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ELECTRIC POWER SYSTEM GROUNDINGBySteve Blumeswblume@gmail.com(760) 612-8488GND1

Electric Power System GroundingPresentation Outline3-Phase Power SystemsReasons for Grounding and BondingSubstation, Transmission, and Distribution GroundingPower Faults and Lightning StrikesFault current distributionGround Potential Rise (GPR)Touch and Step PotentialsSafetyCopyright Protected – Blume Consulting 2

3-Phase Power SystemsSingle Phase GenerationCopyright Protected – Blume ConsultingFaraday’s Law:Voltage is produced on any conductor ina changing magnetic field! VoltsN- VoltsS3

3-Phase Power SystemsThree Phase GenerationNCopyright Protected – Blume Consulting Volts- VoltsS4

3-Phase Generator3-Phase AC GeneratorControlsAC Voltage OutCopyright Protected – Blume ConsultingExciterField/RotorNSStatorSlip Rings5

3-Phase Power SystemsCopyright Protected – Blume ConsultingSymmetrical ConnectionsWinding 1Winding 3Winding 1Winding 2ToLoadWinding 2NeutralToLoadWinding 3DeltaWYE6

3-Phase Power SystemsNeutral vs. Ground vs. BondLWinding1 Winding 2LWinding 3NeutralTo the loadNBondGroundL Grounding: the neutral is connected to earth viaground rods, grids, or conductors. Unbalancedneutral currents flow through the earth connection. Bonding: electrical connectionsbetween equipment andgrounded conductors to provideequipotential during faults.7Copyright Protected – Blume ConsultingWYENeutral

3-Phase Power SystemsReasons for Grounding and BondingControl power fault and Lightning strike currentsProtect equipment and trip energizing equipmentEquipotential GroundingEffects of Ground Potential RiseTouch and Step PotentialsDetect and minimize unbalanced currentsCopyright Protected – Blume Consulting 8

3-Phase Power SystemsCopyright Protected – Blume ConsultingSystem Grounding9

3-Phase Power SystemsSubstation GroundingCopyright Protected – Blume ConsultingGround gridsEquipmentStructuresFence10

3-Phase Power SystemsTransmission Line Shielding and GroundingShield Wires andOptical Ground WiresCopyright Protected – Blume ConsultingLightning Protection through Grounding60º60ºRodLine60º shield angle is typical11

3-Phase Power SystemsDistribution Lines: Wye ConfigurationCopyright Protected – Blume ConsultingMulti-grounded Neutral: Atleast four times per mile per theNational Electric Safety CodeMulti-GroundedNeutralCBNANGrounded neutralA12

3-Phase Power SystemsDistribution Lines: Delta ConfigurationCCopyright Protected – Blume ConsultingDelta three-phase distribution lines use three wires, no neutral. Transformertanks and lightning arresters are connected to ground rods at each pole.BBAANo groundedneutral!13

3-Phase Power SystemsBalanced ConditionsBalanced 3-Phase CurrentsGeneratorLoadTransformerCopyright Protected – Blume ConsultingSourceGridGridNO Earth Return Current!14

Power System FaultSubstation FaultLightning RodsCopyright Protected – Blume ConsultingPower Faultor Lightning StrikeGround Grid WiresGround Rods15

Power System FaultGround Potential Rise (GPR) – unbalanced currentPhase CurrentsGPRsXFMRCopyright Protected – Blume ConsultingGGridGridAssumptionsEarth Return Current Homogenous Soil (i.e., round contours) Power Fault at substation transformer bushing16

Power System FaultMultiple Ground Paths and GPR’sUn-Balanced 3-Phase CurrentNeutral CurrentsGGPRsCopyright Protected – Blume ConsultingShield Wire CurrentsXFMRGridGridEarth Return Current17

Power System FaultMetropolitan GridsGCopyright Protected – Blume ConsultingUn-Balanced 3-Phase CurrentXFMRNO Earth Return Currents!!!NO GPR!!!Current flow through grid: YESVoltage drop on grid: YES18

Power System FaultGPR - Zone of InfluenceSubstationGnd GridCopyright Protected – Blume Consultingx300 volt pointGPR“Zone of Influence”Homogeneous Soil19

Electrical Grounding SafetyTouch & Step PotentialsCopyright Protected – Blume ConsultingSubstationsStructuresGround GridTouchStepGround Potential RiseDistance From Fault20

Electrical Grounding SafetyHuman CharacteristicsNOTE: Current path through body is a critical factor!The average 155-lb man takes the following currents:1.2ma to produce a slight tingling feeling, called perception threshold9ma can produce a painful shock, but still below lock-on conditions16ma can cause the loss of muscle control23ma can cause difficulty breathing50ma approximately can cause burning100ma for 3 seconds can cause heart fibrillation1 amp for 30ms can cause heart fibrillationCopyright Protected – Blume Consulting 21

Electrical Grounding Safety2-Ways to be Safe!CONDUCTION – Equipotential GroundingThe use of materials in situations where good conduction (low resistance) will result in small potentialdifferences and high current flow. (Ground Jumpers)Copyright Protected – Blume ConsultingISOLATION – Personal Protective EquipmentThe use of materials in situations where good insulation (high resistance) will result in large voltagedifferences and low current flow. (Rubber Insulation)22

Electrical Grounding SafetyConduction - Ground Source PreferencesCopyright Protected – Blume Consulting1. Substation Ground Grid2. Multi-Grounded Neutral (MGN)3. Steel Tower or Steel Pole4. Driven or Screw-in Ground Rods5. Anchor Rods23

Electrical Grounding SafetyConduction - Jumper Voltage Drop ProtectionYOUCopyright Protected – Blume ConsultingFAULT CURRENTYOURJUMPERSEarth"TRUE" GROUND24

Electrical Grounding SafetyCopyright Protected – Blume ConsultingConduction - Transmission Structure SafetyExample:Single PointGrounding ametal latticetowerSteel TowersExample: Single Point Grounding for one workeron a wooden “H” frame structure with overheadground wiresWood Structures25

Electrical Grounding SafetyConduction - Distribution Structure SafetyCopyright Protected – Blume ConsultingExample: Worker minimizingexposure to touch potential byoperating equipment controlsfrom a conductive matSingle Point GroundingVehicle Arrangement26

Electrical Grounding SafetyCopyright Protected – Blume ConsultingConduction - Underground EquipmentNeutrals and Lightning Arresters are Grounded.27

Electrical Grounding SafetyCopyright Protected – Blume ConsultingIsolation - Personal Protective Equipment (PPE)28

Electric Power System GroundingAny Questions?Thank you!BySteve Blumeswblume@gmail.com(760) 612-8488

Presentation Outline Electric Power System Grounding 3-Phase Power Systems Reasons for Grounding and Bonding Substation, Transmission, and Distribution Grounding Power Faults and Lightning Strikes Fault current distribution Ground Poten