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Transformer knowledges

1.The significance and difference between transformer's magnetic shielding, transformer magnetic radiation, magnetic influence.
Transformer magnetic shielding means the transformer's metal shell, which make of external installation conduction materials (such as silicon steel, Slope of the alloy etc) , used for shielding the harmful from external magnetic field to the transformer.

Magnetic radiation refers to the transformer leakage magnetic field send out to the space outside the transformer,produced harmful electromagnetic interference,and affect the electronic components which install around the transformer.
The magnetic influence is refers to the  leakage magnetic field of transformer,affect of the normal work of electromagnetic equipment, mainly means the influence degree to the ship equipment (compass).

2 What materials do you need when making a transformer ?
Making a transformer we must learn the  knowledge of the transformer's material first, therefore, I would like to talk about the transformer's material.

1) Iron core
The iron core of a transformer,which mainly contained: iron,Low silicon chips, high silicon chips.  add some silicon to these steel plates can reduce the conductivity of the steel plates, increase resistivity, reduce the eddy current,reduce the losses. We usually called the steel plates which have been added silicon the siliconized plate, it's very important to the quality of a transformer, and the the quality of a siliconized plate express as  magnetic flux  B, normal  black iron B value is 6000-8000, low silicon chips is 9000-11000, high silicon chips is 12000-16000,
2) the winding material of a transformer
Enameled wire, cotton-covered wire, USTC wire,paper covered wire,are the most commonly used enameled wire.some specs of these wires is very important to a transformer, the electrical conductivity must be good, insulation layermust have enough heat resistance, and should have certain corrosion resistant ability. Usually the best enameled wireis QZ type  high intensity and polyester enameled wire.
3) insulation materials
In the winding of a transformer,the resistance of isolation between coil framework layer,  isolation work between winding, need insulation materials.normal transformer frame materials use phenolic cardboard, epoxy board, or cardboard. Polyester film , telephone paper, 6520 composite paper,could be uesed  between coil framework layer for the resistance of isolation.isolation between winding we usually use Yellow wax cloth or imine film.
4) dipping materials
when the transformer is made, it will go to the last procedure--dipping in insulation varnish, it can enhance the transformer mechanical strength, improve the insulation performance, prolong service life, usually,we use cresol varnish  , 1032 insulating varnish, resin varnish and so on,as the impregnated material.

3 The ways to Reducing the noise in the power
transformer
The Noise from the transformer core is the main noise of a transformers's noise, reduce the noise from transformer core is the main measure to reduce the noise of a transformer. We could reduce the noise from the transformer core by these ways below:
1) increase the viscosity between C sheet iron by bond coating.
2) When install the C iron core,use high strength adhesive in both side of the sheet iron, eliminate the hitting between the sheet iron.
3) use little magnetostrictive material, such as silicon steel belt which the silicon content  is 6.5% , reduce noise cause by the magnetostrictive phenomenon.
4) use  E, I iron chip which made of the same roll materials.
5) use high bond strength and low shrinkage ratio materials  dipping the iron core and the transformer.
In addition,use high viscosity and little elongation steel packing;when using the pachytene or copper strip do the coiling,make sure it's tight, substantial and smooth; Improve the mechanical strength of the parts; pay attention to the installation position, direction, avoid acoustic resonance from the parts and  using absorption material etc,are available ways to reducing the noise of a transformer.

4 what  will make the transformer has a low insulation resistance
1) coil damp.
2) the thickness and the number of the insulation layer does not conform to the requirements.
3) the Leave edge distance of the coil and creepage distance does not comply with the requirements.
4) bobbin craze and damp.
5) not dry enough after impregnate the coil, the insulation varnish film is not build, insulating resin is not cured.
6) the coil is wet before impregnate the coil, when drying the coil after the coil is dip, the insulation varnish on the surface of the coil has dry and cured, but the internal does not solidified into film.

5 Please pay attention to these problems when installing electrostatic shielding on a transformer
1)make sure the width of the electrostatic shielding is the same to the width of the coil winding.
2)using the copper foil with good electro conductibility,if for toroidal transformer, we could use enameled wire row a layer around the iron core.
3)pay attention to the insulation work from the head to the end of the shield, to avoid short circuits.
4)insulation between shielding and winding  (including creepage distance and insulating layer number, etc) must comply with the provisions of the safety standards.
5)the lead wire from the shielding layer must be good welding, and pay attention to the insulation of  the lead wire.
6) when using a copper foil shielding,we must be carefully with the edge burr damage,it will brake the insulation.

6 How a transformer could meet the required current which come from the electrical resistance strength test.

To meet the required current,usually,we reduced the insulation capacitance of the transformer. Can adopt the following ways:
1) increase the insulation thickness between transformer windings,and insulation thickness between windings and the iron core.
2) using insulating materials with low dielectric constant.
3) prevent the transformer from damp, choose materials with small water imbibition.
4) using bilayer shield or multilayer shield, reduce the capacitance between windings.

7 How to reduce the no-load current of a  power transformer under industrial frequency?
1) choose materials with low H(magnetic field intensity) value   
2) reduced induction strength properly
3) avoid and reduce magneticairgap
4) avoid short circuit between windings
5) reduce the inner stress of the iron core,when assembling the transformer.

8 why Low power industrial frequency power transformer has a turn-to-turn short circuit,and how to find out if there is a turn-to-turn short circuit?
(1)why a turn-to-turn short circuit happens
1) the enameled wire's quality is poor, especially the fine wire conductor,the standard for that wire allow them to have pinhole points,when coiling,it's very easy to make a short circuit.
2)when coiling,the enameled wire is damaged,such as the paint film is damaged,bowed,knotted,etc.
3)the packing paper for the soldering lug is crushed or the soldering lug shift.
4)the welding spots of lead wire or soldering lug has burrs,constrict the insulating layer.
5)when using a copper shielding,the insulation between layers are not mat good,that makes the shielding layer smashed against the head and tail.
6) when dipping,the insulation varnish is not good,the solvent corrode the enameled wire and have a great shrinkage stress,after drying,the coils shrink,cause a short-circuit.
(2) how to make a turn-to-turn short circuit testing
1)make a induced voltage test under 400 HZ.
2) pulse comparison test.put high-pressure square wave on transformer winding ends, compare the attenuation shock wave of the two windings,you could get an answer from that if there is a short circuit.
3) measure the transformer no-load loss. When the core loss is qualified, but the no-load loss increase,there is a short circuit.
4) high frequency transformer and inductor can measure the Q value, to find out if there is a short circuit.
9 How to reduce the temperature rise of a industrial frequency power transformer?
1. reducing the loss of the transformer
The transformer temperature rise to its loss is proportional. Transformer loss including core loss and winding copper loss. Reduce the work magnetic induction intensity of the core  and choose low loss materials core is the main ways. Reduce the coil current density, and improve the space factor of the copper at the core window is main ways to reduce the  winding copper loss. But these measures will affect the size and the cost of transformer.
The ratio of copper loss and iron loss  of a transformer,will do much influence on the technical and economic index and  the temperature rise of a transformer.Adjust the transformer  copper loss and iron loss ratio could make the transformer at a very good status,with the right technology economic indicators and temperature rise.
2.Improve the transformer cooling capacity(heat-sinking capability)
Transformer heat dissipation, including transformer heat conduction, radiation and convection. increasing the contact area between the transformer and floor installation, especially the area between iron core and floor installation,is the most effective
way to increase the thermal conduction. Upon the transformer surface, coating black paint could increase the thermal radiation ability, open air way between the iron core and coil, could increase the  convection heat dissipation between the iron core and coil, these methods could reduce the temperature rise of the transformer.
3.Increase the size of the winding wire and the cooling area of the iron core
The bigger transformer winding wire and the  cooling area of iron core are, the lower the temperature of the transformer will be.we could  add cooling fin on the iron core, increase the coil area,etc,are the effective ways to increase the heat dissipation area,reduce the temperature rise.

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