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Project: T073700 #3414
 

 

Staff repairing High Voltage (HV) cables are subject to step and touch potentials arising from load and fault currents on parallel circuits. Also faults at terminating stations can be transferred along cables under repair where no parallel circuit is present. This report reviews the performance of existing grounding and bonding procedures. It recommends improved work practices and provides engineering guidelines to designers who specify cable configurations. The scope includes variations among High Pressure Fluid Filled (HPFF) or pipe type, Self Contained Fluid Filled (SCFF) or Low Pressure Fluid Filled (LPFF) and Cross Linked Polyethylene (XLPE) cables. It compares the performance of bare versus insulated ground continuity conductors. It reviews the benefits and drawbacks of isolating sheaths and phases at terminating stations versus bonding them to ground. The report shows how to calculate step and touch potentials due to load current on adjacent circuits. Potentials due to faults depend on many more parameters, including the ground impedance of the terminating stations or overhead line junction. This report offers close to 20 tables and 20 graphs, each describing the sensitivity of the potential to a different parameter. Maximum voltages obtained by these tools may be compared to allowable step and touch potentials, which are typically much lower than the estimated stresses. The user can then explore mitigation options such as isolating the ends of the cable, placing ground rods, using gradient control grids or mats and providing additional protection by using an insulating platform or blanket.

 

Keywords: HV cable maintenance, Ground potential rise, Step and touch potentials, Inductive coupling