Application of Dry Type Transformer in Water Conservancy Project

dry type transformer in water conservancy project

Table of Contents

Water conservancy engineering units are mostly responsible for water supply, drought resistance, flood control, flood discharge and other tasks, and power supply and distribution equipment operates under different weather conditions and environments. According to the comparison of the characteristics of various types of dry-type transformers, water conservancy engineering units should use epoxy resin cast dry-type transformers, which can operate in 100% relative humidity and other harsh environments.

The protection method is usually IP23 protective shell, which can prevent the short-circuit and power failure caused by the entry of solid foreign objects with a diameter greater than 12mm and small animals such as mice, snakes, cats, and birds.

The cooling method adopts forced air cooling, and the output capacity can be increased by 50%. The transformer can run continuously for a long time under the rated capacity, and can run intermittently with overload, or overload in emergency.

Application of dry type transformer

Why do water conservancy projects choose dry-type transformers?

Dry-type transformer refers to the transformer whose iron core and winding are not immersed in insulating oil

According to different structures, it can be divided into open type, closed type and pouring type.

The open type dry-type transformer is a common type. Its body is in direct contact with the air. It is suitable for a relatively dry and clean indoor environment (ambient temperature is 20°C, relative humidity does not exceed 80%). 

Generally, there are two types of cooling: air cooling and air cooling. Way.

The closed dry-type transformer is located in a closed shell and does not directly contact the external air. 

It can be used in relatively harsh environments, and is especially suitable for installation and use in places with high fire protection requirements such as flammable and explosive. 

The pouring type uses epoxy resin or other resins as the main insulation. 

The entire coil conductor is encapsulated by the solid insulating layer of the resin, so it is not only difficult for moisture to penetrate, but also completely blocks the conductor from being damaged by various harmful oxygen and corrosive chemical components. 

The possibility of damage, its moisture-proof and anti-fouling properties are particularly good, and it can work in extremely harsh environmental conditions.

Compared with oil-immersed transformers, dry-type transformers operate more safely and stably because there is no oil, with less maintenance in the later period, and there are no problems such as fire, explosion, and pollution. 

Especially for the new series, the loss and noise have been reduced to a new level, creating conditions for the transformer and the low-voltage panel to be placed in the same power distribution room, which can reduce the construction cost of water conservancy projects and facilitate operation and maintenance.

Inspection and operation and maintenance of dry-type transformers

Application of dry-type transformer

Inspection of dry-type transformers

The dry-type transformer shall be inspected every 2-3 months after it is put into operation, and shall be inspected every year thereafter. The main inspection contents are:

Whether there is dust accumulation, cracking, discoloration, discharge, etc. in the cast-type winding and the connection between phases, whether the insulation resistance is normal; whether the iron core air duct is blocked by dust, foreign objects, and whether there is rust or corrosion;

Whether the winding pressing device is loose;

Whether the operation of instruments and protective devices such as pointer thermometers is normal;

Whether the cooling device, including the motor and the fan bearing, are in good condition.

Load monitoring

Dry-type transformers have strong overload capacity and can allow short-term overload. The transformer can monitor and test the load overload through the temperature control system. The self-cooling transformer is mainly equipped with a temperature control box. 

If the winding temperature exceeds a safe value, the temperature control box will send a signal. The forced air cooling configuration temperature control box will stop the cooling fan, and send an over-temperature alarm signal and an over-temperature trip signal. 

The maximum temperature of the winding and iron core of the dry-type transformer shall not exceed 155°C, and the maximum temperature rise shall be 100K.

During overload operation, pay close attention to temperature changes, and avoid damage to the insulation due to excessive temperature rise, resulting in failure to resume operation.

3. Periodic test cycle of dry-type transformers After the dry-type transformers are installed and operated, preventive tests should be carried out regularly. The period is generally 2 to 3 years. The test items and requirements are shown in Table 1.

Common fault handling of dry-type transformers

  1. Transformer over temperature

Most dry-type transformers are equipped with temperature monitoring devices, which can display the real-time temperature of three-phase windings. Generally, when the winding temperature reaches 130 °C, a high temperature alarm signal will be issued. When the winding temperature exceeds 150 °C, it will trip, that is, over-temperature tripping. Due to the relatively strong overload capacity of dry-type transformers, the general overload situation will not cause the temperature to rise too high. If abnormal over-temperature occurs, it is mostly caused by poor ventilation caused by damage to the fan and poor ventilation. The reasons should be identified. , be processed.

  1. The transformer has discharge sound or short circuit between turns

Dry-type transformers have strict environmental requirements. Excessive dust and moisture on the surface can lead to surface discharge and damage the insulation. In addition, due to manufacturing process problems such as air bubbles, uneven insulation, etc., discharge may occur after running for a period of time under external conditions, so inspections, maintenance, cleaning and preventive tests should be strengthened.

  1. The on-load voltage regulating switch of the on-load voltage regulating dry-type transformer is faulty

The on-load voltage regulating device has a low level of manufacturing technology and a high failure rate. If it is burned out, it should be replaced directly.

  1. The noise is too loud

Noise is an inherent characteristic of transformers, but if the sound is too loud or abnormal, it should be dealt with in time.

The noise of dry-type transformers is too large or abnormal mainly in the following situations:

(1) Voltage problem

Due to the high operating voltage, the transformer is overexcited, and the noise increases and becomes sharp. The tapping gear can be placed in a suitable gear, and on the premise of ensuring the quality of low-voltage power supply, try to increase the high-voltage tapping (low-voltage output voltage is reduced), so as to eliminate the over-excitation phenomenon of the transformer and reduce the noise of the transformer at the same time.

(2) Resonance problems of fans, casings and other parts

The noise caused by the resonance caused by the looseness of the fan, casing and other parts of the transformer is too large. Tighten the relevant screws and bolts, or put rubber on the loose parts to solve the noise caused by the looseness.

(3) Installation problems

The installation foundation of the transformer is not firm and uneven, or the bottom plate is too thin, which will aggravate the vibration of the transformer and cause excessive noise. The original installation method can be modified, or the anti-vibration rubber pad can be added under the transformer to solve some noise.

 

(4) Influence of installation environment

The transformer room is large and empty, or it is too close to the wall, causing echoes or superimposition of noise, resulting in excessive noise. Sound-absorbing materials can be appropriately installed in the transformer room.

 

(5) The problem of the vibration of the busbar bridge

Due to the large current passing through the parallel busbars, the busbars vibrate due to magnetic leakage, and the vibration of the busbar bridge will seriously affect the noise of the transformer, which varies with the size of the load. Fix the busbar, or use a soft connection for the low-voltage outlet.

 

(6) Transformer core self-resonance

The noise is caused by the electromagnetic attraction caused by magnetic flux leakage at the seams of the silicon steel sheets and between the laminations. Part of the noise can be solved by tightening the screws on the transformer, including the screws at the two ends of the clip, the through-the-core screws, the screw for the spacer, or by adding an anti-vibration rubber pad under the transformer.

 

(7) Transformer coil self-resonance

When a load current passes through the winding, the magnetic leakage generated by the load current causes the vibration of the winding to generate uneven noise. Tighten all the spacer screws and increase the axial compression force of the coil to solve the problem.

 

(8) The problem of transformer phase loss

Due to the lack of phase of the transformer, the excitation cannot be performed normally, resulting in noise. The problem can be solved through the power failure of the transformer and the replacement of the transformer high-voltage insurance.

Conclusion

With the arrival of another major water conservancy construction and the further development of dry-type transformers in terms of energy saving and noise reduction, environmental protection and reliability, multi-function and large capacity, it will be more widely used in the field of water conservancy engineering power transformation and distribution.

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