1, national standard:

The national standard of China's power grid harmonics is GBT- 14549-93 "Power Quality Public Power Grid Harmonics", which stipulates the limits of power grid voltage distortion rate and point of common coupling (PCC) harmonic current.

2. Harmonic test data:

Because of the flow and fluctuation characteristics of harmonics, generally speaking, only simple estimation can be made. If it is necessary to design a harmonic control scheme, the most reliable one should be the harmonic test data. This situation is suitable for power grids where existing equipment is put into operation or capacity needs to be increased. Of course, in order to test the reliability and accuracy of the data, it is necessary to be familiar with the working principle and technology of harmonic sources, understand the power grid structure, and adopt a reliable harmonic tester and accurate testing methods according to the requirements of Appendix D of the standard "Harmonic of Power Quality Public Power Grid" (GBT- 14549-93).

3. System capacity:

The larger the capacity of the power supply system, that is, the smaller the equivalent admittance of the system, the lower the harmonic voltage level of the bus. Therefore, improving the capacity of power supply system is one of the important measures to suppress the influence of harmonics.

Because the filtering device is always connected to the system, the influence of system impedance on filtering effect must be considered. In this case, the filtering effect is determined by the comprehensive impedance of the filtering device and the system, and the system situation must be considered when selecting the parameters of the filtering device. In principle, the impedance of the system should be measured, and sometimes the equivalent impedance can be approximately calculated according to the short-circuit capacity of the power supply system or the relevant parameters of the network. This method is generally used for the preliminary selection of parameters of 6~ 10kV medium and small filter devices.

4, harmonic source capacity:

The capacity of harmonic source affects the harmonic control scheme. For large-capacity harmonic sources, local treatment is more economical and reasonable. For small-capacity dispersed harmonic sources, the frequency and content of harmonics change irregularly because of large harmonic variation and many random factors. Beijing suggests to adopt active dynamic harmonic filtering CAPF for centralized control.

5. Characteristic harmonic conditions of harmonic source:

The introduction of characteristic harmonics of the above typical harmonic sources is an important basis for harmonic analysis and harmonic source estimation. It is necessary to analyze the working principle and process requirements of various harmonic source equipment and the working conditions of other harmonic source equipment, and roughly calculate the main subharmonics and harmonics generated, which is an important source of the design basis of harmonic filter device and even an important reference for analysis of measured data.

6. Natural power factor of power grid:

There are harmonics in the power grid, which will also produce a kind of reactive power. For the fundamental wave, the reactive power factor is the COS value. For the power grid with harmonics, there are both fundamental reactive power and harmonic reactive power, and this value is the PF value, which is also the actual displayed value (due to the different working principles of measuring instruments, there will be great deviation). Here, COS value is an important basis for the design of harmonic control scheme. Especially for passive filters, fundamental reactive compensation power is needed as the basis of LC circuit design parameters, and there can be no over-compensation.

7, harmonic source generation process:

The generation process or working condition of harmonic source is an important basis for harmonic analysis of the system. For a large number of harmonic source installation equipment, multiple harmonic source equipment can be operated at the same time, some of which are operated regularly and periodically, which is an important basis for the design of harmonic control scheme. The generation process of harmonic source is that the customer's information determines the difference between the actual operating harmonic amount and the estimated harmonic amount, so that the design of harmonic control scheme can achieve a reasonable and economical goal.

8, harmonic source installation location:

Refers to the relationship between various devices in the distribution network, such as the position relationship between harmonic source and non-harmonic source equipment in the power grid structure. The harmonic source is designed as close as possible to the power supply side, which can reduce the influence of harmonic voltage caused by harmonic impedance on other electrical equipment and increase the system capacity of harmonic source. Non-harmonic source equipment should not share a bus with harmonic source as far as possible, and special lines can be set up to supply power to harmonic source equipment if conditions permit.

9, the degree of mutual influence between equipment:

Some users here have high requirements for the power quality of the power grid, such as precision machining and electronic welding. If there is a large-capacity harmonic source in the user power grid, it will inevitably have an adverse impact on its normal production. For this kind of users, even if the harmonic content does not exceed the national standard after calculation, it is necessary to carry out harmonic control.