New Voltage Regulation Technology of Distribution Transformer

The on-load voltage regulation technology of distribution transformers is of great significance to stabilize the voltage and improve the voltage qualification rate. It is the basic condition for the intelligent distribution station area to realize the comprehensive coordinated control of voltage and reactive power. The new on-load voltage regulation technology of distribution transformers can be roughly divided into three categories: mechanical, power electronic, and composite. Mechanical type can be divided into three types: improved type, with online oil filter device and vacuum arc extinguishing type.

2.1 Mechanical on-load voltage regulation technology

(1) Improved mechanical type. The improved mechanical on-load tap changer is based on the traditional mechanical on-load tap changer, with an additional electronic switch circuit. The tap changer consists of a transition resistor and a small number of thyristors to limit the arc in the tap switching process. It is realized through the cooperation of the electronic switch circuits and a mechanical switch. The technical advantage of the mechanical improved on-load voltage regulating switch is that it does not need to configure a time control loop, and the thyristor can be triggered by operating the mechanical switch; the disadvantage is that the structure is complex and the operation speed is slow.

(2) Type with an online oil filter device. The on-load pressure regulating switch with an online oil filtering device is an additional online oil filtering device on the basis of the traditional on-load pressure regulating switch. The online oil filtering device is composed of a control system, power system, filter element, pressure gauge, operation panel, etc. The power system is composed of an electric motor and an oil pump. The filter element is divided into dewatering filter element and impurity removing filter element, which is used to purify transformer oil and pressure gauge. To monitor the pressure in the filter tank, the filter element replacement prompt.

The control system controls the starter motor to drive the oil pump according to the record of the number of actions of the on-load voltage regulating switch and uses pressure to suck the transformer oil in the tap switch through the connecting pipe into the filter tank for filtering, and then inject the filtered oil into the on-load sub Connect the switch oil chamber. The advantage of this on-load voltage regulation technology is that it can realize online automatic oil filtering, reduce the impact of tap switching arc, and reduce maintenance costs. It is suitable for the on-load voltage regulation transformation of traditional distribution transformers; the disadvantage is that an additional set of the online filter is added. The oil device increases the investment cost and the maintenance workload of the device itself (such as replacing the filter element, etc.).

(3) Vacuum arc extinguishing type. Mechanical vacuum arc extinguishing on-load voltage regulating switch is different from traditional insulating oil arc extinguishing. The tap switching is completed in the vacuum tube, and there is no problem with oil degradation and pollution caused by the switching arc. The key to the realization of the mechanical vacuum arc extinguishing on-load voltage regulating switch is the selection of the vacuum switch and the design of the transition circuit. The performance level mainly depends on the switching parameters of the vacuum contact, including the rated current, rated voltage, and rated capacity.

Mechanical vacuum arc extinguishing on-load voltage regulating switch has a simple structure and reliable action. However, if there is a vacuum leak in the vacuum tube, the arc may not be extinguished or the vacuum electrical breakdown may occur under the action of overvoltage, resulting in an inter-stage short-circuit accident. If backup measures for safety protection are added, the number of transition resistors and vacuum tubes needs to be increased, which increases the cost.

2.2 Power electronic on-load voltage regulation technology

In recent years, power electronics technology has developed rapidly, and the performance of thyristor series products has been greatly improved. The non-impact and non-arc pure power electronic on-load voltage regulating switch has once become the research focus, mainly using the microprocessor to directly control the thyristor power electronic switch to realize the switching of the tap.

2.3 Compound on-load voltage regulation technology

The compound on-load voltage regulating switch is a kind of mechanical and power electronic hybrid voltage regulating technology that comprehensively utilizes the technical advantages of small mechanical switching loss and no arc and impact of power electronic switch switching.

The SCR-assisted commutation on-load voltage-regulating switch technology uses SCR to replace the transition resistance of the traditional on-load voltage-regulating switch in order to prevent arc generation, and the overall structure has not changed much. The thyristor-assisted commutation on-load voltage regulating switch is designed with 2 sets of thyristors. The synchronization requirements for the shutdown of these 2 sets of thyristors at the current zero-crossing point are very high, and no thyristor is allowed to appear Turn on in advance, otherwise, it will cause a short circuit in some coils of the transformer. Similarly, if one of the thyristors is turned on with a delay, the load current will be interrupted, so the high recovery voltage generated will damage the controllable silicon.

A combined tap changer is introduced, which is mainly composed of TADS type diverter switch and selector. The contact system of the diverter switch is composed of thyristor and mechanical contact. As the switching element of the diverter switch, the thyristor undertakes the arc contact function and is responsible for opening Switch off the current during the switching process.

Each phase switch of the combined tap changer adopts a thyristor, the mechanical contacts M1 and M2 are the main contacts, and the current flows through M1 or M2 in the non-switching state.

In the whole process of switch switching, because the mechanical contacts are separated without current, it will not cause contact burnout and oil pollution problems. Compared with traditional mechanical on-load tap-changers, there is no need during the lifetime Replace the contact, the workload of maintenance and repair will be greatly reduced. The combined tap changer is a typical mechanical and electronic hybrid structure, which is composed of mechanical contact and a thyristor, which can realize arc-free switching, but the operation and control of this type of combined switch are more complicated.

The above information is provided by the distribution transformer supplier.