Tag Archives: AC Reactor

Operation and maintenance of 500kV transformer

At present, China\\ s electric power system three-phase AC transmission system, requiring three-phase transformer is, both can be used three single-phase transformer according to a certain wiring together, said three-phase transformer, three-phase winding can also share a core, according to a certain wiring together, said the three-phase transformer. Three-phase transformer or three-phase transformer\\ s wiring combinations known as connection group. Detailed description of the connection group, and in many books are introduced, no longer described. In the power transformer manufacturing practice, usually Y, yn0, d11, and YN, d11 three kinds of connection group. 500kV transformer in a three-winding autotransformer, its wiring group often YN, a0, d11. This connection group, said high voltage winding and voltage windings are used in star connection and the same phase, neutral grounding, wiring and low voltage windings for the angular, and the phase lag of high and medium voltage winding 30 °. 

To make a long-term safe and reliable transformer operation, not only requires good quality transformer manufacturing, operation and maintenance also need the right to try to avoid a temporary power outage transformer maintenance, extended maintenance cycle, reducing the maintenance workload. 

A transformer normal operation and inspection 

1 transformer running 

Transformer in the normal case, the long-term continuous operation, the normal operation of the transformer, including the following aspects: 

(1) transformer in good condition. Includes the transformer body intact, without any defect; various electrical performance compliance; transformer oil standard of the indicators, oil level is correct, the sound is normal; the auxiliary equipment (such as cooling devices, surge devices, casing, gas following the electrical appliances, pressure release valve, etc.) intact, its status in line with operational requirements transformer.

(2) transformer ratings in line with operational requirements, including: voltage, current, capacity, temperature, auxiliary equipment required for the rated operating parameters (such as cooling the power supply unit, power supply control circuit work required, etc.) should also meet the requirements . 

(3) operating environment to meet the requirements. Include a good grounding transformer, fastening the connector; the side of the arrester is working properly; the protection device is working properly and so on. 

(4) cooling system intact. 

2 transformer inspection 

Transformer during operation, should be inspected at least once a day, every week for a night patrol; in case of bad weather but also step up inspections. Detailed records of each visit should be prepared. 

On-site visits to check the following items should be: 

(1) transformer top oil temperature is normal, whether close to or exceed the allowable limit. 

(2) transformer oil pillow oil level is normal, whether it corresponds with the oil temperature. 

(3) the sound of the transformer to run compared with the past without exception, such as increased noise or other sound so new. 

(4) each side of the transformer casing surface is clean, without damage, cracks and traces of discharge, for oil-filled casing should also check the oil level is normal, with or without oil leakage phenomenon. 

(5) each side of the transformer terminals or connection fittings are complete, fastening, with or without signs of overheating. 

(6) the phenomenon of transformer oil tank leaks, tank shell valves on the status of compliance with various operational requirements. 

(7) cooling system is operating properly, such as fans, submersible pump is required to run fans, submersible pump running sound is normal, wind direction and the flow of oil is correct. 

(8) Check the tap changer position indicator is correct. For parallel operation of single-phase transformer or transformer, you should also check the location of the tap changer are the same. 

(9) Check the respirator in the silica gel is red; respirator small oil cup of oil is appropriate. 

(10) electric control boxes and all kinds of electrical devices inside the body is intact, the location and status is correct; tank shell seal is good. 

(11) in the following cases, the primary response variable for special examination: 

a) after each trip. Main transformer overload and over-voltage operation, special attention should be temperature and overheating and vibration, body oil, etc., should be inspected once every half hour, and make records. 

b) Each lightning, high winds, hail, heavy rain and other inclement weather later. 

c) area near the main transformer failure. 

d) other when necessary. 

3 transformer monitoring and operating records 

In the substation control room, there are many instruments and protection devices, used to monitor the operational status of the transformer, to ensure the safety of the transformer. Therefore, the transformer should run in record time voltage, current, active power, reactive power, transformer oil temperature and oil level and other data. If abnormal transformer should be checked immediately. 

Second, the transformer overload operation 

Transformer overload operation, the transformer is in the run-time transmission capacity of more than the rated capacity of the transformer. Three-phase transformer  the rated capacity of S  N = 〖KF (3〗 〖KF)〗 I  NU  N, while the operation is recorded in the output transformer active and reactive power output, it must be converted 

S = S  2  P + S  2  Q

(2-28) 

When S> S  N, then the transformer over-load operation. Transformer overload must be current than the rated current, the transformer load loss when the sharp increase in temperature will inevitably cause the transformer, the transformer temperature, the life of the transformer operation and great harm. Therefore, the transformer must be limited over-load operation. This limitation is actually a transformer winding hot spot temperature control. From this point of view, the transformer overload can be divided into the following three cases.  

1 allows the overload 

Although the transformer overload, but not over-load level, and before the overload, the transformer load is light, transformer top oil temperature is not high, the transformer winding hot spot temperature does not reach a hazardous level, this overload is transformer allowed. 

(2) limit overload 

Greater degree of transformer overload, so that the top oil temperature, transformer winding hot spot temperature may reach harmful levels, but has not yet reached dangerous levels, then the transformer, been able to continue running, but the threat will decrease the insulation strength transformer safety, affect the life of the transformer. This overload must be restricted. 

3 banned load 

Transformer overload of the larger, longer, so that the transformer top oil temperature exceeds allowable value, the transformer winding hot spot temperature has reached dangerous levels. Then continue to run if the transformer, hot oil will break down the insulation surrounding the bubble, a serious decline in dielectric strength may lead to a major transformer failure, this overload is to be prohibited. 

Transformer overload operation, particular attention to the following points: 

(1) closely monitor the temperature of the transformer winding and top oil temperature. 

(2) all start cooling the transformer, or defects in the cooling mainly the cooling efficiency, the transformer overload should not be allowed to run. 

(3) devices with on-load tap transformers, the load level is larger in the past should avoid regulating devices with on-load tap tap. 

(4) The main change in the normal over-load and run accident case overload. Overload its normal value should be based on the main transformer to allow the load curve, the cooling medium and the main transformer overloading brought before the load to determine. Accidents over the normal load and overload of the run must be no anomaly in the main transformer to run. Such as the existence of the main transformer cooler damage, severe leakage of oil, there are serious flaws in the body to protect such cases, the overload is not allowed to run. 

GB / T 15164  94 \"oil-immersed power transformer loading guidelines\" set forth in the design of the transformer according to GB1094 at rated load and normal ambient temperature (20  ° C ), its hot temperature of the reference value of 98  ° C , at this temperature the relative aging rate of 1, that in this condition, the transformer consume normal life. Hot spot temperature for each additional 6K, doubling the rate of aging. According to the transformer factory temperature rise test, converted to 20  ° C  under hot temperature than 98  ° C  much smaller (a difference of nearly 20  ° C ), so in fact the larger the temperature rise transformers are left margin degree. Because with the transformer in operation time increases, the thermal efficiency of its cooling system radiator due to dirt, oil pump reduced efficiency and other reasons than the factory down, the actual temperature may be higher than calculated. Of course, such as the manufacturer has provided a clear table of transformer overload capabilities, should be performed on the data provided by manufacturer.