- In this video, we're
going to have a short look
at how we can visually assess
an electrical transformer
in order to determine it's health.
Now we can't look at
every single failure mode
and every single detail of the transformer
because a lot of it is under cover
inside the transformer tank.
This video focuses on
conservator liquid insulated transformers,
you'll see these a lot at
power generation facilities,
and in substations, and also
at large industrial plants.
By the end of the video,
you should be able to
look at a conservator type transformer
and identify if it has any problem signs
that may lead to failure.
The first thing we need
to do is have a look
at the area surrounding the transformer.
Is the area around the transformer,
or the transformer vault
provided with adequate signage
that indicates common hazards
associated with transformers?
For example, high voltage.
Is the transformer enclosure secure
against unauthorized access?
For example, are there fences
surrounding the enclosure?
Is the transformer vault closed?
Are the doors secure?
Is there any form of video surveillance?
Sometimes transformers are installed
quite close to a road or a railway.
And you have to ask
yourself is the transformer
adequately protected from impact damage?
If the Transformer is
installed near a road,
then perhaps a barrier should be erected
as a precaution against passing traffic.
Transformers are often fitted
in groups, side by side.
If this is the case, are
suitable fire barriers provided?
And are there any penetrations
through the fire barriers?
If so, are they adequately sealed?
Is there any vegetation
growing around the transformer?
If a transformer is installed in a vault,
is the vault well ventilated and clean?
Are there any combustible materials
stored near the transformer?
Is this an appropriate location?
It's not unusual for
people to stack pallets up
near a transformer vault and sometimes
even in front of the
transformer vault doors.
Is there a fixed fire
suppression system installed?
And if not, should one be present?
This depends a lot upon the
criticality of the transformer.
And finally, does the
transformer have a bund
directly underneath it
to capture any oil leaks?
This is particularly important
if the transformer is installed
in an area that is
environmentally sensitive.
So now that we've looked at
the area around the transformer,
and identified any risks
that may be present,
let's have a look at
the transformer itself
in order to perform a visual inspection.
So here is our conservator
type transformer.
It's called a conservator type transformer
because of the conservator
tank in this area.
We're going to visually
assess the transformer
in order to look for any possible risks
that might lead to transformer failure,
or perhaps a shortening
of it's service life.
So let's start with the basics.
How clean is the transformer?
How rusty is the transformer?
Are there signs of corrosion?
Are there signs of oil leaks?
We can actually see that this
transformer is very clean
and there are no signs
of leaves on top of
the transformer casing.
No signs of sand accumulating
around the transformer.
There is also no corrosion
and no oil leaks.
Let's start by looking
at the heat exchangers,
also known as the radiators.
These should be quite clean.
The reason we want them
to be clean is 'cause
we have to pass the heat
from the radiator to the air.
Sometimes when you look
through the radiator panels,
like we're doing here,
you might be able to see
through to the other side.
But if not, you should be
able to get a good indication
of the condition of the panels
just by looking for stuff
like dust that may get
stuck between the panels.
Another way to inspect these panels
is to use a thermographic
camera, but I'm going to assume
that we don't have one of
those with us right now.
If we zoom out, we can have a look
at the other end of the heat
exchanger, or the radiator,
and that is where our fans are installed.
The fans are not in
operation at the moment,
but if we put them in operation
we can see they're turning.
There's no noise, there's no vibration.
So the fan is operating as it should be.
If the bearings are failing,
then the fan will start to make
louder than average
noises, or abnormal noises,
and these abnormal noises usually indicate
that maintenance is required.
While we're talking about noise,
as you approach the transformer you should
be able to hear it making
a light humming noise.
(humming buzz)
This light humming noise indicates
that the transformer is
loaded, or energized.
And as you increase the
load on the transformer,
the noise becomes louder.
As you increase the load
the transformer also becomes hotter.
So if the transformer is making
quite a loud humming
noise, and you can see
that the fans are all in
operation, like they are now,
then that's indicating the
transformer is heavily loaded.
If the fans are off, then we can assume
that the transformer should
be humming quite lightly.
Warning signs are when you
approach the transformer
and it makes a crackling or popping noise.
(crackling popping)
And this is definitely
not a positive thing.
And you might want to ask personnel
the reason, or for how long
this has been occurring.
Around the front of the transformer tank,
we have a tap changer control box.
If you look through the panel here,
you'll often see a tap counter.
This indicates to us how many
taps a tap changer has made.
And the maintenance interval
associated with a tap changer
is usually either time based, for example,
once a year, or once every two years.
Or it's tap based, for
example, every 70,000 taps.
So check the tap counter,
and then compare the number of taps
to the maintenance intervals
that are currently employed.
The tap changer itself is mounted either
inside the transformer tank itself,
it's actually mounted in this space here,
or it's mounted in a separate tank.
It really depends upon
the transformer design.
But we're not going to see
that during our inspection.
So let's have a look at the next item.
This item here is to do
with temperature control
of the transformer and monitoring.
We've got a sensor that's installed here,
it's measuring the oil temperature.
I say oil, oil is used 95% of the time
for a liquid insulated transformer.
But just be aware there
are other instances
where you will not use mineral
oil, particularly in plants
where they don't want to
have a high fire load.
We have a temperature gauge here.
The black needle indicates
the current temperature.
The red needle is a follower needle,
and that indicates the maximum temperature
that was achieved since
the needle was last reset.
So normally if we put the
red needle here for example,
around the 75 degrees Celsius mark,
the black needle if it
comes past the red needle,
it will push the needle along
and for this reason the red
needle is called a follower.
And then the red needle will stay
at the highest temperature it reached,
but the black needle will
go back the other way.
So check the red follower needle.
If the red needle is around
here, at 150 degrees Celsius,
then the reason for that is
definitely worth investigating.
We zoom out here, we can
have a look at the bushings.
Can see we've got the bushings
sticking out of the top
of the transformer tank.
The bushings are a common failure mode
for electrical transformers.
I believe they're in the
top three failure modes for transformers.
So pay attention to the
bushings, look at the condition.
Look for any signs of
cracking on the bushing,
any signs of dust accumulation,
and any signs of scorch
marks, or black dark areas
where the bushing might have
been heated up considerably.
Let's go over to the other
side of the transformer tank.
We've got a Bucholz relay mounted
just above the transformer tank
and underneath the conservator tank.
The Bucholz relay is there
to protect the transformer
should it have a minor
electrical fault internally,
a major electrical fault
internally, and also
if the insulating liquid
level should become quite low.
So it's a very important device.
But when we're walking around,
we want to check things like
is the arrow pointing
in the right direction.
Usually there'll be an indication
like we're seeing here.
That's should point towards
the conservator tank.
If there are valves before
and after the Bucholz relay?
Are they open?
Is the Bucholz relay installed
parallel to the ground?
Sometimes people install
these relays at an angle.
That's incorrect, because
if we get any gas accumulation
from the transformer,
it will form of pocket in this space.
And if we have a Bucholz
relay at an angle,
then we get an incorrect reading.
So they're designed to
be installed in parallel
and that's how they should be.
Check the valves around the Bucholz relay,
for example, this one here,
make sure that it's not half open.
And also see we've got
an electrical connection coming in here,
the cable would come up and connect.
Check that connection for corrosion.
Usually you can just see the
condition from the ground.
And if we zoom further out,
we can have a look at our
next protection device
that we can inspect when
we do our little tour.
We've got a level indicator here.
This is actually hooked up to
a float switch inside
the conservator tank,
and this needle is going
to move up and down,
depending upon the level
in the conservator tank.
The level in the conservator tank changes
because as this transformer gets hotter,
the insulating liquid also
increases in temperature
and expands.
And as the transformer becomes cooler,
when it's less loaded, the
insulating liquid contracts
and the level in the tank goes down again.
But at a certain temperature
we should see here
that at a certain temperature,
we should have this level.
If you notice that the
temperature is indicated
and the level is far off, for
example down here somewhere,
then perhaps there are oil leaks present,
and that's something that
should be investigated.
These red marks here usually
indicate alarm set points,
and an alarm will sound
if we reach these red points here.
On the outside, we can also see,
if we come around here,
a silica gel breather,
also called a desiccant
breather, or simply a breather.
As I mentioned before,
the transformer becomes hotter and cooler
and the insulating liquid
expands and contracts,
and that means that the air,
which is at the top of the
conservator tank roundabout here,
that air is going to be
pushed out and drawn in
as the insulating liquid
expands and contracts.
We're going to have to let
air out of the transformer
and then draw air back in.
And we're going to do
that through the breather.
The problem with drawing air
into the transformer though,
is that we may have contaminants
in the surrounding area
such as moisture or spray
salt, if we're near an ocean.
Or even just bits of dust.
All of that will contaminate
our insulating liquid
and potentially shorten the working life
of the transformer considerably.
So we have an oil cup.
That is this brown area around here.
As the air is drawn into the breather,
we can see there's holes here.
As the air passes through,
it's going to leave the
dust particles on the oil.
The oil is going to attract them.
And then the air will pass up
through these silica gel beads.
Although another drying agent may be used.
Silica gel is the most common.
And then the air,
once the moisture has been
extracted by the drying agent,
will pass up here, and
into our conservator tank.
The most important thing to check here
is that the oil cup is not too full.
Sometimes the oil cup will be
very full and you'll see that
oil has soaked into the drying agent here.
That shouldn't be the
case, that shouldn't occur.
Sometimes you have too little oil
and that means that the air
is just simply passing up
through this tube here,
and the dust particles and not
being adequately separated.
Ideally you want to see the
oil at exactly this level here
so the transformer can
breathe in and out slightly
and the oil will move around
or allow air bubbles to pass through it.
So we've looked at the oil cup,
and we've ensured that
that's actually going to
separate dust particles
and things like that
before they get into the conservator tank.
When we're looking at the drying agent,
we want to make sure
that it's not saturated.
As we're removing more and
more moisture from the air,
the drying agent is actually
going to change color.
It does this because
this helps us see exactly
when the drying agent is saturated,
and when it can no longer
absorb any more moisture.
If we have 25% of the drying agent column,
which is saturated, and 75% not,
then we'll be able to see this
because the lower 25% of the column
will be a different
color to the upper 75%.
As the drying agent becomes
more and more saturated,
this color from the bottom
will creep slowly upwards.
The most important thing
here is that we do not want
more than about 70% of our
drying agent to be saturated
because at that point, the
drying agent is perhaps
not going to be able to
remove all of the moisture from the air
before it gets to the conservator tank.
Moisture entering into
the conservator tank
is a big problem.
If we get that then we may have to dry out
all of our insulating oil,
which is very expensive.
And we also might have to
take the transformer offline.
If the drying agent is one solid color,
then it's always worth asking,
what color should it be
when it's not saturated?
And what color is it when it is saturated?
Sometimes you might be quite surprised
with the answer you get.
So we've conducted
our visual assessment of the transformer.
Obviously, there are many
things that can happen
inside the transformer
that lead to failure.
But this initial assessment
that we've just done
is a very useful and
quick way to determine
the health of the
transformer from the outside.
If we need to determine the
health of the transformer from the inside,
then we're going to have to
have very specialist tools
We're going to have two
highly trained personnel.
And typically, these sort
of tests and procedures
are only conducted maybe once a year,
because they require the
transformer to be shut down.
So compared to what we've just done,
that's actually quite a lot of work.
There is a transformer checklist
associated with this video,
so please be sure
to download that PDF
if you want to use it.
It goes into a lot more depth
concerning how to assess
the health of a transformer,
not just visually but
also by checking paperwork
and performing a criticality assessment.
And if you want to learn more
about transformer protection devices
such as Bucholz relays
and the magnetic oil gauge
which is mounted onto
the conservator tank,
then you can click on
the links in the PDF,
and each of those links will
load up more information
concerning each of the protection devices
associated with the transformer.
Thanks very much for your time.
