TRANSFORMER PAPER DETERIORATION

BY

ESWARAN SUBRAMANIAM

Power Rating – 36MVA/60MVA

Cooling – Oil Natural Air Natural (ONAN)/ONAF

Voltage Level – 23kV +-7.5%/11.5kV

Manufacture – CG

Year of Manufacture - 2001

Functions of paper in transformer are:-

Provide mechanical strength for the transformer (tensile strength)

Part of the electrical insulation system in the transformer

When paper breakdowns, it dissolves as Furan components in the oil

High Furan content observed on all six unit transformers.

Oil results was sent to three different labs

Two labs confirmed Furan level is high (TNBR and SPM)

Six monthly sampling done by TNBR since 2003

Transformer “life” is directly proportional to the paper condition.

Latest Oil Test results

Deterioration is not reversible but possible to slow it down

Unit Transformer

Furan (2FAL) June 2013

Furan (2FAL) Dec 2012

Criticality End Of Life

01BBT20 5942 ppb 4539 ppb 1 Dec 2013

01BBT10 4102 ppb 3696 ppb 2 May 2016

03BBT10 3540 ppb 3017 ppb 3 Dec 2015

02BBT10 3025 ppb 2514 ppb 4 Jan 2016

02BBT20 2335 ppb 1986 ppb 5 Feb 2017

03BBT20 2068 ppb 1762 ppb 6 July 2017

Temperature – Higher Loading

Temperature – Cooling Fans Fail To Operate

Moisture – Transformer Oil Leaks

Moisture – Silica Gel

Reduce Loading on 01BBT20, 01BBT10 and 03BBT10 Avoid using Unit 1 to supply common boards Only run one BFP on each 11kV board (BFP 1 or BFP 3 on Board A and BFP 2

Board B) Avoid using FGD system on Unit 1 Run CEP No 1 on Unit 1 and CEP No 2 on Unit 3 Avoid using ESP on Mode 3 on Unit 1 (High power condition) Call in EMS once transformer fans stops/trips. Fans are now in manual mode. Inform EMS silica gel changes color Inform EMS if oil leaks are observed on the unit transformers

EMS will increase oil sampling frequency unit transformers to a monthly basis. Rate of deterioration will be monitored.

TNBT transformer specialist being consulted on the best possible way to manage the deterioration.

EMS will update the status of the transformer regularly to OPS

Spare Unit Transformer expected to reach TNBJ 1st week of August 2013 (Sailing to Malaysia)

01BBT20 transformer will be replaced with new transformer during Unit 1 Major Overhaul

Repair work is estimated to take 4 months per transformer.

To complete repair on all transformers according to criticality.

To establish root cause based on transformer tear down inspection.

Installation of air bag system for the transformers

Unit transformers are deteriorating

Unit 1 BBT20 unit transformer is in the worst condition

Temperature and moisture accelerates the deterioration process