High frequency transformer heating cause and heat dissipation method
High frequency transformer heating cause and heat dissipation method
In the high-frequency transformer, copper loss and iron loss are generated during operation. The two parts of the loss are all converted into heat energy, which causes the core and winding of the high-frequency transformer to heat up, and the temperature of the high-frequency transformer rises. In addition, the winding also generates heat through the current. When the heat of the high-frequency transformer is radiated to the environment to reach thermal equilibrium, the temperature of each part of the high-frequency transformer should be a stable value. If the temperature of each part of the high-frequency transformer exceeds its allowable range for a long time, especially if the high-frequency transformer oil temperature is higher than normal by 10 °C or the temperature is still rising, the insulation of the high-frequency transformer is easily damaged, and it is easy to be High voltage breakdown causes a malfunction or accident. Therefore, when the transformer is operating normally, it is not allowed to exceed the allowable temperature of the insulation.
Reasons for high temperature transformer temperature rise
(一) Internal reasons
(1) There is internal loss
In the operation of the high-frequency transformer, the hysteresis loss, eddy current loss and copper loss of the coil are converted into heat, so that the temperature rises and the heat is radiated to the surroundings by radiation, conduction, etc., when the heat and heat are balanced. The temperature of each part tends to be stable. The iron loss (hysteresis loss and eddy current loss) is a substantially constant loss, which is related to the structure of the high-frequency transformer, so it cannot be reduced or eliminated during operation; and the copper loss (line loss) changes with load.
(2) Poor contact of the tap-changer
In the high-frequency transformer operation, the tap changer is not enough due to the spring pressure, the contact of the contact is small, the contact resistance of the contact is increased due to oil film, contamination, etc. The contact is overheated most often, and the temperature is continuously increased. Especially when the switching tap changer or the high-frequency transformer is overloaded, it is easy to make the tap-changer contact bad contact and overheat. The main reason for the poor contact of the tap changer is that the pressure at the contact point is insufficient; there is a sludge film between the static and dynamic contacts; the contact surface has a burn or the positioning indication does not correspond to the contact position of the switch.
(3) Winding inter-turn short circuit
If several adjacent turns of the high-frequency transformer winding are damaged or aged due to insulation, a closed short-circuit circulating current will occur, which will reduce the number of winding turns, and the short-circuit circulating current will generate high heat to increase the temperature of the transformer. In severe cases, the high-frequency transformer will be burned. When the high-frequency transformer winding is short-circuited between turns, the arc at the short-circuit point causes the various parts and the cooling oil to be heated. When the cooling oil is boiled, it can hear a "beep" sound, causing the temperature of the transformer to rise sharply.
(4) Local overheating of the core
The iron core is superimposed by insulated silicon steel sheets. During the operation of the high-frequency transformer, the insulation between the silicon steel sheets is damaged due to external force damage or insulation aging and the aging damage of the core screw, and the eddy current is increased, resulting in local heating. The temperature of the transformer oil does not rise. In severe cases, the core is partially heated and the oil temperature rises; the no-load loss increases and the insulation decreases.
(5) High-frequency transformer lacks oil or heat pipe blocking
The high-frequency transformer oil is the main insulation inside the transformer, which acts as insulation, cooling and killing. If the oil is short or the heat pipe is blocked, the circulating cooling rate of the oil will decrease, causing the temperature of the high-frequency transformer to rise during operation.
(2) External causes
(1) High-frequency transformer cooling cycle system failure
In addition to using heat pipe cooling and cooling, the power high-frequency transformer also has a heat dissipation method such as forced oil circulation air cooling and water circulation. Once the cooling system is faulty or the heat dissipation condition is poor, the temperature of the high-frequency transformer in operation will rise (especially during the hot summer season). ).
(2) The inlet and outlet of the high-frequency transformer room are blocked or the dust is serious.
The inlet and outlet of the high-frequency transformer room is the passage of air convection during the operation of the transformer. Once the blockage or dust accumulation is serious, the heating condition of the high-frequency transformer does not change and the heat-dissipation condition becomes worse, and the heat can not be dissipated to the surrounding air in time, resulting in high-frequency transformer operation. The temperature rises.
High frequency transformer heat dissipation method
(1) In the internal loss of the high-frequency transformer, the iron loss is basically constant, and only the copper loss changes with the change of the operating load. Under normal circumstances,the High frequency transformer as long as the copper loss and iron loss can be kept equal, the high-frequency transformer is under the most economical operating conditions, and the high-frequency transformer temperature is also within the normal range.
(2) The poor contact of the tap-changer can often be judged from the frequent action of the gas relay light gas; and it is determined by sampling and measuring the DC resistance of the winding.
(3) The winding short-circuit between the turns is determined by the abnormal sound inside the high-frequency transformer and the frequent action of the gas relay and the DC resistance of the winding of the bridge. It is found that the winding short-circuit between the windings should be processed. The windings are insulated between turns, and in severe cases, the windings are re-wound.
(4) short-circuit light gas operation between iron core silicon steel sheets, listen to transformer sound, shake high-frequency transformer insulation resistance, test high-frequency transformer oil, do high-frequency transformer no-load test, etc., analyze and determine comprehensive parameters, iron Short-circuit between core silicon steel sheets should be overhauled for high-frequency transformers.
(5) The high-frequency transformer lacks oil should be treated for the cause of lack of oil, and the same high-frequency transformer oil qualified by the withstand voltage test is added to the appropriate position. If the heat pipe of the transformer is clogged, the high-frequency transformer is repaired and placed. Oil and hanging cores are used to dredge heat pipes.
(6) Maintenance Excludes the failure of the high-frequency transformer cooling circulation system to enable it to work normally. For example, forced oil circulation air-cooled high-frequency transformer, due to long-term operation, the heat exchanger is blocked by debris, and the hot air emitted from the heat exchanger cannot be discharged in time, resulting in an increase in oil temperature. Especially in the hot summer, this situation is even more dangerous. Therefore, the operator is required to periodically remove the impurities on the heat exchanger to ensure that the heat can be discharged in time.
(7) The blockage and dust at the inlet and outlet of the high-frequency transformer room should be cleaned.