What are the safety operating procedures for transformers?

The safety operating procedures of the transformer, the flange bolts of the outer cover must be tightened symmetrically and evenly.

When inspecting large transformer cores, scaffolding should be set up, and it is strictly forbidden to climb up and down the lead wooden frame. The oil storage and oil treatment sites must be equipped with sufficient and reliable fire-fighting equipment, and a clear fire-fighting responsibility system must be formulated. The site should be level and clean, and there should be no fire and flammable and explosive items within m range.

When the transformer accessories are defective and need to be welded, the residual oil should be discharged, the surface oil should be removed, and the transportation to a safe place should be carried out. When the transformer lead is poorly welded and needs to be repaired on site, insulation and isolation measures should be taken.

Minor leakage of the oil-filled transformer is allowed to be repaired and welded. There should be open holes at the top of the transformer.

The welding part must be below the oil surface. Fire welding is strictly prohibited, and intermittent electric welding should be used.

The oil stains around the solder joints should be cleaned up. There should be proper safety and fire prevention measures, and participants should be given safety technical reports.

Safety technical measures and necessary management systems should be formulated before the transformer is dried. The power supply and wires used in the drying transformer should be calculated, and there should be an overload automatic cut-off device and an overheating alarm device in the circuit.

When drying transformers, thermometers should be installed on the iron core, winding or upper oil surface according to the drying method, but mercury thermometers are strictly prohibited. 。

What should I pay attention to when the transformer is running?

(1) Whether the sound of the transformer is running normally；

(2) Whether the oil color and oil level in the oil pillow and oil-filled casing are normal, and whether there is oil leakage.；

(3) Whether the sleeves on each side are damaged, whether there are traces of discharge and other abnormal phenomena；

(4) Whether the cooling device is operating normally；

(5) Whether the upper oil temperature gauge indicates correct and whether there are any abnormalities.；

(6) Whether the diaphragm of the explosion-proof tube is intact and whether there is any effusion.；

(7) The degree of discoloration of the color-changing selenium glue of the respirator；

(8) Whether the gas relay is full of oil；

(9) Whether the body and accessories have seepage or oil leakage；

(10) Whether the casing pile heads and connecting wires on each side have heat generation or discoloration.；

(11) Whether the surrounding environment and piles near the transformer may pose a threat to the safe operation of the transformer.

Operating principles of transformer shutdown and power transmission：

(1) Circuit breakers must be used for the shutdown of the transformer, not isolation switches, as is the case for no-load transformers.

The no-load current of the transformer is large and is pure inductive current.The no-load current of a large-capacity transformer is 6%-4% of its rated current, and the small and medium-capacity transformer reaches 5%-11% of the rated current.Using an isolation switch to cut off the arc generated by the no-load current of the transformer may sometimes greatly exceed the natural arc extinguishing ability of the isolation switch and cannot be pulled open, and even cause an arc-light short circuit.

Therefore, try to use a circuit breaker to turn on or off the transformer circuit.When there is no circuit breaker in the transformer circuit, it is allowed to use an isolation switch to pull and close the transformer with a no-load current of not more than 2A.

To cut off the no-load current of transformers of 20kV and above, a triple isolation switch with an arc extinguishing cover and a mechanical transmission device installed outdoors must be used.For transformers of 10kV/320kVA and below, 35kV/1000kVA and below, an isolation switch can be used to divide the no-load current.

For example, a distribution transformer below 400kVA does not have a high-voltage circuit breaker, and the no-load current of the distribution transformer can be carried out with a drop-out fuse.The function of the drop-out fuse is to protect the short circuit when it is shorted; during normal operation, it is used for the reverse gate operation of the isolation switch.

When opening the gate, first divide the intermediate phase (Phase B), and then pull the two phases (phases A and C); in case of wind, pull them in order against the wind. Closing the gate is the opposite.

(2) The sequence of operation of the transformer to stop the power transmission.When the transformer transmits power, it is first sent to the power supply side and then to the load side. When there is a power failure, it is in the opposite order.

This is because, when the power is transmitted in the above order, if the transformer fails, the protection device can act on the circuit breaker to jump the gate to remove the fault, so as to facilitate the inspection of the fault according to the power transmission range and the judgment and handling of the fault.Power outages in the above order can also prevent the transformer from reverse charging.

Otherwise, the power supply side will be cut off first, which will increase the burden on the circuit breaker on the power supply side to cut off the circuit. At the same time, in case of an internal transformer failure, the protection may malfunction or refuse to move, prolong the fault removal time or expand the scope of the power failure.

(3) For distribution transformers with isolation switches on the high-voltage side and low-voltage circuit breakers or load switches on the low-voltage side, the high-voltage side should be closed first and then the low-voltage side when closing the gate; the opposite is true when closing the gate.

(4) For transformers connected to the transformer group unit, arrange as much as possible to boost the voltage from zero to the rated value during power transmission, and then juxtapose it with the system.The order is reversed during power outages.

(5) When the transformer is invested or deactivated, the neutral ground isolation switch on each side should be closed first.The purpose of closing the neutral ground isolation switch is, on the one hand, to prevent overvoltage from single-phase grounding and avoid certain operating overvoltage, and to protect the transformer winding group from damage due to overvoltage; on the other hand, after the neutral ground isolation switch is closed, when a single-phase grounding occurs, ground fault current flows through the transformer, causing the transformer differential protection and zero-sequence current protection actions to remove the fault point.

Therefore, before the transformer is put into operation or disabled, the neutral ground isolation switch must be closed first.If the transformer is in a state of charge, the neutral ground isolation switch should also be in the closing position.

(1) The principle of switching between two transformers running in parallel and neutral ground isolation switches.When the two transformers are running in parallel, according to the needs of the system, the neutral point of one transformer is grounded, and the neutral point of the other transformer is not grounded.

When the neutral ground isolation switch of the two transformers needs to be switched, the neutral ground isolation switch of the ungrounded transformer should be closed first, and then the neutral ground isolation switch of the other transformer should be opened, and the zero-sequence current protection switch should be switched.The reason is: if you first open the isolation switch of the neutral point of the grounded transformer, a single-phase short circuit suddenly occurs when the neutral point isolation switch of another transformer is not closed. Since the large grounding system becomes an ungrounded system, the single-phase short circuit essentially becomes a single-phase ground fault. The non-faulty phase will have 3 times the phase voltage (the ground insulation of the high-current grounding system is designed according to the phase voltage), and the neutral point of the transformer will also have a ground voltage as high as the phase voltage.

This is very dangerous for equipment, including transformers.Therefore, the switching principle of the neutral ground isolation switch of the transformer of the high-current grounding system is to ensure that the power grid cannot lose the ground point, that is, the operation method of first closing and then pulling is used: ① Close the spare ground point isolation switch; ② Pull the working ground point isolation switch;③ Switch the zero-sequence protection to the neutral ground transformer.

(2) The principle of protection and use of transformers.Before power transmission, all the protection of the transformer should be invested (the protection that may malfunction or fail the test should be approved for deactivation), and it is forbidden to send and operate unprotected transformers.

After the transformer is out of power, without affecting the backup equipment or operating equipment, or when there is no relay protection work on site, the protected connection piece may not be disconnected. The protection connection piece that needs to be disconnected should be recorded in detail in the shift record book.

(3) Switching of transformer tap switch.

The tap switch is used for voltage regulation of the transformer.By switching the tap switch, the position of the transformer tap is changed (that is, the ratio is changed) to achieve the purpose of voltage regulation.

The tap switch is divided into two types: on-load voltage regulation and no-load voltage regulation. The switching of the no-load tap switch should be carried out in the state of power failure of the transformer.

The on-load tap switch can manually or electrically change the position of the tap to regulate the voltage when the transformer is under load.

(4) When putting into a two-winding transformer, the power supply side should be combined first, and the load side should be combined later; the opposite is true.

(5) Put into a three-winding step-up transformer, first close the low-voltage side, then the medium-voltage side, and then the high-voltage side; remove the opposite.

(6) Put into a three-winding step-down transformer, first close the high-voltage side, then the medium-voltage side, and then the low-voltage side; remove the opposite.

Description: Yes（9）、（10）、（11） In addition, the order of transformer pull-in also has individual different regulations according to different conditions on the site.

(7) When switching transformers, it must be confirmed that the transformer connected to the person has been loaded before the transformer that is in operation can be stopped.

The backup transformer transmits power. If the transmission mechanism of the circuit breaker is welded, the tie rod falls off, or the isolation switch is “leaked”, although the red light is on after the circuit breaker is closed, the primary circuit of the transformer is actually not connected.At this time, if you do not check whether the transformer connected to the person is loaded, the operating transformer will be cut off hastily, which often causes accidents.

Therefore, when switching transformers, just take a closer look, check that the transformer connected to the person has a load current, and then operate it to plug the loopholes and avoid accidents.