How to choose a grounding transformer.

The function of the grounding transformer is to provide an artificial neutral point for the system with no neutral point, which is convenient for the use of arc suppression coil or small resistance grounding mode, so as to reduce the size of the capacitance current to the ground when the grounding short-circuit fault occurs in the distribution network, and improve the power supply reliability of the distribution system.

The grounding transformer is referred to as the grounding transformer, and according to the filling medium, the grounding transformer can be divided into oil type and dry type; According to the number of phases, the grounding variable can be divided into three-phase grounding transformer and single-phase grounding transformer. China's grounding transformer usually adopts Z-type wiring (or zigzag wiring), in order to save investment and substation space, usually add a third winding on the grounding transformer to replace the transformer used, and supply power to the equipment used in the substation.

Working characteristics of grounding transformer:

1. The zero-sequence impedance is low to ensure the output of the zero-sequence current;

2. High excitation impedance to reduce no-load current;

3. Low no-load loss to save energy consumption for daily operation.

The above content refers to Encyclopedia - Grounding Transformer.

It provides an artificial neutral point for the system with no grounding at the neutral point, which is convenient for the grounding mode of arc suppression coil or small resistance, so as to reduce the capacitance current to the ground when the grounding short circuit fault occurs in the distribution network, and improve the power supply reliability of the distribution system.

Foreign grounding transformers usually adopt or Z-type connection, used for 10kV non-grounding system, constituting the grounding protection of the distribution network, when the system grounding fault occurs, the grounding transformer presents high impedance to the positive sequence and negative sequence current, and low impedance to the zero sequence current, so that the grounding protection operates reliably.

Background of the use of grounding transformers

In the 6kV, 10kV and 35kV power grids in the power system, the neutral point is generally not grounded. The low-voltage side of the main transformer in the power grid is generally triangular and there is no neutral point that can be grounded.

When a single-phase grounding fault occurs in the neutral point non-grounding system, the line voltage triangle is still symmetrical, and the power system can continue to supply power to the user for 1 to 2 hours, and the capacitance current is relatively small (less than 10A), which will not cause intermittent arcing, and some instantaneous grounding faults can disappear by themselves, which is very effective in improving the reliability of power supply and reducing power outages.

However, with the continuous expansion of the urban power grid and the continuous increase of cable outlets, the capacitance current of the system to the ground increases sharply, and the capacitance current flowing through the fault point after single-phase grounding is large (more than 10A). The arc is not easy to extinguish, easy to excite ferromagnetic resonance overvoltage and produce interstitial arc grounding overvoltage, which may lead to insulation damage, line tripping, and accident expansion.

The above content refers to Encyclopedia - Grounding Transformer.

The main function of the grounding transformer: it is used to connect the grounding resistance. When the system has a grounding fault, it has high impedance to the positive sequence and negative sequence currents, and low impedance to the zero sequence currents, so that the grounding protection can operate reliably.

The grounding transformer is referred to as the grounding transformer, and according to the filling medium, the grounding transformer can be divided into oil type and dry type; According to the number of phases, the earthing transformer can be divided into three-phase grounding transformer and single-phase grounding transformer.

Three-phase grounding transformer: The role of the grounding transformer is in the system When the neutral point of type wiring or Y-type wiring can not be drawn, the neutral point is used to add an arc suppression coil or resistance, this kind of transformer adopts Z-type wiring (or zigzag wiring), the difference with ordinary transformer is that each phase coil is divided into two groups and is reversed on the phase magnetic pillar respectively, the advantage of such connection is that the zero sequence magnetic flux can flow along the magnetic column, and the zero sequence magnetic flux of the ordinary transformer is circulated along the leakage magnetic circuit, so the zero sequence impedance of the Z-type grounding transformer is very small (about 10), and the ordinary transformer is much larger. According to the regulations, when an ordinary transformer with an arc suppression coil is used, its capacity shall not exceed 20% of the transformer capacity.

The Z-type transformer can be equipped with an arc suppression coil of 90% 100% capacity, and the grounding transformer can be equipped with an arc suppression coil in addition to a secondary load, which can replace the transformer used, thereby saving investment costs.

Single-phase grounding transformer: Single-phase grounding transformer is mainly used for neutral grounding resistance cabinets of generators and transformers with neutral points, so as to reduce the cost and volume of resistance cabinets.

For the medium voltage system of 3-35kV, most of the neutral point non-grounding operation mode is adopted in China to improve the reliability of power supplyHowever, with the increase of the system (the increase of transformer capacity and outgoing wire), when single-phase grounding occurs, the grounding capacitor current will be very large, which may cause "arc grounding overvoltage", damage equipment insulation, and cause equipment damage accidents.

However, most of the secondary coils of the step-down transformers that form the medium-voltage system in China are angle-shaped wiring, and there is no neutral point, so that there is no way to install the arc suppression coilSo people designed the "grounding transformer", the grounding transformer is a "star" wiring transformer, through this star-wiring transformer, man-made a "neutral point", so that the arc suppression coil can be connected to this artificial neutral point, to solve the problem that the medium voltage system has no neutral point.

Therefore, the grounding transformer is a transformer with a primary coil for star wiring and a neutral point for the installation of an arc suppression coil.

The core and other accessories of the transformer are in the electric field around the winding, if not grounded, the core and other accessories will inevitably induce a certain voltage, under the action of the applied voltage, when the induced voltage exceeds the discharge voltage to the ground, the discharge phenomenon will be generated. In order to avoid the internal discharge of the transformer, the iron core should be grounded.

The main reason for grounding is to prevent static electricity on electrical appliances.

Grounding is divided into working grounding and protective grounding.

Working Grounding: Grounding to bring the equipment up to operational requirements.

Protective grounding: Grounding to prevent the metal shell of the operating electrical equipment, the frame of the power distribution device, and the line tower, etc., from being electrified and endangering the safety of people and equipment.

It belongs to working grounding. To prevent overvoltages and certain operating overvoltages that occur when single-phase is grounded.

It is the working grounding, and at the same time, the transformer can provide two voltages (line voltage, phase voltage), as well as the role of balancing the three-phase voltage and stabilizing the neutral point potential.

It is agreed that the upstairs works grounding, and the motor housing is protected grounding.

1. The function of the grounding transformer is to provide a neutral point for the system where the neutral point is not grounded, which is convenient for the use of arc suppression coil or small resistance grounding mode, so as to reduce the size of the ground capacitance current when the grounding short circuit fault occurs in the distribution network, and improve the power supply readability and pure reliability of the distribution system.

2. The grounding transformer is referred to as the grounding transformer, and the grounding transformer can be divided into oil type and dry type according to the filling medium; According to the number of phases, the grounding variable can be divided into three-phase grounding transformer and single-phase grounding transformer.

The function of the grounding transformer is to provide an artificial neutral point for the system with no neutral point, which is convenient for the use of arc suppression coil or small resistance grounding mode, so as to reduce the size of the capacitance current to the ground when the grounding short-circuit fault occurs in the distribution network, and improve the power supply reliability of the distribution system.

Grounding transformers are primarily used to provide an artificially grounded neutral point to a system on the side without a neutral point. It can be grounded through a resistor or arc suppression coil to meet the needs of grounding on this side of the system, and can be used as a station transformer when there is an additional YN wiring winding.

The grounding transformer is connected to the three-phase of the system bus, and the rated primary voltage should be consistent with the rated voltage of the system, and the matching with the rated voltage of the primary system and the matching of the load capacity should be considered. Its rated capacity should match the arc suppression coil or ground resistance capacity, and the secondary load capacity should also be considered if it has a secondary winding.

The function of the grounding transformer is to connect the arc suppression coil when the neutral point of the system is type wiring or the type Y wiring cannot be drawn out.

Principle: The grounding transformer adopts Z-type wiring, and the difference between the ordinary transformer is that each phase coil is wound on two magnetic columns, so the advantage of this connection is that the zero-sequence magnetic flux can flow along the magnetic column, and the zero-sequence magnetic flux of the ordinary transformer flows along the leakage magnetic circuit, so the zero-sequence impedance of the Z-type grounding transformer is very small 10, while the ordinary transformer is much larger.

The intermittent extinguishing and re-ignition of the single-phase grounding arc will produce arc grounding overvoltage, the amplitude of which can reach 4U (U is the peak value of normal phase voltage) or higher, and the duration is long, which will cause great harm to the insulation of electrical equipment and form breakdown in the weak part of the insulation; Causing significant losses.

Due to the dissociation of air caused by continuous arcing, the insulation of the surrounding air is destroyed, and interphase short circuits are prone to occur.

What is the function of a grounding transformer? What about station changes?

The grounding transformer is to provide an artificial neutral point for the power system that is not grounded at the neutral point, and then it is grounded through an arc suppression coil to form the grounding protection of the power system together with the arc suppression coil. Prevent the intermittent arc at the grounding point from causing overvoltage to the system and amplifying the accident when the system is single-phase grounding fault. The station transformer refers to the step-down transformer that provides low-voltage power and lighting for the substation.

The station can sometimes be used to take into account the grounding change.