Internal Fault Detection In Distribution Transformers

Transcript

Internal Fault Detection in Distribution Transformers Energy Council of the Northeast Engineering and Operations C0nference March 13, 2015 Paul Henault – IFD Corporation Presentation Outline An overview of distribution transformer faults Current industry issues and practices Options for improvement Questions Why is internal fault detection important? Why internal fault detection is important Linemen Safety  Operating challenges  Crew pressures  Risk every time we re-close Troubleshooting Effectiveness  Speed  Accuracy System Reliability  Reduce outage times  SAIDI/SAIFI Why internal fault detection is important It’s always been important  Historical Efforts  Tank re-design  Arresters  Flame retardant fluids  Common Utility Objectives:  “Zero accidents”  “Improve customer satisfaction”  “Improve system reliability”  “Increase operational efficiency” Linemen Survey * “Have you ever closed on a faulted transformer?” 84% (74) had closed into a fault – some, several times “If so, what happened?” 42% (37) experienced hearing loss (fuse operations) 26% (19) experienced a cover blowing off during the operation (1) injured with oil burns * 88 Linemen Surveyed at Linemen’s Rodeo, Kansas City ‐ 2013 What does an internal transformer fault look like? A rapid, transient pressure rise occurs in every internal arcing fault Variable peak pressure Consistent rate of rise Different fault locations Near the Surface Near the Bottom What does an internal transformer fault look like? 500A test Normal Fault Arc Voltage Fault Current IFD activates before peak ~ 3 psi Pressure Rise Certification tests at Powertech Labs What does an internal transformer fault look like? 500A test Fuse failure incident Arc Voltage slow fuse Fault Current reaction internal explosion >20psi in 15 ms Pressure Rise Certification tests at Powertech Labs What causes transformer fuses to blow? Causes of transformer fuse operations 50% 46% 45% 40% * Source: 35% 30% 25% 20% 20% 15% 15% 10% 10% 5% 5% 4% Connectors Fuse Holder 0% No Damage Fuse Transformer LV Wires Causes of padmounted transformer fuse operations  Internal Transformer  Faults  Secondary Faults  Overloads  Oil Temperature  (Dual Element Fuse) What about PRV’s?  PRV operation: P > 10±2 psi ≠ Internal fault  (Poppet style PRV) ‘does not have time to react to the overpressure rates of rise and values produced when low-impedance faults occur.’  A. Even et al., “Safety of Distribution Transformers against internal failure”, Conference Publication No. 438., IEEE, 1997 Sudden Pressure Relays Current Troubleshooting Methods Sometimes a problem is obvious… …and sometimes it’s not Current Industry Practices 1) Automatic Replacement 2) Field Testing 3) Trial & Error Automatic Replacement  80-85% of the time the transformer is OK  Expensive and time consuming to remove the transformer, transport it to the shop, test it, and return it to service  Hydro Quebec estimate  300 units/year Automatic Replacement Internal Faults in padmount transformers are usually not obvious externally Portable Field Testers* “Testers are expensive and not every vehicle has them” “They often don’t detect low grade transformer faults at the voltages that they generate” “I no longer use it because it kept indicating unfaulted transformers, but when I re-energized them, many were faulted” *Lineman feedback Trial and Error 1. Visual examination 2. Manual checks,  e.g., overpressure  “sniff…don’t inhale” 3. Attempt to re-energize the transformer  “Push and pray”  “Now, crawl inside your helmet”  “Go get the new guy" An Improved Method Sample utility procedures 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) Always wear the appropriate personal protective equipment including fire retardant clothing, hard hats, safety glasses and rubber gloves. When performing any close inspections of or repairs to the transformer always deenergize the unit and take precautions from any sources of power including customer generators. Prior to re-fusing transformers, make a thorough inspection of the transformer and the surrounding area, looking for indicators such as: animal carcasses, bulged tank or cover, discolored tank, oil leak, burned oil aroma, flashed or broken bushings, any short circuits such as wrapped wires in the secondary or service. Prior to re-fusing transformers, test the transformer with an approved instrument such as a Transformer Turns Ratio tester. Some companies require some form of testing on every transformer before they are energized. When re-fusing a suspected faulty transformer, position yourself as far away as possible by using an extendable live line tool. Some companies specify maintaining a distance of at least 10 ft. when re-fusing transformers. When re-fusing a suspected faulty transformer, always disconnect the customer’s load. Test the transformer with a smaller test fuse. (Some companies have test fuse tables based on the transformer size and voltage). If the transformer blows a fuse and the pressure relieve valve has operated, do not re-fuse and proceed with replacement. If the transformer has an auxiliary current limiting fuse that has blown, do not re-fuse; proceed with replacement. Checking transformer condition Maintain proper distance when re-fusing. In this condition: do not refuse Always make sure the neutral is connected first before connecting a transformer and that it is removed last if disconnecting a transformer. Do not allow the paralleling of transformers across any point that might be used to isolate a line section, such as switches, disconnects and double dead ends to avoid the possibility of back feed into a cleared line section. Always wear rubber gloves when working on the secondary side of a suspected faulty transformer. Take precautions when removing the lid from a suspected faulty transformer by operating the pressure relief valve. If it is an older unit without a valve, tie a sling over the lid before loosing the attachments. Some companies have established step-by-step procedures for investigating transformer problems while others allow the lineworker to access the situation and take precautions they deem necessary within mandatory safety guidelines. It is recommended that step-by-step procedures be developed as they are good training aids and can serve as a refresher for lineworkers. They also help ensure certain key steps are followed Sample utility procedures 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) Always wear the appropriate personal protective equipment including fire retardant clothing, hard hats, safety glasses and rubber gloves. When performing any close inspections of or repairs to the transformer always deenergize the unit and take precautions from any sources of power including customer generators. Prior to re-fusing transformers, make a thorough inspection of the transformer and the surrounding area, looking for indicators such as: animal carcasses, bulged tank or cover, discolored tank, oil leak, burned oil aroma, flashed or broken bushings, any short circuits such as wrapped wires in the secondary or service. Prior to re-fusing transformers, test the transformer with an approved instrument such as a Transformer Turns Ratio tester. Some companies require some form of testing on every transformer before they are energized. When re-fusing a suspected faulty transformer, position yourself as far away as possible by using an extendable live line tool. Some companies specify maintaining a distance of at least 10 ft. when re-fusing transformers. When re-fusing a suspected faulty transformer, always disconnect the customer’s load. Test the transformer with a smaller test fuse. (Some companies have test fuse tables based on the transformer size and voltage). If the transformer blows a fuse and the pressure relieve valve has operated, do not re-fuse and proceed with replacement. If the transformer has an auxiliary current limiting fuse that has blown, do not re-fuse; proceed with replacement. Checking transformer condition Maintain proper distance when re-fusing. In this condition: do not refuse Always make sure the neutral is connected first before connecting a transformer and that it is removed last if disconnecting a transformer. Do not allow the paralleling of transformers across any point that might be used to isolate a line section, such as switches, disconnects and double dead ends to avoid the possibility of back feed into a cleared line section. Always wear rubber gloves when working on the secondary side of a suspected faulty transformer. Take precautions when removing the lid from a suspected faulty transformer by operating the pressure relief valve. If it is an older unit without a valve, tie a sling over the lid before loosing the attachments. Some companies have established step-by-step procedures for investigating transformer problems while others allow the lineworker to access the situation and take precautions they deem necessary within mandatory safety guidelines. It is recommended that step-by-step procedures be developed as they are good training aids and can serve as a refresher for lineworkers. They also help ensure certain key steps are followed OR Look Up Sample utility procedures 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) Always wear the appropriate personal protective equipment including fire retardant clothing, hard hats, safety glasses and rubber gloves. When performing any close inspections of or repairs to the transformer always deenergize the unit and take precautions from any sources of power including customer generators. Prior to re-fusing transformers, make a thorough inspection of the transformer and the surrounding area, looking for indicators such as: animal carcasses, bulged tank or cover, discolored tank, oil leak, burned oil aroma, flashed or broken bushings, any short circuits such as wrapped wires in the secondary or service. Prior to re-fusing transformers, test the transformer with an approved instrument such as a Transformer Turns Ratio tester. Some companies require some form of testing on every transformer before they are energized. When re-fusing a suspected faulty transformer, position yourself as far away as possible by using an extendable live line tool. Some companies specify maintaining a distance of at least 10 ft. when re-fusing transformers. When re-fusing a suspected faulty transformer, always disconnect the customer’s load. Test the transformer with a smaller test fuse. (Some companies have test fuse tables based on the transformer size and voltage). If the transformer blows a fuse and the pressure relieve valve has operated, do not re-fuse and proceed with replacement. If the transformer has an auxiliary current limiting fuse that has blown, do not re-fuse; proceed with replacement. Checking transformer condition Maintain proper distance when re-fusing. In this condition: do not refuse Always make sure the neutral is connected first before connecting a transformer and that it is removed last if disconnecting a transformer. Do not allow the paralleling of transformers across any point that might be used to isolate a line section, such as switches, disconnects and double dead ends to avoid the possibility of back feed into a cleared line section. Always wear rubber gloves when working on the secondary side of a suspected faulty transformer. Take precautions when removing the lid from a suspected faulty transformer by operating the pressure relief valve. If it is an older unit without a valve, tie a sling over the lid before loosing the attachments. Some companies have established step-by-step procedures for investigating transformer problems while others allow the lineworker to access the situation and take precautions they deem necessary within mandatory safety guidelines. It is recommended that step-by-step procedures be developed as they are good training aids and can serve as a refresher for lineworkers. They also help ensure certain key steps are followed OR Look Down IFD Purpose Give electric utility employees the information they need to troubleshoot and restore power to distribution transformers Faster, Safer, and More economically Development  Designed with utilities and transformer manufacturers Mechanical, not electrical sensor Measurable $ value – Safety, Productivity & NPV Low cost compared to other fault detection methods Reliable compared to other fault detection methods Product Requirements 1) Primary function: Reliable detection of internal arcing faults  High visibility  Easy to install  Maintenance free  No effect on transformer 2) Also: Incorporate pressure relief valve in design R&D sponsors & contributors  NRC/CEATI & utilities, e.g.:  Hydro Quebec  BC Hydro  Hydro One  Manitoba Hydro  PG&E  Transformer manufacturers  Canada  US Performance specs Fault testing Field testing Certification Financial support Product value New product ideas Overview :: 2 functions 1. Internal arcing fault detection Flag comes out when internal fault has occurred 2. Pressure relief device Pull the ring to operate manually New line crew practices  If the IFD has activated, replace the transformer – it has failed internally and is dangerous to re-energize  If fuse cutout is open and the IFD has not activated, likely OK – still conduct all your normal safety check procedures How it Works 3 Rapid pressure rise Fault occurs 2 1 IFD activates Installation  Air space, above oil  Process adapted to each transformer manufacturer One-Size-Fits All 3-Phase Overhead Banks  Can be difficult to troubleshoot – Variety of connection types – Access/clearance issues  The IFD speeds up the process – Looks only at sudden pressure – Independent of connection types or any other electrical considerations URD Power Restoration  IFD’s are also effective when used in conjunction with cable sectionalizers and FCI’s.  These devices quickly identify the location of faults in relation to the 2 closest transformers.  The IFD indicates whether the fault is in either of those 2 transformers, or external to them. IFD status today  Installed since 2001  Over 650,000 in service  ̃ 320 Utility Users  ABB / PPI  ERMCO  Howard  Cooper   GE Prolec  Central Moloney   UUS  Solomon  ̃ 50 Installers Florida Transformer  SE Transformer  Canada:  Siemens   Carte  CamTran  PTI  CG Power Systems  Others  80% usage rate IFD customers http://ifdcorporation.com/product/our-customers/ “…this is great, a safety device that makes us money.” Vice‐President T&D Value Summary Typical cost per transformer Cost of adding IFD per transformer Pole mounted Pad mounted $1,000 $10,000 $60 ‐ 80 $60 ‐ 80 $120 – 350 $480 – 960 $400 – 800 $400 – 800 $20 – 30 $20 – 30 $3,000 – 4,000 $5,000 – $15,000 ~ $200,000 / yr ~ $200,000 / yr $1,000 – 60,000 $ thousands to  millions $1,000 – 60,000 $ thousands to  millions Efficiency (Trouble call time savings) 1‐phase 3‐phase bank Materials Saved Fuses Diagnostics Keep good transformers in service Reliability Improve SAIDI / SAIFI Cost Avoidance Environmental Worker / public safety Sample Specification Wording “Each transformer shall be equipped with a non-resettable device which detects and provides external indication of internal transformer faults, and also incorporates pressure relief functionality. The approved device is manufactured by IFD Corporation or approved equal.” THE GOAL Improve linemen safety Enable faster and more accurate decision making Provide condition status information for the entire life of the transformer Keep unfaulted units in service Improve system reliability Thank you…questions?