First, the inspection and acceptance of the newly installed or overhauled distribution transformer before it is put into operation

After the distribution transformer has been overhauled or after the new installation is completed, the transformer must be inspected as follows before it can be put into service:

1-1. Check ingress with transformer protection systems

1-1-1. With the fuse protection of small transformers, before operation should check the selection of fuse specifications meet the requirements, contact is good.

1-1-2. Transformers equipped with relay protection devices should consult the relay protection experiment report to see if the overall value of the relay is consistent, the name and logo are correct, and the experimental signal device is correct in motion.

1-1-3. A transformer equipped with a gas relay requires that there should be no gas inside the relay, the upper electric shock signal should act accurately, the lower contact trip connection should be disconnected, the connection tube of the installation relay should have an upward tilt.

1-1-4. Lightning protection with lightning rod, should be put into use before the test, to ensure that lightning strikes can be reliable action, in addition to the discharge recorder should be installed.

1-1-5. Check whether the grounding device is good and whether the ground resistance value conforms to the specified value.

There is also a measurement check of the insulation resistance before power is sent.

1-2. Inspection of the monitoring device

The current meters, voltmeters and temperature measuring instruments used in monitoring devices should be complete and the measuring range should be drawn red at the rating within the specified range for monitoring purposes. The top of the small transformer is equipped with a temperature-measured thermometer socket, which is inserted into observation with an alcohol thermometer. The thermometer of the temperature measuring device should be installed correctly.

1-3. Transformer appearance check

The oil level gauge on the oil tank should be able to observe clearly and conveniently, the valve of the oil storage and gas-broken electrical connection pipe should be open, the relay should be filled with oil, the shell and the neutral point grounding device should be strong, the connection between the line sleeve and the wire should be strong, and the phase sequence color scale should be correct. The voltage tap switch should be in the correct position. Multiple transformers should be numbered at the case. The explosion-proof tube film should be complete, and the parts should not leak oil.

1-4. The inspection of the experimental report of the transformer shall comply with the requirements of the experimental procedure.

Second, the normal inspection of distribution transformers

The on-duty personnel should make regular checks on the running transformer sits in order to understand and master the operation of the transformer and find problems to be solved in a timely manner.

The normal inspection items for the running transformer are as follows:

2-1. Whether the sound is correct: The normal operation of the transformer emits a uniform ‘'wonwon‘' sound, should be no heavy overload caused by the ‘'wonwon‘' sound, no internal overvoltage or partial discharge fire “zizi” sound; No large power equipment start-up or has harmonic equipment running “wawa” sound, etc.

2-2. Check the transformer load:

2-2-1. Outdoor installed transformers, such as no fixed installed current meter, should use a clamp current to measure the maximum load current and representative load current.

2-2-2. If the transformer installed indoors is equipped with a current meter or a volt meter, the hourly load shall be recorded and the daily load curve shall be drawn.

2-2-3. Measure the balance of three-phase current, for the Yyn0 junction group of transformers, wherein the current on the line should not exceed 25% of the low-voltage winding rated current.

2-2-4. The operating voltage of the transformer shall not exceed the range of the rated voltage of ±5%. If the supply voltage is too high or too low for a long time, the transformer connector should be adjusted to make the low voltage side voltage normal.

2-3. Whether the temperature exceeds the allowable value, the upper oil temperature - like should not exceed 85C.

2-4. Whether the casing is clean, whether there are broken cracks and discharge marks, one or two side leads should not be too tight, too loose, whether the connection points are tight, should be no discharge and overheating phenomenon, temperature measurement with the display of temperature wax tablets should be no melting phenomenon.

2-5. The connection and ground resistance values of the housing ground and neutral point ground should meet the requirements.

2-6. To hand to touch the heat sink temperature is normal, the cooling tube temperature is not.

2-7. Whether the cooling system is operating properly, the transformer with a fan should remain in operation or available (air-cooled, strong oil air-cooled, water-cooled, etc.).

2-8. Transformers equipped with gas relays and explosion-proof tubes should check the complete condition of their filling and film.

2-9. The oil level should be normal, the shell clean no leakage oil phenomenon.

2-10. Respirator should be smooth, silicone should not absorb moisture saturation, oil seal respirator oil level should be normal.

Third, the special inspection of the distribution transformer

3-1. When high temperature and heavy load, check the contact, connector for overheating phenomenon, monitor the load, oil temperature, oil level changes. The cooling system should operate normally.

3-2. Check the surrounding debris before the wind comes to prevent it from blowing to the device. In high winds, watch the distance between phases when the leads are swinging and whether the safety distance to the ground meets the requirements and whether there are no hanging debris.

3-3. After lightning check porcelain insulators for discharge marks, lightning protection, lightning rod whether discharge, lightning recorder is moving.

3-4. Underfog weather, porcelain arm whether there is discharge and fire phenomenon, focus on monitoring porcelain dirty parts.

3-5. Snowy weather, according to the melting of snow to check the hot part of the connector, timely treatment of ice.

3-6. Night lights out patrol, check the insulator for the discharge flash phenomenon and connector sending red.

3-7. When the short circuit fails, check the equipment and connectors for any oddity.

3-8. In case of abnormal conditions, view the voltage meter current meter reading and relay protection action. Check the inside and outside of the transformer when the gas relay raises an alarm.

Fourth, epoxy insulation distribution transformer operation inspection

4-1. Inspection after operation

4-1-1. Whether there is abnormal sound, vibration.

4-1-2. Whether there is a change of color caused by local overheating, harmful gas corrosion, etc. caused by the insulation surface creep marks and carbonation phenomenon.

4-1-3. The temperature in the house or cabinet where the transformer is located is particularly high, whether the ventilation and ventilation state is normal, and whether the air-cooled device of the transformer is operating properly.

4-2. Regular check

4-2-1. The first inspection is carried out during the period of 2 to 3 months after the delivery, and the inspection is carried out every year after that.

4-2-2. Check the pouring winding and interphase connection line for dust accumulation, whether there is cracking, discoloration, discharge and other phenomena, insulation resistance is normal.

4-2-3. Check the iron heart passage for dust, foreign body blockage, rust or corrosion and other phenomena.

4-2-4. Check the regulator tap switch contact for overheated discoloration, poor contact or rust and other phenomena.

4-2-5. Check that the winding compression device is loose.

4-2-6. Check that the instrument stoics such as the pointer thermometer and the protection device are acting correctly

4-2-7. Check that the cooling device, including electric motors, fan bearings, etc. is good.

Fifth. Over-load operation of distribution transformers

When the daily compliance rate of the distribution transformer is K_p<1, the permissible overload curve is shown in the figure below.

If there is a lack of information on the overload curve of the distribution transformer, the upper oil temperature before the overload operation of the distribution transformer can also be determined to determine the duration of the allowed overload and the duration of the overload, see the table below.