Preventing and Identifying Potential Failures of Dead Break Elbows

©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
Preventing and Identifying Potential Failures of Dead
Break Elbows in Wind Farm Applications.
Brian Peyres
Sr. High Voltage Reliability Engineer, EDP Renewables
ABSTRACT
Dead break elbow terminations are commonly used in many wind farm and utility applications.
When constructed properly, dead breaks also known as “T-Body’s” can be very reliable. Failures of this
type of termination can be very dangerous and costly with regards to adjacent equipment damage and
service interruptions. What are some of the causes of failure? How can we prevent failure? How do we
interpret an observed anomaly?
INTRODUCTION
This article will familiarize you with dread break elbow construction and its applications. Wind farms have
been increasing in number globally in the last decade, therefore a large number of transformers, junction
boxes and isolation switches have been constructed using dead break elbows. Unfortunately some
components have been made with lower standards to meet the recent demands. In addition to supply
concerns, lack of experience by installers has resulted in costly failures for many owners. The goal of this
paper is to share valuable lessons learned and provide insight on how to prevent possible failures.
FAILURES
Figure 1 is an example of a failed dead break connection. This type of failure is a common occurrence
when construction of a dead break elbow is not conducted properly. Damage in this example resulted in
losing 25MW of possible generation for roughly 15 hours.
Figure 1. Failed dead break elbow on a 1850 KVA transformer, A phase fault current of 19505 amps to ground.
InfraMation 2015 Proceedings
2015-003 Peyres
1
©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
Figure 2. Failed dead break elbow on a 3 way junction box, C phase fault current of 29,000 amps to ground.
ROOT CAUSE OF FAILURES
Reason #1 Craftsmanship
Poor assembly techniques are the primary reason dead break connections fail. Inexperience, failure to
follow manufactures instructions and working with heavy cable that is difficult to form can all lead to
termination failures.
Figure 3. Anomaly discovered during a routine IR scan on 1850 KVA wind turbine transformer.
InfraMation 2015 Proceedings
2015-003 Peyres
2
©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
Figure 4. Investigation into the IR anomaly on page 2 (Figure 3) lead to the discovery of a severely damaged
termination. Contact surface area is severely damaged due to the installer using a screwdriver to twist the cable
during installation. This action deformed the lug resulted in the hot spot.
Figure 5. Damage to mounting stud resulting in cross threading. This type of issue will cause a false positive torque
reading resulting in inevitable failure. To prevent this, ensure machined areas are free from burrs, defects, and are
clean before assembly. Use extreme care while placing heavy cable over the stud to avoid thread damage.
InfraMation 2015 Proceedings
2015-003 Peyres
3
©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
ROOT CAUSE OF FAILURES
Reason #2 Material defects
Figure 6. The top row of studs represent materials that were supplied with the transformer, these studs are not
uniform in length and cutting depth. The studs on the bottom row were supplied by the T-Body manufacturer, and are
uniform in shape and length. The poor quality studs have higher failure rates due to false positive torque values.
ROOT CAUSE OF FAILURES
Reason #3 Environmental Stresses
Thermal cycling of transformers can stress termination integrity due to expansion, contraction, and
movement of materials. Cables can be weighed down by heavy ice that accumulates in the dead space
below termination cabinets resulting in stresses on the cable. Frost heaving of equipment in winter
months can also play a role in cable movement resulting in potential failure.
Figure 7. Supports used to stabilize conductors on a 1850 KVA wind turbine transformer.
InfraMation 2015 Proceedings
2015-003 Peyres
4
©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
CASE STUDY
The dead break elbow is a fully submersible component with heavy shielding material that protects the
termination. The design makes it difficult to see or determine if a potential problem exist. Determining
the cause of an anomaly is impossible without disassembly of the elbow. The following case study
illustrates differences between exposed and covered terminations with a termination defect. In the first
series of tests, a termination was intentionally damaged, measured for connection resistance and
subjected to 100 amps of current for a period of 75 minutes. IR images were captured illustrating the
results of the high resistance connection. The second series of images illustrates the same termination
with the shielding boot installed to demonstrate the heating pattern and delta between the two areas.
Bushings installed in oil filled transformers may act as a heat sink resulting in a wider Delta T between the
actual fault location and the observed temperature.
Note: The bare aluminum lug was painted with high temperature flat black paint allowing similar emissivity
settings between the two images.
Figure 8. 15 minutes into 100amp test. Bare connector 44.2°C Shielded boot 26.9°C ΔT 17.3°C
Figure 9. 45 minutes into 100amp test. Bare connector 69.6°C Shielded boot 35.7°C ΔT 33.9°C
InfraMation 2015 Proceedings
2015-003 Peyres
5
©2015 Infrared Training Center, All rights reserved. Reproduction and/or redistribution of this document,
either in whole or in part, is prohibited without written authorization from the publisher.
Figure 10. 75 minutes into 100amp test. Bare connector 72.3°C Shielded boot 40.9°C ΔT 38.4°C
SUMMARY
IR imaging is a key tool in the prevention of dead break elbow failures when used on a routine basis.
Workers should understand the mechanics of constructing this type of termination and be mindful of the
small details that should not be overlooked. The case study should provide the user a good insight to the
heat losses typically seen in a dead break elbow when an anomaly is discovered.
ACKNOWLEDGEMENTS
The author would like to thank the fellow employees at EDP Renewables for their hard work in the early
years before IR maintenance came to existence as they suffered through many long days and nights
dealing with equipment failures and for providing several of the images in this manuscript.
Thanks also goes to the Infrared Training Center at FLIR Systems for their excellent instruction and EDP
Renewables for providing the equipment and resources necessary to conduct the case study.
A final thanks to my colleagues for their assistance and attention to detail allowing this paper to be
possible.
ABOUT THE AUTHOR
Brian is a Level II thermographer with 19 years’ experience in the high voltage industry. In 2009 Brian
began working in the wind industry as a high voltage reliability engineer; his infrared experience played a
major role in the identification and prevention of costly equipment failures.
InfraMation 2015 Proceedings
2015-003 Peyres
6