transformer oil filtration
DESCRIPTION
Transformer Oil FiltrationTRANSCRIPT
TRANSFORMER OIL FILTRATIONFILTRATION
The use of transformer oil• act as a cooling medium• act as a dielectric media• isolate winding from the atmosphere• quench the arc
Possible contamination in transformer oil• Solid particle like dust and fiber• Solid particle like dust and fiber• Absorption of Air• Moisture content• Absorption of Gases• Sludge formation• Acidity in oil
The Electrical effects of contamination in oil• Low dielectric strength.• Low resistivity.• Increase in Tan delta value.
The vacuum dehydrated oil purification system (VDOPS)• This machine is used for transformer oil filtration.• Free, emulsified and dissolved water and gaseous contamination can be • Free, emulsified and dissolved water and gaseous contamination can be
removed by this machine.
A high performance VDOPS removes• 100% of free and emulsified water, air and gases.• 90% of dissolved water, air and gases.• Up to 5-10 ppm water content in oil
Overall schematic diagram of an oil purification machine
Oil in take
Heater
Pre filter
The amount of heat is decided by oil vendor
Filter is around 10 micron
Inlet pump
Vacuum chamber
Fine filter
Oil outlet
The vacuum chamber contains PDM for effective vacuum expose
Vacuum pump
Mechanical booster
Filter is around 0.5 micron
outlet pump
Oil Purification Machine
• Boiling point of the water is dependent on the pressure. Normally, at atmospheric pressure ( 1atm) the boiling point of water is 100 C.
• Boiling point of the oil is around 250 C at 1 atm.
• When the surrounding pressure is low the boiling point is also reduced for a liquid.
System Principle
a liquid.
• When oil is exposed to vacuum even at low temperature( around 150 F), the water molecular and other dissolved gases reach its boiling point and are boiled off effectively since the boiling point of the oil is very high.
Operation of Oil Filtration Machine
•Oil is in taken through inlet valve
•A inlet pump circulate the oil through the heater where the oil temperature is raised up to 150 F. The system heat is adjustable
•This oil is filtered through a pre filter ( 10 micron) and pumped to a vacuum chamber. This removes major portion of coarse dirt.
•Then the oil is pumped through vacuum chamber.
•Vacuum chamber contains permanent dispersion media (PDM), a cylindrical type element. The oil flows through the pores of the PDM into shower in order to ensure element. The oil flows through the pores of the PDM into shower in order to ensure more exposure of vacuum to the oil particles. This process, boils off dissolved water and gases effectively.
•The boiled off process is called Degassing.
•Then the dehydrated oil is collected at the bottom of the vacuum chamber and pumped through the fine filter (0.5 micron).
•Then the oils is taken out through the outlet valve
NOTE: At the beginning the outlet valve is closed and the oil is circulated through a by pass valve. This is done to make the system stable
Finding boiling point
• The equation used to find out the boiling point is
T(p)= T0/[1+T0*ln(P0/P)/(L/K0)]
T(p) - boiling point in Kelvin
T0 - boiling point in Kelvin at the pressure P0T0 - boiling point in Kelvin at the pressure P0
L - Latent heat of vaporization/ molecule
K0 - Boltzman’s constant = 1.4 x 10-23 J/K
Boiling point of water at 5 Torr
Data:
1 atm = 760 Torr = 760 mmHg
Boiling point of water is = 100 C or 373 K at 1 atm
L/K0 = 4800 K for water
Boiling point of water at 5 Torr :
T(p) = 373/[1+373xln(760/5)/4800]
= 268.3 K = (268.3 – 273) C
= - 4.7 C
At -4.7 C water reaches its boiling point. So at this vacuum, 150F (around 66C) temperature is enough to boil off all the water content in the oil.
Boiling point of oil (Ex: Nytro Libra X) at 5 TorrData:
1 atm = 760 Torr = 760 mmHg
5 torr = 1/760x5 = 0.0066 atm
1 torr = 1/760 = 0.0013 atm
Pressure ( ATM) Temperature ( Celsius)
0.00001 40
0.0001 68
The following table shows the boiling point of Nytro Libra X at different pressure from vendor data
0.0001 68
0.001 102
0.01 146
0.1 207
1.0 294
5.0 382
10 437
50 593
So the boiling point of Nytro Libra X at 5 torr is 102 < T < 146 Celsius
And also the boiling point at 1 torr is 102 < T < 146 Celsius
Boiling Point and the Temperature in Oil Purification Machine
• When the pressure reduces the boiling point also reduces.
• According to the vacuum created in the oil purification machine, the temperature of the oil purification machine also need to be set
• If the temperature is higher than the oil boiling temperature then the oil also will be vaporized
• In our oil purification test we keep the pressure less than 5 Torr and the temperature around 70 Celsius.
• This temperature is well below than the oil boiling temperature at 1 - 5 Torr so that the oil will not be vaporized.
Transformer oil filtration is done through three main steps1. Vacuum the transformer2. oil filling to transformer3. oil circulation
When shipping the transformers are filled partially with oil. So there is a need of oil filling for new transformers.
Transformer oil filtration
of oil filling for new transformers.
Before filling the oil the transformer need to be vacuum.
After filling the oil to required level, the total amount of oil must be circulated 2 or 3 times through oil filtration machine
Vacuum the transformer
The figure shows the transformer vacuuming diagram
Vacuum the transformer
• Close the valves V3, V7, V10• Open the valves V4, V5, V8, V9• Start the vacuum pump • The degree of vacuum and the vacuum holding time should satisfy the
following table • Vacuuming of transformer can be done by “oil purification machine’s”
vacuum pump other than external vacuum pumpvacuum pump other than external vacuum pump
RATED VOLTAGE ( k V)
BEFORE OIL FILLING
Degree of Vacuum
Vacuum Hold Time
Below 80 < 5 Torr > 2 Hrs
Below 140 < 2 Torr > 7 Hrs
Below 200 <2 Torr > 12 Hrs
Below 500 < 1 Torr > 24 Hrs
Oil Filling to Transformers
The figure shows the transformer oil filling diagram
Main Tank of Transformer
Oil purification machine and external oil tank
Oil purification machine
Oil Filling to Transformers cont…
•The external oil tank is filled with required amount of oil before starting oil filling to transformer.
•This external tank oil filling also done through the oil purification machine
•After finishing the vacuuming of transformer the oil purification machine is connected to the transformer as shown in the figure above.
•Before filling the transformer the oil is circulated through the oil purification machine for 30 min to warm up the system.
•Open the valves V1, V2, V3
•Start the oil purification machine
•When the dial oil level indicator shows a reading more than a little minimum position perform the following procedure
1. temporarily stop the oil purification machine
2. close Valve V9 and V3
3. Close valve V8
Oil Filling to Transformers cont…
•Open the valve V10
•Inject the nitrogen gas into the conservator tank (Inside air bag) until the degree of vacuum become 0 psi
•Remove the nitrogen tank and keep valve V10 opened
•Check the oil temperature versus oil level temperature curve
•If the oil level is lower open valve V3 and operate oil purification machine to adjust the oil level according to “ Oil level temperature curve”
Oil Level Indicator
Oil Circulation
Oil Circulation
•Open valves V3 and V7
•Circulate the oil in tank at 60- 70 Celsius not less than 2 cycles
•Close the valves V3 and V7
•Slightly open Breather pipe flange P1
•Connect the nitrogen tank at valve V10 and inject the nitrogen at the pressure of 0.2 bar until the oil spurt from P1
•Close P1.•Close P1.
•Remove nitrogen tank and make the degree of pressure of conservative tank 0 psi.
•Connect the silica jell breather
STANDARDS USED
Rated voltage/ kV
Break down Voltage of oil Water Content in Oil
Elapse timeIEC ASTM
Below 80 > 50 kV > 35 kV < 20 PPM > 12 HRS
Below 140 > 50 kV > 35 kV < 20 PPM > 24 HRS
Below 200 > 50 kV > 35 kV < 20 PPM > 36 HRS
Below 500 > 50 kV > 35 kV < 20 PPM > 48 HRS
1. After oil filtration, the oil must satisfy these values
2. Elapse time: after oil filtration the transformer must not be energized before elapse time.
END