Selection basis and method guide for dry-type non-excited tap changer

I. Preface

In modern power systems, transformers, as core equipment, the reliability of their voltage regulation directly affects the stability of the power grid and the quality of power supply. Dry-type De-Energized Tap Changer (DE-TC) is an important accessory device for transformers to achieve voltage tapping and voltage regulation. It features oil-free operation, Dry insulation, compact structure and convenient maintenance. The correct selection of dry-type non-excited tap changers not only ensures the safe operation of transformers but also enhances the voltage regulation efficiency and power supply reliability of the power grid. This article will systematically analyze the selection basis and methods of dry-type non-excited tap changers, providing scientific guidance for engineering design and operation and maintenance.

Ii. Overview of Dry Non-Excited Tap Changer

1. Definition and Characteristics

Dry insulation: It uses air or epoxy resin as the insulating medium, is oil-free and environmentally friendly, and reduces the risk of fire and environmental pollution.

No-excitation operation: When adjusting the tap points, the operation must be carried out under power-off conditions to ensure electrical safety.

Compact mechanical structure: Small in size, suitable for various installation environments.

Easy maintenance: Oil-free design reduces maintenance difficulty and the contact points have a long service life.

2. Main uses

Voltage tap regulation: To achieve voltage adjustment of the transformer under different load conditions.

Power system optimization: In line with the operational requirements of the power grid, achieve load balancing and voltage stability.

Safety Assurance: Operate without excitation to reduce the risk of electrical accidents.

Iii. Selection Basis for Dry-type Non-Excited Tap Changer

1. Voltage level

When choosing a tap changer, the primary basis is the rated voltage of the transformer and the system voltage level:

Rated voltage matching: The insulation level of the tap changer must meet the maximum working voltage requirements of the transformer.

Withstand voltage margin: Considering the influence of lightning, short circuits and overvoltage, the insulation grade of the tap changer selected should be a certain margin higher than the system working voltage.

2. Rated current

The tap changer must meet the rated capacity and load current requirements of the transformer.

If the load current exceeds the rated current of the tap changer, it may cause overheating of the contacts, accelerated wear or unstable operation.

When selecting the model, it is necessary to calculate in combination with the actual peak load and the long-term operating load.

3. Tap range and step size

The number of tap points: It affects the voltage regulation accuracy. Generally, the appropriate number of tap points is selected based on the range of load variation.

Tap step size: The voltage variation during each voltage regulation should ensure that the voltage fluctuation is within the allowable range.

Reference application scenarios: For urban power distribution, small-step and multi-tap contact points can be selected to improve the accuracy of voltage regulation. For industrial loads, a moderate step size can be selected.

4. Environmental conditions

Different operating environments have a significant impact on the performance of dry-type non-excited tap changers:

Temperature: In high-temperature environments, high-temperature resistant materials should be selected to ensure the stability of contact and insulation performance.

Humidity: A humid environment may reduce the insulation level. Moisture-proof design should be taken into consideration when selecting the type.

Dust and Corrosion: In industrial or mountainous environments, dust-proof and anti-corrosion measures should be selected to ensure long-term stable operation.

Installation space: The dry design has a small volume and can adapt to places with limited space, but it still needs to ensure operation and maintenance space.

5. Operating methods and safety requirements

Manual operation: Simple and low-cost, but it requires personnel to operate on-site, and safety depends on operation norms.

Electric or mechanical operation: It can achieve remote adjustment or interlocking control, enhancing safety and operational convenience.

Interlock device: Ensures the safety of the operation process and prevents the risk of misoperation and electric shock.

6. Reliability and Maintenance requirements

The contact material, mechanical life and insulation life of the tap changer are important references for selection.

Maintenance frequency and the cost of replacing vulnerable parts should be taken into account during the selection stage to ensure long-term operational economy.

Iv. Selection Method of Dry-type Non-Excited Tap Changer

Method One: Parameter matching method

The rated voltage and current of the tap changer should be determined based on the rated voltage and capacity of the transformer.

Determine the number and step size of tap points to ensure that the load voltage regulation requirements are met.

Check the environmental adaptability, including temperature, humidity and corrosion grade.

Method Two: Environmental Adaptability Selection Method

Urban power distribution: Give priority to small-sized, precise models with moderate insulation grades to meet the requirements of limited space and safety and environmental protection.

Industrial plant areas: Select models that are resistant to high temperatures, dust, and corrosion to ensure stable operation under high loads and harsh environments.

Mountainous and remote areas: Consider models with moisture resistance, lightning shock resistance and mechanical vibration resistance to enhance long-term reliability.

Method Three: Intelligent Compatibility Selection Method

If the power grid adopts an automated or remote monitoring system, models with intelligent interfaces and position sensors should be selected.

Confirm that the tap changer is compatible with the communication protocol of the control system to facilitate remote voltage regulation and status monitoring.

Method Four: Comprehensive Assessment Method of Safety and Economy

Comprehensively compare the safety (insulation grade, interlocking device, protection grade), operating life and maintenance cost of different models.

Give priority to choosing models with high reliability, convenient maintenance and economical overall investment.

V. Analysis of Application Examples

Urban distribution transformer

Selection basis: The rated voltage of the transformer is 10kV, the rated capacity is 500kVA, the environment is dry, and the space is limited.

Selection option: Dry non-excited tap changer, rated current 600A, 5 taps, 2.5% step size, manual operation, with dust cover.

Advantages: It meets the safety requirements of urban power distribution, is compact in size and easy to operate.

2. Industrial high-load transformers

Selection basis: The rated voltage of the transformer is 35kV, the rated capacity is 2000kVA, and the industrial plant is high-temperature and dusty.

Selection option: Dry non-excited tap changer, rated current 2200A, 9 taps, step size 1.5%, electric operation, high-temperature resistant design.

Advantages: Stable operation under high load, excellent dust-proof and anti-corrosion performance, and suitable for industrial environments.

3. Remote substation in mountainous areas

Selection basis: The rated voltage of the transformer is 20kV, the rated capacity is 1000kVA, the environmental humidity is high, and there are many thunderstorms.

Selection solution: Dry non-excited tap changer, rated current 1100A, 7-tap, 2% step size, manual operation, moisture-proof and lightning-proof design.

Advantages: High reliability, adaptability to complex terrains and environmental conditions, and easy maintenance.

Dry-type non-excited tap changers, with their dry insulation, oil-free and environmentally friendly features, compact structure and convenient maintenance, have become important supporting equipment for modern transformers. Scientific selection requires a comprehensive consideration of the following factors:

The voltage level matches the rated current.

The number of tap points and step size meet the requirements of load voltage regulation.

Environmental conditions, including temperature, humidity, dust and installation space.

Operation mode and safety requirements.

Maintain simplicity and economy.

Through methods such as parameter matching, environmental adaptability selection, intelligent compatibility, and safety and economic assessment, the safety, reliability, and economy of dry-type non-excited tap changers in different application scenarios can be effectively guaranteed, providing a solid guarantee for the stable operation of the power grid.