Submit Search
Upload
Grounding pad mounted transformers
•
0 likes
•
719 views
J
Jimmy Chaparro
Follow
Grounding Pad Mounted Transformers
Read less
Read more
Engineering
Report
Share
Report
Share
1 of 4
Download now
Download to read offline
Recommended
Grounding pad mounted transformers
Grounding pad mounted transformers
Jimmy Chaparro
Design of substation (with Transformer Design)
Design of substation (with Transformer Design)
SayanSarkar55
Electric power substation
Electric power substation
qwerty25ty
Sample calculation-for-differential-relays
Sample calculation-for-differential-relays
Roberto Costa
Gas insulated substation
Gas insulated substation
sharique_64
Gas insulated substation
Gas insulated substation
RaushanKumar582
Ehv substation
Ehv substation
Demsew Mitiku
Neutral grounding resistor
Neutral grounding resistor
Nithin Kumar K S
Recommended
Grounding pad mounted transformers
Grounding pad mounted transformers
Jimmy Chaparro
Design of substation (with Transformer Design)
Design of substation (with Transformer Design)
SayanSarkar55
Electric power substation
Electric power substation
qwerty25ty
Sample calculation-for-differential-relays
Sample calculation-for-differential-relays
Roberto Costa
Gas insulated substation
Gas insulated substation
sharique_64
Gas insulated substation
Gas insulated substation
RaushanKumar582
Ehv substation
Ehv substation
Demsew Mitiku
Neutral grounding resistor
Neutral grounding resistor
Nithin Kumar K S
Facts
Facts
Ahmed M. Elkholy
Principles of Cable Sizing
Principles of Cable Sizing
Leonardo ENERGY
Gas insulated substation
Gas insulated substation
himanshu kumar
Substation grounding grid design using Alternative Transients Program-ATP and...
Substation grounding grid design using Alternative Transients Program-ATP and...
Jose Dariel Arcila
Troubleshooting of Electrical Switchyard & Substation Equipments
Troubleshooting of Electrical Switchyard & Substation Equipments
Marcep Inc.
Ppt
Ppt
gudlavalleru engineering college
EDS Unit 3 (Part 1).pptx
EDS Unit 3 (Part 1).pptx
Dr. Rohit Babu
Ieee transfer schemes for M-T-M distribution systems
Ieee transfer schemes for M-T-M distribution systems
Vincent Wedelich, PE MBA
Bus Bar protection
Bus Bar protection
srini09
Phasor Measurement Unit (PMU) Implementation and Applications
Phasor Measurement Unit (PMU) Implementation and Applications
Power System Operation
Types Of Substations
Types Of Substations
sapna186
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
Jobin Abraham
Gis substation
Gis substation
Asif Eqbal
Lv switchgear & lv cable sizing
Lv switchgear & lv cable sizing
Asif Eqbal
IEEE substation design
IEEE substation design
Vincent Wedelich, PE MBA
Protection of transmission lines (distance)
Protection of transmission lines (distance)
Rohini Haridas
Power cables
Power cables
ahmdfurkan
Lv genset protection
Lv genset protection
rkdheepan
132kV GSS ppt
132kV GSS ppt
Abhishek Dosaya
Subestacion mtbt
Subestacion mtbt
Mario Victor Soto Vargas
11.[21 28]voltage stability improvement using the 21st century power transformer
11.[21 28]voltage stability improvement using the 21st century power transformer
Alexander Decker
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
IJRST Journal
More Related Content
What's hot
Facts
Facts
Ahmed M. Elkholy
Principles of Cable Sizing
Principles of Cable Sizing
Leonardo ENERGY
Gas insulated substation
Gas insulated substation
himanshu kumar
Substation grounding grid design using Alternative Transients Program-ATP and...
Substation grounding grid design using Alternative Transients Program-ATP and...
Jose Dariel Arcila
Troubleshooting of Electrical Switchyard & Substation Equipments
Troubleshooting of Electrical Switchyard & Substation Equipments
Marcep Inc.
Ppt
Ppt
gudlavalleru engineering college
EDS Unit 3 (Part 1).pptx
EDS Unit 3 (Part 1).pptx
Dr. Rohit Babu
Ieee transfer schemes for M-T-M distribution systems
Ieee transfer schemes for M-T-M distribution systems
Vincent Wedelich, PE MBA
Bus Bar protection
Bus Bar protection
srini09
Phasor Measurement Unit (PMU) Implementation and Applications
Phasor Measurement Unit (PMU) Implementation and Applications
Power System Operation
Types Of Substations
Types Of Substations
sapna186
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
Jobin Abraham
Gis substation
Gis substation
Asif Eqbal
Lv switchgear & lv cable sizing
Lv switchgear & lv cable sizing
Asif Eqbal
IEEE substation design
IEEE substation design
Vincent Wedelich, PE MBA
Protection of transmission lines (distance)
Protection of transmission lines (distance)
Rohini Haridas
Power cables
Power cables
ahmdfurkan
Lv genset protection
Lv genset protection
rkdheepan
132kV GSS ppt
132kV GSS ppt
Abhishek Dosaya
Subestacion mtbt
Subestacion mtbt
Mario Victor Soto Vargas
What's hot
(20)
Facts
Facts
Principles of Cable Sizing
Principles of Cable Sizing
Gas insulated substation
Gas insulated substation
Substation grounding grid design using Alternative Transients Program-ATP and...
Substation grounding grid design using Alternative Transients Program-ATP and...
Troubleshooting of Electrical Switchyard & Substation Equipments
Troubleshooting of Electrical Switchyard & Substation Equipments
Ppt
Ppt
EDS Unit 3 (Part 1).pptx
EDS Unit 3 (Part 1).pptx
Ieee transfer schemes for M-T-M distribution systems
Ieee transfer schemes for M-T-M distribution systems
Bus Bar protection
Bus Bar protection
Phasor Measurement Unit (PMU) Implementation and Applications
Phasor Measurement Unit (PMU) Implementation and Applications
Types Of Substations
Types Of Substations
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
POWER SYSTEM PLANNING AND DESIGN. DESIGN OF EHV TRANSMISSION LINES & BUNDLED ...
Gis substation
Gis substation
Lv switchgear & lv cable sizing
Lv switchgear & lv cable sizing
IEEE substation design
IEEE substation design
Protection of transmission lines (distance)
Protection of transmission lines (distance)
Power cables
Power cables
Lv genset protection
Lv genset protection
132kV GSS ppt
132kV GSS ppt
Subestacion mtbt
Subestacion mtbt
Similar to Grounding pad mounted transformers
11.[21 28]voltage stability improvement using the 21st century power transformer
11.[21 28]voltage stability improvement using the 21st century power transformer
Alexander Decker
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
IJRST Journal
Cascade Protection with Transient Voltage copy
Cascade Protection with Transient Voltage copy
Jesus A Borjas P.E., California
Assessment of Electric Field Distribution Inside 500/220 kV Open Distribution...
Assessment of Electric Field Distribution Inside 500/220 kV Open Distribution...
IJAPEJOURNAL
Techno economic study of series current limiting reactor and its impact in th...
Techno economic study of series current limiting reactor and its impact in th...
Alexander Decker
Training at 132 kv substation
Training at 132 kv substation
Tejveer Choudhary
Technical presentation on modern earthing
Technical presentation on modern earthing
Pankaj Chakraborty
IRJET - A Zero Voltage Switching Pulse Width Modulated Multilevel Buck Converter
IRJET - A Zero Voltage Switching Pulse Width Modulated Multilevel Buck Converter
IRJET Journal
Wireless Power Transfer Project
Wireless Power Transfer Project
sagnikchoudhury
WIRELESS POWER TRANSMISSION Project
WIRELESS POWER TRANSMISSION Project
sagnikchoudhury
Introduction to mv switchgear
Introduction to mv switchgear
Modal Holong Education
kamal project ppt
kamal project ppt
kamaldeep singh
International Journal of Computational Engineering Research (IJCER)
International Journal of Computational Engineering Research (IJCER)
ijceronline
Analysis of example_capacitor_bank_switching_solution_and_recommendations_for...
Analysis of example_capacitor_bank_switching_solution_and_recommendations_for...
f95346
132 33kv substation documentation
132 33kv substation documentation
Rajashekar Gurrala
Your electrical safety specilist for all equipments Powered AC and DC
Your electrical safety specilist for all equipments Powered AC and DC
Mahesh Chandra Manav
High efficiency three phase nine level diode clamped multilevel inverter
High efficiency three phase nine level diode clamped multilevel inverter
International Journal of Science and Research (IJSR)
2
2
swathi99
Investigation of Electric Field Distribution Inside 500/220 kV Transformation...
Investigation of Electric Field Distribution Inside 500/220 kV Transformation...
IJAPEJOURNAL
Analsis of very fast transient over voltages in gas insulated substations
Analsis of very fast transient over voltages in gas insulated substations
eSAT Journals
Similar to Grounding pad mounted transformers
(20)
11.[21 28]voltage stability improvement using the 21st century power transformer
11.[21 28]voltage stability improvement using the 21st century power transformer
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
Review of Reduction of Leakage Current in Cascaded Multilevel Inverter
Cascade Protection with Transient Voltage copy
Cascade Protection with Transient Voltage copy
Assessment of Electric Field Distribution Inside 500/220 kV Open Distribution...
Assessment of Electric Field Distribution Inside 500/220 kV Open Distribution...
Techno economic study of series current limiting reactor and its impact in th...
Techno economic study of series current limiting reactor and its impact in th...
Training at 132 kv substation
Training at 132 kv substation
Technical presentation on modern earthing
Technical presentation on modern earthing
IRJET - A Zero Voltage Switching Pulse Width Modulated Multilevel Buck Converter
IRJET - A Zero Voltage Switching Pulse Width Modulated Multilevel Buck Converter
Wireless Power Transfer Project
Wireless Power Transfer Project
WIRELESS POWER TRANSMISSION Project
WIRELESS POWER TRANSMISSION Project
Introduction to mv switchgear
Introduction to mv switchgear
kamal project ppt
kamal project ppt
International Journal of Computational Engineering Research (IJCER)
International Journal of Computational Engineering Research (IJCER)
Analysis of example_capacitor_bank_switching_solution_and_recommendations_for...
Analysis of example_capacitor_bank_switching_solution_and_recommendations_for...
132 33kv substation documentation
132 33kv substation documentation
Your electrical safety specilist for all equipments Powered AC and DC
Your electrical safety specilist for all equipments Powered AC and DC
High efficiency three phase nine level diode clamped multilevel inverter
High efficiency three phase nine level diode clamped multilevel inverter
2
2
Investigation of Electric Field Distribution Inside 500/220 kV Transformation...
Investigation of Electric Field Distribution Inside 500/220 kV Transformation...
Analsis of very fast transient over voltages in gas insulated substations
Analsis of very fast transient over voltages in gas insulated substations
Recently uploaded
Application of Residue Theorem to evaluate real integrations.pptx
Application of Residue Theorem to evaluate real integrations.pptx
959SahilShah
CCS355 Neural Network & Deep Learning UNIT III notes and Question bank .pdf
CCS355 Neural Network & Deep Learning UNIT III notes and Question bank .pdf
Asst.prof M.Gokilavani
VICTOR MAESTRE RAMIREZ - Planetary Defender on NASA's Double Asteroid Redirec...
VICTOR MAESTRE RAMIREZ - Planetary Defender on NASA's Double Asteroid Redirec...
VICTOR MAESTRE RAMIREZ
🔝9953056974🔝!!-YOUNG call girls in Rajendra Nagar Escort rvice Shot 2000 nigh...
🔝9953056974🔝!!-YOUNG call girls in Rajendra Nagar Escort rvice Shot 2000 nigh...
9953056974 Low Rate Call Girls In Saket, Delhi NCR
Microscopic Analysis of Ceramic Materials.pptx
Microscopic Analysis of Ceramic Materials.pptx
purnimasatapathy1234
Call Girls Delhi {Jodhpur} 9711199012 high profile service
Call Girls Delhi {Jodhpur} 9711199012 high profile service
rehmti665
Introduction-To-Agricultural-Surveillance-Rover.pptx
Introduction-To-Agricultural-Surveillance-Rover.pptx
k795866
Current Transformer Drawing and GTP for MSETCL
Current Transformer Drawing and GTP for MSETCL
DeelipZope
OSVC_Meta-Data based Simulation Automation to overcome Verification Challenge...
OSVC_Meta-Data based Simulation Automation to overcome Verification Challenge...
Soham Mondal
VIP Call Girls Service Hitech City Hyderabad Call +91-8250192130
VIP Call Girls Service Hitech City Hyderabad Call +91-8250192130
Suhani Kapoor
young call girls in Rajiv Chowk🔝 9953056974 🔝 Delhi escort Service
young call girls in Rajiv Chowk🔝 9953056974 🔝 Delhi escort Service
9953056974 Low Rate Call Girls In Saket, Delhi NCR
HARMONY IN THE HUMAN BEING - Unit-II UHV-2
HARMONY IN THE HUMAN BEING - Unit-II UHV-2
RajaP95
Heart Disease Prediction using machine learning.pptx
Heart Disease Prediction using machine learning.pptx
PoojaBan
SPICE PARK APR2024 ( 6,793 SPICE Models )
SPICE PARK APR2024 ( 6,793 SPICE Models )
Tsuyoshi Horigome
9953056974 Call Girls In South Ex, Escorts (Delhi) NCR.pdf
9953056974 Call Girls In South Ex, Escorts (Delhi) NCR.pdf
9953056974 Low Rate Call Girls In Saket, Delhi NCR
Introduction to Microprocesso programming and interfacing.pptx
Introduction to Microprocesso programming and interfacing.pptx
vipinkmenon1
Artificial-Intelligence-in-Electronics (K).pptx
Artificial-Intelligence-in-Electronics (K).pptx
britheesh05
Past, Present and Future of Generative AI
Past, Present and Future of Generative AI
abhishek36461
★ CALL US 9953330565 ( HOT Young Call Girls In Badarpur delhi NCR
★ CALL US 9953330565 ( HOT Young Call Girls In Badarpur delhi NCR
9953056974 Low Rate Call Girls In Saket, Delhi NCR
Gfe Mayur Vihar Call Girls Service WhatsApp -> 9999965857 Available 24x7 ^ De...
Gfe Mayur Vihar Call Girls Service WhatsApp -> 9999965857 Available 24x7 ^ De...
srsj9000
Recently uploaded
(20)
Application of Residue Theorem to evaluate real integrations.pptx
Application of Residue Theorem to evaluate real integrations.pptx
CCS355 Neural Network & Deep Learning UNIT III notes and Question bank .pdf
CCS355 Neural Network & Deep Learning UNIT III notes and Question bank .pdf
VICTOR MAESTRE RAMIREZ - Planetary Defender on NASA's Double Asteroid Redirec...
VICTOR MAESTRE RAMIREZ - Planetary Defender on NASA's Double Asteroid Redirec...
🔝9953056974🔝!!-YOUNG call girls in Rajendra Nagar Escort rvice Shot 2000 nigh...
🔝9953056974🔝!!-YOUNG call girls in Rajendra Nagar Escort rvice Shot 2000 nigh...
Microscopic Analysis of Ceramic Materials.pptx
Microscopic Analysis of Ceramic Materials.pptx
Call Girls Delhi {Jodhpur} 9711199012 high profile service
Call Girls Delhi {Jodhpur} 9711199012 high profile service
Introduction-To-Agricultural-Surveillance-Rover.pptx
Introduction-To-Agricultural-Surveillance-Rover.pptx
Current Transformer Drawing and GTP for MSETCL
Current Transformer Drawing and GTP for MSETCL
OSVC_Meta-Data based Simulation Automation to overcome Verification Challenge...
OSVC_Meta-Data based Simulation Automation to overcome Verification Challenge...
VIP Call Girls Service Hitech City Hyderabad Call +91-8250192130
VIP Call Girls Service Hitech City Hyderabad Call +91-8250192130
young call girls in Rajiv Chowk🔝 9953056974 🔝 Delhi escort Service
young call girls in Rajiv Chowk🔝 9953056974 🔝 Delhi escort Service
HARMONY IN THE HUMAN BEING - Unit-II UHV-2
HARMONY IN THE HUMAN BEING - Unit-II UHV-2
Heart Disease Prediction using machine learning.pptx
Heart Disease Prediction using machine learning.pptx
SPICE PARK APR2024 ( 6,793 SPICE Models )
SPICE PARK APR2024 ( 6,793 SPICE Models )
9953056974 Call Girls In South Ex, Escorts (Delhi) NCR.pdf
9953056974 Call Girls In South Ex, Escorts (Delhi) NCR.pdf
Introduction to Microprocesso programming and interfacing.pptx
Introduction to Microprocesso programming and interfacing.pptx
Artificial-Intelligence-in-Electronics (K).pptx
Artificial-Intelligence-in-Electronics (K).pptx
Past, Present and Future of Generative AI
Past, Present and Future of Generative AI
★ CALL US 9953330565 ( HOT Young Call Girls In Badarpur delhi NCR
★ CALL US 9953330565 ( HOT Young Call Girls In Badarpur delhi NCR
Gfe Mayur Vihar Call Girls Service WhatsApp -> 9999965857 Available 24x7 ^ De...
Gfe Mayur Vihar Call Girls Service WhatsApp -> 9999965857 Available 24x7 ^ De...
Grounding pad mounted transformers
1.
Grounding Considerations for
Large kVA Pad-Mount Transformers Ruwan Weeransundara P.E. Member, IEEE ESC Engineering Senior Planning Engineer 3540 JFK Parkway, Fort Collins, Colorado 80525, USA Phone 970-212-1525 ruwanw@thinkesc.com Abstract - Utilities in the United States and Canada have done extensive analysis of the ground grid design for substations in order to limit step and touch potentials to safe values; however, few have analyzed the potential hazard and designed grounding systems for pad-mount transformers. Since the kVA size and voltage ratings of pad-mounts have increased and the exterior of these facilities are accessible not only to qualified electric utility workers but also the general public, there is a need to analyze and properly design and construct grounding systems which will render these facilities safe for switching and fault conditions. This paper analyzes and develops the design for several different pad-mount transformer voltages and kVA sizes through 5,000kVA. I. INTRODUCTION The primary purpose of grounding is to limit voltages across insulated or non-insulated portions of equipment within a person’s reaching capabilities and the potential differences between different points on the ground within one step. These voltages are known as “touch” and “step potentials,” respectively. The evaluation of these voltages is required not only during normal operating conditions, but also during abnormal situations such as lightning strikes, faults and switching surges. A large Ground Potential Rise (GPR), with respect to remote earth potential, can occur during abnormal conditions if the fault current (I) and ground (Rg) are high (GPR = I x Rg). Voltage potential rises during fault conditions can be significant even when established grounding practices are used. Pad-mount transformers are being used in ever increasing kVA sizes and with higher primary and secondary voltages. Pad-mount transformers are now available in sizes up through 5,000kVA. Pad-mount transformers are frequently used in lieu of smaller kVA size traditional substations when the primary voltage is 34.5kV and lower. Secondary voltages up to 24.9/14.4kV are available. These trends necessitate a review of established grounding practices for pad-mount transformer installations to ensure that the grounding system will limit step voltage and touch potential to safe levels. Limiting the maximum step potential is especially important for these transformer installations because they are often placed in locations where the general public can be exposed to danger. II. PAD-MOUNT TRANSFORMER CONNECTIONS The large majority of three-phase pad-mount transformers are connected grounded-wye on the secondary. Secondary voltages include 208/120 volts, 480/277 volts, and common distribution primary voltages (4.16/2.4, 12.47/7.2, 13.2/7.6, 24.9/14.4 kV). Delta connected primary connections are not common due to the susceptibility of this connection to ferro-resonance over voltages. Although not common for utility application, grounded-wye primary with impedance grounded secondary are used for industrial applications to limit phase-to-ground fault currents. The primary Ho and secondary Xo are separated when the secondary Xo bushing is grounded through impedance. III. ASSUMPTIONS The following assumptions were used to determine the adequacy of various grounding systems for different kVA size and voltage rated pad-mount transformers. These assumptions are conservative for most conditions but should be checked for particular installations to insure they are applicable and provide safe results. Pad-mount transformers rated 750kVA and larger were assumed to have 5.75 percent impedance. Top soil resistivity of 2,000 m was used. This is typical for sand, gravel and dry soil. Lower soil resistivity of 1,000 m was used. The weight of the person is 50 kilograms (110 lbs.) Thickness of the surface material is 0.5 ft. Fault duration is 0.5 seconds The maximum secondary line-to-ground fault currents for different kVA size and voltage transformers were assumed to have nearly an infinite primary source: 5,000kVA with 12.47/7.2kV secondary, available fault current 4,000 amps. 2,500kVA with 12.47/7.2kV secondary, available fault current 2,000 amps. 5,000kVA with 4.16/2.4kV secondary, available fault current 12,000 amps. 2,500kVA with 4.16/2.4kV secondary, available fault current 6,000 amps. The current distribution factor equals 1.0 (i.e., all fault current goes into the grid and none returns through the source distribution circuit). The touch and step potential values calculated from the equations specified in IEEE Guide for Safety in AC Substations Grounding Std. 80-2000 are the maximum values which should be allowed for pad-mount transformer installations. IEEE Std 80 provides equations for the allowable touch and step potentials for both 50 and 70 kilograms persons. The weight of 50 kg was used because the potential limits for the lighter person are more restrictive. Two types of ground grid were initially investigated: the two ground rod schemes required by Rural Utilities Services (RUS) for all A3-1 978-1-61284-054-3/11/$26.00 ©2011 IEEE
2.
three-phase underground pad-mounted
equipment applications in their unit UM 48-2 and the Canadian Standards Association Rule 36-302 in the Electrical Safety Authority, which requires a ground rod on each of the four corners around the pad-mount transformer. These grounding schemes are shown in Figures 2 and 3, respectively. In addition, a suggested sample design (Figure 4) for a 5000kVA, 34.5/4.16kV pad-mount transformer is included. The potential contour for the grounding arrangement is shown in Graph 4. IV. CALCULATIONS The ground potential rise (GPR), maximum allowable touch ( and step ( potential calculations were performed using the equations specified in IEEE Std 80-2000. The grounding analysis was performed for different kVA sizes and voltage ratings of pad- mount transformers with both the RUS and Canadian Standards. The EDSA Advanced Ground Mat Program V4.70.00 was used to perform sample calculations on pad-mount transformers, ranging from 500kVA to 5000kVA. These calculations were compared with the maximum allowable values calculated from the equations specified in IEEE Standard 80-2000. Step and Touch Voltage Criteria The safety of a person depends on preventing the critical amount of shock energy from being absorbed before the fault is cleared and the system is de-energized. The maximum driving voltage of any accidental circuit should not exceed the limits defined as follows. The limit for Step Voltage is: 1 (1) For body weight of 50kg: 1 (2) Similarly, the touch voltage limit is: (3) For body weight of 50kg: (4) (5) Where: Estep-The step voltage in volts Etouch-The touch voltage in volts Cs -The surface layer de-rating factor S- The surface material resistivity in m - The resistivity of the earth beneath the surface material in m ts -The duration of shock current in seconds hs -The thickness of the surface material The following values were used for grounding analysis: Cs=1.0 (No earth beneath surface material), = S = 2000 m ts = 0.5 sec, hs=0-.5 ft. From (2) & (4) = 2312.6V (6) = 656.2V (7) 1 IEEE – Guide For Safety in AC Substation Grounding, IEEE – Std. 80-2000, pp- 23-37 The actual step and touch voltages, metal to touch and step to step voltages, should be less than the respective maximum allowable voltage limits to ensure safety. It should be noted that the above calculations assume 0.5 seconds fault duration. With a square root of ts in the denominator of equations (6) and (7) above, the allowable step and touch voltages will both be decreased with an increase in fault clearing time. Increasing the fault duration time from 0.5 seconds to 2.0 seconds will reduce the above values by one-half. Although not common in the electric utility industry, some industrial electrical users separate the primary H0 and secondary X0 connection points to obtain an impedance grounded secondary system. When this is done, the maximum voltages during fault conditions will not be limited by the secondary windings and the touch potentials as well as the step potentials will exceed those which would occur for a grounded wye to grounded wye connection with the H0 and X0 points bonded. Figure 1 Human Tolerances Model Figure 2 RUS Std UM48-2, 3-Phase Pad-Mounted Grounding Figure 3 Canadian Standard for Pad-Mounted Grounding A3-2 978-1-61284-054-3/11/$26.00 ©2011 IEEE
3.
Graph 1 Potential
3D graph for 5000kVA, 34.5/4.16kV RUS Std Graph 2 Absolute potential along an axis – 34.5/4.16kV RUS Std Graph 3 Potential 3D Graph for 5000kVA, 34.5/4.16kV Canadian Standard Figure 4 Suggested grounding arrangement for 5000kVA 34.5/4.16kV pad-mount transformer Graph 4 Potential 3D graph for 5000kVA, 34.5/4.16kV with suggested grounding arrangement V. RESULTS Table 1 shows the comparison of maximum surface voltage on both RUS Std and Canadian Standard for different sizes and voltages of pad mount transformers. The maximum allowable touch and step voltages are 656.2V and 2312.6V respectively. Table 1 Transformer Secondary Voltage (kV) Size (KVA) Maximum Line-Ground Fault Current (A) Maximum Surface Potential (V) Meets the Safety Requirement Maximum Surface Potential (V) Meets the Safety Requirement 12.47 5000 4000 1655 707 12.47 2500 2000 875 338 12.47 1500 1250 601 205 4.16 5000 12000 4551 1491 4.16 2500 6000 1848 911 4.16 1500 3500 1454 515 4.16 1000 2250 933 404 4.16 750 2000 875 338 4.16 500 1000 A3-3 978-1-61284-054-3/11/$26.00 ©2011 IEEE
4.
VI. CONCLUSIONS AND
RECOMMENDATIONS With the RUS two ground rod standard, the maximum surface potential as well as the maximum 1.0 meter gradient potential can be exceeded for large kVA size pad-mount transformers with 4.16/2.4kV and higher secondary voltages. The Canadian Electrical Safety Code which requires four grounding rods, one on each corner, provides better results but still fails for some larger kVA sizes and higher secondary voltages. A detailed engineered grounding design should be prepared by a qualified person for pad-mount transformer installations exceeding 750kVA when the secondary voltage is 4.16/2.4kV or higher or if the fault clearing time exceeds 0.5 seconds. Since the allowable step and touch potentials decrease with an increase in the shock current duration time, it is important to consider the maximum fault clearing time when designing ground systems for pad-mount transformers. A detailed grounding design requires knowledge or measurement of the soil resistance at the pad-mount transformer location plus information regarding any possible deviation from the assumptions used in this paper. In addition, a detailed grounding design should be done for all grounded wye to impedance grounded secondary when the H0 and X0 are not connected to provide an impedance grounded secondary. VII. REFERENCES [1] IEEE for Safety in AC Substation Grounding IEEE Standard 80-2000. [2] Canadian Electrical Safety Code, 2009, by Electrical Safety Authority. [3] RUS Standard 1728F-806, June 2000, Specifications and Drawings for Underground Electric Distribution. [4] IEEE Recommended Practice for Grounding of Industrial & Commercial Power Systems, ANSI/IEEE Std 142-1982 VIII. BIOGRAPHY Ruwan Weeransundara received a BSEE from the University of Peradeniya Sri Lanka in 1987 and a MSEE from the University of Windsor, Ontario Canada in 2004. From 1987 to 2000, he worked as a Power System Engineer for Ceylon Electricity Board in Sri Lanka with an emphasis on Power Distribution, Protection of Transmission and Generating Stations and Substation Design. In 2000, he joined Siemens Canada as a Field Service Engineer. In 2004, he joined Schneider Electric Canada as Senior Power System Engineer and in 2009, he joined ESC engineering, Inc. as a Senior Planning Engineer. He is a member of IEEE and a Registered Professional Engineer in the Province of Ontario Canada. A3-4 978-1-61284-054-3/11/$26.00 ©2011 IEEE
Download now