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Earthing systems, Harmonics Currents and GFP E54530.

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Presentation on theme: "Earthing systems, Harmonics Currents and GFP E54530."— Presentation transcript:

1 Earthing systems, Harmonics Currents and GFP E54530

2 DBTP - 140pre - 06/99 - En 2 2 Contents Basic Principle3 Earthing System Technique and Suitable Devices6  IEC  NEC and GFP GFP Technique19 Harmonics and Neutral conductor27  network studies  Multi-source and Multi-grounding  conclusion NEC

3 DBTP - 140pre - 06/99 - En 3 3 Basic Principle Definition The 3 phases The Neutral conductor N The Protection conductor PE Role Active conductors: 3 phases + Neutral Normal current in these conductors Protection conductor PE Insulation Fault current Measuring this fault current is the principle of Earthing System E56885 L1 L2 L3 N PE

4 DBTP - 140pre - 06/99 - En 4 4 Basic Principles PE conductor The A point (star point of LV transformer) can be:  solidly grounded  isolated  linked with an impedance to the PE Fault current in A, the vectorial sum of the current is equal to 0  Iph + I N + I PE = 0  2 ways to measure If ( =I PE )  don’t forget the Neutral current E56886 L1 L2 L3 N PE A

5 DBTP - 140pre - 06/99 - En 5 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 DBTP - 140pre - 06/99 - En 6 6 Earthing System Techniques The target Protection of people Protection against fire risks The economical constraints Continuity of the power supply Avoiding tripping nuisance due to the EM Effects IEC and NEC standards have got the same targets and the same constraints E56887

7 DBTP - 140pre - 06/99 - En 7 7 Earthing system IEC TT system Definition The Neutral point of LV transformer is directly connected to an earth electrode The exposed conductive parts of the installation are connected to an electrically separate earth electrode RnRu PE E56888 L1 L2 L3 N

8 DBTP - 140pre - 06/99 - En 8 8 Earthing system IEC TT system Earth fault study The fault current generates a dangerous touch voltage Uc > U L The SCPD is usually not suitable for eliminating this type of fault (I f = a few A eg from 1 to 10 A) Earth Leakage Relays (ELR) must be used (Setting at 300 mA to 10 A) 400V / 230V L1 L2 L3 N If = 11,5A Ru 10  Rn 10  Uo = 230 V Uf = 115 V Exposed conductive metallic part E56889

9 DBTP - 140pre - 06/99 - En 9 9 Earthing system IEC TN 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 L2 L3 N PE

10 DBTP - 140pre - 06/99 - En 10 Earthing system IEC TN-S system Definition The PE and Neutral conductor are separate L1 L2 L3 N PE E56890

11 DBTP - 140pre - 06/99 - En 11 Earthing system IEC TN-C system Definition The PE and Neutral conductor are common = the PEN E56892 L1 L2 L3 PEN

12 DBTP - 140pre - 06/99 - En 12 Earthing system IEC TN 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 L2 L3 N PE

13 DBTP - 140pre - 06/99 - En 13 Earthing system IEC IT 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 L2 L3 N PE

14 DBTP - 140pre - 06/99 - En 14 Earthing system IEC IT system Earth Fault Study There isn’t a fault current The fault is not dangerous but it must be signaled by PIM Principle of PIM Injection of current, Measurement of IR (*). (*) Insulation Resistance E56895 L1 L2 L3 N PE

15 DBTP - 140pre - 06/99 - En 15 Earthing system IEC IT system Principle of the FTD (*) Detection of fault current Type of FTD (*): Movable tracking Fixed tracking (*) Fault Tracking Device E56896 L1 L2 L3 N PE

16 DBTP - 140pre - 06/99 - En 16 NEC / US Installation Standard TN-S details  Neutral conductor is not broken  the protective conductor PE is achieved by bonding the metallic parts of equipment  protection against fire is achieved by GFP Defines IT - or IG (Insulated Grounding) - System and TN-S - or SG (Solidly Grounded) - System

17 DBTP - 140pre - 06/99 - En 17 Protection against fire  the NEC imposes a maximum protection sensivity of: 1200 A NEC / US Installation Standard Example of an installation complying with the NEC E56897

18 DBTP - 140pre - 06/99 - En 18 Earthing System conclusions IEC 60364NEC EarthingTN-CTN-STTITidem SystemTN-S I faultHighHighLowVery lowHigh ProtectionSCPDSCPDRCDNo problemSCPD of people FireForbiddenNotRecommendedRecommendedGFP Protectionrecommendedwith RCDwith RCD TT and IT Systems naturally manage the Fire Risk by limiting the fault current

19 DBTP - 140pre - 06/99 - En 19 Ground Fault Protection GFP GFP types External CT installation  measurement of all Currents (don’t forget the Neutral) GFP co-ordination  with the CB Magnetic or ST tripping  with the other GFP

20 DBTP - 140pre - 06/99 - En 20 Residual Sensing: vectorial sum of the currents in the phases and the Neutral GFP Types E56899 L1 L2 L3 N E56898 L1 L2 L3 N E56900 L1 L2 L3 N Source Ground Return: single sensor placed on the Neutral earth link Zero Sequence: - for low current detection - single sensor placed all live conductors

21 DBTP - 140pre - 06/99 - En 21 External CT installation 3 poles CB on 3 phases + N: on T option, the External CT must be compulsory both  installed on primary and  connected on secondary according to this diagram E56901

22 DBTP - 140pre - 06/99 - En 22 GFP coordination Upstream GFP must be coordinated with any downstream Short Circuit Protection Device - SCPD - or GFP Discrimination types  current and Time discrimination with the respect of - asymptote at 1200A A / 1s point  logic (ZSI) E56902 GFP upstream GFP downs- tream

23 DBTP - 140pre - 06/99 - En 23 Upstream GFP / downstream SCPD Discrimination rules E56903 Down- stream short delay Down- stream fuse 2 Upstream GFP 1  I 30 % I down- stream I up- stream T I step 2 step 1 Fuses  GFP sensibility setting up > 10 to 15 times down. fuse rating  GFP I²t function Circuit breakers  GFP sensibility setting up > 1,5 times down. CB short time setting up  GFP short delay setting up > down. CB breaking time setting

24 DBTP - 140pre - 06/99 - En 24 Upstream GFP / downstream GFP Discrimination rules Ampermetric  up. GFP sensibility setting up > 30% down. GFP senstivity setting up Chronometric  up. GFP short delay setting up > down. SCPD breaking time setting   t1 (GFP1) >  t2 (GFP2) +  t2 (SCPD2) E56904 Downstream GFP 2 Upstream GFP 1 I down- stream I up- stream T I 1200 A3000 A 30 % 3000 A 1s step 2 step 1

25 DBTP - 140pre - 06/99 - En 25 Is current  THDI = 53% Harmonics breakdown Electrical diagram  capacitive impedance for harmonics current Fluorescent lighting E56915 E56914 E56916 T FL Is Ph N

26 DBTP - 140pre - 06/99 - En 26 Computer power supply Electrical diagram  single phase loads high level of harmonics E56913 E56891 E56917 Is C T Is current  THDI = 115% Harmonics breakdown  I3=85%, I5=65%, I7=40%, I9=20%

27 DBTP - 140pre - 06/99 - En 27 On the equipment:  capacitor, transformer, motor, alternator, …  overload and overheating, loss of the available power, added vibration Harmonics current Their effects E56905 On the installation E M disturbance On the Neutral conductor cumulating of harmonic 3 and their multiples

28 DBTP - 140pre - 06/99 - En 28 Harmonics current conclusion IEC 60364NEC EarthingTN-CTN-STTITidem SystemTN-S EMForbiddenGoodVery goodVery goodGood disturbancesPE andBut be carefulNo problemsNo problemsBut be Neutral areavoiding PEeven if Neutraleven if Neutralcareful togetherand Neutral toand PE are inand PE are inavoiding (PEN)be in contactscontactscontactsPE 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 DBTP - 140pre - 06/99 - En 29 Application Study of network  one source / two sources  with harmonics  TN- S with Neutral conductor not broken (according to NEC standard)  with GFP E56912

30 DBTP - 140pre - 06/99 - En 30 Harmonics current / Earth fault (one source) Harmonics current without earth fault no fault current measured by GFP Service ground PEGFP Ground bus N E56907 PE Service ground GFP Ground bus N E56906 Harmonics current and earth fault the right fault current is measured by GFP

31 DBTP - 140pre - 06/99 - En 31 Harmonics current / Earth fault (two sources or more) Both the main circuit breakers are closed, the bus coupler is open E56907 Service ground Ground busPE GFP Neutral Loads

32 DBTP - 140pre - 06/99 - En 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 PE Service ground Ground bus Neutral Loads

33 DBTP - 140pre - 06/99 - En 33 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 Harmonics current / Earth fault (two sources or more) E56910 GFP PE Service ground Ground bus Neutral Loads

34 DBTP - 140pre - 06/99 - En 34 Avoiding to have the problem by using a 4 poles switch on the bus coupler (to break the Neutral) Dealing with the problem by using particular GFP diagrams (Modified GFP, for instance) How to improve Network dependability ? E56911 GFP PE Service ground Ground bus Neutral Loads

35 DBTP - 140pre - 06/99 - En 35 Breaking the Neutral conductor Is the more efficient solution Is the sole solution to avoid EM effects How to improve network dependability ? E56911 GFP PE Service ground Ground bus Neutral Loads


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