2. DETECT/PROTECT
I GARD’ HRG d d• I‐GARD’s HRG systems can detect a ground
fault, signal an alarm, and locate the affected
branch or feeder removing maintenance
personnel from the dangers of higher fault
currents.
MITIGATE
• I‐GARD’s FALCON provides arc flash mitigation
at the speed of light by using adjustable light
sensitivity to reduce arc‐flash energy with fast
detection and tripping, under 1ms.
ARC FLASH ANALYSIS
• I‐GARD’s ARC FLASH ANALYSIS will calculate your
Risk using IEEE and NFPA equations and
h d d d l hmethods and develop a comprehensive
protection plan to achieve a safer environment
for your people and plant.
5. Power System Grounding MethodsPower System Grounding Methods
UngroundedUngrounded
Solidly Grounded
Corner Delta GroundedCorner Delta Grounded
Mid phase grounded
Resistance Grounded
6. METAL ENCLOSURES
Solidly Grounded System
TO
LOAD
METAL ENCLOSURES
LOAD
BONDING
JUMPERJUMPER
Grounding and Bonding means a permanent and continuous conductive
path to the earth with sufficient ampacity to carry any fault current liable
t b i d it d f ffi i tl l i d t li it th ltto be imposed on it and of sufficiently low impedance to limit the voltage
rise above ground and to facilitate the operation of the protective
devices in the circuit.
8. RiskRisk
Electrical deficiencies are the leading ignition
source and cause of fire and explosion.p
Empirical data indicates that approximately 80%
of all electrical faults are ground faults.of all electrical faults are ground faults.
9. ConsequenceConsequence
From 1992 to 1999 the customers from one major
insurance company reported 228 losses that were
tt ib t d t d f lt ith t t l t f US $180attributed to ground faults with a total cost of US $180
million.
12. Bolted and Arcing Fault Characteristics
Arcing fault incident energy produced isArcing fault incident energy produced is
Greater at higher bolted fault current levels
Reduced by dynamic impedance (air)
And increased by the time duration of the arc
The most controllable factor in reducing the
incident energy is timeincident energy is time
Current flow in an arcing fault is approximately half
that of the bolted fault current (impedance of air)that of the bolted fault current (impedance of air)
13. Electrical Arc Factsec ca c ac s
• Arc is electric current passing through air
– Shock potential from contact with arc
• Temperature of arc plasma center is greater than 5000°F (some say
much higher)much higher)
– Radiated heat burns
• Pressure wave generated from arc
h i– Impact to hearing, etc
– Gaseous copper is 44,000 times solid
– Molten metal expelled from equipment at high speed– Molten metal expelled from equipment at high speed
• Arc fault results from something wrong or out of place
14. IEEE – Arcing FaultsIEEE Arcing Faults
• IEEE Std 242‐2001
Recommended Practice for the Protection and Coordination of Industrial andRecommended Practice for the Protection and Coordination of Industrial and
Commercial Power Systems
8.2.2
One disadvantage of the solidly grounded 480 V system involves the high
magnitude of destructive, arcing ground‐fault currents that can occur.g , g g
• IEEE Std 141‐1993
Recommended Practice for Electric Power Distribution for Industrial Plants
7.2.4
Th lidl d d h h hi h b bili f l i iThe solidly grounded system has the highest probability of escalating into a
phase‐to‐phase or three‐phase arcing fault, particularly for the 480 and 600 V
systems. The danger of sustained arcing for phase‐to‐ground fault…is also high
for the 480 and 600 V systems, and low or near zero for the 208 V system.
15. Solidly Grounded SystemsSolidly Grounded Systems
• Line to Ground Fault does not cause transient
overvoltage but often causes voltage sag
• Permits line‐to‐neutral loads (lighting, heating
cables)cables)
• Ground faults easy to locate, but cause unscheduled
service interruptionservice interruption
• Danger from low‐level arcing ground faults
• Since 1970s, ground fault protection mandatory for , g p y
solidly grounded 600V services rated 1000A and
higher by the CEC and the NEC
17. Ungrounded Systems ‐ Voltage g y g
Rise on Ground Fault VA-G = 600 V
VB-G = 0 V
VC-G = 600 V
V = 347 V
VA-G = 459 V
V 174 V
N
C A
C A
VA-G = 347 V
VB-G = 347 V
VC-G = 347 V
VN-G = 0 V
VN-G = 347 V
C A
VB-G = 174 V
VC-G = 459 V
VN-G = 174 V
60°
B
N
120°
C A
G
N
G
82°
B
No Ground Fault
Full Ground Fault on Phase B
B
Partial (50%) Ground Fault on Phase B
• Neutral point voltage is zero only when no ground fault present
• Neutral voltage rises whenever a ground fault is present
• Neutral voltage ranges from 0 V at no fault to 347 V at full fault
18. System Charging Current 3IC0System Charging Current 3IC0
AA
B
C
I 3II3 I3 IF = 3IC0IC03 IC03
19. Ungrounded SystemsUngrounded Systems
• Negligible fault current and no tripping on firstNegligible fault current and no tripping on first
ground fault
• Difficult to locate ground faults• Difficult to locate ground faults
• 5‐6 times transient voltage escalation on
i i i i d f lintermittent, sputtering arcing ground faults
due to DC voltage buildup across the stray
i dcapacitance to ground
21. Resistance GroundingResistance Grounding
• Used in Process Industries, Water and Waste Water,Used in Process Industries, Water and Waste Water,
Hospitals, Data processing Centers
• Used on MV systems to limit ground fault currenty g
• No arcing ground faults as with solid grounding
• No overvoltages as with ungrounded systemsNo overvoltages as with ungrounded systems
23. High Resistance GroundingHigh Resistance Grounding
Canadian Electrical Code and National ElectricCanadian Electrical Code and National Electric
Code permit continuous operation when
neutral grounding device is used to control theneutral grounding device is used to control the
ground current to a low value where :
A visual or audible alarm or both clearly–A visual or audible alarm, or both, clearly
identified to indicate the presence of a
ground fault is providedground fault, is provided.
24. High Resistance GroundingHigh Resistance Grounding
• Limit ground fault current to 10 A or lessg
• Provides service continuity on first ground fault
• Prevents arc flash incidents on first ground faultsg
• Allows faults to be located without de‐energizing
feeders (ground fault pulse locating)
• Used in continuous process industries, hospitals and
data centres where unscheduled downtime is costly
26. Distribution System Design Criteria
High Resistance Grounded
Reliabilit Po er contin it No trips on gro nd fa lt• Reliability Power continuity, No trips on ground fault
• Safe No Arc Blast or Flash Hazard on
Ground Fault
• Cost effective 3 Wire Systems are cheaper than 4 wireCost effective 3 Wire Systems are cheaper than 4 wire
• Scheduled Maintenance Faulty equipment can continue to run,
scheduled shut downs and lower
repair costsp
• Prioritized load Overcurrent Coordination maintained
Selective second fault protection
available
27. Low Resistance GroundingLow Resistance Grounding
• Used on medium voltage (MV) premises distribution g ( ) p
systems
• System charging current too high for high resistance
dgrounding
• Ground fault current limited to 25 – 400 A typically
T i d f lt• Trip on ground fault
• Prevents arc flash incident on ground fault
31. Resistance Grounding and IEEEResistance Grounding and IEEE
IEEE Std. 142‐1991 Recommended Practice for Grounding of Industrial and
C i l P S tCommercial Power System
1.4.3
The reasons for limiting the current by resistance grounding may be one or
more of the following:g
1. to reduce burning and melting effects in faulted electric equipment, such as
switchgear, transformers, cables and rotating machines.
2. to reduce mechanical stresses in circuits and apparatus carrying fault currents
3 to reduce electric‐shock hazards to personnel caused by stray ground fault3. to reduce electric shock hazards to personnel caused by stray ground fault
currents in the ground return path
4. to reduce arc blast or flash hazard to personnel who may have accidentally
caused or who happen to be in close proximity to the fault current
5 to reduce the momentary line‐voltage dip occasioned by the occurrence and5. to reduce the momentary line voltage dip occasioned by the occurrence and
clearing of a ground fault
32. ComparisonComparison
Ungrounded
Solidly
Grounded
Low Resistance
Grounded
High
Resistance
Grounded
Productivity Impact
System Type
System System System System
Overvoltages Severe None Limited Limited
Overcurrent - Damage
t i t f f lt U k S Mi i l N
Equipment
Damage
at point of fault Unknown Severe Minimal None
Maintenance Costs High Reasonable Reasonable Low
Continuous Operation
with Ground Fault
Possible but not
recommended Not possible Not possible Ideal
Relay Co ordination
a age
Relay Co-ordination
(Appropriate Equipment
Tripped, Ease of fault
location) Difficult Difficult Good Excellent
Personnel Safety to Personnel Poor Good Reasonable Excellent
Downtime
Personnel y
33. Insurance PerspectiveInsurance Perspective
“We tell our customers to first
determine whether they have a
resistance ground system or ground
fault detection.
D t i th t f d tDetermine the type of ground system
you have, and then, consider
conversion from an ungrounded
system to a resistance groundedsystem to a resistance grounded
system.
Using a high-resistance groundUsing a high resistance ground
system could knock 10% off the price
of insurance”.
34. Alarming and RelayingAlarming and Relaying
• Resistance grounding is not enoughResistance grounding is not enough
• Must sense ground faults
k i• Take action
• Either alarm only, and locate the fault
• Or trip on fault
35. Ground Fault Sensing
R id l CT M th dResidual CT Method
A
LOAD
B
IA
IB
C
N
IC
I
RELAY
IN
G
IG
• Typically 50 A to 1200 A pickup
Used on solidly grounded LV & MV systems
G
BONDING CONDUCTOR
GROUND FAULT CURRENT
• Used on solidly grounded LV & MV systems
37. Approaches For Ground DetectionApproaches For Ground Detection
• Voltage Sensing GF RelayVoltage Sensing GF Relay
• Current Sensing GF Relay
• Swbd Multi‐Feeder GF Alarm Relay• Swbd Multi‐Feeder GF Alarm Relay
• Swbd GF Relay with 2nd Fault Protection
GF R l f MCC’• GF Relay for MCC’s
• Combination wall‐mounted NGR and GF Relay
f R t fitfor Retrofits
40. Zero Sequence Current Sensing
and Arc Flash sensing Relay ‐ Sentri
• Selective – responds to leakage current to ground,Selective responds to leakage current to ground,
identifies faulted feeder
• 3‐ Optical sensor Inputs to detect arc flash p p
5 A
1 A
PICKUP
1 A
PICKUP
1 A
PICKUP
1 A
PICKUP
RRRR
5 A
NGR
PICKUP PICKUP PICKUP PICKUP
41. SENTRISENTRI
• Ground fault and arc flash built into 1 relay.
• Solidly grounded or Resistance grounded systems.
• 0.1 A to 1200 A trip settings.
• Can connect to 3 self‐monitoring arc flash sensors.
• Less than 1ms trip time on arc flash.
• Solid state relays with mechanical relay backup.
• Pre‐trip relay for indication prior to main relay tripping.
• 1 A and 5 A CT inputs as well as ZSCS inputs for sensitive ground fault
protection.
• Monitor current with mGARD‐SYM display from up to 50 relays.
• Modbus capability with mGARD‐SYM display.
• ZSI Zone Selective Instantaneous Protection
47. DSP OHMNI F tDSP OHMNI Features
• Identifying faulty phase and faulty feeder. First Fault Alarm y g y p y
and Selective Second Fault trip or First fault trip
• Modbus communications
• Enhanced relay security ‐ inrush detection prevents nuisance
tripping on severe magnetizing inrush
• DIN rail mounted – takes much less space on switchgear –DIN rail mounted takes much less space on switchgear
now fits in 22”‐wide sections
• Pulsing system
• Local Display ‐
52. A li ti C id tiApplication Considerations
1. Where to apply the Grounding Resistorpp y g
• At the transformer or
• At the main bus
2 When to apply first fault alarm only
3. When to add 2 nd fault trip function
• Selective Instantaneous feeder tripping
• Coordination with down stream Over current in 2nd
f lfault trip
4. When to use 1 st fault trip
54. Parallel GeneratorsParallel Generators
TYPICAL PARALLEL GENERATOR HIGH RESISTANCE GROUNDING SCHEME
GENERATORS 600V
600V
G G G G
Zero Sequence Current Sensors
(one per feeder; one per generator)
DDR2-6
DSA
15-20A, 3P
100 kAIC
To BMS
S-PM2
To BMS
5A, 600V
Zig-Zag Grounding2 - #16AWG, 24 Vdc
See Notes 1 and 2.
DS
Optional DS-PM2 Pulsing Card
5A, 347V Neutral
Grounding Resistor
Optional
Pulsing Resistor
Zig-Zag Grounding
Transformer
2 #16AWG, 24 Vdc
for pulsing control
Notes:
1. NGR/Zig-Zag assembly w ith pulsing resistor, IPC Part Number: OHMNI-6PM-5-ZZ
2. NGR/Zig-Zag assembly w ithout pulsing resistor, IPC Part Number: NTR600-5-ZZ
AWG#8 as per
CEC 10-1108(3)
55. HRG Retrofit of Parallel LV Generators
G G G G
15A, 3P
100 kAIC
TO
SCADA
52 52
52 5252
15A, 3P
100 kAIC
TO
SCADA
52 52
525252
52
V
A
GROUND FAULT
RELAY
V
A
GROUND FAULT
RELAY
ALARM
SLEUTH
SLEUTH
2A, 347V
2A, 600V
2A, 600V
PULSING
CONTACTOR
GROUND FAULT
RELAY
ALARM
ALARM
TO SCADA
ALARM
TO SCADA
PULSING
CONTACTOR
NGR 2A, 347V
PULSE TO 4A
NGR 2A, 347V
PULSE TO 4A
STOPLIGHT
WITH ZIG-ZAG,
VOLTMETER,
STOPLIGHT
WITH ZIG-ZAG,
VOLTMETER
V
A
2A, 347V
GROUND FAULT
RELAY
ALARM
V
A
ALARM
TO SCADA
VOLTMETER,
AMMETER
VOLTMETER,
AMMETER
ALARM
TO SCADA
52 5252
5252
52 5252
52 52
52
M2 M1
56. Combination NGR and GF RelayCombination NGR and GF Relay
• SLEUTHSLEUTH
• For retrofit
applicationsapplications
