if the relay is at the beginning of the line and the error is at the end; Does the resistive current decrease or increase along the line towards the fault location? Or is it the same size at both ends? That would be important to me. If my line is 10 km long, but I have 5 stations every 2 km, I need to know what resistive currents I have to expect at each station in order to set the relays correctly.
Here in Slovenia we use on medium voltage (20kV) passive coils (can choose steps of L) in paralel with fixed 80 ohm resistor for grounding neutral. The ohm resistor makes sure that current is below 150 amps so the pretection devices can diferentiate fault currents. What I dont understand, is if we look at figure at 5:00, i replace the 9900ohm resistor with a 80 ohm and then calculate the Xtotal = cca. 80ohm as indicated at 6:04 and Izero=cca 144amps which is not ok since that should already be the fault current. Should the 80 ohm real life resistance be modeled as a 240ohm resistance (3x80ohm) for my calculation?
So good! Very good and practical explanation!
if the relay is at the beginning of the line and the error is at the end; Does the resistive current decrease or increase along the line towards the fault location?
Or is it the same size at both ends? That would be important to me. If my line is 10 km long, but I have 5 stations every 2 km, I need to know what resistive currents I have to expect at each station in order to set the relays correctly.
Here in Slovenia we use on medium voltage (20kV) passive coils (can choose steps of L) in paralel with fixed 80 ohm resistor for grounding neutral. The ohm resistor makes sure that current is below 150 amps so the pretection devices can diferentiate fault currents.
What I dont understand, is if we look at figure at 5:00, i replace the 9900ohm resistor with a 80 ohm and then calculate the Xtotal = cca. 80ohm as indicated at 6:04 and Izero=cca 144amps which is not ok since that should already be the fault current.
Should the 80 ohm real life resistance be modeled as a 240ohm resistance (3x80ohm) for my calculation?