joseph d. gierlach jr. vice president abm franchising ... · operating parameters transformer phb...

Joseph D. Gierlach Jr.

Vice President – ABM Franchising Group ~

TEGG Service

Electrical Ultrasound - Past and Present

What assets are critical?How important can ultrasound be?

Can anything really be gleaned?


We will discuss the 5 common faults in these components and review their spectral signatures

1) Arcing

2) Tracking

3) Corona (above 1000 Volts)

4) Mechanical Vibration

5) Mechanical/Electrical Looseness (Contact Chatter)


Transformers are one of the most critical components in the

electrical system

Most often, they are not readily available in the event of a failure

It does not matter if it is a liquid filled or dry type unit, maintenance is key

to longevity, as the components are the same internally.


Today’s example involves a unit similar to the ones pictured below.

The initial service was performed in October 2011

It is in a hospital in Ohio and was manufactured in October 2004


Energized services were conducted in the beginning of

October 2011

This was a 2nd year visit to the customer in which assets

were maintained the previous year with no issues noted

The technicians obtained recordings of each winding in

question, along with a comparison of another unit under

similar operating conditions


A Phase B Phase C Phase

Click each winding to play

This is what

they heard


A Phase B Phase C Phase

Click each winding to play

There was a

sister

transformer

nearby for

comparison

recordings


FFT display

illustrating

comparison

between the

two units “B”

Phase Coil

Clearly a

qualitative

difference


Time Domain

for the suspect

coil


Time Domain

for the

comparative

coil


“Sliced” view of

the time on

suspect coil…..

Note the

differences in

the amplitude

of the peaks

and variations

in timing


The FFT illustrated “fault frequencies” that were NOT 60 hZ harmonics,

which indicates something other than electrical

However, there was an abundant amount of “frequency content

throughout the spectrum…..something electrical


With a 30 hZ harmonic cursor, the mechanical component can be seen

Although it is a small, negative type “peak”, not electrical


Operating Parameters

Transformer PHB (Bad)

Winding 1 (A phase) = 870 amps

Winding 2 (B phase) = 877 amps

Winding 3 (C phase) = 960 amps

Square D , Power Dry II , Serial# 17157191-008-01 , Type=VPI

2000 KVA , class AA/FFA , Temp Rise 115 deg C

High=12,470 Volts

Low=480Y/277 3 phase LV

Amps=2406

Z=5.76

Exposure=Cat C , 12200 lbs Tapped at E&G

Manufacturer Date=10/1/2004

Transformer PHA (Good)

Winding 1 (A phase) = 830 amps

Winding 2 (B phase) = 830 amps

Winding 3 (C phase) = 890 amps


Another good indicator that something was in fact occurring was the

comparative Infrared images………

Note the saturation on the suspect winding…(Dynamic range exceeded)

PHA (Good) PHB (Suspect)


With the suspect winding “exceeding” the calibrated range of the IR

camera, we know the temperature is now higher 150 Degrees C…..

The thermal source is also within the winding itself on the vertical core

section, based on conductive heat transfer patterns.

PHA (Good) PHB (Suspect)


With this evidence and supporting data, a shutdown was recommended to the

customer.

This would allow for further diagnostic testing as well as a thorough visual

examination to determine the root cause of both the ultrasonic emissions and

the elevated thermal energy present on the B Phase coil.

The electrical tests that would be necessary to determine if any damage has

occurred electrically would be as follows:

1. Insulation Resistance

2. Winding Resistance

3. Turns Ratio Testing

4. Power Factor Dissipation


The electrical tests did not reveal any abnormalities and were within industry

standard limitations:

Winding resistances are within the balance limits of 1%




Insulation resistances are within the Polarization Index requirements




Turns ratio measurement are within the +/- 0.5% tolerances of the

calculated ratio and the adjacent windings


Power factor dissipation measurements were within the NETA specified

limits, indicating no excessive losses through the insulation


Visual Image

of the suspect

winding and

area of highest

emission


This is good news for the customer, or is it……

The answer is “yes and no”……as the visual inspection reveals

something far more telling…….Can you spot the item of interest?

A Phase B Phase


A Phase

Welded retaining strap to tightly join vertical clamping steel with

horizontal

Top Horizontal Steel

Vertical Clamping Steel –Outside Phase, Low Voltage

Side

NOTE: This joint is FLUSH, and the sections are even and flat


B Phase

Clearly, these steel pieces are NOT flush, which indicates a distortion of the top horizontal section bowing out on the B Phase winding, low voltage side


This is EXACTLY where the ultrasonic emission was at its greatest intensity!


B Phase

Visual evidence of excessive heating on the core laminations, backing up what was observed with the infrared camera


B Phase

Visual evidence of

laminate separation

within the horizontal

core piece

For perspective, a flat

head screwdriver fit

into this separation

“with ease”


Lamination separating

even further into the

core toward the high

voltage side


One more

indicating

thermal

effects on

the varnish

of the core

laminations


Because the miter joint that

connects the center phase to the

top horizontal laminations is no

longer connected properly due to

the “bowing” of the joint………

The magnetic flux path becomes

“interrupted” or “disturbed” ,

thereby making it the most likely

cause of the ultrasonic emission

and leading to the additive thermal

heating


The sister unit that was used for

the comparative recordings was

also examined

It is exhibiting signs of cracking in

the varnish

Because it is the same design, it is

safe to say it could be subjected to

the same problem


A follow up visit to the location one

year later, and after multiple

conversations with the

manufacturer proves the issue is

still present…………….and

worsening

Click to play

It’s only a matter of time before the

electrical fault/failure occurs as a

result


REVIEW OF TYPICAL MECHANICAL LOOSNESS

SIGNATURES:

1) Typically all fault frequencies up to 900 hZ on relative

frequency scale (offset from 60 hZ in this case)

2) Lacking “frequency noise” in between harmonics (not the

case in this example, electrical fault developing as a result of

the mechanical issue)

3) Time series has consistent, uniform amplitude bursts

ALL ARE PRESENT IN THIS EXAMPLE EXCEPT #1

**Delamination of the core pieces due to magnetic field

interaction, which led to winding insulation damage

Would you think a

simple 30 amp

240 volt circuit

breaker have an

ultrasonic

emission?


Take a listen to

what was heard in

Atlanta Georgia…

Click Image to

Play


This observation was supported by the infrared camera in this

instance…


With moderate loading (72% of rating), the temperature was

almost 20 degrees C above the ambient air……….expect no

more than 10 degrees C


FFT comparison to a tracking sample reveals the nature of

the emission………………………electrical


Larger view (Red = Known---------------White = Suspect)


Time Series reveals signature inconsistencies in amplitude and timing of

events


Sliced up it is even more convincing……………….


Combination of

a bad internal

contact and line

side connection

issue was the

result as

evidenced by

the thermal

patterns



Another low voltage, 240 volt, double pole breaker……. 3-8-2010

Click to play


Suspect breaker is feeding a critical load and running at 45% of rating


FFT shows electrical in nature…


Comparison to known sample, (fault in red, sample is white)…


Full recording time series……


512 ms view…….


278 ms view (appx 25 cycles……. Clarity is achieved for tracking picture


Another tracking event, only this is on a 50 hZ system……. 2-10-16

Click to play


Balanced loads of 500 amps per phase, 1600 amp rating


Surface temps are “low”………or are they……….INDIRECTLY


At the source (i.e. contacts), temps are MUCH HIGHER…


FFT Indicates has a familiar signature…..ELECTRICAL


Some 50 hZ harmonics, rich frequency noise………. = TRACKING??


We need the Time Series to determine exactly…..and we see on the

large view variations/inconsistencies in time and amplitude…..


Sliced to ¼ second (appx 12 cycles), it is CLEAR now…


REVIEW OF TYPICAL TRACKING SIGNATURES:

1) Several fault frequencies (not present in this case)

2) Abundant “frequency noise” in between harmonics

3) Time series has bursts or excursions throughout recording

period

4) The amplitude of the bursts are not uniform in nature

ALL ARE PRESENT IN THIS EXAMPLE

**Most likely arcing and tracking within the unit / contacts

respectively


Maintenance Panel Circuit Breaker 3-2015, 60 hZ

Click to play


Very similar FFT spectrum to tracking with a twist…..


The 60 hZ harmonics are more abundant in the spectrum with

frequency noise…..


The Time Series looks more like a mix of arcing and tracking ……


Variations were due to changing load levels…..


REVIEW OF TYPICAL CONTACT ISSUE SIGNATURES:

1) Abundant fault frequencies


3) Time series has bursts or excursions throughout recording

period

4) The amplitude of the bursts are not uniform in nature

ALL ARE PRESENT IN THIS EXAMPLE

**Most likely arcing and tracking within the unit / contacts

respectively


UK Packaged Substation Arcing………..

Click to play


UK Packaged Substation Arcing………..


FFT shows no 50 hZ fault frequencies


Full 30 second recording on time series shows a different story………


Notices the bursts , total silence, then bursts again


5 second sliced view……………………..


2 second sliced view, far more pronounced and evident……………..


REVIEW OF TYPICAL ARCING SIGNATURES:

1) Several fault frequencies (not present in this case)


3) Time series has large bursts and some apparent

periods of silence

**Contact degradation due to misalignment and/or

poor seating pressure


One more with destructive corona, packaged sub 7-2009:


Initial recording on top left of switch was made…

Click to play


FFT shows some frequency noise but little fault peaks….


Time series has some tale,tell signs of something familiar….


We need a closer look with a smaller time base…


2 Months later, another recording……9-2009, but a different location

Click to play


FFT shows more pronounced harmonic and noise content


Particularly when compared to previous recording


Full Time Series looks similar, but greater amplitudes


Intensity increase visualized on scale differences…….


300 ms view of second recording


300 ms view of second recording, again illustrating intensity

increase


Shutdown was immediately scheduled for 2 weeks later, visual

evidence of the fault was observed


Nitrates had materialized already, failure has begun…


Destructive corona, as indicated by the Spectralyzer analysis is

confirmed and repairs completed…

ANY [email protected]

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joseph d. gierlach jr. vice president abm franchising ... · operating parameters transformer phb...

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