Installation and Operation Manual of 35kV Oil-Immersed Transformers

1.Transportation

1.1  Packing

The transformer ≤ 4000 kVA is normally transported in a whole. As the moisture absorber and the temperature controller are easy to be bumped therefore transformer is detached before transportation.

The transformer ≥ 5000 kVA is transported separately. It is required to discharge insulation oil 100 mm down to the cover of the tank, and all radiator, oil conservator, moisture absorber, temperature controller and high/low voltage sleeves and fan for transformer of 10000kVA and upward should be detached and packed in separate boxes for transportation, and carry enough insulation oil together with the main body for replenishment.

1.2  Transportation

When the transformer is transported, the long shaft direction of the main body couldn’t be tilted over 15° while the short shaft direction couldn’t be tilted over 10°; the average speed should be 40 km/h and no more than 60 km/h in maximum.

When the transformer ≥ 31500 kVA is transported, it should mount the three-dimensional impact recorder mounted on the wall of the oil tank or the cover of the tank. The measurement range is ±1±5g (g is gravity acceleration), the record sensitivity is 1.5~2 mm/g and it can record 500~3000 times.

1.3  Unload

When the transformer is transported to the destination, unload and place it at specified location.

2. Acceptance after Check

2.1  After receiving the transformer, customer should check records before unloading, and take photo for reference if necessary.

1. The displacement of the transformer on the vehicle (check the mark at the contact place of the product and the bottom of the vehicle when the transformer is loaded on the vehicle).
2. In steel wires pulling the product are broken.
3. If surfaces of the product are bumped and damaged.

2.2  After unloading, check model, size, number of the product on the nameplate if they are identical with that on the order; check accompanied documents with the list of ex-works documents if they are complete, if size and number of accompanied documents are perfect after careful check.

2.3  If the product has oil leak, check the part of oil leak and its reasons.

3. Storage

When the product is stored, the oil level should be kept above the cover of the oil tank thus to ensure that the oil level is higher than the cover of the oil tank and can suit the demand of change of temperature. If the site where the transformer is placed is under engineering construction, the transformer should be covered so as to avoid to be damaged.

4. Installation of the Transformer

1.1 If the product is normal in the course of transportation and meet stipulations in paragraphs 3.1 and 4.2, it can carry out mounting of attachments, oil filling, static placement, test and trial operation without the center-hoisting.

4.2.1  Preparation of the Center-Hoisting

1. Be familiar with concerned technical materials.
2. Measure DC resistances at high and low voltage sides by the electric bridge and make comparison with ex-works values. If differences ≤ 5%, it means internal connections of the product are good otherwise internal wires are broken or cracked.
3. Materials: dried NOMEX paper tape with width of 25 mm, 0.5 mm NOMEX paperboard and phosphor-copper welding rod.
4. Tools and equipments: movable spanner, sealing tape clamp (made of 8# iron wire), oil barrel, square skids, oxygen bottle, acetylene cylinder, welding gun, sealing tape, electrician knife, asbestos rope, water kettle, asbestos plate, electric bridge, mega-ohm meter etc.

4.2.2  Conditions of the Center-Hoisting

1. Start counting time from oil is discharging when the body is exposed under air;

Relative humidity of air ≤ 65%, 16h; mm

Relative humidity of air < 75%, 16h;

Relative humidity of air > 75%, no center-hoisting is allowed.

1. Environment temperature > -15°C.
2. The site of the center-hoisting should be clean without rain, snow, dust and other pollutants.

4.2.3  Center-Hoisting

As transformers have different capacity and structure of oil tank, those ≤ 6300kVA normally have barrel oil tank. First of all discharge oil down to about 100 mm under the tank cover, remove bolts of the cover diagonally and evenly, hang the rope on the hoist plate of the cover and start hoisting intermittently. Adjust the position of the hook at the same vertical line of the gravity center of the body, hoist up the body if trail hoisting is normal. Before move levelly the body cover the oil tank to prevent oil to drop on the body. Finally place the body on the square skids. When making trial hoisting the body cannot be hoisted up, it means the nuts on the hanging screw rod have dropped. Place down the body and remove the high voltage sleeve at the side which couldn’t be hung up, extend hand through the hole to touch if the nut on the hanging screw rod under the cover is dropped, mount the spare nut if it is dropped then hoist the body, otherwise continue to touch the nut at the lower end of the hanging screw rod to see if it is dropped. Mount the spare nut if it is dropped. If the fastener at the other end of the hanging screw rod is also dropped, mount it in same manner, or remove all sleeves and tap switches on the tank cover to hoist the tank cover from the body, then hoist up the body.

The transformer ≥ 8000 kVA has normally the bell-jar oil tank. First of all, discharge all oil and remove bolts on the edges of the tank diagonally and evenly, and all high and low voltage sleeves, grounded sleeve and tap switches, then hoist up the upper part of the oil tank and place it on the square skids, the body of the transformer is completely exposed.

4.2.4  Check and Test Items of the Center-Hoisting

1. Generally observe if the body has severe torsion or deformation, if displacement against the bottom of the tank exists (regarding to the bell-jar oil tank).
2. If the pad at the end of the winding is moved.
3. If leads are off-welded or broken.
4. If insulation of leads are perfect.
5. If fasteners are loosened.
6. If contact resistance of the tap switch is ≤ 500μΩ.
7. If the iron core is grounded with one point or if insulation against the ground is good.

4.2.5  Treatment and Installation

Treat problems found in the center-hoisting check and make records well, then clean the body and remount the lower case, close the cover and fill oil to the level 20~30 mm higher than the stipulated level.

Referring to mixing of transformer oil with different brands, the mixed oils should have same oil base and replenished oil should have qualified voltage-proof value and tgδ.

4.3 Remount all removed attachments such as mercury thermometer, temperature controller, gas relay, pressure relief valve, quick-acting oil pressure relay, moisture absorber etc. Points for attention of installation can be seen in appendix <Operation Manual of Assembles> or as per material provided by the manufacturer.

4.4  Test

4.4.1  Airtight Test

After oil is filled up in the transformer, open all butterfly valves and pipelines (i.e. butterfly valves of the radiator and quick-acting oil pressure relay), then fill with 50kPa dried and compressed gas from the oiling hole at the top of the oil conservator and statically place it for 8h, then check if oil leak exists.

4.4.2  Test of Transformer Oil

After conforming no oil leak exists in the transformer, discharge gas from the gas relay and sleeves, statically place it for 21h then take oil sample for voltage-proof test. The breakdown voltage couldn’t be less than 35kV.

4.4.3  Points for Attention of Handing-Over and Acceptance

1. Open the lock lever on the top of the pressure relief valve.
2. Sleeves and the gas relay should be filled with transformer oil.

4.4.4  Test Items of Handing-Over and Acceptance

1. Measure the insulation resistance of the winding, which should be ≥ 70% of ex-works value.
2. Measure the DC resistances of all taps of the winding, the unbalance rate of the linear resistance should be ≤ 2% while the unbalance rate of the phase resistance should be ≤ 4%.
3. Applied power frequency voltage-proof test, which is 90% of standard test voltage lasts for 1 minute.
4. Measure unload current and loss if conditions allow and compare with ex-works values, which should have no obvious differences.
5. Variable ratio test of the tap switches and ensure three-phase taps are at the same tap position.

4.4.5  Check and Adjustment Items after Test

1. Setting protection device: such as gas relay, quick-action oil pressure relay, over-current relay and differential relay.
2. Check oil level of the conservator (check air pressure in capsule if it is available) and check if the butterfly valve on the top of the gas relay is opened.
3. Calibrate temperature of the temperature controller.
4. Check if abnormalities occur in everywhere of the transformer.
5. Check grounding of the transformer if it is good, if it is grounded with one point.
6. If oil leak exists.
7. Before putting into trail operation, connect the signal terminal of the gas relay to the current tripping circuit, the setting of time limit of over-current is the value of instantaneous action.
8. If the quick-action oil pressure relay is mounted, connect its signal terminal to the power supply of the middle relay and the tripping circuit before putting into trail operation.

5.  Putting into Operation of Transformer

5.1  Putting into Trial Operation

When stipulations in paragraph 6.4.5 are finished, connect the power supply from the power side of the transformer and carefully listen if abnormal sound occurs, monitor changes of current and voltage, switch off power supply if abnormality occurs and check reasons otherwise switch off power supply after lasting for 30 minutes.

5.2  Putting into Operation

5.2.1  If all are normal after trial operation for 30 minutes, connect the signal terminal of the gas relay to the signal circuit and connect the heavy gas terminal to the tripping circuit, and reset the settings of over-current and over-voltage protection.

5.2.2  Make 3 to 5 times of unload impact switch-on of the transformer, lasting 5 minutes each time with interval of 10 minutes to check the reliability of the relay protection under the role of leak current of excitation.

5.2.3  Discharge off all gas in sleeves and the gas relay at the last time.

5.2.4  Connect the transformer to the power network if everything of the transformer is normal and run it under unload for 24h. Add load if no abnormality occurs and load should be increased step by step.

6.  Points for Attention after New Transformer is Putting into Operation

a.  For the transformer mounted with the gas relay, as new transformer oil shall decompose a few of gas into the gas relay when it is just putting into operation, discharge it in time if found so as to avoid error action of the gas relay.

b.  After putting into operation under load, watch the temperature rising of the oil, which should be no higher than 55K, otherwise check reasons such as incorrect measurement of the thermometer or no transformer oil in the thermometer seat etc.

c.  The maintenance of the transformer in normal operation should follow the “Regulation of Operation” from the power supply department.