How to Deal With the Broken Distribution Transformer? Maintenance Manual Detailed Explanation

Distribution transformer, referred to as "distribution transformer", refers to a static electrical device that transforms AC voltage and current according to the law of electromagnetic induction and transmits AC power in a power distribution system. In some areas, power transformers with voltage levels below 35 kV (mostly 10KV and below) are called "distribution transformers", or "distribution transformers" for short. The place and place where the "distribution transformer" is installed is the substation. Distribution transformers should be installed on poles or on the ground in the open. The installation method, installation precautions, supply and distribution method, capacity selection, operation and maintenance, etc. are introduced in detail.

1. Introduction of distribution transformer

Distribution transformer refers to a static electrical device used in power distribution system to transform AC voltage and current according to the law of electromagnetic induction and transmit AC power. China's transformer products can generally be divided into UHV (750KV and above), ultra-high voltage (500KV) transformers, 220-110KV transformers, and 35KV and below transformers according to their voltage levels. Distribution transformers usually refer to power transformers operating in the distribution network with a voltage level of 10-35KV and a capacity of 6300KVA and below to directly supply power to end users.

A power distribution transformer is a static electrical device that is used to convert a certain value of AC voltage (current) into another voltage (current) with the same frequency or several different values. When the primary winding is supplied with alternating current, alternating magnetic flux is generated, and the alternating magnetic flux induces an alternating electromotive force in the secondary winding through the magnetic conduction of the iron core. The level of the secondary induced electromotive force is related to the number of turns of the primary and secondary windings, that is, the voltage is proportional to the number of turns. The main function is to transmit electric energy, therefore, the rated capacity is its main parameter. Rated capacity is a customary value for expressing power. It represents the size of the transmitted electric energy, expressed in kVA or MVA. When the rated voltage is applied to the transformer, it is used to determine the rated current that does not exceed the temperature rise limit under specified conditions. The more energy-saving power transformer is an amorphous alloy core distribution transformer, and its biggest advantage is that the no-load loss value is extremely low. Whether the no-load loss value can be guaranteed in the end is the core issue to be considered in the entire design process. When laying out the product structure, in addition to considering that the amorphous alloy core itself is not affected by external forces, it is also necessary to accurately and reasonably select the characteristic parameters of the amorphous alloy during calculation.

2. Development of distribution transformers

Since 2000, driven by urban and rural power grid renovation projects, China's distribution transformer industry has maintained a good momentum of development. In 2008, the annual output of China's distribution transformers exceeded 400 million KVA, accounting for nearly 40% of the total annual output of transformers. In 2010, the output of China's transformers reached 1.223 billion KVA. Calculated according to the 40% ratio, it is estimated that the output of new distribution transformers in 2010 will reach 534 million KVA. In 2010, the distribution transformer manufacturing industry achieved an output value of about 42.518 billion yuan, a year-on-year increase of 18.84%.

With the continuous deepening of China's "energy saving and consumption reduction" policy, the state encourages the development of energy-saving, low-noise, and intelligent distribution transformer products. Some high-energy distribution transformers operating on the grid are no longer in line with the development trend of the industry, and are facing the need for technology upgrades and replacements. In the future, they will be gradually replaced by energy-saving, material-saving, environmentally friendly, and low-noise transformers.

The mainstream energy-saving distribution transformers mainly include energy-saving oil-immersed transformers and amorphous alloy transformers.

Amorphous alloy transformers are both energy-saving and economical. Its notable feature is that the no-load loss is very low, only about 20% of the S9 series oil-immersed transformers. It meets the national industrial policies and the requirements of power grid energy saving and consumption reduction. The distribution transformer with ideal effect is especially suitable for places with low load rate such as rural power grids. Although the National Development and Reform Commission began to encourage and promote amorphous alloy transformers as early as 2005, due to the constraints of insufficient production capacity of raw material amorphous alloy strips, China's amorphous alloy transformers have not been mass-produced. Amorphous alloy transformers used in grid operation account for only 7%-8% of distribution transformers, and only Shanghai, Jiangsu, Zhejiang and other regions use amorphous alloy transformers in large quantities nationwide.

The competition of distribution transformers is fierce, facing the pressure of high raw material costs, and the lack of energy-saving evaluation system construction and market supervision and management, the high initial investment faced by the selection of energy-saving transformers makes the promotion of energy-saving transformers bring certain difficulties.

Although the development of China's transformer energy-saving standard policy started late, the pace is fast. With the further revision and promotion of distribution transformer energy efficiency standards, it will be at the same level as the highest energy efficiency standards of developed countries in the world. Regardless of energy conservation or technical strength, China's transformer industry will be at the forefront of the world's transformer development. More importantly, the energy saving of transformers is not only reflected in the loss fixed value calibrated by the transformer equipment factory, but also the establishment of the whole life cycle management mode of users, for the economic operation and management of transformers, can give full play to the maximum value of product energy saving, thus Realize the real benefits of transformer energy saving.

3. Classification of distribution transformers

Distribution transformers are divided into oil-immersed transformers and dry-type transformers according to different insulation media; according to different voltage regulation methods, they are divided into non-excitation tap changer transformers and on-load tap changer transformers.

3.1 Oil-immersed transformers are classified according to the shell type:

3.1.1 Non-enclosed oil-immersed transformers: mainly include S8, S9, S10 and other series products, which are widely used in industrial and mining enterprises, agriculture and civil buildings.

3.1.2 Enclosed oil-immersed transformers: mainly include S9, S9-M, S10-M and other series products, which are mostly used in places with a lot of oil and chemicals in the petroleum and chemical industries.

3.2 Dry-type transformers are divided into:

3.2.1 Encapsulated coil dry-type transformer: mainly SCB8, SC (B) 9, SC (B) 10, SCR-10 and other series products, suitable for high-rise buildings, commercial centers, airports, stations, subways, hospitals, Factories and other places.

3.2.2 Non-encapsulated coil dry-type transformers: mainly include SG10 and other series products, which are suitable for high-rise buildings, commercial centers, airports, stations, subways, petrochemical and other places.

4. Installation of distribution transformers

4.1 Installation method of distribution transformer

Under normal circumstances, the distribution transformer should be installed on the pole or on the ground in the open air. Distribution transformers in factories, workshops, and suburban living areas can be installed indoors according to specific conditions.

The composition and characteristics of distribution transformer installed on pole or open-air floor installation

Mounting on a pole:

4.1.1 Single column

The transformer, high-voltage dropout fuse and high-voltage arrester are installed on the same pole. The structure is simple, the installation is convenient, the material is less, and the land occupation is small. It is suitable for installing distribution transformers below 50KVA.

4.1.2 Double column

It consists of a high-voltage line terminal pole and another auxiliary pole (about 7.5M in length). It is stronger than the single-column type, and can be installed with a 63-315KVA distribution transformer. The open-air floor-mounted transformer is directly placed on a platform (pier) made of bricks and stones with a height of not less than 2.5M. It is convenient to disassemble and assemble the transformer, and the capacity of the transformer is not limited.

4.2 Safety technical requirements for distribution transformer installation

4.2.1 Safety technical requirements for distribution transformers mounted on poles

The base of the transformer should not be less than 2.5m from the ground, and all iron parts should be grounded. The height of the exposed conductive part from the ground should be more than 3.5m. The base of the transformer should be fixed to the stand, and the upper part should be fixed with hardware and poles. Both the upper and lower leads of the transformer should use multi-strand insulated wires. The distance between the high-voltage drop-out fuse and the ground should not be less than 4m, the distance between the middle phase and the side phase of the high-voltage fuse should not be less than 0.5m, and the included angle between the center line of the high-voltage fuse and the vertical line is 250-300. A warning sign saying "No Climbing, High Voltage Danger!" should be hung.

4.2.2 Safety technical requirements for distribution transformers installed in the open air

The foundation of the floor-standing transformer should be 0.2m above the ground. If it is in a waterlogged area, a drainage ditch should be set around the transformer; a masonry fence should be set around the transformer, and the height of the fence should not be lower than 1.8m. The door of the fence should be made of refractory materials. Manufactured and designed to be on the low-voltage side of the transformer, the door should open outwards, and a lock should be installed on the door. Bamboo and wood fences should not be used.

The transformer is installed in platform (pier) type, and the height of the platform (pier) should not be lower than 2.5m. If two or more transformers are installed outdoors, the distance between their casings should not be less than 1.25m. The transformer enclosure should be properly connected. The distance between the transformer and flammable buildings should not be less than 5m, and the distance from fire-resistant buildings should not be less than 3m. On the fence or platform (pier), hang a warning sign of "stop, high voltage danger".

4.2.3 Safety technical requirements for distribution transformers installed indoors

There should be good natural ventilation indoors. The fire resistance rating of the transformer room shall be Class I. The net distance between the transformer outline and the rear wall and side wall should not be less than 0.6m, and the net distance from the door should not be less than 0.8m; the doors and windows of the transformer room should open outward, and there should be shutters under the doors and windows.

5. Supply and distribution mode of distribution transformer

The 10KV high-voltage power grid adopts the operation mode of the three-phase three-wire neutral point ungrounded system. Most of the users' transformer power supply adopts the D/yn11 connection mode and the neutral point direct grounding system operation mode, which can realize the three-phase four-wire system power supply.

6. Capacity selection of distribution transformers

In the operation of distribution transformers, some are under-loaded due to excessive capacity, and some are overheated or even burned due to overload or over-current operation. Improper selection of the capacity of this device affects the reliability and economy of the power system power supply.

The capacity of the transformer is selected on the basis of load statistics. Since load estimation is not easy to be accurate, it is generally selected according to the estimated maximum load. As a result of such selection, the capacity setting is often too large, which brings adverse effects on the operation of the power system. If it is selected according to economic operation, it is to use the condition that the copper loss and iron loss of the transformer are equal to derive the maximum economic load rate of the transformer and the ratio of the rated capacity of the transformer to the maximum load. Since the actual operating load is not necessarily the maximum load calculated by the load statistics, and the load is random, the operating efficiency is variable, and its economical operating benefits are difficult to realize.

At present, new low-loss transformers are being used to replace high-energy transformers in power distribution systems, and the single iron loss can be reduced by about 40%. Due to the large number of distribution transformers and large load changes, the economic benefits are very significant.

How to make full use of the set capacity of the transformer without damaging the normal service life of the transformer should be the main basis for selecting the capacity of the distribution transformer.

The recommended method is: according to the estimated maximum load Smax and typical daily load curve of the load, select the capacity of the distribution transformer according to the International Electrotechnical Commission (IEC) standard (1972) oil-immersed transformer and load guideline. This standard has been adopted by China. The advantage of this method is that the normal overload capacity of the transformer is considered, and the setting capacity of the transformer can be fully utilized under the premise of not shortening the life of the transformer. This reduces investment and improves the operating conditions of the distribution network, and its economic benefits are also significant.

According to the computer program compiled by this method, the distribution transformer capacity selection table corresponding to six typical daily load curves has been calculated, and the load reference type of the load-load curve is .

I: for watering the ground and wheat fields;

II: Village payment industry; lighting, yard use;

III: pay for business; lighting, watering, yard use;

IV: Industrial use in prefectures and counties;

V: Village comprehensive load with industrial load;

VI: Urban industrial comprehensive load.

The method of making wind in the attached table is as follows

6.1 Determine the load type and select a typical daily load curve.

6.2 Determine the equivalent air temperature θδ; the ambient temperature in the IEC standard is not the average temperature of the environment, but the equivalent air temperature, which means: within a certain time interval, under load, if the θδ remains constant, then the insulating The deterioration is equal to the insulation deterioration when the air temperature changes naturally; here for convenience, it is suggested that: Jiangnan region takes 22°C, 24°C in Jiangbei region takes 20°C, Northwest and Northeast regions take 16°C, 18°C.

6.3 According to the estimated maximum load value (kVA), look up the table to determine the rated quality Sn of the selected transformer. For example: load curve I, the annual equivalent air temperature is 9°C; the maximum load is 1000 kVA, and a distribution transformer of 800 kVA should be selected.

6.4 Determine the normal overload capacity of the working transformer according to the environmental conditions and load type.

For example, class VI load curve, the annual equivalent air temperature is 22°C, the frontal capacity of the working transformer is 315 kVA, and the maximum load that the transformer can carry is 340 kVA.

It should be noted that: in accordance with the above method to select the capacity of the transformer, in actual operation, it should also accept the constraints of the maximum load continuous operation allowable time; in order to ensure safety. If the allowable time is exceeded, there is still the risk of burning the transformer. The permissible time can be obtained according to the formula for calculating the maximum temperature of the natural circulation oil-immersed transformer winding. For convenience; the maximum load limit operating time has been calculated in the attached table τmaxe calculation conditions are: the ambient temperature is 35°C, and the winding hottest point temperature does not exceed 140. For example: the yearly equivalent air temperature of Attachment IV is 20°C and the penalty load limit operating time It is 17 hours, which can be obtained from six tables, when the ratio of the maximum load to the rated capacity is 3dl. When the temperature is lower than 1.17, the maximum load is extremely limited, that is, there is no danger of overheating.

7. Technology of distribution transformer

7.1 Process guarantee for distribution transformers

The high-voltage coils wound by the same winding process are wound by a high-speed winding machine, which uses mechanical tension on the wires and the tension is constant. The servo system is to realize the automatic control of the electrodeless gauge, the cable is tight and compact, and the automatic counting is accurate; because the wires are tightened and close to each other during the winding process of the high-voltage coil, the wires of the high-voltage coil are solid and insulated from the end Between them are rigid and next to each other with no compression margin, and the same is true for low-voltage coils. Therefore, the axial height of the phase winding after the same winding can ensure the design size (thereby ensuring the accuracy of the impedance voltage).

7.2 Stacking of Distribution Transformer Cores

The iron core is assembled on a stacking table that is pneumatically flipped and erected. The special position positioning tool is used, and the iron yoke is not stacked on the stacking iron. After the iron core is clamped, the lower clamp is clamped. The upper clamp is temporarily clamped, and the C-shaped clamp is used to clamp the column iron in the space; the standing mobile storage area is painted with fixative, and after drying and curing, the temporary clamp is removed and transferred to the body assembly process. The bonding between the iron chips is firm, with low loss and low noise.

7.3 Distribution transformer body assembly

Since the iron core does not have an iron yoke, the phase unit of the winding type, the iron yoke pad is made of injection-molded epoxy resin, and the insulation of the high-voltage lead wire and the tap lead wire adopts a special matching combination such as reinforced PVC pipe threading. Body insulation and lead wire assembly are carried out on the rolling platform assembly line. The assembly speed is fast, the quality is good, and it is clean and hygienic.

7.4 Distribution transformer corrugated oil tank

The corrugated oil tank uses the "corrugated sheet folding machine" in the corrugated production line to automatically fold the specifications of the cold-rolled steel sheet into the sheet shape required by the design drawings, including the corrugated sheet height, pitch, corrugated sheet, straight edge length and Overall length and width. The folding quality is good and the speed is fast; the corrugated sheet is welded after being folded, and the folded end seam and reinforced iron welding are completed. The corrugated oil tank has a tank bottom, a tank edge, and a rectangular mailbox formed by butt-welding of corrugated sheet groups in the middle. The corrugated sheets are processed by folding thin plates. In addition to good heat dissipation performance when the transformer is working, the corrugated fins of the corrugated sheets also have the function of expanding to relieve the internal pressure rise.

7.5 Characteristics of distribution transformers

The capacity range of the distribution transformer is 30-3150KVA; the iron core is three-phase three-column type, multi-step stepped cylindrical; the coil adopts the same winding technology, the concentricity is good, the short-circuit resistance is strong, and the main technical indicators have reached the domestic advanced level of similar products.

8. Operation and maintenance of distribution transformers

8.1 Overload operation of distribution transformers

Transformer overload operation means that the load current exceeds the rated current of the transformer. Under normal circumstances, when the transformer is running at a small load, its insulating material cannot fully play its role, and in continuous overload operation, the transformer will generate high temperature, which will cause the insulation part of the winding to be burned and fall off, forming a short circuit between turns; at the same time, the transformer oil will generate Oil sludge accumulates on the oil tank plate, winding and iron core, resulting in poor heat dissipation of the transformer oil. This vicious cycle not only seriously affects the life of the transformer, but also causes accidents such as high voltage breakdown and transformer burnout. Therefore, always observe the three-phase load current. The three-phase load current strives to be consistent, and if there is any deviation, it should not exceed 10%.

8.2 Abnormal sound from distribution transformer

When the alternating current passes through the transformer winding, a normal and uniform "hum" sound will be produced due to the self-vibration of the iron core. If there is an abnormal sound, it is necessary to find out the reason and report it to the relevant department in time. The sound of the transformer is also different when it is unloaded and when it is loaded. According to the abnormal sound characteristics compared with the past, it can be put into operation after the cause is found out.

8.3 Inspection of distribution transformer temperature

The operating temperature of the transformer has a great relationship with its life. When the transformer operates below the normal temperature of 95 ℃, its service life is 20 a; if it is operated at 110 ℃, its service life will be shortened to 7 a; if the temperature is raised to 130 ℃, its service life will be shortened to 2 a; If it continues to run at low temperature, it will be scrapped after about d. 10 If the temperature exceeds the allowable value of the transformer, find out the reason and take countermeasures in time.

8.4 Whether the oil level of the distribution transformer is normal, whether there is seepage, oil leakage or abnormal oil color

There are many reasons for the oil level to drop. Due to poor welding quality and sealing, heat pipes, valves, box edges, etc. are prone to seepage and oil leakage. When the oil level drops below the upper cover of the transformer, the contact surface between the oil and the air increases, and it is easy to oxidize and deteriorate and absorb moisture in the air, resulting in a decrease in the compressive strength of the oil, thereby destroying the insulation performance of the winding. When the oil shortage is serious, the insulation between the conductive parts of the transformer and the ground and between them will be reduced, resulting in phase-to-phase or ground-to-ground breakdown discharge. If you continue to use it at this time, the transformer oil will not be able to circulate and convect normally, causing the temperature of the transformer oil to rise, shortening its life and even burning it out.

8.5 Whether the insulation bushing of distribution transformer is damaged, cracked and discharged

If the insulating bushing is not cleaned for a long time, or there are damaged cracks and discharge traces, in rainy or foggy weather, the leakage current of the insulating bushing will increase due to the humidity of the air, the insulation will drop, and a flashover to the ground will occur. In addition, severe fouling of the insulating sleeve, and large fragments and cracks on the insulating sleeve will also cause flashover or explosion accidents. To solve this phenomenon, in addition to observing the insulating bushing itself, it is also necessary to pay attention to the dirt accumulation rules of the bushing, such as wind direction and surrounding environment, so as to do a good job of cleaning.

8.6 Regular cleaning of distribution transformers

It is necessary to regularly clean the dirt on the distribution transformer, check whether the bushing has flashover discharge, whether the grounding is good, whether there is disconnection, desoldering, or fracture, and the grounding resistance must be measured regularly, and its resistance value is not greater than 4 Ω (capacity 100 kV A and above) or 10 Ω (capacity less than 100 kV A), or take anti-fouling measures and install anti-fouling caps for bushings. When connecting and dismantling the lead wires of the distribution transformer, it is necessary to strictly follow the process to avoid internal breakage of the lead wires.

9. Common fault analysis of distribution transformers

9.1 Unbalanced three-phase load or seasonal overload

The unbalanced three-phase load of distribution transformers exists in a large number according to the survey results, especially in rural areas, most of the electric loads are single-phase loads, and the load changes greatly. Therefore, there are many unbalanced three-phase loads of distribution transformers. So that the three-phase can not run symmetrically, resulting in zero-sequence current. On the one hand, this increases the loss of the transformer, and on the other hand reduces the effective capacity of the transformer. The above two conditions will lead to overheating of the transformer, aging of the insulating oil, reduction of the insulation level of the winding, and eventually damage to the transformer. The following measures can be taken:

9.1.1 Investigate the load conditions of distribution transformers, including the loads of 24 hours a day and the loads of 4 seasons a year, find out the general situation of the load, and try to adjust the three-phase load to make it close to symmetrical operation;

9.1.2 Adjust the peak and valley time of electricity consumption to reduce the overload situation; at the same time, increase the capacity of the transformer in time to avoid long-term overload operation of the transformer.

9.2 Poor grounding

The lightning protection work for distribution transformers subjected to lightning strikes has generally been done, but there are still two problems: ① The lightning arrester is not well grounded; Dore area). If the arrester is poorly grounded and the overvoltage occurs, the arrester cannot discharge the current well, which will damage the insulation of the transformer; if the arrester is not installed on the low-voltage side, when the arrester on the high-voltage side discharges a large lightning current to the ground, A voltage drop is generated at the grounding position, and this voltage also acts on the neutral point of the low-voltage side winding while passing through the transformer shell, and the low-voltage side winding is grounded through the wave impedance of the low-voltage line. The following measures can be taken:

9.2.1 Find out the poor grounding related to the lightning arrester, and reconnect as required. Note: Firstly, connect the grounding wire of the arrester directly to the shell of the transformer and the neutral point of the low-voltage side, and then share the grounding device. Its earth resistance does not exceed 4 Ω;

9.2.2 For multiple minefields, a set of low-voltage surge arresters should be installed on the low-voltage side.

9.3 Oil leakage and oil leakage

There are also many leakages of transformer oil in distribution transformers. Due to leakage, the amount of oil in the transformer is reduced, and the oil level is lowered, causing the infiltration of air and water vapor, accelerating the oxidation of the oil and deteriorating it, increasing the viscosity of the oil, reducing the convection speed, and affecting the heat dissipation of the transformer. The temperature rise is higher, which further accelerates the deterioration of the oil. At the same time, the acidity of the deteriorated oil increases, which leads to a decrease in the insulation resistance of the winding, and even damages the insulation. If things go on like this, it will inevitably lead to damage to the transformer. The following measures can be taken:

9.3.1 Find out where the oil is leaking and deal with it;

9.3.2 Check whether the transformer oil is deteriorated or not, and conduct a simple oil analysis. If the transformer oil gradually changes from the initial light yellow to orange and brown, and the viscosity of the oil is high, it means that the transformer oil has deteriorated and must be purified or replaced;

9.3.3 When the transformer oil is not deteriorated, check whether the oil level is too low. If it is too low, add oil to the scale marked on the transformer oil conservator;

9.3.4 Check the insulation resistance of the winding.

10. Prevention of burning out of distribution transformers

10.1 Reasonably choose the installation location of distribution transformer

The installation of distribution transformers must meet the voltage requirements of users, and try to avoid installing distribution transformers in wild mountains, places that are easily attacked by lightning and far away from residential areas. This is not convenient for regular maintenance by operators, and it is not convenient for staff to manage .

10.2 Reasonably choose the capacity of distribution transformer

Reasonable selection of the capacity of the distribution transformer is also very important, neither can it cause the distribution transformer to burn out due to overload, nor can it cause waste of large horse-drawn carts. The capacity of the distribution transformer should be reasonably selected according to the user's load situation and statistical capacity. For example: a 100kV·A distribution transformer can carry a load of 85kW when the power factor is 0.85.

10.3 Strengthen the measurement of electric load

During the peak period of electricity load, the measurement of the load of each distribution transformer should be strengthened, and the number of measurements should be increased if necessary. The distribution transformer with unbalanced three-phase current should be adjusted in time to prevent the lead wire from being easily burned due to excessive neutral wire current. Cause user equipment to burn out.

10.4 Avoid installing low-voltage metering boxes on distribution transformers

The low-voltage metering boxes installed on distribution transformers in remote mountainous areas should be gradually removed and installed indoors as much as possible. For example, when our bureau eliminated powerless townships in the past few years, in order to facilitate management and prevent power loss, low-voltage metering boxes were installed in remote mountainous areas. Due to the long-term operation of the metering box, the glass of the metering box is damaged or the low-voltage pile head of the distribution transformer is damaged and cannot be replaced in time, resulting in damage to the distribution transformer due to the burning of the electric energy meter due to rain and other reasons.

10.5 Rationally configure the high and low voltage fuses of distribution transformers

The unreasonable configuration of the high and low voltage fuses of the distribution transformer may easily cause serious overload of the distribution transformer and burn out the distribution transformer. The configuration of high and low voltage melts should follow: transformers with a capacity below 100kV·A should be equipped with fuses with 2.0 to 3.0 times the rated current; transformers with a capacity above 100kV·A should be equipped with fuses with 1.5 to 2.0 times the rated current; The wire should be configured according to the rated current slightly larger.

10.6 It is not advisable to adjust the tap changer without authorization

Due to the difference in electricity load between winter and summer, the voltage level is slightly different. In order to meet the voltage requirements, some rural electricians adjust the tap changer at will without conducting relevant tests, resulting in the tap changer not being in place, causing a short circuit between phases and burning out the switch. Electric transformer.

10.7 Installing an insulating cover at the height of the distribution transformer

In order to prevent natural disasters and external damage, if necessary, install high and low voltage insulating covers in residential areas with narrow roads and forest protection areas, so as to prevent the transformer from being burned out due to low voltage short circuit caused by falling things on the distribution transformer.

10.8 Lightning arresters should be installed on both the high and low voltage sides of the distribution transformer

Lightning arresters should be installed at all levels of distribution transformers in multiple minefields. If the quality of lightning arresters is unqualified or fails to be replaced in time, it is easy to be damaged by lightning and burn out the transformer. In the thunderstorm season every year, the lightning arrester should be sent to the repair and test department for installation in time after passing the test, and the use of unqualified products is prohibited.

10.9 Periodically measure the grounding resistance of distribution transformers

The distribution transformer is severely oxidized after long-term operation (especially the grounding lead is replaced by aluminum wire), and the grounding resistance increases. In addition, the buried grounding body is corroded and broken, causing the neutral point potential to shift. When lightning strikes or overvoltage , prone to accidents. According to the regulations, the grounding device should meet: the grounding resistance of distribution transformers below 100kV·A is not greater than 10Ω, and the grounding resistance of distribution transformers above 100kV·A is not greater than 4Ω.

10.10 Strengthen daily management

Regularly inspect the lines, cut down trees, and prevent the branches from hitting the wires and causing low-voltage short-circuits to burn out the distribution transformers. The lack of daily management of the distribution transformer by the staff makes the transformer run without oil for a long time, and the respirator is not installed or the silicone is not replaced in time, so that the distribution transformer gets wet from water, which is easy to cause accidents. The distribution transformer itself has quality problems. Because the installation location of the distribution transformer is far away, some construction workers put the untested distribution transformer into operation without authorization, temporarily using electricity, and burning out the transformer.

10.11 Periodically check the low-voltage leads of distribution transformers

It is strictly forbidden to use the wire itself as a wire lug and directly connect it to the low-voltage pile head of the distribution transformer. Regularly check and strengthen the contact between the lead wire and the distribution transformer pile head to prevent the low-voltage pile head of the distribution transformer from being burned due to looseness.

In order to make the distribution transformer operate safely for a long time without failure, as an operation manager, we must do frequent inspection, maintenance and measurement, find problems in time and deal with them in a timely manner, so as to avoid the expansion of faults and burn out the distribution transformer.

11. Maintenance of distribution transformers

11.1 Before maintenance, the power switch of the previous level must be switched off to cut off the power, and a power-off sign board must be hung. Then check with an electroscope pen to confirm that the device to be repaired has been powered off before repairing;

11.2 During maintenance, two people must be present, one for maintenance and one for guardianship;

11.3 Maintenance personnel must be professional electricians who are familiar with power distribution devices;

11.4 Maintenance personnel must wear protective equipment and use electrical insulation tools

11.5 The replacement electrical appliances must be consistent with the original specifications, and the use of unqualified substitutes is prohibited;

11.6 During maintenance, the wiring of the original power distribution device shall not be changed arbitrarily, and the original switching devices shall not be removed at will;

11.7 At the end of the maintenance, the power distribution device should be disconnected, and then the power supply side should be closed and energized step by step. After confirming that the power is turned on with an electroscope, the next level of power should be tested.

11.8 At the end of the maintenance, remove the power switch of the upper level and hang the power-off sign board.