Transcript vacuum drying - Welcome to Vishvas Power Engineering

SEMINAR ON
PREVENTIVE MAINTAINANCE AND
CONDITION MONITORING FOR
POWER TRANSFORMERS
PRESENTED BY M/s VISHVAS POWER
ENGINEERING SERVICES PVT.
LTD. NAGPUR
INFORMATION ABOUT
COMPANY
 NAMES OF DIRECTORS :Mr. R. M. Bhave
: Mr.S.V.D’mello
:Mr.Kiran Joharapurkar
 PRODUCT SKILLS OF DIRECTORS
:HT switchgrars
: Transformers (all make)
:On load tap changers (all type)
 No. of engineers/site managers:10
 Office staff:04
 Other staff/skilled workers:80
INFORMATION ABOUT COMPANY
AREAS OF BUSINESS INTEREST
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Capital overhaul/servicing of power transformers
Servicing of SF6 breakers
Servicing of on load tap changers.
Annual maintenance contracts for substation and control
room maintenance.
Testing of oil and bushings.
RLA studies on power transformers.
Testing of oil and bushings.
Installation services for power transformers, HT
switchgears and substation equipments
Retrofitting of LT air circuit breakers
Installion of rubber balloons in conservator of power
transformers to retard oxidation of oil
Testing and commising of substations
Testing of transformers
Doubts raised by users
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Whether oil filteration or dry out
Criterions of stopping dryout/filteration
Whether overhauling/reinsulation
Frequency of condition monitoring
Oil mixing ---------- preconditions
Dissolved Gas Analyis
PLEASE LET ME KNOW
WHAT YOU EXPECT FROM THIS
SESSION?
Areas of concern
 OIL
 PAPER
 Wood (treated /
parmali
 WINDING
 TANK
 LEADS
 OLTC
 BUSHING
 COOLING BANKS/
HEAT EXCHANGER
 AUXILIARIES
IMPORTANT STANDARDS
TRANSFORMER USER SHOULD
KNOW
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IS 335
IS 12463
IS 1866
IS 2099
IS 2026
TRANSFORMER FOR
OVERHAULING
PROCESS OF OVERHAULING
TESTING
POST SHUT DOWN
OBSERVATIONS
POST SHUT DOWN
OBSERVATIONS(CONT..)
OIL DRAINING
DISMANTLING
125 MVA TOP
COVER LIFTING
GASKET REPLACEMENT
INTERNAL INSPECTION
PREPARING TRS FOR EVACUATION
N2 PRESSURE TEST
VIEW OF LEAD TAKE OFF
IEEE GUIDELINES INTERNAL
Inspection
 Winding - Lead clamping
Winding support system
Clamping
Insulation discoloration
Lead distortion
Lead movement
Indications of hot spots
IEEE GUIDELINES INTERNAL
Inspection
 Loose connections -
 Physical status-
Tap leads
Bushings
Terminal Boards
Spacers
Core bolt nuts.
Contacts
Operating mechanism
Coupling shafts
Shielding
IEEE guidelines for
Internal Inspection
– Oil-
 DiscolorationTerminals
Corona shields
Copper connectors
Bus bars
Odour
Color
Moisture
Free Water
Tank walls
Bushing
Vacuum drying
Vacuum drying is based on the principle of
Thermodynamics
Boiling point of moisture in insulation is
reduced by way of Pressure Reduction
Principle
Thermal energy needs to be imparted
externally for achieving faster and better
moisture extraction
DRY OUT PROCESS
INVOLVING CYCLES
Vacuum drying( continued)
Under vacuum (pressure reduction)boiling
point of water reduces to 500c
medium of heating can be
Old oil
Nitrogen
Hot air
other methods of heating are also under use.
Process of dryout
Prepare TRS for evacuation
Fill N2 over air to get pressure
0.2KG/CM2
Attend leakages
PRESSURE TEST
NITROGEN PRESSURE
Continue to heat till
Core_< 70 c
Med _< 75c
Wdg _<70c
COMPARISON OF HEATING
METHODS
OI L
NITROGEN
 REQUIRES OLD OIL
FOR HEATING
 REQUIRES NITROGEN
GAS
 REQUIRES FILTER
PLANT OIL
RESERVIORS
 REQUIRES EXTRNAL
HEATING ELEMENTS
SUCH AS HEATERS
 REQUIRES LESS
MONITORING
 REQUIRES MORE
VIGILLANT
MONITORING
 OIL SOAKED INSULATION
DOES NOT RELEASE
MOISTURE VERY FAST
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 IF OIL IS ACIDIC THEN IT
CAN AFFECT INSULATION
PAPER
 DRY AND NON
SOAKED INSULATION
RELEASES MORE
MOISTURE AND IN
FASTER WAY
 THIS METHOD IS NOT
CONSIDERED PRESENTLY
AS USER FRIENDLY
METHOD
 IF NITROGEN IS
PURE IT CANNOT
AFFECT INSULATION
PAPER & COPPER
OIL
 MONITORING
PARAMETERS ARE OIL
BDV & MOISTURE
CONTENT OF OIL USED
FOR HEATING PURPOSE
 OIL WILL LOSE/REDUCE
ITS PARAMETERS SUCH
AS RESISTIVITY,
TANDELTA WHEN HEATED
ABOVE 600C
NITROGEN
 THIS METHOD IS
PRESENTLY CONSIDERED
AS USER FRIENDLY AND
TECHNICALLY BETTER .
 MONITORING
PARAMETERES ARE
CONPARISON OF IR
VALUE AND DRYNESS OF
NITROGEN GAS USED
FOR HEATING PURPOSE
 NITROGEN HEATING
DOES NOT INVOLVE
OIL HEATING ABOVE
600C
Details of nitrogen heating
 Nitrogen gas: 99.6% pure
Dew point-40c &
better
 Pressure gauge: 0.1 To 1.0KG/SQ.CM
 Vacuum gauge: MM scale: Bourden
torr scale: Macleoid
M-bar scale
HEATING ARRANGEMENT
VIEW OF HEATING ARRANGEMENT
HALOGEN HEATING OF TANK
VIEW OF SHED FOR HEATING
DRY OUT IN
PROGRESS
PT 100 SENSOR FOR
TEMPERATURE MONITORING
Heating cycle duration will depend upon size of
trs
100-250 MVA
72 hrs
50 MVA
48 hrs
25 MVA
24hrs
Vacuum cycles 1 for
60/72 hrs
Heating cycles 2 :36/48 hours
Vacuum cycle 2 : 48/60 hrs
Heating cycle 3 :24/36 hrs
Vacuum cycle 3 :36 hrs
Heating cycle 4 :36 hrs
Vacuum cycle iv
N2 filling Ir. value
measurement dew pt
measurement
Take vacuum and
fill up oil
While filling oil fill under vacuum
and fill from top filler valve
Break vacuum over oil
by N2/ dry air
Oil toppling up oil circulation
Oil testing at site for
BDV >_ 60 kV
moisture content
<- 10 ppm
Stop filtration if oil parameters
are satisfactory as per voltage
class of trs.
VIEW OF FILTERPLANT OIL
TANK AND DG SET
TRANSFORMER AFTER
OVERHAULING
TRENDS IN OIL
Napthene based oil
1. Low pour point enabling the use in low
ambient temp.areas
2. Oxidation products are soluble in oil.
3. High resistivity.
4. High Viscosity.
Paraffin based oil
1. High pour point but no problem in country like
INDIA.
ALKYL BENZENE BASED OIL
1. Low Tan Delta
2. High resistivity.
3. No sludge.
4. Low viscosity.
5. Very low pour point.
6. Non hygroscopic and does not form
gum and sludge.
OIL COMPARISION
PARAFFIN NAPTHA ABTO
TAN DELTA
0.09
0.03
0.0009
RESISTIVITY
2*10
10*10
50*10
IFT
18
21
42
VISCOCITY
23
21
15.1
SLUDGE
CONTENT
0.1
0.05
NIL
SYNTHETIC OIL
1. Used due to fire resistance property
2. Contain polychlorinated biphenyl.
3. Hazardous for dumping in earth or
otherwise.
EFFECT OF MOISTURE CONTENT IN OIL ON
IMPULSE STRENGTH
100%
70%
IMPULSE
STRENGTH
30 ppm
MOISTURE CONTENT
Oil color Interpretation
ASTM- color
ASTM - D1500-91
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Clear
Pale yellow
Yellow
Bright yellow
Amber
Brown
New condition
Good condition
Service condition
Marginal condition
Bad condition
Severe bad condition
OIL COLOUR INTERPRITATION
 Dark brown - Extremely bad condition
Sludge - To detect presence of pentane
insoluble sludge in serviced oil
THE TEST IS not Performed unless
IFT <26 dynes/cm
ACIDITY> 0.15 mg of KOH gm of oil
IS 335
Density
Viscosity
IFT
Flash point
Pour point
BDV
TAN DELTA
RESISTIVITY
o.89 gm/cm3 at 29.5º C
27 MAX at 27º C
0.04 N/M
1400c
-60c
30 KV unfiltered
60 KV filtered
0.002
35*1012 ohm-cm AT 90º c
1500*1012 ohm-cm AT 27º c
IS 335
Acidity
Sludge
Corrosive sulphur
oxidation inhibitor
Water content
0.4(max)
0.1% (max)
No traces
0.05% (max)
50 PPM max
(unfiltered)
15 PPM max
(filtered)
DISSOLVED GAS ANALYSIS
 Most widely used and effective technique.
Requires skill to draw inference.
FAULTS
 Thermal aging - overhead metallic parts
 Partial discharge
 Arcing
FACTORS INFLUENCING GAS
PRODUCTION
Meaningful assessment of a Transformer on
basis of DGA is possible if information and
data is considered on following factors
which influence gassing rate & gassing
comparison
 Oxygen content of oil
 Oil temperature
 Ambient temperature
Dissolved Gas Analysis
Methodology
 Gas tight syringe with a 3 way stop cock
 Stainless steel tubular bottle
 Bottle capable of being air/gas tight with
screwed cap
Labeling
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Details of transformers
Date of sampling
History of transformers
Temp of transformer
Charged/service condition
Ambient Temp.
STAGES
 Collection of oil sample.
 Extraction of gases in dissolved oil.
 Separation identification and
quantitative determination of gas
 Interpretation.
Key gas and fault pattern
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C2H2 (Acetylene)
:Arcing
H2 (Hydrogen)
:Partial discharge
C2H4 (Ethylene)
:Oil overheating.
Co/Co2 (Carbon monoxide & Carbon
Dioxide)
:Conductor
overheating
Various
h2 ch2 c2h6 c2h4 c2h2 co co2
sources
IEEE
140 160 115 190 11 580 -GTR
100 120 65 50 35 350 2500
CIGRE
28.6 42.2 85.6 74.6 -- 289 3771
DOBLE
100 100 60 100 5 250 -New Trs
200 100 100 150 15 500 ---Old trs
250 200 200 300 35 1000 -Oil overheating
c2h4 c2h6 ch4
Cellulose overheating
co
Partial discharge in oil
h2 ch4
Arcing in oil
c 2h 2 h 2
 KEY GAS : Hydrogen
 ARCING : Between leads. Leads to coil.
 KEY GAS :Acetylene , Hydrogen
IEEE
Arcing
:Acetylene C2H2
:Hydrogen H2
Carona
: H2
Overheated oil :Ethylene C2H2
:Methane CH4
 Thermal degradation of insulation material
=Co, Co2, H2o
Healthy ratio of Co/Co2 = 5
If ratio is below 3, it indicates severe
overheating of paper.
Oil degradation : Methane(CH4),
Ethane(C2H6)
Ethylene(C2H5)
 Partial Discharge : Occurs due to ionization
in high stressed areas where gas/vapour
filled voids.
STRATEGIC END OF LIFE
ECONOMIC END OF LIFE
TECHNICAL END OF LIFE
DEGREE OF POLYMERIZATION
INITIAL : 1200
POOR : 300
AFFECTING PARAMETERS
TEMPERATURE
MOISTURE
ACIDITY
Comparison of Furful content in
various generator transformers
Sr. Of
GTR
Nameplate Calculated Actually
Elapsed
Found Furful Age
age
Furful
Content
mg/lit
1
15.60
0.216
3.170
29.30
2
14.66
0.180
0.150
13.65
3
6.0
0.030
0.035
6.30
4
5.0
0.027
0.032
6.00
Site
DP
A
392
Estim Furful Estim
ated value ated
age
age
25.0 0.60 20.6
B
710
12.0 0.20 15.6
C
978
1.0
D
458
22.0 0.4
0.01 02.0
18.8
Interpretations of impedance test
Variation in short circuit impedance of a
transformer winding indicates possible
movement of winding/deformation within the
transformer
 Variations upto 2%
--Negligible
 Variations upto 3%
--Significant
CASE III
16 MVA
TRANS
110/22KV
EXCITATION
CURRENT IN
MILI AMPS
2U-N
2V-N
2W-N
232
175
52
54
232
175
18
215
232
350
95
101.9
AGEING OF INSULATING PAPER
With advanced instruments available for
technical analysis of aged insulation it is
possible to determine /measure following
properties of insulation paper
1. Thickness
2. Water content
3. Tensile strength
4. Degree of polymerization
TENSILE STRENGTH
1. Determined as per IS 1924 determined in
both machine direction and cross machine
directions.
2. Deterioration of tensile strength is further
dependent on temp. factor.
3. The rate of tensile strength deterioration is
exponential with time.
Tensile
strength
Ageing (days)
Degree of polymerization
This proves to be the most informative
parameter for assessing the ageing or the
process of ageing of cellulose . The
connection between deterioration in material
properties and formation of aging products
is degree of polymerization.
This is also direct decomposition of cellulose.
DETERIORATION OF PAPER
900 c
Degree
of
polymeri
zation
1050c
1200c
150
Days
Source documents / forums
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IEEE
ANSI
I.S.
C.B.I.P.’s INT. Conference
CIGRE’s working group
Our own field experience
Abnormalities observed during internal
inspection/ capital overhauling
EXTERNAL
1 Pumps running in
reverse direction
2 Thermosyphon
blanked
3 Thimble-terminal
cap fusion due to
heating.heat
generated due to
faulty
term.connector.
INTERNAL
1 Cotton tape used for
gasket locating not
removed causing
leakage
2 Core bolt insulation
zero
3 Selector switch
contact arm assy
not making
adequate contact
Abnormalities(continued)
4 Bucholz pipeline slope
not proper
5 Lens screw of OLTC
shaft not properly fitted
6 Oil leakges in box type
stiffner, between main
tank and stiffner
4 Core earthing melted.
Part of laminations
fused.
BUSHING
TYPE
 SRBP/OIP/RIP
TEST TAP
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FOR MEASUREMENT
MUST BE EARTHED
PROPER EARTHING
CORROSION OF THREADS ON
CONNECTION CAUSES HIGH
RESISTANCE AND SPARKING
3
Measurement of mounted bushing done
in UST mode , using test tap connection
4
Measurement of winding is done in GST
mode using connections between
bushing top terminal and grounded.
1
GST
SPECIMEN
INSULATION
SPCIMEN IS
GROUNDED
UST
UNGROUNDED
MEASURING UNGROUNDED GROUNDED/g
IS PROVIDED
CIRCUIT/
THROUGH
EQUIPMENT
EQUIPMENT
2
 10 kV is a referred as a preferred reference
voltage although usually measurements of
tan delta and capacitance should not vary
with applied voltage.
 Usually measurements at 2 KV,5KV and
10KV are taken at site.
 Capacitance value measurement is equally
important.
 Tan delta value measurement may get
affected by conditions such as oil.
temperature, humidity, surface cleanliness
and inductions in the switchyard.
DGA OF OIL FOR BUSHING
[IEC-36A]
Type of key gas
H2
CH4
C2H6
C2H4
2 2
CH
CO
2
CO
Permissible limit
100 ppm
30 ppm
50 ppm
300 ppm
02 ppm
1000 ppm
3000 ppm
Predictive maintenance for OLTC
 Contact resistance measurement .
 Measurement of divertor motor acoustic
signals.
 Temp difference between oil in main tank
and oil in divertor switch.
 Dissolved gas analysis.
 Deposition of solid carbon.
Predictive maintenance(cont...)
 Changes in switching time weak springs,
 Overhauling
 Contact wear
Precautionary steps for ensuring
correct installations
Paper Moisture
420 KV
0.5 or less
245 KV
less than1.0
145 KV
less than 2
Oil Moisture
420 KV
less than 10
245 KV
less than 15
145 KV
less than 20
SETTLING TIME
KV
420 KV
245 KV
145 KV
Time
72 hours
48 hours
36 hours
Magnetic balance test is like a
signature test
Diagnostic tool with focus on current
is more important
Quality of core is not assessed
if voltage distribution is in order but
current are not then further analysis
is required
Partial Discharge
1 Effective for comparing at factory/ at site
after repairs.
2 Advanced diagnostic system used for
off line PD detection.
3 Background noise suppression, using a
Spectrum analyzer to do selective
filtration.
FREQUENCY RESPONSE ANALYSIS
Short circuit high fault currents can lead to
displacement of windings.
An already weak coil or an insulation system
can fail, during over voltage stress.
Background.
Electrical measurements are not sufficient to
indicate this type of displacement of coil or
insulation.
Principle
Deformation results in minor changes of
internal inductance and capacitance of
winding.
These deformations can be noted by
noting a difference in response of
particular winding on network analyzer
when 1 signal (sinusoidal) having
frequency band 50 Hz to 500 Hz is
connected to bushing and response is
measured through neutral bus.
Procedure for FRA
 Identify two ends of winding.
 Connect two cables from measuring
 Unit giving sinusoidal output of two
V rms and one measuring input
 Other end of winding is connected to
measuring input.
 Other windings are grounded.
 Voltage transfer function is measured
for each winding for four frequency
scans between 5 Hz to 2 MHz.
FREQUENCY
RESPONSE ANALYSIS
BENEFITS
 Immune to Electro-magnetic interference.
 Easy to perform on site.
 Identical results for similar transformers.
DRAW BACKS
Above data required effectively used more as
signature
INDICATIONS
 Shift in response of winding
 Differences in response between
phases of same transformer.
 Difference between responses of
transformer of same design.
CONTROL OF LEAKAGE FLUX IN
POWER TRANSFORMER
NETT FLUX WHICH IS NOT LINKED BY BOTH
COILS
 Magnetic flux which energizes core abd induces
required flux density.
 Load flux which is balanced by load flux of
secondary winding.
 Leakage flux which links the winding conductors
and returns through a path outside the core.
EFFECT OF LEAKAGE FLUX
 Leakage flux will follow a path of low resistance
 Will be attracted to magnetic steel.
 This induces Eddy Currents and hence generate
heat.
REMEDY
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Increase the distance of tank wall from source of
leakage flux.
Continuously transposed conductor (CTC).
To provide shunt plates to carry leakage flux.
CASE STUDY
PROBLEM
New 390 MVA generator transformer
Core overheating
Yoke overheating
Tank & top cover overheating
VISIBLE EFFECTS
Due To overheating caused by eddy currents flowing
in top cover or bell cover visible deterioration of
gasket was observed
DESIGN REMEDY:
 To subdivide the plate width of outermost pockets
 Use of nonmagnetic material for frames.
 Use of flux shunt plates at LV side of the tank
CONCEPT OF AIR CELL
1. Oil Deteriorates majorly because of Oxidation.
2. Atmospheric breathing is a continuous process.
3. To avoid atmospheric breathing, rubber
cell/balloon/separator is inserted in conservator.
4. The balloon / air cell is INFLATED INITIALLY. The
breathing of transformer is then through this cell.
5. When air expands, air cell contracts.
6. When oil contracts , air cell expands
7. There can be a substantial reduction in oil
deterioration, preserving or at least retarding its
increase parameters like acidity moisture content and
dielectric dissipation factor.
THERMOSYPHON FILTER
CHAMBERS
1
2
3
4
5
6
On line acidity Reduction
Acidity of oil is bad for insulation.
Aluminum granules can reduce acidity and
Fuller’s earth can reduce acidity.
Above materials are contained in cylinder
chamber/chambers in wire mesh.
Cylinder/ cylinders are fitted to transformer tank
and connected through valves.
Oil passing through the column of Alumina or
fuller’s earth reduces the acidity
Continuous use of facility can help in
maintaining acidity low since commissioning.
Hydran 2011 system
 Continuos monitoring of key gases
 Alarm facility
 Hourly and daily changes in level
 Adjustable alarm levels
 Self test system
 Possibility of connection to SCADA systems
SF6 INSULATED
TRANSFORMERS
 MANUFACTURING RANGE: 275KV300MVA
COMPACT SIZE
REDUCED SIZE
EXTRA LIFE
HIGHER COST ALMOST DOUBLE
RATE OF LOWERING DP VALUE IS RELATIVELY
MUCH SLOWER IN SF6 THAN NITROGEN AND
OIL
THANK YOU
FILTER PLANT HIGH
VACUUM WITH DOUBLE
DEGASSING CHAMBER
TRANSFORMER ASSEMBLY IN PROGRESS