Internal Fault Detection in
Distribution Transformers
Distribution system challenges
Safety for lineworkers
Operating budgets
System reliability…outage management
Asset utilization
Prepare for the future…workforce & systems
Other directives & priorities shift as well
About your system
An overview of distribution
transformer faults
Current industry practices
A Better Way
Questions
Causes of transformer fuse operations*
50%
46%
45%
40%
* Source:
35%
30%
25%
20%
20%
15%
15%
10%
10%
5%
4%
Connectors
Fuse Holder
5%
0%
No Damage
Fuse
Transformer
LV Wires
Internal transformer fault
A rapid, transient
pressure rise occurs in
every internal arcing
fault
Variable peak pressure
Consistent rate of rise
Internal fault characteristics
500A test - Both fuses used were brand new
1…normal fault
2…fuse failure incident
Arc Voltage
Arc Voltage
Fault Current
IFD activates
before peak
Fault Current
(500 Amps)
~ 3 psi
Pressure Rise
Certification tests at Powertech Labs
slow fuse
reaction
internal
explosion
>20psi in 15
ms
Why internal fault detection is important
Always…
 Operating challenges
 Crew pressures
 Risk every time we re-close
 Worst case…recreation of a
real event
It’s always been important
 Historical Efforts
 Tank re-design
 Arresters
 Flame retardant fluids
 Common Utility Objectives:
 “Zero accidents”
 “Improve customer satisfaction”
 “Improve system reliability”
 “Increase operational efficiency”
Linemen Perspective *
“Have you ever closed on a faulted transformer?”
84% (74) had closed into a fault – some, several times
“If so, what happened?”
42% (37) experienced hearing loss (fuse operations)
26% (19) experienced a cover blowing off during the
operation
(1) injured with oil burns
* 88 Linemen Surveyed at Linemen’s Rodeo, Kansas City - 2009
Obvious
problem
Not obvious
& difficult
Current Industry Practices
1) Field Testing
2) Automatic Replacement
3) Trial & Error
Portable Field Testers*
… “testers are expensive and not
every vehicle has them”
… “they often don’t detect low grade
transformer faults at the voltages
that they generate”
… “I no longer use it because it kept
indicating unfaulted transformers,
but when I re-energized them, they
often faulted – sometimes
violently.”
*Lineman feedback
Automatic replacement
 80-85% of the time the
transformer is OK
 Expensive and time
consuming to remove
the transformer,
transport it to the shop,
test it, and return it to
service
 Hydro Quebec estimate
 300 units/year
Trial and error
1. Visual examination
2. Manual checks,
 e.g., overpressure
 “sniff…don’t inhale”
3. Attempt to re-energize
the transformer
 “Push and pray”
 “Now, crawl inside your
helmet”
 “Go get the new guy"
Sample utility procedures
1)
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Always wear the appropriate personal protective equipment including fire retardant clothing,
hard hats, safety glasses and rubber gloves.
When performing any close inspections of or repairs to the transformer always deenergize
the unit and take precautions from any sources of power including customer generators.
Prior to re-fusing transformers, make a thorough inspection of the transformer and the
surrounding area, looking for indicators such as: animal carcasses, bulged tank or cover,
discolored tank, oil leak, burned oil aroma, flashed or broken bushings, any short circuits
such as wrapped wires in the secondary or service.
Prior to re-fusing transformers, test the transformer with an approved instrument such as a
Transformer Turns Ratio tester. Some companies require some form of testing on every
transformer before they are energized.
When re-fusing a suspected faulty transformer, position yourself as far away as possible by
using an extendable live line tool. Some companies specify maintaining a distance of at
least 10 ft. when re-fusing transformers.
When re-fusing a suspected faulty transformer, always disconnect the customer’s load.
Test the transformer with a smaller test fuse. (Some companies have test fuse tables based
on the transformer size and voltage).
If the transformer blows a fuse and the pressure relieve valve has operated, do not re-fuse
and proceed with replacement.
If the transformer has an auxiliary current limiting fuse that has blown, do not re-fuse;
proceed with replacement. Checking transformer condition
Maintain proper distance when re-fusing. In this condition: do not refuse
Always make sure the neutral is connected first before connecting a transformer and that it
is removed last if disconnecting a transformer.
Do not allow the paralleling of transformers across any point that might be used to isolate a
line section, such as switches, disconnects and double dead ends to avoid the possibility of
back feed into a cleared line section.
Always wear rubber gloves when working on the secondary side of a suspected faulty
transformer.
Take precautions when removing the lid from a suspected faulty transformer by operating
the pressure relief valve. If it is an older unit without a valve, tie a sling over the lid before
loosing the attachments.
Some companies have established step-by-step procedures for investigating transformer
problems while others allow the lineworker to access the situation and take precautions
they deem necessary within mandatory safety guidelines.
It is recommended that step-by-step procedures be developed as they are good training
aids and can serve as a refresher for lineworkers. They also help ensure certain key steps
are followed
…with IFD
Look Up
The internal fault detector (IFD)
 Our Purpose
 Operation
 Installation
 Business Impact
 Development
Our Purpose
To give electric utility employees the
information they need to troubleshoot and
restore power to distribution transformers
faster, safer, and more economically.
How it works
3
Rapid
pressure
rise
Fault
occurs
2
1
IFD activates
IFD status today
 Over 450,000 in service
 200+ utility customers
 Canada: 80% usage
 Simple, safe, reliable…
 Howard
 ABB / PPI
Cooper
GE Prolec
ERMCO
Central Moloney
UUS
Solomon
 Moloney Electric
 ABB
 Siemens
 Carte
 CamTran
 PTI
 CG Power Systems
“See the flag…replace the
transformer”
“…this is great, a safety device that makes us money.”
Vice-President T&D
Value Summary
Savings*
 Efficiency
 Trouble call time savings
 Materials Saved
 Fuses
 Diagnostics
 Keep good transformers
 Reliability
 Improved SAIDI & SAIFI
scores
 Cost Avoidance
 Environmental
 Personnel & Public safety
$120 – 350 / event (1-ph)
$480 – 960 / event (3-ph
banks)
$20 – 30 / event
$3,000 – 4,000 / event
Up to $200,000 / year
$1,000 – 60,000 / event
$ thousands – millions / event
*Customer supplied data
Typical Business Cases
 Hydro Quebec
 30 year planning / evaluation period
 NPV: $1.0 spent returns more than $1.55
 keeping approx. 300 more good units in service / year
 BC Hydro
 Triple Bottom Line (Economic, Social, Environmental)
 PG&E
 safety is primary driver
Product development co-sponsors
 National Research
Council
 CEATI utilities, e.g.:
Technical spec’s
Fault testing
 Hydro Quebec
Field testing
 BC Hydro
 HydroOne
 Manitoba Hydro
 AEP
Certification
 Transformer
manufacturers
Financial support
Product value
New product ideas!
Underlying Magic
Built with utilities
Mechanical ≠ electrical sensor
Measurable $$ value…productivity & NPV
Customer driven R&D company
Product requirements
1)
Primary function: Reliable detection of internal arcing faults
 >0.5 psi/5-7ms transient internal pressure [± 500 amps]
 High visibility
 Easy to install
 Maintenance free
 No effect on transformer
 Etc…
2)
Also: Incorporate pressure relief valve in design
IFD Orca innovations
For Utilities
 One size fits all – pole type,
padmounts, & voltage regulators
 Ester fluids certified
 Easy-to-use shipping lock
 More indicator exposed
 Cap-style dust cover
 Higher flow PRD
 Sealed after activation
For Manufacturers
 Lower profile cup
 Tapered gasket seat
 Larger keyway
 Added thread length
 Thicker nut
 Standard Tooling
One-Size-Fits All
Strategic value
New lineworker is different
ROI improves dramatically over time
SAIDI / SAIFI / Safety  CEO focus
Customer driven technology evolution
Together with customers…
R&D
Products
Applications
Next applications?
Smart-grid extensions
Submersibles
Larger Tx’s
…?
Intelligence
you can trust
“Great idea”
Easy to use
Faster decision making
‘information’…for the entire life
of the transformer