Transformer-related terminology

concept：
1、 The law of electromagnetic induction：
The size of the induced EMF (electromotive force) in the circuit is in direct proportion to the energy change rate which go through the circuit. (This is Faraday's law of electromagnetic induction.) Regardless of the method used, as the magnetic flux throuth the closed circuit changes, there is induced current generated in the closed circuit, and this phenomenon is called as electromagnetic induction.
2、 Lenz's Law：
Induced current has such a direction, that is, the magetic field of the induced current always result in the change of magnetic flux of the induced current, and that is what called Lenz's law.
3、 Energy conservation：
The energy will not produce without any foundation, and will not disappear without any foundation, it just transforms to another, or transfers from one object to another, and the total energy will not change during the process of transform or transfer. That is what called energy transform and conservation law. And the power is a measure of the energy transform.
4、Magnetic induction intensity：
The electricify straight wire which is perpendicular to the magnetic direction in the magnetic field, and what the ratio with the magnetic force (F), current (I), and the length of wire (l) is what called magnetic induction intensity. (B=F/IL, the unit of magnetic induction is decided by the unit of IL (F,I,L). In the internation unit system, the unit of magnetic strength is Tesla, T for short. The magnetic strength of 1M long wire through 1A current received is 1 Niu, and the magnetic strength is 1T. 1T=A*M/Niu).
5、 Magnetic line：
field in the direction of some of the curves. His point of the tangent direction Dugen the point of magnetic induction intensity the same direction. The magnetic line is some curves of direction produced in the magnetic field. The tangential direction of any poit in the curved shape is of the same as the direction of magnetic strength.
6、 Flux：
the flux Ø=BS (B is the geometric plane surface which is perpendicular to magnetic strength, S is the area). The meaning of flux can also be illustrated by the magnetic line. The increased number expressed by the flux is the magnetic lines of a certain surface of the magnetic field. In the International Unit System, the unit of flux is weber, and the symbol is Ø. 1Ø=BS. Than means magnetic strength equivalent to the magnetic flux through the unit are, and that's why magnetic strength is always called magnetic flux density. 1T=1Ø/m ²-Niu/A*M.
7、 power capacity：
The power of transformer includes input power P1 and output power P2, the input power has something to do with the effeciency of the transformer, and the supply transformer power is an important basis to determine the size of the core.
8、 Power factor：
The ratio of input power to its voltammetry capacity of the transformer is called power factor cosØ, and it has something to do with the magnetic current, the higher proportion of the magnetic current in the primary current, the lower of the power factor.
9、 efficiency：
The effeciency is the ration of output power (P2) to input power (P1).
10、 Voltage adjustment rate：
when the transformer is from no-load to full load, because of that the voltage produced by the primary copper resistance r1,r2 is lowered by U1, U2 and thus making the load current is lower than no-load current, and the decline rate is stated by voltage adjustment rate. (voltage adjustment rate control the value of current density, and the output power is in direct proportion to the allow voltage adjustment rate).
11、 No-load current：
The transformer no-load current is equvilant to the vector sum of magnetic current and iron loss. Phase separation of the magnetic current and iron loss is 90. For the small iron loss current, the main no-load current of the transformer is the magnetic current. The no-load current is closely related to the performance of core: the bigger allowance of the no-load current and the higher magnetic strength value, and this can reduce the bulk of the transformer. If the core is made of general performance material to reduce the cost, yet the no-load current will increase, and the power factor then drops, and thus affect the grid or power performance, the low allowance no-load current, the low core magnetic strength value, and that's why the core should apply the high performance materials.
12、 Temperature Rise：
When the transformer comes into service, the coil working temperature is higher than the ambient temperature, and the temperature seperation is what called coil temperature rise. And the difference in temperature of the core working temperature and the ambient temperature is called core temperature rise. The temperature rise includes hottest-spot temperature rise and average temperature rise. And the coil average temperature rise is a index for the transformer temperature rise. And temperature rise is an important parameter for the medium power or above power supply transformers. The temperature rise dominates the value of the magnetic parameter and also affect the life of the transformer.

common sense of transformer work

Tansformer are nearly used in all electronic products. Its principal is simple yet the winding technology is different according to the different use places. The main functions of the transformers are: voltage transfer, impedance transfer, isolating, voltage regulation (magnetic saturation transformer) and so on. And the main used core shape includes E-type and C-type.

一、The basic principles of transformers

Picture 1 is the principal minic diagram. When sine AC voltage (V1) added to the two ends of the primary coil, then there is alternating current (I1) in the wire and alternating flux (ф1) produced, which forms the magnetic circuit by along the core through the primary coil and secondary circuit. And the mutual inductance electric potential (U2) is produced in the secondary coil, and at the same time ф1 will induces a self-induced potential E1 in the primary coil, and the direction of E1 is opposite to that of voltage (U1), and yet the amplitude of the two is similiar and thus limit the I1. There is a need of energy consumption in order to maintain the existance of ф1, and the transformer itself has a certain loss, and therefore even the secondary arr not connected with load, there is current in the primary coil. And the current is what we called no-load current.
　　If the secondary is connected with load, current (I2) and magnetic flux (ф2) is produced in the secondary coil, the direction of ф1 and ф2 is opposite, and thus has a function of equits and therefore reduces the magnetic flux in the core, and therefore the self-induced voltage E1 is reduced, and the I1 increased. When the secondary load current increase, I1 and ф1 increase, and the increased part of ф1 replenish the magnetic flux counteracted by ф2 in order to maintain the total number of magnetic flux. In spite of transformer loss, the load loss power in the secondary coil is that get fron the primary coil of an ideal transformer. The change of cyclomatic number of secondary coil can change the secondary voltage, yet the allowance load loss power can not be changed.

二、Transformer Loss

　　When the primary winding is switched on, the magnetic flux produced by coil flows in the core, and for the core is also an inductor, and can induce the potential on the surface which is perpendicular to the magnetic line, the potential forms the closed circuit in the cross-section of the core and yield the current, which is like a swirl and so is called wortex. The wortex increases the transformer loss, and causes transformer core heating and therefore the transformer temperature rise increases. The loss yielded by the wortex is called iron loss. And there is a large demand of copper for winding the transformer, and there exist resistance in the copper conductor, and it will consumption a certain power when the current switch on, and the consumption always transform the heat and we call the heat loss as copper loss. And therefore the transformer temperature rise incluses iron loss and copper loss. And for the existance of the two losses, the output power is smaller than the input power, and we use the efficiency parameter to descripe the phenomenon η=output power/ input power.

三、Transformer material

　　To wind a transformer need to be familiar with the knowledge of transformers or its relative informations.
1、Core Materials：The main core material of the transformers includes iron sheet, low sillicon, high sillicon, adds sillion to the copper can lower the conductance of the copper, and increase the impedance rate, and reduce the wortex and thus lower the loss, and we also call the copper which added sillion the sillicon sheet, the quality of the transformer has much to do with the quality of the sillicon sheet, and the symbol of the sillion sheet quality is B (magnetic flux tensity), the B value of general black iron is from 6000-8000, that of the low sillion is 9000-11000, that of the high sillion is from 12000-16000.
2、The main materail for winding the transform includes lacquered wire (the most used materail), sandbag wire, and silk covered wire. The wire should be of good conductance, and the insluation layer should withstand the hot, and withstand the corrosion. Generally, it usually applies the Q2type high tensity polyester lacquered wire.
3、Insulation material：During the process of winding the transformer, the isolation material of the coil framwork interlaminar, the isolation of winding all should be insulated. The general framework material can apply the phenolic cardboard, and the interlaminar can apply the mylar or Tel paper as the isolation material, and it can apply the yellow wax cloth as the insulation material between the winding.
4、Impregnated materials：After the winding process, it is the varnish insulation paint, which can strengthen the mechanical strength, improve the insulation level, prolong the use life. Generally, it can apply the cresol varnish as the impregnating materail.

Transformer detection methods and experience

1、test of Color-coded inductors

　　 put the multimeter in R x 1 block, and the red, black pen connected with each of the outputtings of the color-code inductor, then the clock hand swings. According to the resistance value, it can be classified as three conditions：
　　The resistance value of the measured color-coded inductor is zero, that means the internal exists short-circuit fault.
　　 B、The DC resistance value of the measured color-coded inductor has direct relation with the lacquered wire for the winding and the number of turns of the winding coil. The color-coded inductor is normanl if the resistance value can be measured.

2、detection of intermediate transformer

　　 A、put the multimeter in R x 1 block, and determine whether the intermediate transformer is normal by check the winding whether is make-and-break according to the law of the winding-pin.
　　 B、Testing of insulation 　　put the multimeter in R x 1 block, do the following tests：
　　(1)the resistance value between primary winding and secondary winding；
　　(2)the resistance value between primary winding and the crust；
　　(3)the resiatance value between secondary winding and the crust.
　　There are three results according to the test：
　　(1)the resistance value is infinite: normal；
　　(2)the resistance value is zero:there is short-circuit fault；
　　(3)the resistance valur is smaller than infinite, yet bigger than zero: there is creepage fault.

3、Detection of power transformers

　　A、To check whether the transformer is normal by observing its appearance, such as whether the down-lead of the coil is rupture, sealingoff, whether the insulation materail has sorched mark, whether the core tighten crew is loosen, whether the sillion sheet has corroded, and whether the winding coil is bare.
　　B、Insulation test.To measure the resistance value between core and primary winding, the resistance value between primary and other seconary windings, the resistance value between core and othe secondary value, the resistance value between static and shielding layer, the resistance value among the secondary windings by the multimeter R X 10K block, the clock hand should point at the infinite place, or otherwise, the transformer insulation lelve is not so good.
. C、Detection of the coil. put the multimeter in R x 1 block, and if there is a certain winding's resistance value is infinite then the winding exists the turnoff fault.
　　D、distinguish of the primary and secondary windings.The primary pin and the secondary pin of the power transformer are all lead out from the two sides, and the primary windings are marked with 220V, and the secondary winding marked with the rated voltage value, such as 15V, 24V,35V and so on. And it distinguish the windings by these marks.
　　E、No-load current testing.(a)Direct measurement.All the secondary windings are incomplete circuit, and the multimeter was in the AC current gear (500ma, connecting in series with primary winding. When the plug was inserted into the AC 220V commercial power, what the hand of the multimeter poins at is the no-load current value. The value should no more than the 10%-20% of the value of full-load current. The general normal no-load current of the electronic equipmen-power transformer is 100ma. If the value exceed too much that means there is short-circuit fault.(b)Indirect measurement.The primary winding connect in series with a 10/5W resistance, and the secondary winding is still the no-load. Put the multimeter in the AC current gear, and use the instrument pen to measure the voltage drop (u) of the two ends of the resistance after electrify, and then calculate the no-load current I by the Ohm's law, that is I=U/R.
　　F、No-load voltage detection.Conect the primary of the power transformer with the 220V commercial power, and measure the no-load current value (U21, U22, U23, U24) of each winding by the multimeter AC vlotage connection and all the value should comply with the standard value, and the error range is : HV winding ≤±10％, LV winding ≤±5％, the voltage difference of the symmetrical winding with centretap ≤±2％.
　　G、The allowance of temperature rise of samll power supply transformer is 40℃～50℃, and the allownace of temperature rise is more higher than that if the inualtion material is of good quality.
　　H、Detection and determine the homonymic end of each winding. In order to get the needed secondary voltage when use the power tansformer, two or more windings can be series work together. It should ensure the correct connection of the homonymic end of each winding. Otherwise, the transformer can not work properly.
　　I、The comprehensive test and distinguish of the power transformer short-circuit fault. The main symptom of the short circuit fault is severe heating and abnormal power transmission of secondary winding. The more of the coil turns, the greater of the short-circuit current. The simple way to detect whether the power transformer has short-circuit fault is to measure the no-load current value. The no-load current value is much greater than 10% of the full-load current value if there is short-circuit fault. And the transformer will be quick heated in a few dozen seconds when the short-circuit fault is severe and you will get a feeling of hot to touch the core. And under such a condition, there is no need to measure the no-load current to know that there is short-ciracuit point.

The common failure of transformers

1、Unusual noise

(1It is may be the transformer core problem if the sound is large and noise. For example, when the clampingpiece or the core screw is loose, the instrument is normal, and the color of the insulation oil, temperature and oil level does not change too much, yet at the moment it is need to stop the transformer for check.
(2)If there is a mixture of water boiling sound-the bubble escaping sound, it may be that the windings are serious failured and thus cause the nearby components emit heat and then the oil gasficated. The overheat of the partial poit or the transfsormer turns is short-circuit result from the poor contact of tap changer, and such noise will be produced, and at this moment, the transformer should stop at once for the repair.
(3)If there is explosion sound, large and uneven, it may be that there is a breakdown of body insulation. And the transformer should stop for overhaul.
(4)If there is a mixture of discharging noise, it maybe that the surface partial discharge exists in the transformer body or the bushing. If it is the bushing problem, the corona glow or the blue, purple small park can be seen in the bad wheather or at night. And at the moment, it need to clean the dirt of the bushing surface and then painted with oil or silicone grease. The transformer should also stop to check the distance of the iron earthing and other charged parts whether comply with the standard.
(5)If there is a mixture of continous and regulationed clash or grating sound, it maybe that the mechanical frication of a certain parts of the transformer resulted from the core vibration or static discharging, all the measurement instructions and temperatures do not have any response. The noise is though abnormal, yet does not have bad effect on operation and therefore it does not need to stop the transformer, and it can exclude these problems when shedualed overhaul.

2、abnormal temperature

Under the condition of constant load and cooling, temperature, the temperature is more higher and has the trend of rising, it together with the super-elevated temperature limit rise is the phenomenon of abnormal temperature.
reasons for abnormal temperature rise：
①short-circuit between transformer turns, layers and bumps；
②transformer partial core short-circuit；
③tank and cover heats for leakage of wortex；
④long-term of overload operation or accidenat overload；
⑤bad cooling condition.
When found the temperature is abnormal during operation, it first should to check the reasons and then apply appropriate measurement to lower down the temperature, and if it is caused by the internal fault, the transformer should stop to prepair.

3、Injection explosion

The reasons for injection explosion is the internal fault short-circuit current and the high temperature voltaic arc make the oil rapid aging, and the relay protection device does not cut off the power promptly, and then the fault has existed for a long time, and the internal pressure continous grow, the oil gas of the HV emit from the weakness of the explosion-proof box or of that of gas pipe.
(1)insulation damage：Insulation damage by the partial overheat of short-circuit of the turns, by the water logging and by the struck of lightning and other factors.
(2)broken wire produces the voltaic arc：Poor welding of the leads of wire group, loose lead connection and other factors will cause the wire broke under the large current impulse, the high temperature voltaic arc produced on the breakpoit make the oil gasification and internal pressure increase.
(3)Tap changer fault: the voltage regulation coil of distribution transformer HV windings connect with the tap changers, the tap changer contact connect in series with the HV winding loop, and get through the load-current and short-circuit current with the windings. If the dynamic and static contact of the tap changers get heat, sparking arc starting and therefore cause the voltage regulation short-circuit.

4、Serious oil spill

The oil leakage is a common phenomenon during the transformer operation, the oil level can continously work or plan for the organization overhaul in the scope of provision. Yet if the transformer oil leakage seriously, or continous overflow from the damaged places resulting in the oil-level indicator does not work, and at this moment the transformer should at once stop to repair and refuel. The oil level is too low and thus cause the bushing lead and tap changer exposed to the air, and therefore the insulation level has lowered greatly, and it is easy to breakdown and discharge. The reasons for the leakage are welding crack or seal failure, experience shock, external impact when operating, severe corrosion of the tank, and so on.

5、Casing flashover

The incrusting transformer bushing form the pollution flashover under the conditon of fog or light rain, and thus cause the transformer HV side single phase earthing or phase to phase short-circuit. Transformer bushing breaks by the external force, mechanical stress, thermal stress are also the reasons for the flashover. The foreign body on the tank cover such as the tree branches will also cause the bushing discharge of phase to phase short circuit.
The above analysis of the transformer fault from the noise, temperature, oil level, and apperance and other phenomenons is the initial judgement of the site. The internal fault of the transformer is not only the single direct reflect, it also involves many factors, and some times it even shows the false phenomenons, sometimes there is a need to do the transformer test and comprehensive analysis to find the cause, and therefore promote the rational approach.

6.1Transformer common fault

　　The common fault and abnormal phenomenons of distribution transformer in the process of power transmission and operation：
　　(1)The transformer is always abnormal when the transformer tranmiss the power after stop or commissioning transmission, for example, two phase high one phase low or the the value is zero; or the voltage of three phase of some commissioning transformers are all very high and thus some elctrical equipment are burned down for the over high voltage；
　　(2)The HV fuse burn down and therefore can not transmiss the power；
　　(3)the transformer can not tranmiss the power after thunderstrom；
　　(4)transformer noise is abnormal, for example,the "zizi" or "pipi" sound, or the frog sound during the operation；
　　(5)The HV post heat burnt down, and there are serious damage or flashover signs in the HV bushing；
　　(6)the oil temperature continuously rise under the normal cooling condition；
　　(7)great change of the oil color, it maybe that there is carbon in the oil；
　　(8)There is abnormal sound, and the oil injects from the pressure-relief vent, oil conservator, the oil tank and the radiating collar distort, leak oil and penetrate and so on.

6.2Transformer failure analysis

6.2.1judgement of the transformer failure by sound

　　（1）the sound of lack phase
　　When the transformer lack phase, and if the second phase does not connect, it remains silent when electrified, and only when submitted to the third phase that can have the sound; if the third phase does not connect, there is no change about the sound just the same as the second phase. There are about three reasons about the lack of phase: ① the lack of elctrical power; ② transformer HV fuse burns down the first phase; ③the uncareful transport and the thin HV lead result in the vibration break (not shell).
　　（2）voltage regulation tap changer is not in the right place or bad connected
　　When the transformer comes into service, and if the tap chager is not in the right place, there is a big chirps sound, and even will cause the HV fuse burns down; and if the tap changer is bad connected, it will squeal of the spark discharge sound, and if to increase the load, it will be burn the contact of the tap changer. If the aboved situation happens, it should promptly stop the power for repair.
　　（3）there are foreign bodies or the screw with tang is loose
When the screw with tang of the transformer core taptite is loose, there are screw cap component remain on the core or small metal parts fall into the transformer, then the transformer will give the wind sound and the sound like the magnet suck the gasket, while the voltage, current and temperature of the transformer is normal, and the treatment can be after the power cut.
　　（4）transformer HV bushing is dirt or cracking
　　When the transformer HV bushing is dirt or the surface enamel loss or crack, there will the flashover phenomenon or the sound of hiss will be heard, and if it was in evening, the spark can be seen.
　　（5）transformer core earthing breaks
　　when transformer core earthing line breaks, the transformer will give a light discharging sound.
　　（6）internal discharge
　　when there is a sharp sound of hammering during the process of transmission, it is the discharging voice of the conductive lead to the transformer shell through the air; And if it is a clatter sound, it is the discharging sound of the conductor to the shell through the transformer oil. And if there is not enough insulation distance, then it should cut power for hanging inspection to strengthen the insulation ability or set the insulating baffles.
　　（7）external line breaks or is short-circuit
　　When the circuit breaks in the conductive line contact or T-contact, or break-contact alternating when it is windy, and there will be arc light or sparks when contact, and the transformer will give a frog sound; when there is earthing or short-circuit fault about the LV lines, the transoformer will give a sound of skirr; and if the short-circuit is at close, the transformer will give a tiger screaming sound.
　　（8）transformer overload
　　when severe overload, the transformer will give a sound of buzzing.
　　（9）over voltage
　　when the power voltage is too high, the transformer will overexcited, the noise is lounder and sharp.
　　（10）winding short-circuit
　　when the short-circuit happens among the layers or turns of the winding and cause the burning, the transformer will give a water boiling sound.
　　there are many factors for the transformal abnormal noise, and the fault places are also different, it can only make the right judgement by the accumulated experience.

Distribution Transformer common fault analysis

1、the fault and abnormal phenomenon of distribution transformer：

　　1）The transformer is always abnormal when the transformer tranmiss the power after stop or commissioning transmission, for example, two phase high one phase low or the the value is zero; or the voltage of three phase of some commissioning transformers are all very high and thus some elctrical equipment are burned down for the over high voltage；
　　2）HV fuse burn down that can not tranmiss the power.
　　3）the transformer can not tranmiss the power after thunderstrom.
　　4）transformer noise is abnormal, for example,the "zizi" or "pipi" sound, or the frog sound during the operation.
　　5）The HV post heat burnt down, and there are serious damage or flashover signs in the HV bushing.
　　6）the oil temperature continuously rise under the normal cooling condition.
　　7）great change of the oil color, it maybe that there is carbon in the oi.
　　8）There is abnormal sound, and the oil injects from the pressure-relief vent, oil conservator, the oil tank and the radiating collar distort, leak oil and penetrate and so on.
　　

2、judgement of the transformer failure by noise

　　After the transmission, the current will produce the alternating flux in the core, the alternating flux continously give the elctromagnetic sound when through the core. The electromagentic sound is directly proportial to the current size. The bigger of the current, the londer of the noise. If the current suddely increases then the noise suddenly increase; the current cut off then the voice disappear. And therefore, according to the noise change of the transformer together with the appearance inspection, it can fully judge the nature and location of the internal fault.
　　1）normal and lack phase.During the process of power supply, the normal situation is: there is no current when the first phase is transmissed and there is no sound; when the second phase is transmissed, as the HV side current circuit is open, the transformer give the light and balanced buzz sound, and then the third phase is transmissed, as there is third phase current, the buzz sound increase. And if it is abnormal: if the second phase does not switched, there is no sound even when the second phase is transmissed, and there is sound only when the third phase is transmissed; and it the third phase is not switchedm the sound does not chage just the same as the two-phases.
　　there are about three reasons for the lack of first phase：①the power source lack the first phase power；②transformer HV fuse first phase burns down；③the uncareful transportation and the thin HV lead cause the vibration break (not shelled).
　　2）voltage regulation tap changer is not in the right place or bad connected.When the transformer comes into service, and if the tap chager is not in the right place, there is a big chirps sound, and even will cause the HV fuse burns down and the fuse falls;and if the tap changer is bad connected, it will squeal of the spark discharge sound, and if to increase the load, it will be burn the contact of the tap changer.
　　3）there are foreign bodies or the screw with tang is loose.When the screw with tang of the transformer core taptite is loose,there are screw cap component remain on the core or small metal parts fall into the transformer，the transformer will give the hammering sound or the wind sound or the sound like the magnet suck the gasket, yet the voltage, current and temperature of the transformer is normal.
　　4）transformer HV bushing is dirt or cracking.When the transformer HV bushing is dirt or the surface enamel loss or crack, there will the flashover phenomenon or the sound of hiss will be heard, and if it was in evening, the spark can be seen.
　　5）transformer core earthing line breaks.when transformer core earthing line breaks, the transformer will give a light discharging sound.
　　6）internal discharge.when there is a sharp sound of hammering during the process of transmission, it is the discharging voice of the conductive lead to the transformer shell through the air, and it is usually caused by the lower part of the transformer tank-radiating collar or the bottom of the tank shell leak oil , and therefore the top of the transformer lack phase. And if it is a clatter sound, it is the discharging sound of the conductor to the shell through the transformer oil. It is for that there is not enough shell distance of the conductor or there is water in the insulation oil.
　　7）external line breaks or is short-circuit.When the circuit breaks in the conductive line contact or T-contact,or break-contact alternating when it is windy,and there will be arc light when contact，and the transformer will give a frog sound; when there is earthing or short-circuit fault about the LV lines, the transoformer will give a sound of skirr; and if the short-circuit is at close, the transformer will give a bellow sound.
　　8）transformer overload.when severe overload, the transformer will give a sound of buzzing.
　　9）winding short-circuit.when the short-circuit happens among the layers or turns of the winding and cause the burning, the transformer will give a water boiling sound.

standard procedure of installation distribution transformer

1、Ratification, acceptance of construction work, the construction team apply for the ratification to the competent department according to the equipment voltage class. And the competent department should approve the work ing the written form.
2、on-the-spot investigation：（1）、The on-the-spot investigation in in the charge of the superintendent and the technical staff, and it is also them to do the inspection record and to identify the dangerous site and controlling measurement, and plan for the programme.（2）、The content of on-the-spot investigation: to check through the operational and environmental condition of the site, such as the construction transmission road, yong crop damage and compensation and so on.
3、the construction work begins before the class meeting……

the effect to the transformer of too many times of no-load transformer switch-on and switch-off

the no-load current drops greatly when the switch-off the no-load transformer, and the magnetic field in the core disappear quickly, and the overhigh volatge produced in the coil and thus it maybe puncture the weak insulation place. A larger excitation flow will be produced when switch-on the no-load transformer, and the coil maybe distorted or the insulation maybe damaged for the great mechanical force. And therefore too may times of switch-on or switch-off will affect the transformer service life.

there are two ways about the transformer over-voltage damage：

（1）the breakdown of the insulation between winding to winding, winding to core, winding to tank will cause the winding short-circuit or winding earthing.
（2） the puncture of the insulation between turn to turn, segment and segment will cause the turn short-circuit.
Generally, the atmosphere over-voltage will cause two or more kinds of damage. And therefore, it usually applies the arrester to protect the transformer.
the way to protect the damage of over-voltage: besides to improve the insulation level of the HV winding, it also should strengthen the insulation level of the two ends turns, or applies the electrostatic ring or electromagnetic screen to balance the voltage of the first few turns of the winding. To 35KV or above transformer, it also should apply the neutral point earthing system to protect the over-voltage damage.

dry the transformer body

the transformer body should do the drying process under the following situations:
（1） after the change of winding or insulation.
（2） the result of the insulation test: the absorptance R60/R15 is less than 1.2 hour, ir the insulance ability drops greatly.
（3） the transformer body exposed to the air for too long a time after core suspended, or excced the regulated time (12 hours in the humidity environment, and 16 hours in the dry air).
it should pay attention to the following when doing the drying process：
（1） winding average temperature should no higher than 95℃ when heating, and the upper oil temperature should no higher than 85℃ when doing the oil dreying.
（2） when doing the heating and dreying, it should measure the temperature, winding insulance and the oil withstanding pressure intensity of all parts every 2 or 4 hours to regulate the heating temperature, it can stop the drying process if the insulance continously rise and remian stable for 6hours.
（3） if possible, the tank can apply the insulation layer and equiped with the fire unit (FU).
（4） There should be exhaust passage to exclude the moisture produced during the process of drying.

the reasons for the hign temperature rise

there are several reasons for the over temperature rise：
（1） tap changer is bad connected for there is not enough pressure of the tap changer contact, or the contact is filthy, the contact resistance increases, and the contact get heat, especially after change the tap changer jouint or when transformer overload operates, it is more easy to cause the bad connection of the tap changer.
（2） short-circuit of the coil turns: the short circuit of the turns make the number of coil turn reduces and therefore the temperature of the short-circuit place rise, and the oil give the purr sound.
（3） short circuit of the core silicon steel sheet: for the reasons of internal force or insulation aging or other reasons, the insulation of the silicon sheet is damaged, and the wortex increases, and thus cause the partial is over-heat.
In the operation, it the temperature rise is too high, it should judge which part has fault on the basis of transformer sound, the working condition of buchholz relay and other abnormal phenomenon and give the promptly dealment.

the reasons for transformer backup protection and the treatment

the reasons for transformer backup protection are：
（1） Short-circuit of high-voltage side of the transformer
（2） short circuit of low-voltage busbar of the transformer
（3） differential protection fails for there are fault in the differential protection range.
（4） Backup protection malfunction。
（5） the faults in the LV linesand the move of output protection cabinet cause the tripping operation for the transformer is overloaded.
Treatment principle is：
（1） if the overload protection device find the phenomenons of voltage drop, shock, arc light, sound and son on, it should check the outside of the transformer, and if the problem resolved at once, then it can commissionging operate, otherwise, it should be prepare to take security measurements: if there is no problem, it can also do the commissiong operate; to those transformer without differential protection, it should also do the insulation test besides the outside inspection.
（2） If it is the LV outputting lines happen faults, and the line protection moves, it can manually remove the falut line switch, and then tranmiss the power to the transformer.
（3） If the differential protection range happens fault and the differential protection failure, it should deal with according to the differential protection action.
（4） If it is the secondary circuit happens fault which belongs to the false function or mistouch, the person on duty should commissioning tranmiss the power.

What project of transformer should experience the special inspection?

When the transformer operates under special conditions, it should experience the special inspection which includes the following items：
（1） under the overload, it should monitor the changes of load, oil temperature, and oil level, the connection joints should be good, the wax disc tempil no melting phenomenon.cooling system operate normally.
（2） In windy weather, it should pay attention to the tightness, swing of the lead, and if there is foreign body on the transformer or on the lead.
（3） In the lightning strom weather, it should pay attention to whether there is flashover or discharging phenomenon of the porcelain bushing, and to the duscharging record of the arrester.
（4）In the fog weather, it should check whether there is discharging or flashover phenomenon, especially the porcelain filthy part.
（5）In the snow weather, it should check the heat part of the joint according to the snow melting, and deal with the snow and ice slush promptly.
（6）After big short-circuit fault, it should check the relative equipment and the joint.
（7）After the alarm signal of the gas relay, it should check the external situation of the transformer.

the inspection and monitoring of the operated transformers

the operated transformer should always inspected and monitored to find the abnormal phenomenon or fault to void the severe accidant.
the projects should be checked and monitored generally include：
（1） abnormal noise,such as uneven beep or noise of discharge.
（2） Oil-level, whether there are seepage, oil spills phenomenon.
（3） oil temperature (the upper oil temperature is no more higher than 85℃).
（4） whether the casing is clean, and whether there are phenomenons of crack, damage or discharge.
（5） whether there are fever phenomenon in the joints.
（6） whether rupture membrane of the explosion stack is complete
（7） whether the gas relay has the phenomenon of oil spills and whether the inner is full of oil.
（8） whether the respirators are clear, and whether the oil-level of the respirator is normal and whether the silica gel of the respirator has been saturated by moisture absorption.
（9） whether the cooling system runs normally, especially the forced oil recycling or the air-cooled transformers, the oil, water, temperature, pressure and flow war all needed to be checked whether meet the standard.
（10）whether the Shell grounding line is intact.

Services and processes:

we suppy the advanced technology, safe, reliable and good quality products for the users. Too satisfy the users is the ultimate goal of the company.
We give the promise to improve the quality of the products and strengthen the contact with the users：
1、The company provide customers general descriptive information: brochures, quotations, product samples, and other relevant qulifications before the customer order products
2、the company provides the hand, the base diagram, nameplate diagram, type test reports and transformer installation, operation commisioning, and all the attanchment including instructions, data, drawings and basic techical requirements.
3、the company freely trains the technical persoonel for the maintenance for the customer.
4、the company assures that all the technology, group attachment, testing are in accordance with national standard during the process of production
5、the company assign the technicians to the installation venues to instruct the process
6、after the installtion, all the spare parts should be transfered
7、to examine the quality of the key parts, process, installation of components, debugging coordinate with the customers.
8、the company deal with the installation problems.
9、during probationary period, the company should assign the technicians to the customers if any problems occured.
10、during the warranty period, the product is in three guarantees and the customer will get free service if there is quality problems.
11、The company assign members to visit customers regularly after operation
12、the company only charge the material cost after the waranty period.