Fault Detection On-Line Monitoring
Transformer On-line monitoring Case Study 206 2006
October 2006 – April 2007
3 phase, 300/336 MVA, 230/100/44 kV FOA Class
This transformer exhibited periodic sudden increases of combustible gases.
The unit was tested acoustically in June 2006, two areas of acoustic activity detected
A DGA was performed using a portable gas chromatograph
DGA indicated a thermal fault of high temperature
Due to the criticality of this transformer, an all-acoustic on- line monitoring system (Sensor Highway II) was installed on this unit.
The day of the installation, a new DGA sample was taken with surprising results
The TDCG value increased from 3,144 ppm to 16,089 ppm changing the condition of this transformer from Condition 3 to Condition 4 according with IEEE Std. C57.104.
A high temperature (>700 C) thermal fault suspected
AE Sensor Highway II
16 AE Channels with independent signal processing (always active, no multiplexing)
Four 4-20 mA and digital I/O
Connectivity to Ethernet with options for other interfaces (wireless and cell phone).
NEMA 4 Enclosure ~ 20” x 16” x6” with removable bottom panel.~ 40 pounds
Compact Flash Interface (up to 4GB)
Wide temperature range (- 35 to+70 C)
Power: 85-260 VAC or 9-28 VDC
Low Power AC/DC operation(12W + sensor requirements ~ 48W)
ON-LINE MONITORING
On-line monitoring started inOctober 2006
The same two areas of activity detected in June 2006 were detected during the entire monitoring period (Clusters 1 & 2).
An on-line multiple combustible gases monitor was also installed
No changes in TDCG were detected by the DGA monitor
The two areas of acoustic activity corresponded to:
– Middle section of Phase A coil
– Upper part of Phase C coil
The on-line system collected data from October 2006 – April 2007
ON-SITE OVERHAUL (April 2007)
1. The general vicinity of the H3/X3/Y3 winding assembly was noted as being considerably littered with dark/carbonaceous paper.
2. This unit by design incorporates the direct flow cooling system; speculation is that this material most likely originated from the inner layers of this winding assembly with the oil flow providing the vehicle for spreading this debris.
3. There is also considerable coverage of copper particulate in and around the top of this winding. This material ranges in size from “dust” to pieces similar in stature to that of a “pinhead” with a small percentage of larger “BB” size pieces found.
• Subsequent testing was conducted.
• TTR identified and out of tolerance measurement associated with the Y3 winding.
• Winding resistance testing revealed an abnormality with the Y3 winding.
• Megger testing did not reveal any concerning issues.
• By design, the Y3 winding is located within the H3/X3 assembly. Based on the test data, it is likely that the paper and copper discharge found originated from the Y3 winding being pushed out via normal oil flow.
OPENED @ FACTORY (NOVEMBER 2007)
• Factory inspection indicated that the failure mode at the fault location was turn to turn in the layer winding.
• If the unit remained in operation for several months under these conditions; it is possible the fault could have opened up the delta an C phase andthe TV could have been running opendelta.
CONCLUSIONS
• This Case Study demonstrate the usefulness and effectiveness on an all acoustic on-line monitoring system.
• The continuous on-line monitoring of this unit allowed this utility to continue the operation of the transformer during a critical load period and also provide an accurate location of the fault.
• The practicability and accuracy of portable gas chromatographers is also shown
• The overhaul performed on-site indicated that the fault was not on the external part of the winding.
• Traditional electrical tests indicated a problem on the Y3 winding.
• Factory internal inspection confirmed the existence of a turn-turn fault on the area indicated by acoustic and electrical tests
• Important observation: even Combustible gases did not increase fromOctober 2006 – April 2007, Acoustic Activity was still been detected