The capsule-type oil conservator is an important component on top of the transformer oil tank. Its main function is to compensate for the change in transformer oil volume and isolate the outside air from the oil. The oil conservator is usually installed on the top of the transformer and connected to the transformer’s main oil tank. This structure is widely used in the power industry, and understanding its working mechanism can help maintenance personnel operate the equipment better.
The capsule-type oil conservator consists of a shell, a capsule, an oil level gauge, a respirator, and other components. The shell is usually a cylindrical metal container with a rubber capsule hanging inside. The inside of the capsule is connected to the respirator, and the external space is filled with transformer oil. The oil level gauge is used to observe the oil volume, and a desiccant is placed in the respirator to prevent moisture from entering.
What is the function of the oil conservator in transformer
Adjust the oil level
When the transformer is running, the internal oil temperature will change with the load, causing the oil volume to expand or contract. The oil conservator maintains a constant oil level in the transformer’s main oil tank by expanding and contracting to prevent oil overflow or air from entering the oil tank.
Reduce air contact
The top of the oil conservator usually has a diaphragm or rubber bag to isolate air and transformer oil, reduce oil oxidation and moisture absorption, and extend the service life of the oil.
Prevent oil leakage
The oil conservator prevents transformer oil from overflowing at high temperatures and prevents air from entering at low temperatures through its design, thereby maintaining the tightness of the transformer.
Oil conservator structure composition and function
1. End cap
2. Cabinet
3. Cover
4. Capsule hoist
5. Plug
6. Air cell
7. Oil level gauge
8. Butterfly valve
9. Gas Chamber
10. Moisture absorber
End Cover
Installed at the top or end of the cabinet, it is used to close the entire oil cabinet system. It is usually equipped with a sealing structure to prevent impurities or water vapor from entering from the end.
Cabinet Body
The main part of the oil conservator is used to support and accommodate the bladder and other internal components. It is generally made of steel and has good strength and corrosion resistance.
Cover
Located at the top, it is convenient for installing or removing internal components. It is detachable in design to facilitate capsule replacement or maintenance.
Capsule Hoist
Used for hoisting operations when installing or replacing capsules, connecting hoisting equipment to avoid tearing or squeezing the capsules.
Plug
Mostly used to seal the oil filling port, air vent or inspection port, which can be opened for maintenance or checking the status of the capsule.
Air cell
The core component of the oil conservator, made of rubber material, is soft and retractable. The capsule contains transformer oil inside and the outside is an air cavity, so the oil and air are not in direct contact.
Oil Level Gauge
Real-time monitoring of the liquid level changes of the transformer oil in the capsule. It is convenient for operators to observe whether the oil volume is normal and whether there is leakage.
Butterfly Valve
Used to control the oil flow path between the oil tank and the transformer body. Closed during maintenance, replacement of capsules or cleaning to prevent oil flow.
Gas Chamber
The space outside the capsule is connected to the external atmosphere. As the capsule shrinks or expands, gas enters and exits the space to achieve volume adjustment.
Moisture absorber
Installed in the gas channel to prevent moisture in the air from entering the gas chamber outside the capsule. It is usually made of silica gel and has the function of hygroscopic discoloration, which can visually determine whether it needs to be replaced.
Working principle of capsule type oil conservator
When the transformer is running, the oil temperature rises, causing the volume to expand and the pressure inside the oil tank to increase. At this time, the oil conservator takes effect – the expanded oil flows from the oil tank to the space between the oil conservator shell and the capsule, the capsule is squeezed and contracted, and the internal air is discharged through the respirator. When the oil temperature drops, the oil volume shrinks, and the capsule expands by its own elasticity, pressing the stored oil back into the oil tank. At the same time, the external air enters the capsule after being filtered by the respirator to maintain the system pressure balance.
The key role of the capsule is to isolate the air. Traditional open oil conservators are in direct contact with the air, and the oil is easily oxidized and degraded. The capsule structure forms a physical barrier, and the oil always exists between the closed metal shell and the outer wall of the capsule, and does not react chemically with the outside air. The silica gel in the respirator absorbs moisture and impurities, and doubles the protection to ensure the stability of the oil quality.
Pay attention to the integrity of the capsule in actual operation. Check the oil level gauge scale regularly. Abnormal fluctuations may indicate that the capsule is damaged or the respirator is blocked. During maintenance, the oil conservator needs to be drained, and the inspection port needs to be opened to check whether the capsule surface is cracked or adhered. Before installing a new capsule, an air tightness test should be performed, and 0.02-0.03MPa compressed air should be filled in, and soapy water should be applied to check for leaks.
Changes in ambient temperature have a significant impact on the operation of the oil conservator. Low temperatures in winter may cause the capsule to shrink excessively, and it is necessary to pay attention to whether the oil level is below the minimum warning line. High temperatures in summer should prevent the capsule from over-expanding and contacting the respirator pipeline. The operation and maintenance regulations require that the oil level curve be recorded once in spring and autumn, and the system sealing should be judged by comparing the temperature change curve.
Compared with the diaphragm oil conservator, the advantage of the capsule structure is that the elastic compensation is more sensitive. The ductility of the rubber material allows a larger range of volume change compensation, which is particularly suitable for areas with large temperature differences between day and night. However, the problem of rubber aging needs to be taken seriously. Generally, the capsule needs to be replaced every 8-10 years, and it is recommended to be shortened to 5-7 years in coastal areas with high humidity.
There is a strict process for oil conservator oil filling. First, slowly fill the oil through the bottom filling valve, and open the exhaust plug at the same time until the oil overflows. After observing that the oil level gauge reaches the scale corresponding to the ambient temperature, let it stand for 2 hours and then fill the oil again. When filling the oil with electricity, the flow rate must be controlled to prevent the sudden deformation of the capsule from causing the oil flow to be electrified.
In terms of troubleshooting, abnormal bubbling of the respirator may indicate that the capsule is damaged. At this time, the oil sample should be taken immediately for chromatographic analysis, and the acetylene content should be tested to determine whether there is internal discharge. The respirator valve can be closed in an emergency.
Technical requirements for oil conservator
1. The oil conservator should specify the minimum and maximum oil levels to ensure that after the transformer is selected, the oil level is visible at the lowest oil level and the oil conservator oil does not overflow at the highest oil level.
2. The oil level of the oil conservator should have a clear indication (red float or pointer), and there should be a striking oil level mark or indication scale, with three position marks of -30°C, +20°C, and +40°C (normal use conditions).
3. The sealed oil conservator should use a rubber diaphragm (or capsule) that is oil-resistant, gas-proof, oil-proof, has high tensile strength and good aging resistance. The capsule should be able to withstand a 20kPa pressure test without leakage.
4. The oil conservator should be able to withstand a 50kPa pressure test for 30 minutes without leakage and permanent deformation.
5. Before welding the cabinet, the cabinet wall, cabinet cover connecting pipe, bracket and other parts should be cleaned of rust, oil stains, mud, etc. on the inner and outer surfaces.
6. After the oil level gauge is welded, the vertical center line of the oil level gauge should be aligned with the vertical line of the cabinet end face, and the allowable deviation should not exceed 3mm.
7. When welding the connecting pipe to the cabinet body, the dimensional deviation between the horizontal center line of the connecting pipe and the horizontal center line of the cabinet wall 6 should not exceed 2mm, the inclination a of the flange end face and the plumb plane should not exceed 2mm, and the angle between the horizontal center line of the connecting pipe and the vertical center line of the cabinet wall should be 90°, and the deviation should not exceed 2°, as shown in the figure.
8. Length of connecting pipe extending into the cabinet wall:
The connecting pipe without gas relay extends into the cabinet wall for 15~20mm, and the connecting pipe with gas relay extends into the cabinet wall for 30~40mm.
9. The magnetic oil level gauge should ensure that the connecting rod is flexible, the indication is accurate, and the limit position alarm is correct.
Installation of oil conservator
The installation steps are the same as removing the gas relay and installing the oil conservator during transportation. The difference is that when injecting oil into the oil conservator, the air release plug or exhaust valve on the oil conservator, the butterfly valve in front of the gas relay, and the oil injection ball valve are opened to inflate the inside of the capsule, promoting the capsule to fully expand. When injecting oil, the capsule rises, and the air inside the capsule is discharged through the moisture absorber. The air in the oil conservator is discharged through the air release plug or exhaust valve. When the oil is full and overflows from the vent plug or exhaust valve, tighten the vent plug or close the exhaust valve, and drain the excess oil from the oil filling valve to the oil level specified in the oil conservator. At this point, there is negative pressure in the oil conservator, and the capsule is in a normal open state.
