Main components and functions of power transformer
Power transformer
The primary and secondary coils of ordinary transformer are concentrically sleeved on an iron core column, with low-voltage winding inside and high-voltage winding outside. (the primary and secondary coils of the welding machine transformer are respectively installed on two iron core columns)
When the transformer operates with load, when the secondary side current increases, the transformer must maintain the main flux in the iron core unchanged, and the primary side current must also increase accordingly to balance the secondary side current.
Secondary active power of transformer generally = rated capacity of transformer (kVA) & times; 0.8 (transformer power factor) = kW.
. power transformers mainly include:
A. Moisture absorber (silica gel cylinder): silica gel is installed inside, the insulating oil in the oil conservator (conservator) is connected with the atmosphere through the moisture absorber, and the desiccant absorbs moisture and impurities in the air to maintain good insulation performance of the internal winding of the transformer; Silica gel discoloration and deterioration are easy to cause blockage.
B. Oil level gauge: it reflects the oil level of the transformer, which is generally about 20O. If it is too high, drain the oil, and if it is too low, add oil; In winter, when the temperature is low and the load is light, the oil level changes little or decreases slightly; In summer, when the load is heavy, the oil temperature rises and the oil level rises slightly; Both are normal.
C. Conservator: adjust the oil volume of the oil tank to prevent the transformer oil from being oxidized too quickly, and there is a refueling hole on the upper part.
D. Explosion proof pipe: to prevent explosion hazard caused by sudden accident to the pressure accumulation in the oil tank.
E. Signal thermometer: monitor the operating temperature of transformer and send signal. It indicates the upper oil temperature of the transformer, and the transformer coil temperature is 10 higher than the upper oil temperature. The national standard stipulates that the limit working temperature of transformer winding is 105oC; (i.e. when the ambient temperature is 40oC), the upper temperature shall not exceed 95oc, and it is generally appropriate to set the monitoring temperature (upper oil temperature) at 85oc or below.
F. Tap changer: change the voltage ratio by changing the tap of high voltage winding and increasing or reducing the number of winding turns.
Generally, no-load voltage regulation is adopted for the transformer, which needs to be powered off: normally divided into three gears I, II and III 5%, 0% and - 5% (10.5kv, 10kV and 0.95kv for the primary and 380V, 400V and 420v for the secondary). It is generally placed in gear II when leaving the factory.
G. Gas signal relay: (gas relay) light gas and heavy gas signal protection. The upper contact is light gas signal, which generally acts on signal alarm to indicate abnormal operation of transformer; The lower contact is heavy gas signal, which will trip, drop card and alarm the circuit breaker at the same time when sending the signal after action; Generally, if the gas relay is filled with oil, there is no gas. When there is gas in the oil tank, it will enter the gas relay. When it reaches a certain degree, the gas will squeeze out the oil storage to make the contact act; Open the outer cover of the gas relay, there are two adjusting rods on the top, and unscrew one of the caps to release the gas in the relay; The other adjusting lever is the protection action test button; Wear insulating gloves and emphasize safety during live operation.

Treatment after secondary open circuit:(1) Try to short-circuit the current transformer for the second time on the nearest test terminal, and then check and deal with the open circuit point. During the short-circuit, the special short-circuit wiring for short-circuit shall be used. The short-circuit shall be proper and reliable. It is forbidden to use fuse or general conductor winding, and it shall be carried out according to the drawing.(2) Pay attention to the phenomenon of short-circuit. If there is spark during short-circuit, the short-circuit is effective. The fault point is in the circuit below the short-circuit contact, which can be further found. If there is no spark during short-circuit, the short-circuit may be invalid. The fault point may be in the circuit before the short contact. The short contact can be changed forward point by point to narrow the range.


(3) When shorting the secondary circuit, the staff must adhere to the operation monitoring system, one person operates and one person monitors. Keep an appropriate safe distance from live equipment. Operators must wear insulating boots, insulating gloves and tools with insulating handles. It is forbidden to carry out any work on the circuit between the current transformer and the short-circuit point.
(4) Within the fault range, check the terminals and components prone to failure, and check the parts of the circuit that have been touched during operation. For the faults detected, those that can be handled by themselves can be handled immediately, and then the exited protection can be put into operation. If the open circuit point is on the wiring terminal of the transformer body, the power shall be cut off for treatment. In case of failure that cannot be handled or found out by yourself, report to the superior and send someone to check and deal with it. At this time, the current transformer shall be short circuited for the second time, or the load shall be transferred and the power shall be cut off.
(5) If the secondary open circuit of current transformer is found, it is necessary to distinguish which group of current circuit the fault belongs to, the phase of the open circuit and whether it has an impact on the protection, report to the dispatcher and remove the possible misoperation protection.Cause of secondary open circuit:(1) When the secondary line terminal connector is not crimped tightly and the current in the circuit is large, it will be heated, burned out or oxidized, resulting in an open circuit.
(2) The outdoor terminal box and junction box are damp, and the terminal bolts and gaskets are excessively rusted, resulting in an open circuit.(3) Due to the defects in structure and quality, the test wiring terminal in AC current circuit has poor contact between screw and copper plate screw hole during operation, resulting in open circuit.(4) For the test terminal pressing plate in the current circuit, because the glue wood is too long, the metal sheet of the rotating terminal is not pressed on the metal sheet of the pressing plate, but is wrongly pressed on the glue Wood sleeve, resulting in an open circuit.


(5) Errors made by the maintenance and test personnel in their work, such as forgetting to connect the internal connector of the relay, could not be found during acceptance.

The current situation of power transformer MMS anti-theft alarm system and the supply of power, especially the safe and reliable supply of power, have always been the focus of society, enterprises, people and the media. Because a safe, stable and reliable power supply is related to the development of the national economy, the construction of a harmonious society and the vital interests of the people. Power grid security has become a sharp sword hanging over power enterprises.Overview


According to statistics, in the first two quarters of 2005, there were more than 550 cases of theft and destruction of power facilities in the system of Sichuan electric power company, with a direct economic loss of more than 2.6 million yuan. According to conservative estimates, in recent years, the direct economic losses caused by the theft of power facilities alone have exceeded 200 million yuan. Power grid security has become a sharp sword hanging over power enterprises. The supply of electricity, especially the safe and reliable supply of electricity, has always been the focus of attention of society, enterprises, people and the media. Because a safe, stable and reliable power supply is related to the development of the national economy, the construction of a harmonious society and the vital interests of the people.
According to the survey, the current maintenance, management and anti-theft of power facilities are summarized as follows:1. Most transformers and other power facilities are located outdoors and scattered in streets, urban-rural fringe, rural areas and other places, which brings a lot of trouble to the safety management of transformers.2. It is impossible for the power department to assign a large number of manpower to monitor each transformer in real time in an artificial way to prevent the equipment from being stolen or damaged.
3. In China, some provinces have also used methods such as infrared, limited distance wireless communication and physical anti-theft card to solve the anti-theft problem of transformer. However, due to the limitations of the principle of these systems or products, false alarm, weak anti-interference ability, and unable to receive the alarm signal in time, resulting in a large waste of human, material and financial resources. At the same time, the wireless transmission mode has high power (energy consumption) and needs to be approved by the management committee, which also has certain restrictions on the promotion of the system and products.
To sum up, the theft of power lines and transformers is relatively serious, and the relevant state departments attach great importance to it. Civil air defense plus technical defense is the most effective method. According to the actual situation, our company has developed a power transformer MMS anti-theft alarm system. This system is mainly used for power transformer anti-theft alarm. Its characteristics are: not limited by distance, quantity and climate. It has the characteristics of practical function, excellent quality and stable and reliable operation. It is suitable for various outdoor environments. It is widely used in the safety protection of all outdoor working equipment such as electric power, petroleum, base station and mine. It is the most advanced MMS alarm system among similar products in China.

1) Insulation performance: increase the insulation strength of various components in the transformer. The oil insulation strength of the transformer is good and has fluidity. It can fill all parts and any space of the transformer and discharge the air, so as to avoid moisture contact between the parts and the air and affect the insulation strength, so as to maintain good insulation between windings, between windings and iron core, and between windings and oil tank shell.2) Heat dissipation performance: the transformer oil cools the iron core and winding of the transformer. During the operation of the transformer, the temperature of the oil near the winding and iron core increases after heating, the volume expands, the specific gravity decreases and rises, and then enters the bottom of the transformer oil tank after cooling by the cooling device, so as to form oil circulation. During the cycle, heat is radiated to the cooling device, so that the iron core and winding are cooled.3) Anti corrosion performance: transformer oil can keep the original chemical and physical properties of insulating materials (such as wood) and make metals (such as steel) play an anti-corrosion role


General principles for power transformer when supplementary oil is requireda) Transformer oils with different oil bases shall not be used together;b) Oils of different grades (freezing point) of the same oil base shall not be used together;
c) The quality of mixed oil shall comply with the provisions of gb7595;d) When new oil or transformer oil of the same oil base and different grades equivalent to the quality of new oil is mixed, its availability shall be determined according to the measured freezing point of the mixed oil. It cannot be mixed only according to the qualified chemical and electrical properties:e) When the in-process oil is mixed with new oil of the same brand, the oxidation stability test of the mixed oil sample shall be carried out in advance, and the mixed oil can be used only when there is no sediment.
f) When imported oil or oil of unknown source is mixed with operating oil of different brands, the aging test of various oils and mixed oil samples shall be carried out in advance. The mixed oil can be used only when the quality of the mixed oil is not lower than that of the original operating oil; If the mixed oil is new oil, the quality of the mixed oil shall not be lower than the worst new oil.What are the protective functions of power transformerRole of gas protection
The main protection measure in the transformer is gas protection. The reduction of transformer oil level and the faults in transformer oil tank are reflected by gas. When the transformer has a slight fault, the oil level will drop, and the light gas will send a signal. When the gas has a serious fault, a large amount of gas will be generated, and the heavy gas will also trip.When there is a fault in the transformer, there will be heating in the fault part. In this way, the oil expansion will occur in the nearby transformer, the air will be discharged and the bubbles will gradually rise, while other materials and oil will produce gas under the action of discharge, so as to reduce the oil level.When the fault is very serious, after the gas gas is generated, the pressure inside the transformer is increased, so that the oil flows to the conservator. The baffle will overcome the resistance of the spring when the oil flow impacts, so as to move the magnet towards the dry spring and connect the contact of the dry spring. In this way, tripping will occur.


Function of differential protectionDifferential protection is the main protection of the transformer, which mainly reflects the faults of the outgoing line and winding of the transformer. It can trip the circuit breakers on each side of the transformer. According to different devices, differential protection can be divided into the following types: transverse differential protection is often used in shunt capacitor and short-circuit protection. When the equipment adopts double bus and double winding, transverse differential protection will be adopted; Longitudinal differential protection mainly reflects short circuit and inter turn short circuit, and the protection scope mainly includes outgoing line and bushing.Backup protection
The main transformer has the characteristics of large impedance during operation. Therefore, the fault of the main transformer on the low-voltage side will not affect the operation of the high-voltage side. The stability of high voltage side can effectively realize the protection function of voltage locking. However, when the main transformer fault is abnormal during operation, it can not respond in time. Therefore, during the operation of the main transformer, backup protection measures shall be taken. The parallel opening mode of high-voltage side and low-voltage side can be adopted to make the opening of locking circuit flexible.Function of voltage and current protection of transformerWhen a fault occurs outside the transformer, overcurrent will be generated; When there is an internal fault in the transformer, the backup of differential protection and gas protection will be generated. In the transformer, current protection devices should be installed. Different protection methods are selected according to different transformer capacity and system short-circuit current.
The requirements for current transformer for relay protection are: reliable insulation; A sufficiently large accuracy limit factor; Sufficient thermal and dynamic stability. The transformer for protection can meet the requirements of accuracy level under rated load. The maximum primary current is called rated accuracy limit primary current. The accuracy limit factor is the ratio of the rated accuracy limit primary current to the rated primary current. When the primary current is large enough, the iron core will be saturated and can not reflect the primary current. The accurate limit coefficient represents this characteristic. The accuracy grade of transformer for protection is 5p and 10p, indicating the allowable error of 5% and 10% at the rated accuracy limit primary current.

On the cause of switching power transformer ringing(1) Technological problems of transformer The in-service paint baking f is not in place, resulting in loose combustion core and mechanical vibration:


The length of air gap is not suitable, resulting in unstable T. operation state of claw changer and sound: If the wire package is not wound tightly, it may also cause noise; There is an air gap in the magnetic core assembly, which causes air vibration and makes a sound at high frequency (generally, the transformer will not make a sound if it is fully switched on through vacuum)
(2) Loop problem of transformerThe loop problem of transformer means that the loop of transformer oscillates, which causes the claw converter to vibrate. Improper wiring of the circuit board causes 1 disturbance and oscillation, resulting in sound:
Improper setting of feedback loop parameters leads to loop instability, resulting in oscillation and sound: Quality problems of element devices in the loop, such as insufficient input filter capacitor capacity, fast recovery diode quality of transmission rectifier, poor quality of power MOS tube, poor quality of high-voltage capacitor or diode of RCD recoil absorption circuit, etc. these problems may lead to vibration and sound.(3) Iron core problem of claw changer
When the transformer core is saturated, the current in the coil increases, the transformer instrument generates heat and generates self-excited oscillation. The oscillation of the coil causes the surrounding air,It vibrates and makes a sound.(4) Load problem of switching power supply


In the case of no-load or light load, the switching power supply will oscillate at some T. operating points, which is characterized by the noise of the variable instrument and the instability of the output.This phenomenon occurs because the instantaneous opening time of the switch is too long during no-load / light load, resulting in too much power transmission, and then a large voltage overshoot. It takes a long time to recover to the normal power supply. Therefore, the switch needs to stop this work for a period of time, so that the switch can work in time. As a mode, the converter vibrates at a lower frequency (regular intermittent total cut-off u!; the frequency of sharp change in cycle or duty cycle). Transformer T. in a serious overload state, it can be burned at any time. This is the origin of "scream" before many power supplies are burned.
Abnormal noise of switching transformer and its solution exampleExample 1
After the switching power supply is powered on, there is a hiccup sound. The measured output DC voltage of each circuit is very low and unstable. Check the load circuit first, and there are no damaged components. Later, the voltage absorption network connected in parallel with N1 winding was mainly detected, and it felt that there was no abnormality. Take the oscillation board and replace all the oscillation chips and peripheral circuits. The fault remains after power on. Note: there are no problems in the, oscillation and voltage stabilizing links, and there are no abnormalities in the load circuit after rechecking. The maintenance is in trouble.
Think of whether the switch transformer is broken? We have to rule out this possibility first.
Connect dc18v directly to pins 7 and 5 of 3844, and connect dc100v at the dc530v power input of switching power supply. After power on, the circuit vibrates and works. After a while, Z101 in the circuit in figure (c) begins to smoke. Observe that this circuit is a composite voltage absorption circuit, and there are resistance capacitance absorption circuits connected in parallel at both ends of Z101. After temporarily removing Z101, measure the DC output voltage of each circuit, and its height is proportional to the input voltage (at this time, the quality of the switching transformer is self-evident).
So far, the truth of the fault reason has been revealed. Three 100V voltage stabilizing tubes are connected in series instead of Z101. Power on and test the machine, and the switching power supply returns to normalExample 21. High frequency transformers, like iron core transformers, emit noise because the iron core is not tight. But the frequency of the switching transformer is very high, so it makes a high-frequency "squeak".
2. In general, the squeaking sound from switching power supply has little effect. If the sound is loud (the magnetic core is very loose), it will cause heating. Compress the magnetic core and drop 502 instant dry glue.Example 3
During the commissioning of the transformer, there should be no problem with the switching circuit. If the transformer rings, it must be the problem of the transformer. The transformer will ring if the coil is not wound well, the proportion of the primary and secondary coils of the transformer is inappropriate, the insulation paint is unqualified, the quality of the magnetic core, the air gap of the magnetic core is inappropriate, etc. In fact, it is also simple to solve the problem. Mainly check the dip insulating paint, the air gap of the magnetic core and the proportion of the primary coil of the transformer. If you still can't solve this problem, please replace the magnetic core and try it. When the air gap of the magnetic core is the same, some permeability of the magnetic core is different, which will cause the magnetic core to adapt to different switching frequencies, which will naturally produce a sound.
Example 4Class I: if you have conditions, you can separate the power circuit from the load, find a good switching power supply and turn on the load. Check whether the whole circuit works normally at this time. If the whole circuit works normally at some time, some problems are caused by the switching power supply on the original machine; If the transformer of the new switching power supply also affects the squeaking, it indicates that it is a load problem and has nothing to do with the switching power supply on the original machine.Class II: when it is determined that the switching power supply causes the squeaking, focus on checking whether there is a short circuit in any place. I have also encountered the squeaking fault caused by short circuit many times during maintenance. If there is no short circuit, please refer to the information on the maintenance of switching power supply. There is much to say here. In short, we will consider replacing the switching transformer after.