limit the magnitude of fault current to a safe value.

Grundig

 

[CoryA]

You are correct vennivivi- in general the minimum neutral-grounding-resistor let-through current should be equal to, or larger than the system charging-current. The document linked below contains detailed information about the selection of a neutral-grounding resistor.

Ground-Fault Detection, Charging Current, and Neutral-Grounding Resistor Selection

Typically, charging current will be 0.5 A per 1000 kVA on low-voltage systems, and 1.0 A per 1000 kVA on medium-voltage systems. Consequently, 5-A, 15-A, and 25-A grounding resistors are common.

---
Cory Anderson

http://startco.ca/