On load tap changer (OLTC) explode?
Transformer
Vector group: Ynd11
Rated Power: 353MVA
Rated Current: 693A
Voltage:294/20KV
OLTC
Type: T III Y1000 110/c 12193w
Max Operation Current: 295A
Step Voltage: 550V
Arrangement in Tx windings: Y Connection
Problem: Damage of Unit 1 Generator Transformer On Load Tap
Changer (OLTC)
Description of Incident:
9.00 a.m. :- Generator No Load test on excitation system
started
10.30 a.m :- Carried out AVR change over
test
11.30 a.m :- Preparation for Generator Manual Synchronizing
test
12.00 a.m :- Manual Synshronizing test started.
Observed incoming generator voltage higher than running voltage.
CECR operator operated Generator Transformer OLTC to bring down
the incoming generator voltage
12.03 a.m :-Generator Transformer abnormal alarm operated at
Gen.Control Desk (CECR)
CECR operater at Generator transformer bay informed that the
transformer
oil splashed out from OLTC.
CECR operater informed that he heard explosion inside OLTC.
Observed Oil level & Oil Flow alaram operated at Tranformer
local annunciator.
12.05 am :- CECR operator 'Open Gen Field Breaker”
12.10 a.m. :- Elec1 team inspected the OLTC and found the
OLTC rupture disk was broken
and oil spilled at OLTC area.
- Elec1 found the OLTC top cover bulging.
Do anyone know why and possibility cause happen in this OLTC.
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Answer Posted / sudheer
please check the OLTC inside
connections ,carefully .because some times the connector
plate rollers not touch properly. so the winding temp.
increases continuously and oil will over-heated.
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