1. Daily inspection requirements
In order to ensure the long-term safe and reliable operation of the photovoltaic box transformer, and timely discover equipment defects and abnormal phenomena in the operation of the box-type transformer, the operation and maintenance personnel shall check the box-type transformer body, high-voltage room, low-voltage room devices, equipment and connection busbars, Whether the running status of the cable is normal, and the regular patrol inspection work (see Figure 1). During the inspection, focus on operating parameters such as voltage, current, temperature, and temperature rise of the box-type transformer and their changes within the normal range are the normal operation of the equipment. Mainly include the following aspects:
(1) Whether the transformer’s operating sound is normal, whether there is abnormal noise and discharge phenomenon.
(2) Whether the indication of the transformer thermometer is normal, and whether the indication of the remote measurement and control device is correct.
(3) Whether the porcelain bottle and casing are clean, whether there are breakages, cracks, discharge marks and other abnormal phenomena.
(4) Whether the grounding point of the transformer shell is in good contact.
(5) Whether the cooling system is operating normally.
(6) Whether each control box and secondary terminal box are tightly closed, whether the cable perforation is tightly blocked, and whether there is moisture.
(7) Whether the warning signs are hung correctly, and whether the various signs are complete and obvious.
In addition to daily inspections, special inspections of transformers also include:
(1) In windy weather, check whether there are hanging objects on the transformer.
(2) After a thunderstorm, check whether there is flashover discharge and whether the lightning arrester discharge counter operates.
(3) During heavy rain, check the water accumulation around the transformer and the cable trench to see if there are hidden dangers of natural disasters such as floods, landslides, mudslides, and collapses.
(4) In the foggy weather, check whether there is discharge phenomenon, and should focus on monitoring the cable head, lightning arrester, connecting copper bar and other parts for discharge phenomenon.
(5) In snowy weather, check the surrounding conditions of the transformer based on the snow, and deal with the snow and icicles in time.
(6) After the transformer protection action trips, check whether the transformer body is damaged or deformed, and whether the connections of each part are loose.
(7) When the transformer is running at full load or overload, patrol should be strengthened.
2. Operation regulations for box-type transformers
New transformers or transformers with replacement windings should be fully protected, with no-load full-voltage closing shocks from the power supply side for 3 times to check the relay protection action under the excitation inrush current. In addition, the following aspects should be noted during operation:
1) The transformer can operate continuously for a long time according to the nameplate parameters under the rated cooling condition.
2) The operating voltage fluctuation range of the transformer is ±5% of the rated voltage, and the voltage applied to each winding shall not exceed 105% of the rated value when the rated capacity remains unchanged.
3) When the transformer cooler fails to resume operation, effective measures should be taken to transfer the load, or the transformer should be shut down. Over-temperature operation of the transformer is strictly prohibited.
4) When the transformer has serious defects (the cooling system is abnormal, there is partial overheating, etc.), it should not be operated beyond the rated current.
5) The normal operating temperature limit of the transformer is 90℃, and it is prohibited to operate above 110℃. The transformer can run for a long time with 105% load when the ambient temperature is 0~40℃.
6) The transformer is not allowed to run under overload under the following conditions:
(1) The cooling system is faulty and cannot be put into operation normally.
(2) The transformer body has local overheating.
(3) It runs at full load all day, and the temperature of the transformer is relatively high.
3. Commissioning and shutdown of transformers
1) Inspection before the transformer is put into operation
Before putting the transformer into operation, check carefully to confirm that the transformer and its protection device are in good condition and have live operating conditions before it can be put into operation. The transformer in the hot standby should be put into operation at any time, and the standby transformer that has been out of service for a long time should be charged regularly and put into the cooling device at the same time.
The following items should be checked before the transformer is put into operation after long-term outage, new installation, overhaul or test:
(1) The contact points are good, the leads and busbar bridges are intact, and the phase sequence signs are correct and clear.
(2) The position of the tap changer is consistent with the dispatch notice.
(3) The ventilation cooling device can be put into operation manually or automatically, and the signal is correct.
(4) The remote temperature measuring device and the on-site thermometer are normal and the indications are consistent.
(5) There are no leftovers on the transformer body, and the temporary safety measures are completely removed.
(6) There is no sinking or cracking in the transformer foundation.
(7) The shell should be grounded at two points, and the grounding should be reliable.
(8) The transformer body has no defects and the paint is complete.
(9) Corresponding drawings and documents are complete, various test data including insulation resistance, and various maintenance and test items meet the power transmission requirements.
(10) Before the transformer is put into operation, the corresponding protection must be put into operation according to the regulations, and it is strictly forbidden to charge the transformer without protection.
(11) Two transformers are operated in parallel, one of which should be checked for overload before the other is powered off.
2) Transformer power failure process
(1) Power transmission process.
Step 1: Close the high-voltage load switch (see Figure 2).
Operation matters:
A. Check that the live display on the high-voltage side is normal, and the cable has no discharge or abnormal phenomena; the high-voltage fuse core is normal; whether the tap switch gear is correct;
B. Before closing, put in “ultra-high temperature trip” and “pressure release trip” protection connecting piece;
C. Professional safety tools and equipment must be used, and check whether the safety tools and equipment are in good condition before operation;
D. When closing, the operating lever and the switch are 90°, turn clockwise to close;
E. After closing, check whether the sound of the transformer is normal, and whether the voltage of the low-voltage side voltmeter is normal.
Step 2: Close the low-voltage side circuit breaker (see Figure 3).
Operation matters:
A. Before closing, check whether the energy storage of the low-voltage side circuit breaker is normal; whether the mechanism is intact; confirm that the low-voltage side cable has no phase sequence connection and abnormal conditions;
B. Switch the No. 1 and No. 2 low-voltage side remote local switch to the “local” position;
C. Think of the “close button” on the low voltage side of No. 1 and No. 2 in turn;
D. Observe whether the equipment is abnormal after closing.
(2) Power failure process.
Step 1: Disconnect the low-voltage side circuit breaker (see Figure 4).
Operation matters:
A. Confirm that the inverters belonging to the No. 1 and No. 2 low-voltage sides have been shut down;
B. Switch the No. 1 and No. 2 low-voltage side remote local switch to the “local” position;
C. Think of the “opening button” on the low-voltage side of No. 1 and No. 2 in turn.
Step 2: Disconnect the high-voltage load switch (see Figure 5).
Operation matters:
A. Professional safety tools and equipment must be used. Check whether the safety tools and equipment are in good condition before operation
B. The operating lever and the switch are 90° when opening, and turning counterclockwise is opening.
4. Inspection and maintenance of transformer
The point inspection and maintenance of the transformer is to ensure the long-term safe and reliable operation of the transformer, and to discover the equipment defects and abnormal phenomena in the operation in time. Check whether the status is normal and the maintenance work performed.
(1) When the box-type transformer is out of power, the low-voltage end should be cut off first, followed by the medium-voltage end, and finally the high-voltage end. When energizing, the grounding switch should be turned on before discharging.
(2) Do a good job in the maintenance of the box-type transformer. First of all, you should wear insulating shoes and insulating gloves when maintaining and repairing the box-type transformer; secondly, you should clean the box-type transformer shell on time and check whether the shell is cracked or the wiring is aging; thirdly, in order to ensure the box-type transformer To have a good ventilated environment, the accessories around the box transformer should be cleaned regularly; finally, all interfaces, screws, and connection wires should be strictly checked for tight installation.
