DC Circuit Breaker - Voltage Regulation Method of Transformer Tap Changer

Both DC circuit breaker and on-load tap changer refer to the voltage regulation method of transformer tap changer. There is a short-time disconnection process, disconnecting the load current will cause arcing between the contacts and burn the tap changer or short circuit, so the transformer must be powered off when shifting gears. Therefore, it is generally used for transformers that do not require very strict voltage requirements and do not require frequent gear adjustments. On the other hand, the on-load tap-changer can switch gears with load, because there is no short-term disconnection process in the process of shifting the gears of the on-load tap-changer. Therefore, there is no arcing process in which the load current is disconnected. It is generally used for transformers that have strict voltage requirements and need to be frequently adjusted.

1. Classification of DC circuit breakers

DC circuit breakers mainly include neutral bus breaker (NBS), neutral bus grounding breaker (NBGS), metal return transfer breaker (MRTB), and earth return transfer breaker (ERTB).

2. Difficulties in the development of DC circuit breakers

The difficulties in the development of DC circuit breakers are manifested in two aspects: first, the current in the DC system does not have a natural zero-crossing point, and the mature arc extinguishing technology in the AC circuit breaker cannot be applied; second, the inductive components in the DC system store huge energy, which increases significantly This increases the difficulty of breaking the DC fault current.

3. Classification of DC circuit breakers

The topological principle of DC circuit breakers is complex and diverse. According to the key breaking devices in DC circuit breakers, DC circuit breakers can be divided into three categories: mechanical DC circuit breakers, all-solid-state DC circuit breakers, and a combination of mechanical switches and solid-state switches. hybrid DC circuit breaker.

4. Working conditions of DC circuit breaker

4.1 The altitude of the installation site shall not exceed 2000m;

4.2 The ambient air temperature is not higher than +40°C and not lower than -5°C; and the 24-hour average value does not exceed +35°C (except for special orders)

4.3 The relative humidity of the air at the installation site. When the maximum temperature is +40°C, it should not exceed 50[%], and a higher relative humidity can be allowed at a lower temperature, for example, it can reach 90[%] at 2O°C. Special measures should be taken for the occasional condensation caused by dry temperature changes.

4.4 A place where there is no explosive medium in the air and no gas and conductive dust sufficient to corrode metals and damage insulation.

4.5 A place free from rain and snow.

4.6 The pollution level is level 3.

4.7 Installation category: The installation category of the main circuit of the circuit breaker is III, and the installation category of auxiliary circuits and control circuits not connected to the main circuit is II.

5. Wiring method of DC circuit breaker

5.1 Wiring behind the board. The advantage of wiring behind the panel is that when maintaining the DC circuit breaker, etc., it is only necessary to disconnect the front-end power supply without rewiring. This type of structure is quite special, and it is equipped with a special mounting plate and screws. The installation must be strictly in accordance with the manufacturer's requirements to avoid affecting the normal use of the circuit breaker.

5.2 Plug-in wiring. The advantage of plug-in wiring is that when the circuit breaker needs to be replaced, just pull out the old circuit breaker and replace it with a new one. In operation, it is faster and more convenient than wiring before and after the board. When using this method of installation, ensure that the plug is securely fastened, thereby reducing contact resistance and improving safety and reliability.

5.3 Drawer wiring. The entry and exit drawers of products such as DC circuit breakers are realized by the clockwise or counterclockwise rotation of the rocker, and the plug-in structure must be adopted on the main and secondary circuits. In this way, one machine can be used for two purposes, which not only saves the cost of use, but also has great advantages in terms of convenience in operation, update and maintenance.

6. Function of DC circuit breaker

The DC circuit breaker has super-class current limiting performance, which can accurately protect relay protection and automatic devices from overload, short circuit and other fault hazards. DC circuit breakers have the advantages of current limiting and arc extinguishing capabilities. After a large number of comprehensive scientific experiments, they can realize full selective protection between main (sub) screens, protection screens, and relay screens in DC systems below 3000Ah.

The DC circuit breaker adopts a special arc extinguishing and current limiting system, which can quickly break the fault current of the DC power distribution automation system and greatly improve the level difference coordination. The DC circuit breaker is especially aimed at accidents such as leapfrog tripping between the protection screen and the distribution screen in the DC system of electric power engineering. This series has excellent performance and can avoid the above-mentioned failures. The differential matching characteristics of DC circuit breaker products are the best among similar products at home and abroad.

The principle of the hybrid DC circuit breaker is simple and straightforward, and the technology is relatively mature. The key points of its development are:

6.1 Improve the operating speed and reliability of mechanical switches;

6.2 Reduce the number of components of the overall circuit breaker;

6.3 Reduce the size of the circuit breaker;

6.4 Reduce costs and improve application feasibility.

7. Applicable places for DC circuit breakers

7.1 Power system

In power systems with large capacity and high voltage such as power plants and substations, the DC system provides reliable power for equipment such as relay protection, operation control, signal audio, and emergency lighting. Small DC circuit breakers are the most important components in the DC system. As one of the components, its stable and reliable operation will directly ensure the safety of the entire power system.

7.2 DC power supply

The vigorous development of the information industry has ushered in the great development of the communication power supply, EPS, UPS and other DC power supply industries. Base stations and data centers have sprung up on the land of China. In order to ensure the high precision requirements of the DC power supply, as a DC power supply The DC circuit breaker, the most important operation and protection component in the feeder circuit at all levels, plays a very important role in protecting equipment and limiting the scope of accidents with its reliable selective classification coordination.

7.3 Rail Transit and Electric Locomotives

At present, my country's urban rail transit system is powered by DC system. However, most of its DC power supplies are provided by high-power silicon rectifier devices. Due to the low overload capacity of silicon rectifier device components, the requirements for DC power grid protection components are higher. Quickly analyze the important components in the rail transit of the DC special circuit breaker.

7.4 Ships

In ship power system and electric propulsion system, DC circuit breaker is one of the very important components. It protects the faults of the power transformation and distribution system and electrical equipment, and adopts multiple protections to ensure the safety of the ship's power supply system and electrical equipment.