earthing systems, harmonics currents and gfp
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Earthing systems,Harmonics Currents and GFP
E54530
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Contents
Basic Principle 3
Earthing System Technique and Suitable Devices 6o IEC 60364o NEC and GFP
GFP Technique 19
Harmonics and Neutral conductor 27o network studieso Multi-source and Multi-groundingo conclusion NEC
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Basic Principle
Definitionn The 3 phasesn The Neutral conductor Nn The Protection conductor PE
Rolen Active conductors: 3 phases + Neutral
Normal current in these conductors
n Protection conductor PEInsulation Fault current
Measuring this fault current is the principle of Earthing System
E56885
L1L2L3N
PE
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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 = 0
o 2 ways to measure If ( =IPE)o don’t forget the Neutral
current
E56886
L1L2L3N
PE
A
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Basic Principles
Main Ideas
Measuring the current in the PE conductor is the principleof the Earthing System Techniques
Any other Normal current mustn’t flow in the PE (especially theNeutral current) in order to avoid the tripping nuisances
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Earthing System Techniques
The targetn Protection of peoplen Protection against fire risks
The economical constraintsn Continuity 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
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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
Rn RuPE
E56888
L1L2L3N
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Earthing system IEC 60364TT system
Earth fault study The fault current generates
a dangerous touch voltageUc > UL
The SCPD is usually not suitable for eliminating this typeof 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)
400V / 230V
L1L2L3N
If = 11,5A
Ru10 W
Rn10 W
Uo = 230 V
Uf =115 V
Exposedconductivemetallic part
E56889
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Earthing system IEC 60364 TN systemDefinition The star point of the LV
transformer is directlyconnected to an earthelectrode (source earth)
The exposed conductiveparts of the installation areconnected by the PE to thesame earth electrode
E56890
L1L2L3NPE
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Earthing system IEC 60364 TN-S systemDefinition The PE and Neutral
conductor are separateL1L2L3NPE
E56890
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Earthing system IEC 60364 TN-C systemDefinition The PE and Neutral
conductor are common = the PEN
E56892
L1L2L3PEN
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Earthing system IEC 60364 TN systemEarth fault study Fault current is equal to a
Phase/Neutral short-circuit
The fault current generatesdangerous touch voltage
Tripping of the circuit breakerby Short Time Protection orMagnetic
E56893
L1L2L3NPE
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Earthing system IEC 60364 IT systemDefinition The star point of the LV
transformer is not connectedto an earth electrode
The exposed conductive partsof the loads are connected bythe PE conductor to a commonearth electrode
E56894
L1L2L3NPE
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Earthing system IEC 60364 IT systemEarth 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
L1L2L3NPE
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Earthing system IEC 60364 IT systemPrinciple of the FTD (*) Detection of fault current
Type of FTD (*): Movable trackingn Fixed tracking
(*) Fault Tracking Device
E56896
L1L2L3NPE
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NEC / US Installation Standard
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
Defines IT - or IG (Insulated Grounding) - Systemand TN-S - or SG (Solidly Grounded) - System
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Protection against fireo the NEC imposes a maximum protection sensivity of: 1200 A
NEC / US Installation Standard
Example of an installation complying with the NEC
E56897
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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
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Ground Fault Protection GFP
GFP types
External CT installationo measurement of all Currents
(don’t forget the Neutral)
GFP co-ordinationo with the CB Magnetic or ST trippingo with the other GFP
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Residual Sensing: vectorialsum of the currents in thephases and the Neutral
GFP Types
E56899
L1L2L3N
E56898
L1
L2
L3
N
E56900
L1L2L3N
Source Ground Return: singlesensor placed on the Neutralearth link
Zero Sequence: - for lowcurrent detection - single
sensor placed all live conductors
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External CT installation
3 poles CB on 3 phases + N:on T option, the External CTmust be compulsory both
installed on primary ando connected on secondary
according to this diagram
E56901
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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 point
o logic (ZSI)
E56902
GFPupstream
GFPdowns-tream
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Upstream GFP / downstream SCPD
Discrimination rules
E56903
Down-streamshortdelay
Down-streamfuse 2
UpstreamGFP 1
D I30 %
I down-stream
I up-stream
T
I
step 2
step 1
Fuseso GFP sensibility setting up > 10
to 15 times down. fuse ratingo GFP I²t function Circuit breakerso GFP sensibility setting up > 1,5
times down. CB shorttime setting up
o GFP short delay setting up> down. CB breaking timesetting
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Upstream GFP / downstream GFP
Discrimination rules Ampermetrico up. GFP sensibility setting up
> 30% down. GFP senstivitysetting up
Chronometrico up. GFP short delay setting
up > down. SCPD breakingtime setting
o Dt1 (GFP1) > D t2 (GFP2)+ dt2 (SCPD2)
E56904
DownstreamGFP 2
UpstreamGFP 1
I down-stream
I up-stream
T
I1200 A 3000 A
30 %3000 A1s
step 2
step 1
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Is current
THDI = 53% Harmonics breakdown
Electrical diagram
capacitive impedancefor harmonics current
Fluorescent lighting
E56915
E56914
E56916
T
FLIsPh
N
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Computer power supply
Electrical diagram
single phase loadshigh level of harmonics
E56913
E56891
E56917
Is
CT
Is current
THDI = 115% Harmonics breakdown
I3=85%, I5=65%, I7=40%, I9=20%
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On the equipment:o capacitor, transformer, motor, alternator, …o overload and overheating, loss of the available power,
added vibration
Harmonics currentTheir effects
E56905
On the installationE M disturbance
On the Neutral conductorcumulating of harmonic 3 and their multiples
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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 carefultogether and Neutral to and PE are in and PE are in avoiding(PEN) be in contacts contacts contacts PE and
Neutralto be incontacts
There isn't any fault current in TT and IT System even if the PEand Neutral are in contact
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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
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Harmonics current / Earth fault (one source) Harmonics current without earth fault
no fault current measured by GFP
Service ground
PE GFP
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
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Harmonics current / Earth fault (two sources or more)
Both the main circuit breakers are closed, the bus coupleris open
E56907
Service groundService ground
Ground busPE
GFP GFP
Neutral
Loads
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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
PE
Service groundService ground
Ground bus
Neutral
Loads
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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 thiscurrent may be present throughout the metallic frames
Harmonics current / Earth fault (two sources or more)
E56910
GFP GFP
PE
Service groundService ground
Ground bus
Neutral
Loads
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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 GFP
PE
Service groundService ground
Ground bus
Neutral
Loads
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Breaking the Neutral conductor Is the more efficient solution Is the sole solution to avoid EM effects
How to improve network dependability ?
E56911
GFP GFP
PE
Service groundService ground
Ground bus
Neutral
Loads