Distribution Transformer Failures and Counter Measures

Transcription

1 Distribution Transformer Failures and Counter Measures Dr. Katsutoshi Toda Executive Chairman, Toshiba Transmission & Distribution Systems (India) Pvt. Ltd.

2 Role of Distribution Transformer In Network Performance, Customer Satisfaction & Profitability of any Distribution Network completely depends on functional performance of Distribution Transformer

3 What is Distribution Transformer Failure o A simple Internal (or) External fault which obstructs functioning of transformer in network. o Transformer failure causes black-out of power to the whole area. o It can also lead to risk of fire and explosions, as the transformers contains substantial quantity of oil. o Though it looks simple, transformer failure will lead to chain of adverse effects on: End User Distribution Utility Company

4 Types & Sources of Distribution Transformer Failure Source -1 External Conditions Source -2 Network Operator Source -3 Manufacturer Source -4 Procurement Stage Unauthorized Tapping Vandalism Oil Leakages Faults on LV System Lightening Strikes External shortcircuit Improper installation Improper terminations Faulty earth connections Bypassing of Protection systems Inadequate maintenance Prolonged Over loading & Unbalancing Faulty design Quality of Raw Materials Poor workmanship Improper Mfg. Process Improper transportation Chances for Underrated Transformers Improper Technical Specifications Improper Inspection Process

5 Few Examples indicating Improper Installation and Operating Conditions

6 Unauthorized Tapping (Power Theft)

7 Improper Termination

8 Improper Earthing

9 Bypassing of Protection Systems Low voltage Terminal Connection provided directly bypassing MCCB

10 Failure due to Overloading

11 Arcing Horns - Improper Assembly/Not used

12 Failures due to Low Oil Level resulted from Oil Leakage

13 Lightning Strikes Vandalism Fault on LV System (Short Circuit) Broken Bushings Burnt/Broken Rods Oil Leakage Accidental Damage Overload Failed on Commissioning Internal Defects Dist. Trfr Failure Statistics in Kenya (Aug-2015 to Dec-2016) Kenya Power is the main distributor of electricity in Kenya. It has Installed around Nos distribution transformers in network The approx. failure rate is 7-8% 35.00% 32.19% 30.00% 25.00% 20.00% 15.00% 10.00% 5.00% 0.00% 13.88% 10.59% 3.55% 9.52% 11.33% 0.93% 5.42% 1.51% 11.08% Source: M/s. KPLC, Kenya.

14 What Next? Can we really control these failures? Counter Measures to overcome Transformer failures

15 Problem Sources of Failures & Counter Measures Source: External Conditions Solution Way Forward Unauthorized Tapping Vandalism Oil Leakages Faults on LV `System Lightening Strikes External short-circuit Proper Maintenance and Checks to be done. Transformer should be manufactured with Anti-Theft arrangements. Aluminium Winding may be one of the Solutions to prevent Vandalism Training on Installation, Operation & Maintenance All Technical measures to be incorporated in Specifications.

16 Problem Source: Network Operator Sources of Failures & Counter Measures Solution Way Forward Improper installation Improper terminations Faulty earth connections Bypassing of Protection systems Inadequate maintenance Prolonged Over loading & Unbalancing Know the Right Practices of Installation and Maintenance Improve Skill Levels of Operation and Maintenance Staff. Training for the field Engineers and Staff. Some of the counter measures

17 LT cables connected to MCCB through rubber grommet Example Measure-1: LV Termination through MCCB for Overload Protection ( ) Don t bypass MCCB LT terminals should connect through MCCB only ( ) Do s: LT cable passing through MCCB (bottom view) Cables connected to transformer ( ) LT cables towards Customer end Always connect LT terminals through MCCB to protect transformer from overloading & external faults on LT side. Don ts: Do not bypass MCCB to avoid transformer tripping in fault conditions

18 Example Measure-2: Arcing Horns Assembling Procedures Do s Don'ts ( ) 85mm Do s : Ensure the assembling of top and bottom arcing horns alignment with 85mm gap for 11KV. Don ts: Never assemble arcing horns in misaligned or missing condition as shown in above photos Toshiba Corporation

19 Do s Example Measure-3: HT Fuse link connecting procedures Don'ts ( ) Connect HT lead and terminal stem through Fuse link Don t Bypass Fuse link Don t Fix HT lead directly to terminal stem without fuse link Do s: Always connect HT phase leads through fuse links to avoid transformer failures due to overload or fault currents. Don ts : Never Bypass or connect fuse links directly as shown in above figures.

20 Problem Source: Manufacturer Sources of Failures & Counter Measures Solution Way Forward Faulty design Quality of Raw Materials Poor workmanship Improper Mfg. Process Improper transportation Chances for Under-rated Transformers Select Reliable Manufacturer Ensure, transformers are manufactured as per the Specifications. Technical Evaluation of Manufacturing facilities & processes by a Competent Team Proto Testing in 3 rd Party independent laboratory. Adopt Stringent FAT Conduct Post Landing Inspection

21 Mini Test Set-up (Upto 500kVA) (Tests: No Load & Load Loss, Impedance Voltage, Winding Resistance and Oil BDV) (This is an example test setup for explanatory purposes only)

22 CONCLUSIONS In Procurement Stage, all the Counter measures should be taken in to Consideration o Vendor Pre-Qualification Processes o Product Qualification Processes o Factory Acceptance Test o Post Landing Inspection o Training for field Engineers and Staff

23 Thank you!