This document discusses generator grounding and neutral grounding. It provides information on different grounding methods like solid grounding, low resistance grounding, and high resistance grounding. It explains that the method used depends on factors like system voltage level, generator design, fault current levels, and capacitive charging currents. High resistance grounding is generally preferred as it limits fault currents while allowing faults to be detected.
What is Grounding?
• Importance of Grounding
• Types of Grounding
• Applications of Grounding in power system
• Instruments employed in Grounding
• Grounding procedure & calculations
• Hazards due to lack of Grounding
• Good Grounding practice
• IEEE rules regarding Grounding
• Conclusion
Grounding or earthing offers two principal advantages. First, it provides protection to the power system. Secondly, earthing of electrical equipment ensures the safety of the persons handling the equipment.
Phase-ground short-circuit current of the transformer and the generator is calculated to determine the limit current of the neutral grounding resistor. The resistor is designed to limit the failure current to 10% of this short-circuit current. This value shall be optimal to allow detection of the selected limited fault current value by the relays. Therefore, primary value of the current transformers used on the neutral grounding resistor can be different from the limited fault current value.
More information:https://aktif.net/en/product-and-services/Grounding-Resistors/neutral-grounding-resistors
This PPT explains about the circuit breaker, and its types. Then about the need and purpose of the circuit breaker. And finally the testing and types of testing of circuit breakers.
The following topics are covered: components of power distribution systems, fuses, padmounted transformers, pole mounted transformers, vault installed transformers, transformer stations protection, transformer connections, thermometers, pressure relief devices, restricted ground faults, differential protection current transformers connections, overexcitation, inrush current, percentage differential relays, gas relays, characteristics of CTs.
Since the loads having the trends towards growing density. This requires the better appearance, rugged construction, greater service reliability and increased safety. An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. The interference from external disturbances like storms, lightening, ice, trees etc. should be reduced to achieve trouble free service. The cables may be buried directly in the ground, or may be installed in ducts buried in the ground.
What is Grounding?
• Importance of Grounding
• Types of Grounding
• Applications of Grounding in power system
• Instruments employed in Grounding
• Grounding procedure & calculations
• Hazards due to lack of Grounding
• Good Grounding practice
• IEEE rules regarding Grounding
• Conclusion
Grounding or earthing offers two principal advantages. First, it provides protection to the power system. Secondly, earthing of electrical equipment ensures the safety of the persons handling the equipment.
Phase-ground short-circuit current of the transformer and the generator is calculated to determine the limit current of the neutral grounding resistor. The resistor is designed to limit the failure current to 10% of this short-circuit current. This value shall be optimal to allow detection of the selected limited fault current value by the relays. Therefore, primary value of the current transformers used on the neutral grounding resistor can be different from the limited fault current value.
More information:https://aktif.net/en/product-and-services/Grounding-Resistors/neutral-grounding-resistors
This PPT explains about the circuit breaker, and its types. Then about the need and purpose of the circuit breaker. And finally the testing and types of testing of circuit breakers.
The following topics are covered: components of power distribution systems, fuses, padmounted transformers, pole mounted transformers, vault installed transformers, transformer stations protection, transformer connections, thermometers, pressure relief devices, restricted ground faults, differential protection current transformers connections, overexcitation, inrush current, percentage differential relays, gas relays, characteristics of CTs.
Since the loads having the trends towards growing density. This requires the better appearance, rugged construction, greater service reliability and increased safety. An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. The interference from external disturbances like storms, lightening, ice, trees etc. should be reduced to achieve trouble free service. The cables may be buried directly in the ground, or may be installed in ducts buried in the ground.
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
How is power transformer protected??? This provides a basic understanding of power transformer. Furthermore, the protective relay application on power transformer is included.
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It presented a good summary of switch gear components and types and practicing on AL.HAMOOL W.T.P M.D.B design using SIEMENS SIVACON S8
Main equipment in the power plant is Generator. It's cost is much higher than any other equipment so we will have to protect the generator from all the possible faults and errors.
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
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This Presentation is about l.v switch gear design, presented during the graduation project final discussion 15/7/2018.
It presented a good summary of switch gear components and types and practicing on AL.HAMOOL W.T.P M.D.B design using SIEMENS SIVACON S8
Main equipment in the power plant is Generator. It's cost is much higher than any other equipment so we will have to protect the generator from all the possible faults and errors.
In offshore oil & gas installation, the electrical power system consists of a large distribution
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Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Final project report on grocery store management system..pdfKamal Acharya
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This document will discuss each of the underlying technologies to create and implement an e- commerce website.
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This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
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A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
2. Power resistors
aren’t color-coded
Resistors have no
polarity
Know your system
before ordering
Resistors get hot
IEEE Std 32
Time Rating and Permissible Temperature
Rise for Neutral Grounding Resistors
Time Rating
(On Time)
Temp Rise (deg C)
Ten Seconds
(Short Time)
760o
C
One Minute
(Short Time)
760o
C
Ten Minutes
(Short Time)
610o
C
Extended Time 610o
C
Continuous 385o
C
3. • Greater safety for personnel
and equipment
• Increased service reliability
• Lower operating and
maintenance expense
• Reduced magnitude voltage
transients
• Simplified ground-fault
location
4. Ungrounded Generator
IEEE Std 242-2001 (Buff Book)
12.4 Generator Grounding
Generators are not often operated ungrounded. While this approach greatly
limits damage to the machine, it can produce high transient overvoltages
during faults and also makes it difficult to locate the fault.
5. NEMA Std MG 1-2003 Motors and Generators
32.34 Neutral Grounding
• For safety of personnel and to reduce over-voltages to ground, the generator
neutral is often either grounded solidly or grounded through a resistor or
reactor.
• The neutral may be grounded through a resistor or reactor with no special
considerations required in the generator design or selection unless the
generator is to be operated in parallel with other power supplies.
• The neutral of a generator should not be solidly grounded unless the
generator has been specifically designed for such operation
6. Minimize the damage for internal ground
faults
Limit mechanical stress in the generator from
external ground faults
Provide a means of system ground fault
detection
Coordinate with other system/equipment
requirements
7. Best suited for LV 3Ø, 4W
systems
Generator must be rated for use
as solidly grounded
System trips on first fault
Coordinated relay scheme may
be difficult
8. Generator neutral
unbonded from
case ground
Single neutral to
ground connection
Not considered
separately derived
systems
9. IEEE Std. 142-1991 (Green Book)
1.8.1 Discussion of Generator Characteristics
• …Unlike the transformer, the three sequence reactances of a generator are not equal. The
zero-sequence reactance has the lowest value, and the positive sequence reactance varies as
a function of time. Thus, a generator will usually have higher initial ground-fault current than
a three-phase fault current if the generator is solidly grounded. According to NEMA, the
generator is required to withstand only the three-phase current level unless it is otherwise
specified…
A generator can develop a significant third-harmonic voltage when loaded. A solidly grounded
neutral and lack of external impedance to third harmonic current will allow flow of this third-
harmonic current, whose value may approach rated current. If the winding is designed with a
two-thirds pitch, this third-harmonic voltage will be suppressed but zero-sequence impedance
will be lowered, increasing the ground-fault current…
Internal ground faults in solidly grounded generators can produce large fault currents. These
currents can damage the laminated core, adding significantly to the time and cost of
repair…Both magnitude and duration of these currents should be limited whenever possible.
10.
11. Low Resistance
More often at MV than LV
Less than 1000 amps for
ten seconds
Safely shutdown
Less damage than solidly
grounded
High Resistance
• More often at LV than MV
• Less than 10 amps
continuously
• Avoid shutdowns
• Least damage
12. Allows multiple layers of GFP, different
grounding methods, multiple generators
13. Medium Voltage Wye (Four-Wire) Connected Neutral Grounding Resistor
N
G
R
Transformer Neutral
Single
Phase
Grounding
Transforme
r
H1
H2
X1
X2
14. Usually paired with resistor to
give HRG at MV
Using line to neutral rated
resistor not size/cost efficient
Current normally less than 15A
Voltage equal to system line to
neutral voltage
Secondary typically 240 V
15. Conductor
Cable
insulation
Cable tray
A capacitor is an electrical device that can store energy in the electric
field between a pair of closely spaced conductors
(Thank you, Wikipedia)
• Capacitance re-charges during an arcing
fault, creating a larger overvoltage
• Overvoltage stresses insulation, leading to
further faults
16. In ungrounded systems, a
voltage is held on the system
capacitance after a fault. In an
arcing or intermittent fault, this
can lead to a significant voltage
build-up.
In a high resistance grounded
system, the resistance must be
low enough to allow the system
capacitance to discharge
relatively quickly.
17. Only discharges if Ro < Xco, so Ir > Ixco
( per IEEE142-1991 1.4.3)
◦ That is, resistor current must be greater than
capacitive charging current.
◦ ‘Rule of thumb’ numbers for 480V system
Transformer (kVA) Charging Current (A)
1000 0.2 - 0.6
1500 0.3 - 0.9
2000 0.4 - 1.2
2500 0.5 - 1.5
18. Chose fault current
higher than capacitive
charging current
Ex. If charging current
is determined to be 1.9
A, chose at least 3 A of
fault current
19. • Low resistance
grounding overcomes
capacitive charging
current
• After generator is
isolated the LRG is
removed, limiting fault
current to 5 A
20. Source Ground – monitors current flow in
system grounding conductor connected
between neutral and ground
Zero Sequence – detects vector unbalance of
current sum in each phase
Residual Connected – uses multiple CT’s and
relays, indicating any leakage to ground
21. Neutral current
includes ground fault
current and
harmonics/noise
Cumulative current
may be sufficient to
alarm/trip
Use filter/tuned relay
to avoid nuisance
alarms
Itotal = Ifault + I3rd + I5th +
I7th …
22. Network
Protection
Scheme
Faulted feeder has one
phase ∼ 0 V
Zero Sequence CT
detects fault current
Integration of HRG (via
Ethernet or RS-485)
allows for selective
tripping
23. Less sensitive than
ZSCT
Less costly than
ZSCT
Effective for feeder
identification
24. Easy if all generators are same design and pitch, always
operated at equal loading and are not switched with
three pole transfer switch
IEEE Std. 142-1991 (Green Book)
1.7.3 Paralleled Generators in an Isolated System
25. • Collecting neutrals and solidly grounding them
collectively creates a path for excessive 3rd harmonic
current
• Collecting neutrals through a single grounding resistor
may exceed the continuous duty of the resistor
26. AWG Stranded Copper Wire Resistance
Size Diameter Resistance @ 77ºF
AWG inch mm ohm/1000' ohm/km
18 0.0465 1.182 6.5227 21.400
14 0.0740 1.880 2.5756 8.450
12 0.0933 2.371 1.6215 5.320
10 0.1177 2.989 1.0180 3.340
8 0.1484 3.770 0.6401 2.100
6 0.1871 4.753 0.4023 1.320
4 0.2360 5.994 0.2533 0.831
0 0.3752 9.530 0.1003 0.329
NEC 250.36
In no case shall the ground
system conductor be smaller
than 8 AWG copper or 6 AWG
aluminum or copper-clad
aluminum.
27. • Separately grounding prevents circulating 3rd harmonic
current
• Must have means of disconnecting neutral if generator is
being serviced
• Multiple NGR’s has cumulative effect on ground fault
current
28. • A neutral deriving transformer holds the fault current
on the main bus to a consistent current rating
• Each generator is protected against internal faults by
HRG
29. • Creates a neutral point
in a 3 wire system
• Rated for system
voltage, expected
current and duty cycle
• Two methods to
establish a neutral
30. • High impedance to
normal phase currents
• Low impedance to fault
current
• Duty cycle same as
resistor
31. • Uses 3 industrial
control transformers
• Connect to create
neutral
• Low voltage resistor
32. Solidly ground only at LV when generator
permits, loads are non-critical and primarily
single phase
HRG at LV
LRG at MV or where charging current is
excessive
