Insulated Cables

Capacitance of three core cables

Grounding

Advantages of neutral grounding:

• Voltage of phases are limited to phase to ground voltage.
• High voltages due to arcing grounds or transient line-ground faults are eliminated.
• Sensitive protective relays against LG faults can be used.
• Overvoltages due to lightening are discharged to ground.

Advantages of isolated neutral

• It is possible to maintain supply with fault on line.
• Interference with communication lines is reduced because of no Z sequence current.

Effective grounding systems:

X0 / X1 < 3

Least Expensive is = maxm Vphase= 0.8 V line

Series or Shunt Capacitor

Voltage Boost:

Shunt Capacitor: Evenly distributed over transmission line.

Series Capacitor: -----------------------I  I-------------------------
                                                   V1            V2
                                     Sudden change of voltage

• Shunt Capacitor improves power factor of the load whereas Series capacitor has little effect on pf.
• For long transmission line, where total reactance is high, series capacitors are effective for improvement of system stability.