Motor/System Charging current
Motor/System Charging current
(OP)
If I wanted to install a resistance grounded system (480 volt or 4160 volt), I know that there is a theoretical maximum resistance that is recommended. If I remember correctly, it is based on the system charging current. Can anyone help me with this issue?
Regards,
Raisinbran
Regards,
Raisinbran





RE: Motor/System Charging current
Normally this will be less than 5 amps.
RE: Motor/System Charging current
This is on a 480 volt system, but the same is true for the 4 kV systems used in many underground mines. Those cables are shielded, so I would think that the capacitance is considerably higher than the cables used at 480 volts. There have been no problems that I am aware of, but maybe that is because the cable is switched off with the motor, and the capacitance issues go away.
I am just curious if someone can shed some insight on this or if these high resistance grounded systems (0.5 ampere limit) are used in other industries.
Regards,
Raisinbran
RE: Motor/System Charging current
In general, it is better to have a little too much current than too little current, in terms of stabilizing the neutral point and limiting overvoltages.
The calculation to determine the exact system capacitance is difficult because the parameters are hard to come up with.
RE: Motor/System Charging current
Depends on the cables you are using. Please provide more info so we can give specific answers. If this is a mining underground, the capacitance of the cable used determines the charging current.
CODE
where:
C = capacitance of cable
e = 2.3 for XLPE; 2.8 for EPR
D = diameter over the insulation
d = diameter under the insulation
Icharging = 2 x pi x f x C x Eo
where:
Ic = mA / 1000 feet
f = frequency (Hz)
C = capacitance in F/1000ft
Eo = line-to-ground voltage (kV)
RE: Motor/System Charging current
Ground-Fault Detection, Charging Current and Neutral-Grounding Resistor Selection
The paper addresses your enquiry in detail.
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Cory Anderson
http://startco.ca/