Dry-Type Transformer

For customers, if only low costs is considered,oil immersed transformers can be considered. If safety operation, maintenance costs, and environmental protection are taken into account, it is recommended that customers use dry-type transformers.

A dry-type transformer is mainly composed of the following components:

1.Core;2.Windings; 3.Fastening and supporting parts; 4.Leads; 5.Insulation; 6.Cooling device:temperature controller and fan;7.Protective device: transformer casing. 

SCZB9-1000/10 is a three-phase dry-type on-load tap-changing transformer with a capacity of 1000 KVA. Dry type transformer's high-voltage winding is wire-wound with a voltage level of 10 kV; the low-voltage winding is foil-wound with a voltage level of 0.4 kV.

The no-load loss of the 9 type product is in accordance with the GB/T10228-2008 standard.

The no-load loss of the 10 type product is on average 10% lower than that of the 9 type product, and the load loss is on average 5% lower than that of the 9 type product.

① Winding process

② Core production process

③ Assembly process

Temperature. Generally, forced air cooling and reducing the load are adopted for control.

 The maximum temperature of dry type transformer is at F-class.

By optimizing the design,selecting high-quality materials, and improving the processing and manufacturing techniques.

There two methods:

1, setting up sound insulation walls around the transformer can significantly lower the sound of the transformer.

1. Taking measures in the manufacturing process, such as using step joints for the core,bonding the cut edges with resin paint after stacking the core; binding and coating the core columns with resin fixing paint; and using silicon rubber plates for vibration reduction at the connection points of each component, can be effectively reduce noise.

The main types of Dry-type transformers include: dry-type power transformers,distribution transformers, traction rectifier transformers, grounding transformers, arc suppression coils and other special dry-type transformers, non-standard dry-type transformers, dry-type reactors, etc.

The common width of copper foil is 600 to 1000mm, with a maximum thickness of 2mm.

The common width of aluminum foil is 600 to 1200mm, with a maximum thickness of 2mm.

0.2mbar.

Generally, it is class F, with and insulation system temperature of 155°C.

The overload capacity of a dry-type transformer refers to the duration for which the transformer can continuously operate under conditions exceeding its rated load.

Three conditions must be met:1. The connection groups are the same. 2.The rated voltage ratios are the same. 3. The rated impedance voltages are the same(allowing a deviation of ±10%)

Before powering on and running, clean the transformer body thoroughly and conduct insulation measurement.

Epoxy resin, curing agent, plasticized, accelerator, and color paste are required. If it is a filled resin, fillers such as Si02 are also needed.

Dry-type power transformers are widely used electrical equipment in power systems. Compared with oil-immersed transformers, they have advantages such as fire prevention, explosion-proof, no pollution, and maintenance-free. Their cooling methods mainly include natural air cooling (AN) and forced air cooling (AF). This type of transformer is suitable for places with high safety and environmental protection requirements, such as high-rise buildings, hospitals, schools, shopping malls, and other densely populated areas, as well as some industrial sites with special fire protection requirements.

The transformer is without a casing and has a protection grade of IP00. As it is not advisable to touch or approach the transformer during operation, it is recommended to use a protective fence to ensure safety. The protective casing provides further safety protection for the transformer. The protection grades available include IP31, IP30, IP21, IP20, etc. The casing materials available for users to choose from include cold-rolled steel plate, stainless steel plate, and aluminum alloy.

To ensure the normal operation of the transformer, regular inspection and maintenance are required. The specific requirements are as follows:

• The temperature display value of the temperature controller should be frequently monitored to keep track of the transformer's operating conditions promptly.

• The operating noise of the transformer should be frequently monitored to listen for any abnormal sounds, especially discharge sounds.

• In a dark environment, observe whether there is any abnormal discharge on the surface of the transformer coils and spacers.

• For transformers with a Yyn0 connection, the neutral current should be monitored. The maximum value of this neutral current should not exceed 25% of the low-voltage phase current; an excessively high neutral current may cause severe three-phase voltage imbalance, affecting power supply safety.

• When the transformer has the following conditions, such as abnormal fan operation, abnormal temperature display, and minor cracks in the appearance of the winding resin insulation, it is not allowed to operate beyond the nameplate rating. The cause should be investigated, and the manufacturer should be contacted for confirmation.

Precautions for transformer maintenance:

• The main inspection items include the dust accumulation on the surface of the coil and whether there is discharge on the surface of the coil and the surface of the spacer.

• The inspection of dust accumulation on the surface of the coil should be carried out under sufficient illumination, while the inspection of surface discharge should be conducted in a dark environment.

• The locations for power-off cleaning mainly include the surfaces of the coil and the upper and lower end faces, the surfaces of the spacers, and both sides of the air ducts, as detailed in the transformer body assembly diagram.

• If it is impossible to perform power-off cleaning at the prescribed frequency due to special reasons, dry type transformer manufacturers should be informed for assessment.

• If the operation site has a distinct rainy season, dry type transformer is recommended to carry out power-off cleaning before the rainy season and increase the frequency of transformer operation checks during the rainy season and periods with large temperature differences between day and night.

The 8 factory tests include: Ratio measurement, DC resistance measurement, insulation resistance measurement, power frequency withstand voltage test, induced withstand voltage test, no-load current and no-load loss measurement, load loss measurement, and partial discharge measurement.

The 2 routine tests are: lightning impulse test and temperature rise test.

Partial discharge refers to the discharge that only exists in a local position of the insulation and does not immediately form a complete insulation breakdown or flash-over.

Its hazards are as follows: 1. The direct bombardment of the insulation at the discharge point causes local insulation damage, which gradually expands and leads to insulation breakdown; 2.The chemical effects of heat,ozone, nitrogen oxides and other active gases produced by discharge cause local insulation corrosion, increased conductivity, and eventually thermal breakdown.

The feature of dry-type transformer products include safety, non-flammability,fire resistance, no pollution,direct installation at the load center,maintenance-free, simple installation,and low comprehensive operating costs. They have good moisture resistance and can operate normally under 100% humidity. After shutdown, they can be put back into operation without pre-drying. They have low losses, low partial discharge, low noise, strong heat dissipation capacity, and can operate at 150% of the rated load under force air cooling conditions. They are equipped with complete temperature protection and control system,providing reliable protection for the safety operation of the transformer.

Dry-type transformers are cooled by air self-cooling or force air cooling, and their heat dissipation method is air duct heat dissipation. They have the following features: safety, flame retardancy, fire resistance,no pollution and can be directly installed at the load center. They are maintenance-free, easy to install, have low comprehensive costs, and have good moisture resistance. They can normally at 100% humidity and can be put into operation immediately after being shut down without pre-drying.

The cooling method of oil immersed transformers is oil circulation cooling.which use oil channels for heat dissipation. Therefore each oil immersed transformer must be equipped with an oil tank.

Its characteristic is good heat dissipation performance. However compared with dry type transformers, oil immersed transformers are flammable, not fireproof, require frequent maintenance, and cause certain pollution to environment. Therefore, in ares with high population density, oil immersed transformers are rarely used.

1. Coil winding aspect:

For SCB type products, the low-voltage coil adopts foil winding:

Winding structure: single or double layer winding with copper(aluminum)foil, and the interlayer material uses epoxy resin containing latent curing agent and F-class composite foil(DMD paper);

Winding material: uses oxygen-free copper with excellent conductivity, with a cooper content of 99.99%.

For SC type products, the low-voltage coil adopts wire winding:

Winding structure: cylindrical coil;

Multiple ordinary glass fiber insulated flat copper wires are wound in parallel.

2. In terms of resisting sudden short-circuit accidents:

The low-voltage part of the SC(L)B type product adopts a copper(aluminum) structure, with the height of the reactance being the same as the height of the winding, which is equivalent to the high-voltage coil. Thus,under the condition of a sudden short circuit in the transformer,it generates as relatively small axial short circuit force. Additionally, as the entire winding is made from a single wide and thin foil, it has a strong resistance to axial tensile breakage.

The SC type product, due to its use of multiple parallel windings, has a very large end helix angle, generating a strong end leakage magnetic field. Under the condition of a sudden short circuit in the transformer, it generates a very large short-circuit force. If the structure is not adequately reinforced,it is very likely to cause axial damage.

The insulation forms of resin-insulated dry-type transformer coils generally have four manufacturing techniques:

1. Thin insulation structure with epoxy resin casting (referred to as thin insulation type);

2. Epoxy resin winding structure (referred to as winding type);

3. Thick insulation structure with epoxy resin filled with fillers (referred to as filled type);

4. Vacuum impregnation structure (referred to as open type).

Dry type transformer company uses German Jorg core transverse shearing lines to produce the core.it feature high shearing accuracy, small burrs,multi-head feeding, automatic stacking, and step-by-step stacking functions. This reduce the vibration times of the slices and ensures the intact crystal structure of the silicon steel sheets.

Design--Adjust the core proportion to avoid resonance frequency.

Materials--Use high-quality silicon steel sheets to reduce hysteresis strain rate.

Processing--Utilize advanced core production lines to ensures burrs below 0.03mm.

Assembly--Adopt advanced five-step lamination technology to minimize core joint air gaps.

The function of the temperature controller is to conduct three-phase inspection, control the start and stop of the cooling fan (80°C and 100°C), issue an over-temperature alarm(130°C), and trip due to over-temperature(150°C), and a dry type transformer can also send signals to the computer terminal remotely.

The function of the enclosure is to prevent human and foreign objects from approaching the transformer when it is energized to avoid danger.

The function of the fan is increase the air flow rate, reduce the temperature rise caused by the heat generated by the transformer during operation, and ensure that the transformer can operate normally and continuously.

30--The thickness of the silicon steel sheet is 0.30mm.

Q--Cold-rolled oriented silicon steel sheet.

130--Maximum specific iron loss.

P17/50=1.30W/Kg

Yyn0 has a high-voltage star connection and a low-voltage star connection with the neutral point drawn out. Dyn11 has a high-voltage delta connection and a low-voltage star connection with the neutral point drawn out.

The Dyn11 connection method can eliminate the third harmonic voltage. Since the primary side uses a D connection, the neutral point on the secondary side is stable and can be grounded.

Yyn0 is often used in small-capacity transformers. For large capacity transformers, due the significant eddy current loss in metal structural components,it is not advisable to use it.

The standard horizontal side outlet busbar--that is , the outlet busbar is arranged parallel to the transformer.

The standard vertical side outlet busbar--that is , the outlet busbar is arranged perpendicular to the transformer.

A transformer produced with a core made by widing a special winding device to form a core roll is called a wound core transformer.

A transformer made with non-alloy materials as the raw material for the core is called a non-alloy transformer.

Casting form bottom to top is to ensure that the resin can fully penetrate the interior of the insulating materials and completely cover the coils. Heating and vacuuming are necessary to fully degas the cast resin, avoiding the formation of bubbles and ensuring the quality of the casting.

There are various lead-in and lead-out methods such as bottom-in bottom-out, bottom-in top-out, bottom-in side-out, top-in top-out, top-in bottom-out,side-in side-out, side-in bottom-out, and side-in top-out.

Capacity, voltage ratio,short circuit impedance, load loss, no-load loss, connection group, no-load current, insulation level, protection grade, etc.

No, dry type transformer cannot be used interchangeably because dry type transformer rated voltages and rated transformation ratios are different.

A sudden short-circuit is a simulation test that mimics the most severe damage a transformer may encounter during operation. Due to extremely high sudden short-circuit current, the dry type transformer causes significant losses, leading to rapid heating and severe thermal damage to the transformer coils and result in damage. Moreover, the electromagnetic force acting on the transformer is very large, which will disrupt the dynamic stability of the transformer body and cause the coils to crack.