TRANSFORMER OIL FILTERING, DEGASSING AND DRYING UNIT MODEL S 500
Maximal oil flow rate 500 lit / h
Heating capacity 7,5 kW (2 x 3.75 kW)
Adjustable oil temperature range 45 °C – 100 °C
Differential temperature (inlet/outlet) approx. 27 °C
Minimal oil inlet temperature 5 °C
Vacuum pump capacity 16 m3/h
Filter fineness 3 microns
Total power 10 kW
Final oil qualities, after three passes:
- water content 2 - 5 ppm
- gas content 0.05 % Vol
Operating pressure in degassing tank 2 - 9 mbar
Unit, size: cca.1650 mm x 900 mm
x H = 1600mm
Unit, weight approx. 350 kg
Above mentioned values after conditioning are guaranteed when treating naphtenic based mineral oils with
normal foaming conditions
The Unit is delivered ready for operation, together with:
- control panel, wiring, two connecting hoses for oil (each 10 m long) and safety devices which provides maximum
- specially designed system in the degassing tank which provides uniform distribution of the processed oil in the
low-pressure environment, in order to achieve best treatment results;
- spare filter cartridge with 3 micron fineness;
- spare heating element;
BRIEFLY ABOUT THE UNIT
The Unit S500 is designed for filtering, drying and degassing of transformer oil. The model and the example that
were kept in mind during development and construction of this Unit were the units, which proved to be most
efficient in operation, built by leading European manufacturers. All essential parts of the Unit (vacuum pump, gear
pump, electromagnetic valve and floater) are produced by leading German manufacturers. Some of the
components (such as fine and coarse filters, temperature control, construction of the heaters, gear pump) had to
be modified to improve the operation of the Unit and to eliminate shortcomings noticed in the operation of some
other units of this kind.
BRIEFLY ABOUT THE PROCESS
The electrical properties of insulating oil (such as puncture voltage and coefficient of losses) can be considerably
improved by its filtering, degassing and dehydration. Only properly and sufficiently filtered and dried oil is suitable
for filling up of the transformer. Even brand-new oil is rarely clean enough to be used in high-voltage installations,
as it is often already polluted in the transporting barrels and it may absorb too much moisture in contact with air.
During its operation, transformer-insulating oil is absorbing moisture over its free surface in the expansion vessel
and it becomes polluted by absorbing dirty particles, fibers, soot and aging products. Therefore, oil conditioning
has to eliminate the following:
- solid particles
- free and dissolved water
- dissolved gasses
The puncture voltage can be considerably increased and the coefficient of loses tangδ improved by filtering,
degassing and dehydration of insulating oil to the extent depending on moisture content.
THE UNIT CONSISTS OF:
1. Inlet valve a spherical valve 3/4“ with special “Teflon” gaskets at the oil inlet at the Unit.
2. Coarse filter as oil is often very polluted, the Unit is fitted with a large sized, easy to open and clean, coarse
filter. Oil is conveyed at a reduced flow rate through a mesh and a strong permanent magnet which retains steel
particles and protects the gear pump from damages.
2a. Service valve a spherical valve 3/4“ with special “Teflon” gaskets for maintenance and cleaning of coarse
3. Oil heater 7.5 kW power of the heater is divided into two stages, both of 3.75 kW. Oil is heated indirectly by
means of electric heating elements insulated from oil by pipes and air. The heating process is thereby gradually
accomplished and, with the sufficiently large heating surface, any damage of oil is excluded. Temperature load of
the heaters is <1 W/cm2. Together with the thermal control (details of which are given in the following text) this
allows heating of oil in individual stages, e.g. at higher temperatures quite “tenderly”. Special electrical
connection prevents the heater to be turned on if the gear pump is not operating. This is to protect the non
circulating oil from overheating. To access each of the heating elements, the protective cap from the heater
should be removed, by unscrewing the bolts (Unit must be disconnected from the power supply!).
4. Safety valve with teflon gasket is installed at the oil heater and it prevents increase of pressure in case of
oil is overheated, or the outlet valve is negligently closed. It is calibrated to open when the pressure raises over 5
5. Safety & control thermostat the Unit is equipped with a double acting – precise thermostat, acting as a safety
thermostat with incorporated control thermostat. This control thermostat is fitted with an external button for the
temperature range from 300C up to 900C. This control thermostat is used to regulate the oil heating step no. 2. By
means of other control thermostat, both heating stages can be controlled. The safety thermostat is designed to
allow max. temperature of 900C, with a construction that allows it both safety and control role.
6. Control thermostat fitted with an external button for the temperature range from 300C up to 900C; the button
maximum position is 900C, thus these control thermostat act as another safety device to prevent oil overheating.
This control thermostat is used to regulate the oil heating step no. 1. Control thermostats should be adjusted to
cca.60-65 0C which represents an optimal temperature for oil processing.
7. Thermometer Is positioned on the control panel for easier viewing. It measures the oil temperature at the outlet
of the oil heater.
8. Electromagnetic valve a special magnetic valve capable of operating in vacuum, resistant to transformer oil
and high temperatures. Together with the floater, it automatically controls the oil level in degassing tank.
9. Degassing tank of a welded construction, with specially shaped separating sheets for equal distribution of oil.
Oil is conveyed over the “RASIG” rings, where oil surface is significantly increased and gas fractions can be
efficiently separated. In addition, the resting time of oil is increased to the maximum. The degassing tank is
equipped with a sight-glass for the visual control of the process, as well as with a special lamp for illumination of
the tank interior. The power supply of the lamp is 12 V for safety reasons.
10. Floater this floater protects the degassing tank from overfilling and, together with electromagnetic valve,
prevents the insulating oil to penetrate into the vacuum pump.
11. Gear pump with 500 l/h capacity. This pump is specially designed to operate under vacuum conditions and it
is used for evacuation of oil from the degassing tank.
12. Overflow valve is installed on the gear pump and it protects the Unit from an excessive rise of pressure in case
outlet valve is negligently closed or because of some other reason.
13. Mano-vacuum meter for reading of fine filter dirtiness, through oil pressure rise. Filter should be cleaned when
the pressure raises up to 2.5 bar.
14. Sampling valve a spherical, closing valve for insulating oil sampling.
15. Fine filter container the fine filter container is of a size that allows it to accept a standard filter separating
particles of 3 microns.
16. Outlet valve a spherical valve 3/4“ with special “Teflon” gaskets at the oil outlet of the Unit.
17. Aeration valve a spherical valve for aeration of the degassing tank in case of an excessive foaming of oil.
18. Sight-glass for process control equipped with search-light fitted on its left side to illuminate the interior of the
19. Vacuum meter used for measuring of vacuum in the degassing tank during the process.
20. Discharge valve a spherical valve for discharging of condensate from the separator.
21. Separator of a special construction for separation of liquid fractions from gasses which are extracted out of
degassing tank. It is equipped with sight-glass for control of separated water.
22. Vacuum pump of 16 m3/h capacity, provides vacuum for operation of the Unit, equipped with a so-called
“gas-ballast” valve. Maximal vacuum that could be achieved with this pump is 0.5 mbar. With the Unit there is a 2
m hose delivered for evacuation of gasses form vacuum pump if working in the indoor conditions.
23. Air valve a spherical valve installed on the filter container for elimination of trapped air from the filter.
24. Drainage valve a spherical valve for drainage of transformer oil from oil heater.
25. Control panel has and IP 55 protection rating and it consists of fuses, contactors, electric motors electrical
protection, protection relays, transformer, main switch, internal wiring etc., for an automatic operation of the Unit.
Control panel is equipped with total-stop taster for immediate shut down of the complete Unit in urgent situations.
In addition on the front of control panel, there are three green indicator lights (L1, L2 and L3) for phase presence.
Beside this, above every cam switch, there is also an green light, that serves as an indicator of the current state
(on / off) of the respective components.
26. Framework a welded, sectional steel construction, which represents foundation for all described components
of the Unit. At the base construction of the Unit, there is a detachable push-bar installed for its easier
27. Electric equipment consisting of driving motors for the gear and vacuum pump and of internal wiring of the
Unit. Suitable for three-phase, 50 Hz power supply. Unit is delivered with male 32A CEE connection installed at
the control panel.
THE UNIT IS SUPPLIED WITH THE FOLLOWING ACCESSORIES:
28. Two flexible hoses specially designed, suitable for operation in vacuum and oil, both equipped with hose
connections for 3/4’’ tread; each hose 10 m long. Each hose has installed crimped elbow hydraulic connection for
tight seal with the Unit. When connecting them to the Unit, please fasten them securely to allow complete tightness
of the process.
29. Oil tub oil retaining tub in case of oil leakage. It is placed under the complete Unit with a purpose of preventing
environmental accidents and spillage of oil into the surroundings.
30. Rollers for base frame rollers are installed for easier manipulation with the Unit. There are 4 swivelling rollers
installed at the bottom of base frame.
The Unit is delivered with following spare parts:
1. two spare filter cartridge with 3 micron fineness;
2. spare heating element 3.75 kW;
3. exhaust hose, 2 m long for evacuation of gasses from vacuum pump;