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WHAT LIES BENEATH The Basics of a Substation Ground Grid

WHAT LIES BENEATH The Basics of a Substation Ground Grid. By Grant Gershmel. Today’s Presentation. Why a ground grid is needed inside a substation What happens when a substation isn’t properly grounded Real world examples of ground grids. Why is a grid needed?.

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WHAT LIES BENEATH The Basics of a Substation Ground Grid

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  1. WHAT LIES BENEATHThe Basics of a Substation Ground Grid By Grant Gershmel

  2. Today’s Presentation • Why a ground grid is needed inside a substation • What happens when a substation isn’t properly grounded • Real world examples of ground grids

  3. Why is a grid needed? • Fault in a substation makes ground a conductor, current must get back to source. • Ohms law V=I*R • Resistance in ground times fault current creates a ground potential rise.

  4. 2 Types of shock • Step Potential • Step across ground of unequal potential • Touch Potential • Touch something grounded

  5. How can we lower risk of shock? • Can’t lower system fault current • Can lower Ground Potential Rise (GPR) • Make the ground a better conductor by adding a ground grid. • Can insulate people from ground • Use an insulating material such as crush rock on top of the soil in a substation.

  6. Example Ground Grid • Substation Fence 100’ by 100’ • Soil resistivity averages 50 ohm-m • Fault will clear in 0.5 seconds • Six inches of crushed rock on top of grade • System fault current is 11,000 amps

  7. ===========< M A L Z ( SYSTEM INFORMATION SUMMARY ) >=========== Run ID......................................: Lunch Learn System of Units ............................: British Earth Potential/Magnetic Field Calculations : Potentials Number of Energization Source Busses .......: 1 Current Injected in Reference Source Bus....: 11000 Amps Energization Scaling Factor (SPLITS/FCDIST/specified)..: 1.0000 Number of Original Conductors ..............: 29 Number of Frequency Values to be Analyzed...: 1 Power Source Frequency......................: 60.000 Hertz Impedance Values are Based On...............: 60.000 Hertz Total Length of Conductor Network...........: 1925.7 feet 1 CHARACTERISTICS OF MEDIA SURROUNDING NETWORK ============================================ AIR LAYER : Resistivity............: 0.100000E+13 ohm-meters >>> SOIL TYPE : Uniform/Two Layer Horizontal TOP LAYER : Resistivity............: 50.0000 ohm-meters Thickness of Layer (H) : 5.0000 feet BOTTOM : Resistivity............: 20.0000 ohm-meters LAYER Case Number.................................: 1 Frequency for This Case.....................: 60.000 Hertz GPR of Reference Source Bus.(# 1)....Magn..: 4039.890 Volts Angle.: 0.4227644 degrees Impedance of Grounding System.........Magn..: 0.3672627 Ohms Angle.: 0.4227644 degrees

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