Problems:
In the distributed photovoltaic system, the self-owned photovoltaic system is generally adopted, and the surplus is used for access to the Internet. State regulations, 220V system, maximum access to 8KW, 380V system, maximum access to 400KW, 10KV system, maximum access to 6MW; there is a condition The maximum capacity of photovoltaic shall not exceed 25% of the capacity of the transformer at the previous stage. In distributed photovoltaic power plants, most of the photovoltaic power generation is consumed on the low-voltage side. However, on holiday, the factory's holiday can not be consumed by itself. This part of the photovoltaic power generation can pass the power step-down transformer and in turn use the boost pressure. , through this transformer to 10KV grid system. This problem is a common concern of many owners, design institutes, and power supply companies. Since there is no precedent, everyone's views are not the same. The following is based on the principle of transformers and practical applications, with reference to opinions of several domestic transformer R&D personnel. A survey is for your reference. My purpose is to initiate a project and I hope to get the opinions of a real expert.
1, do not agree with the argument
The principle of step-up transformers and step-down transformers cannot be reversed. Because the step-up transformer is equivalent to raising the low voltage to high voltage, then for the system, the low voltage side is equal to absorbing energy equivalent to the load, the high voltage side sending energy is equivalent to the power supply, and the system load receives the standard rated voltage. The output voltage of the power supply side takes into consideration the voltage drop of the line and the transformer itself by about 10%. To ensure that the voltage delivered to the user is exactly the rated voltage, the voltage output from the high voltage side is equal to a voltage 10% higher than the rated voltage.
For example, if a step-down transformer has a rated voltage of 380V and a high-voltage capacitor has a rated voltage of 10KV, the rated voltage at the low-voltage side is 380V. The voltage delivered from the high-voltage side cannot be a rated voltage, and should be higher than the rated voltage. 10% higher is 11KV. If you consider the ratio, the low-voltage side is 380 turns (for example), the high-voltage side cannot be 10,000 turns and must be 11,000 turns. If this step-down transformer is used as a step-up transformer, the voltage on the low-voltage side will rise to 420V, and the voltage on the high-voltage side will reach 10KV. However, if the voltage on the low-voltage side increases, the operating equipment will be damaged.
In addition, structurally speaking, step-down transformers have low-voltage windings on the inside and high-voltage windings on the outside, and tap-changers are all mounted on the high-voltage windings. This not only facilitates the tapping of the taps, but also because the high-voltage windings have small currents and the lines are thin. Taps. Step-down transformer to adjust the high-voltage side tap can adjust the low-voltage side voltage. As a step-up transformer, the tap-changer should be connected to the low-voltage side to meet the voltage regulation requirements, and the current of the low-voltage winding is large, the conductor cross-section is also large, and the danger of switching is obviously increased.
In addition, the step-down transformer generally uses the delta connection in order to suppress the effect of the third harmonic on the voltage waveform, and usually only has a small amount of station load and some reactive power compensation equipment, especially a three-winding transformer. Generally, the low-voltage side has a smaller capacity. , it is difficult to work as a step-up transformer.
In order to limit the short-circuit fault current and the low-voltage side bus recovery voltage, the boosted short-circuit impedance used in the power plant is also different from the general step-down transformer.
The three-phase change of the core structure must consider the power transmission and the coupling problem between the transformer windings. Generally, the order of the windings of the transformer outward from the core is: low, medium, and high; and the order of the boost voltage change is : Medium, low, high.
2, agree with the argument
According to the relationship between the magnitude of primary and secondary voltages, transformers can be divided into: step-down transformers and step-up transformers. A primary voltage higher than the secondary voltage is called a step-down transformer, and the primary voltage is lower than the secondary voltage, which is called a step-up transformer. With the same frequency and the same capacity, a power transformer can be used as a step-down transformer, reversed, or used as a step-up transformer.
The basic principle of the transformer is: electromagnetic induction. Simply put, electromagnetic induction means that electric energy is converted into magnetic energy, and magnetic energy is converted into electric energy. This is consistent with the law of energy conversion and conservation.
The following is the basic physical model of the transformer:
In the above figure, the physical entity running I1 is the primary winding, and the physical entity running I2 is the secondary winding, which is the circuit part of the transformer; Φ is the magnetic field line, and the physical entity in which it is located is the core, which is the magnetic circuit of the transformer.
When the transformer's capacity P (kVA) and the number of turns of the winding W are constant, the magnetic flux Φ in the core (Webb (wb) is set, and a power transformer is used either as a step-down transformer or as a step-up transformer. There is no change in the physical and physical meaning of the road entity.
The transformer is a static appliance that changes the voltage according to the needs of life, and its voltage ratio is equal to the turns ratio. In the figure above: U1/U2=W1/W2. W1: number of turns of primary winding, W2: number of turns of secondary winding, W1 and W2 of a power transformer are unchanged (except that the constant voltage has to be changed by the number of turns on one side), so in addition to the factor of the voltage fluctuation of the power grid The voltages U1 and U2 are also unchanged. If the original secondary winding W2 is used as the primary winding W1, the original primary winding W1 is changed to the current secondary winding W2. The above formula U1/U2=W1/W2 is the inverse of U2/U1. =W2/W1 is still fully established.
From the above physical model of the power transformer to the theoretical derivation, it is concluded that one power can be used as a step-down transformer at the same frequency and with the same capacity, reversed, or used as a step-up transformer.
From the practical operation experience of a professional transformer manufacturer, it can be concluded that the step-up transformer and the step-down transformer have no difference in design, process, manufacture, test, etc., so we can draw from practice: the same frequency and the same capacity Under conditions, one power can be used as a step-down transformer, reversed, or used as a step-up transformer.
3, the conclusion:
In theory, the transformer does not divide the flow of power. Normally, it transfers electric energy from high pressure to low pressure. When it is abnormal, it can of course transfer electric energy from low pressure to high pressure. The PV inverter has a wide output voltage range and can be adjusted from 360 to 440V. Therefore, the step-down transformer can be used for boosting and transforming. However, depending on the actual application, some adjustments and measures must be taken to prevent reverse flow from occurring.
1, the original step-down transformer voltage drop is not very large, generally (10/0.4KV) oil becomes less than 5%, dry change is below 6.5%, 35/10KV main transformer is within 8%.
2. Inverter and step-down transformer should be put together as much as possible to reduce line loss.
3. If it is a newly installed transformer, one more tap can be designed on the high-voltage side or the low-voltage side. When the current surge changes, it automatically switches.
4. Install an anti-backflow controller to reduce the inverter output power when detecting current flow to the grid.
It's 100% waterproof,fire proof and mould proof,also very easy to install .
SPC Wall Panel is abbreviation of Stone Plastic Composite, a kind of rigid material with a density at around 2kg/m3,We can apply many diferent design on the finish,such as wood and stone.
SPC WALLPANEL can be use in both commercial and residential area,which can enhancing the interior decoration .
Spc Wall Panel,Cement Wall Panel,Foam Cement Wall Panel,Waterproof Cement Wall Panel
CHANGZHOU ART DECORATION MATERIALS CO.,LTD , https://www.cnartdecor.com