CN201820605U - Decentralized Compensation Capacitor Current Transformer for Medium Voltage System - Google Patents

Abstract

The utility model relates to a disperse-compensation capacitance-current transformer for a medium voltage system, belonging to the technical field of ungrounded neutral point power supply system and ground capacitance and current compensation. The transformer comprises a flexural winding transformer, a fixed grounding inductor and a magnetic isolation plate, wherein the magnetic isolation plate is arranged between the flexural winding transformer and the fixed grounding inductor; primary windings of the flexural winding transformer are characterized in that each phase of winding is divided into an upper section and a lower section; each section of winding has the same turns; one phase of the upper winding section and the other phase of the lower winding section of winding are reversely connected in series to form one group, wherein the upper sections of winding A, B and C are led out and used as the high-voltage three-phase line out end of the transformer; and the lower sections of winding are connected with one another and used as neutral N which is led out and connected with a fixed grounding resistor X. the disperse-compensation capacitance-current transformer has the benefits of being simple to install, needing no debugging, being flexible for use, being maintenance-free, being capable of compensating the ground capacitance current in real time, and improving the power supply reliability of a power gird radically.

Description

Decentralized Compensation Capacitor Current Transformer for Medium Voltage System

technical field

The utility model belongs to the technical field of a neutral point ungrounded power supply system and compensation for ground capacitance current.

Background technique

In the neutral point ungrounded power supply system, when the capacitance current of the system to the ground increases, once the single-phase of the line is grounded, the arc will not be able to stop the arc itself, and the overvoltage generated by the arc re-ignition will endanger the insulation of the sound phase and cause a two-phase short circuit Faults, for single-phase grounding faults, it is not uncommon to cause distribution network accidents, causing insulation breakdown, bushing burst, two-phase short circuit, and even causing the switchgear of the substation to be "fired"; for this reason, the existing neutral point is not Grounded power supply systems usually use arc suppression coils to ground at the neutral point, and compensate the ground capacitance current through the arc suppression coil inductance current to limit the ground capacitance current of the power grid. Regulation DL 620-1997 "Overvoltage Protection of AC Electrical Installations" "Coordination with Insulation" stipulates in detail the limitation of the ground capacitance current of the power grid: "For 3kV ~ 10kV systems that are not directly connected to generators and 35kV and 66kV systems, when the single-phase ground fault capacitance current does not exceed the following values, no Grounding method; when it exceeds the following values and needs to operate under ground fault conditions, the arc suppression coil grounding method should be used: 3kV ~ 10kV reinforced concrete or metal tower overhead line system and all 35kV, 66kV systems, 10A", other The purpose is to ensure the stable and safe operation of the system and meet the needs of power supply reliability.

In recent years, the neutral point ungrounded power grid system, especially the 10-66kV power grid, has developed rapidly. The capacitive current exceeds the compensation capacity of the arc-suppression coil, so that many arc-suppression coils put into operation in the power grid are under-compensated for a long time. hidden dangers; the method of continuously adjusting the compensation capacity and compensation range of the arc suppression coil in the substation has been unable to adapt to the development of the power grid, and new methods and methods are needed to try to break through the traditional compensation capacitor current mode and solve the lag of the compensation capacity of the arc suppression coil in the substation design. Due to the increase of the system capacitor current, it eliminates the potential safety hazards of the power grid operation.

At present, many enterprises and scientific research institutions at home and abroad have conducted research on decentralized compensation capacitor current transformers, and there are similar results. : 99235580.X, name: dry-type grounding transformer with arc suppression coil"; "application number: 200520071473.7, name: zero-sequence short circuit high impedance grounding transformer type arc suppression coil" and its structural characteristics are: arc suppression coil and grounding transformer, Installed together on a three-core five-column conjugate core or a four-column core together, these inventions have the disadvantages that they are mainly used in substations for centralized compensation of system-to-ground capacitance currents, and in addition, the electromagnetic interaction between arc suppression coils and grounding transformers Influence, once there is a problem with the arc suppression coil, it will directly affect the normal operation of the transformer, the system operation mode changes, and when it needs to be out of operation, the secondary power supply will not be guaranteed.

Contents of the invention

The utility model provides a decentralized compensation capacitor current transformer for a medium voltage system to solve the problem of increasing the capacity of the arc suppressing coil of the neutral point ungrounded power supply system of the medium voltage power supply system and the problem of low power supply reliability of the neutral point ungrounded power grid , the technical solution adopted by the utility model is: including a meander winding transformer, a fixed grounding inductor and a magnetic isolation plate; the magnetic isolation plate is located between the meander winding transformer and the fixed grounding inductor, and the primary winding of the meander winding transformer is each phase winding Divided into upper and lower sections, each section has the same number of winding turns, and the upper section winding of one phase is connected in series with the lower section winding of the other phase to form a phase, in which the upper section winding A, B, C lead out as a high-voltage three-phase transformer. The phase outlet terminal and the lower winding are connected as the neutral point N to be connected to the fixed grounding reactance X.

The utility model is a three-phase transformer which has the function of compensating a certain capacitance current to the ground and has power supply capability. It can be seen from the flow direction of the zero-sequence current that because the coil winding method of the upper and lower sections is reversed, when there is a zero-sequence When the currents pass through equally, they cancel each other so that the zero-sequence magnetic potential of the core column is approximately zero, so the zero-sequence reactance of the winding is also approximately zero. When the neutral point is connected to a fixed grounding inductance, a single-phase ground fault occurs in the grid , the zero-sequence current will flow smoothly, and the inductive current of the fixed grounding inductance coil can directly compensate the ground-to-ground capacitance current of the grid, thereby reducing the grounding current at the fault point, reducing the generation and development of arcs, and preventing arcing grounding voltage.

Due to the magnetic isolation board, it ensures that the meander winding transformer and the fixed grounding inductance are relatively independent, and the electromagnetism does not affect each other. Once there is a problem with the compensation inductance, it will not affect the normal operation of the transformer. When the system operation mode changes, disconnect X and N as needed. Connect to take the compensation inductance out of operation.

For the current transformer with distributed compensation to ground capacitance, because the grid maintains three-phase symmetrical line voltage, the primary side obtains positive sequence electromotive force from the power supply, and the positive sequence current generates positive sequence magnetic flux and positive sequence electromotive force, and the magnetic flux also induces positive sequence in the secondary winding Electromotive force, so the secondary side can supply power for low-voltage users. Since there is a winding transformer with a magnetic isolation plate and the fixed grounding inductance is relatively independent, the input and withdrawal of the fixed grounding inductance will not affect the power supply for low-voltage users on the secondary side.

The utility model overcomes the deficiencies of the prior art, combines the compensation inductance and the grounding transformer into one, and at the same time separates them internally through a magnetic isolation plate to ensure that they are relatively independent, and the electromagnetics do not affect each other, and the compensation inductance does not affect the existing problems. The normal operation of the transformer, the change of the system operation mode, the compensation inductance can be taken out of operation according to the need, and the reliability of the secondary power supply is guaranteed. Beneficial effects: simple installation, no need for debugging, less investment, small footprint, flexible use, and maintenance-free; line commissioning and withdrawal The distributed compensation capacitor current transformer installed on the line is put into and out accordingly, and the compensation inductance can also be used according to the system The operation needs to exit the operation directly, realize the change of the power grid, and the compensation will change accordingly. The operation is simple, and the capacitance current to the ground is compensated in real time, which fundamentally improves the power supply reliability of the power grid.

Description of drawings

Fig. 1 is the structural representation of the utility model.

Detailed ways

It includes a meandering winding transformer 1, a fixed grounding inductor 2 and a magnetic isolation plate 3; the magnetic isolation plate is located between the meandering winding transformer and the fixed grounding inductor, and the primary winding of the meandering winding transformer 1 is divided into upper and lower windings for each phase. The winding turns of each section are equal, and the upper winding of one phase and the lower winding of the other phase are anti-series to form a phase, in which the upper winding A, B, and C lead out as the high-voltage three-phase outlet of the transformer, and the lower winding Connect them as neutral point N to lead out and connect with fixed grounding reactance X.

Claims (1)

1. A medium-voltage system decentralized compensation capacitor current transformer is characterized in that: it comprises a meandering winding transformer, a fixed grounding inductor and a magnetic isolation plate; the magnetic isolation plate is located between the meandering winding transformer and the fixed grounding inductor, and the meandering winding transformer The primary winding is divided into upper and lower sections for each phase winding, and the number of turns of each section is equal. The upper winding of one phase and the lower winding of the other phase are anti-series to form a phase, of which the upper windings A, B, The C lead is used as the high-voltage three-phase outlet of the transformer, and the lower winding is connected as the neutral point. The N lead is connected to the fixed grounding reactance X.

Images