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Earthing systems, Harmonics Currents and GFP

Earthing systems, Harmonics Currents and GFP. E54530. Contents. Basic Principle 3 Earthing System Technique and Suitable Devices 6 o IEC 60364 o NEC and GFP GFP Technique 19

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Earthing systems, Harmonics Currents and GFP

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  1. Earthing systems,Harmonics Currents and GFP E54530

  2. Contents • Basic Principle 3 • Earthing System Technique and Suitable Devices 6oIEC 60364o NEC and GFP • GFP Technique 19 • Harmonics and Neutral conductor 27onetwork studieso Multi-source and Multi-groundingo conclusion NEC

  3. Basic Principle Definitionn The 3 phasesn The Neutral conductor Nn The Protection conductor PE RolenActive conductors: 3 phases + Neutral Normal current in these conductorsn Protection conductor PE Insulation Fault current Measuring this fault current is the principle of Earthing System E56885 L1 L2 L3 N PE

  4. Basic Principles PE conductor • The A point (star point of LV transformer) can be:o solidly groundedo isolatedo linked with an impedance to the PE • Fault current in A, the vectorial sum of the current is equal to 0SIph + IN+ I PE = 0o 2 ways to measure If ( =IPE)o don’t forget the Neutral current E56886 L1 L2 L3 N A PE

  5. Basic Principles Main Ideas • Measuring the current in the PE conductor is the principle of the Earthing System Techniques • Any other Normal current mustn’t flow in the PE (especially the Neutral current) in order to avoid the tripping nuisances

  6. Earthing System Techniques The targetn Protection of peoplen Protection against fire risks The economical constraintsnContinuity of the power supplyn Avoiding tripping nuisance due to the EM Effects IEC 60364 and NEC standards have got the same targets and the same constraints E56887

  7. Earthing system IEC 60364TT system Definition n The Neutral point of LV transformer is directly connected to an earth electrode n The exposed conductive parts of the installation are connected to an electrically separate earth electrode E56888 L1 L2 L3 N PE Rn Ru

  8. Earthing system IEC 60364TT system Earth fault study • The fault current generates a dangerous touch voltage Uc > UL • The SCPD is usually not suitable for eliminating this type of fault (If = a few A eg from 1 to 10 A) • Earth Leakage Relays (ELR) must be used (Setting at 300 mA to 10 A) E56889 Uo = 230 V L1 L2 L3 N 400V / 230V If = 11,5A Exposedconductivemetallic part Uf =115 V Rn 10 W Ru 10 W

  9. Earthing system IEC 60364TN system Definition • The star point of the LV transformer is directly connected to an earth electrode (source earth) • The exposed conductive parts of the installation are connected by the PE to the same earth electrode E56890 L1 L2L3 N PE

  10. Earthing system IEC 60364TN-S system Definition • The PE and Neutral conductor are separate E56890 L1 L2L3 N PE

  11. Earthing system IEC 60364TN-C system Definition • The PE and Neutral conductor are common = the PEN E56892 L1 L2L3 PEN

  12. Earthing system IEC 60364TN system Earth fault study • Fault current is equal to a Phase/Neutral short-circuit • The fault current generates dangerous touch voltage • Tripping of the circuit breaker by Short Time Protection or Magnetic E56893 L1 L2L3 N PE

  13. Earthing system IEC 60364IT system Definition • The star point of the LV transformer is not connected to an earth electrode • The exposed conductive parts of the loads are connected by the PE conductor to a common earth electrode E56894 L1 L2L3 N PE

  14. Earthing system IEC 60364IT system Earth Fault Study • There isn’t a fault currentn The fault is not dangerous but it must be signaled by PIM Principle of PIM • Injection of current,n Measurement of IR (*).(*) Insulation Resistance E56895 L1 L2L3 N PE

  15. Earthing system IEC 60364IT system Principle of the FTD (*) • Detection of fault current Type of FTD (*): • Movable trackingn Fixed tracking(*) Fault Tracking Device E56896 L1 L2L3 N PE

  16. NEC / US Installation Standard • Defines IT - or IG (Insulated Grounding) - System and TN-S - or SG (Solidly Grounded) - System • TN-S detailso Neutral conductor is not broken • the protective conductor PE is achieved by bonding the metallic parts of equipmento protection against fire is achieved by GFP

  17. E56897 NEC / US Installation Standard Example of an installation complying with the NEC • Protection against fireo the NEC imposes a maximum protection sensivity of: 1200 A

  18. Earthing System conclusions IEC 60364 NEC Earthing TN-C TN-S TT IT idemSystem TN-S I fault High High Low Very low High Protection SCPD SCPD RCD No problem SCPDof people Fire Forbidden Not Recommended Recommended GFPProtection recommended with RCD with RCD TT and IT Systems naturally manage the Fire Risk by limiting the fault current

  19. Ground Fault Protection GFP • GFP types • External CT installationomeasurement of all Currents (don’t forget the Neutral) • GFP co-ordinationowith the CB Magnetic or ST trippingo with the other GFP

  20. E56898 L1 L2 L3 N E56899 L1 L2 L3 N E56900 L1 L2 L3 N GFP Types • Residual Sensing: vectorial sum of the currents in the phases and the Neutral • Source Ground Return: single sensor placed on the Neutral earth link • Zero Sequence: - for low current detection - single sensor placed all live conductors

  21. External CT installation • 3 poles CB on 3 phases + N: on T option, the External CT must be compulsory both • installed on primary ando connected on secondary according to this diagram E56901

  22. GFP coordination Upstream GFP must becoordinated with any downstreamShort Circuit ProtectionDevice - SCPD - or GFP • Discrimination typeso current and Time discrimination with the respect of - asymptote at 1200A - 3000 A / 1s pointo logic (ZSI) E56902 GFP upstream GFP downs- tream

  23. E56903 T Down- stream short delay Down- stream fuse 2 Upstream GFP 1 step 2 step 1 D I 30 % I I down- stream I up- stream Upstream GFP / downstream SCPD Discrimination rules • Fuseso GFP sensibility setting up > 10 to 15 times down. fuse ratingo GFP I²t function • Circuit breakersoGFP sensibility setting up > 1,5 times down. CB short time setting upo GFP short delay setting up > down. CB breaking time setting

  24. E56904 T Downstream GFP 2 Upstream GFP 1 30 % 3000 A 1s step 2 step 1 I I down- stream I up- stream 1200 A 3000 A Upstream GFP / downstream GFP Discrimination rules • Ampermetrico up. GFP sensibility setting up > 30% down. GFP senstivity setting up • Chronometrico up. GFP short delay setting up > down. SCPD breaking time settingoDt1 (GFP1) > D t2 (GFP2) + dt2 (SCPD2)

  25. Is current THDI = 53% Harmonics breakdown Electrical diagram capacitive impedance for harmonics current Fluorescent lighting E56914 E56915 Ph Is FL T N E56916

  26. Electrical diagram single phase loads high level of harmonics Is current THDI = 115% Harmonics breakdown I3=85%, I5=65%, I7=40%, I9=20% Computer power supply E56913 E56891 Is C T E56917

  27. E56905 Harmonics currentTheir effects • On the equipment:o capacitor, transformer, motor, alternator, …o overload and overheating, loss of the available power, added vibration • On the installation E M disturbance • On the Neutral conductor cumulating ofharmonic 3 and their multiples

  28. Harmonics current conclusion IEC 60364 NEC Earthing TN-C TN-S TT IT idemSystem TN-S EM Forbidden Good Very good Very good Gooddisturbances PE and But be careful No problems No problems But be Neutral are avoiding PE even if Neutral even if Neutral careful together and Neutral to and PE are in and PE are in avoiding (PEN) be in contacts contacts contacts PE and Neutral to be in contacts There isn't any fault current in TT and IT System even if the PE and Neutral are in contact

  29. Application • Study of network • one source / two sourceso with harmonics • TN- S with Neutral conductor not broken (according to NEC standard)o with GFP E56912

  30. E56906 E56907 PE N GFP PE N GFP Ground bus Ground bus Service ground Service ground Harmonics current / Earth fault (one source) • Harmonics current without earth fault no fault current measured by GFP • Harmonics current and earth fault the right fault current is measured by GFP

  31. Harmonics current / Earth fault (two sources or more) • Both the main circuit breakers are closed, the bus coupler is open E56907 GFP GFP Neutral PE Ground bus Loads Service ground Service ground

  32. Harmonics current / Earth fault (two sources or more) • Harmonic current without earth fault a "false" earth fault current is measured, harmonic current are present throughout the metallic frames E56909 GFP GFP Neutral PE Loads Ground bus Service ground Service ground

  33. E56910 GFP GFP Neutral PE Loads Ground bus Service ground Service ground Harmonics current / Earth fault (two sources or more) • Earth fault with / without harmonic current the "right" earth fault current is not measured by the "right" GFP, a "false" earth fault current is measured by the other one this current may be present throughout the metallic frames

  34. E56911 GFP GFP Neutral PE Loads Ground bus Service ground Service ground How to improve Network dependability ? • Dealing with the problem by using particular GFP diagrams (Modified GFP, for instance) • Avoiding to have the problem by using a 4 poles switch on the bus coupler (to break the Neutral)

  35. How to improve network dependability ? Breaking the Neutral conductor • Is the more efficientsolution • Is the sole solution to avoid EM effects E56911 GFP GFP Neutral PE Loads Ground bus Service ground Service ground

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