Power Quality Methods - Harmonics and Interharmonics

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Power Quality Methods - Harmonics and Interharmonics

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power quality methods GB/T 17626.30

Harmonics of power quality parameters

8 Voltage harmonics

GB/T 14549-1993 "Power Quality Public Grid Harmonics"

4 Harmonic voltage values (Table 1)

5 Allowable values of harmonic current (Table 2)

Please refer to Appendix D for the method of measuring harmonics and the regulations on measuring instruments for data processors.

condition

D1.1 Harmonic voltage (or current) measurement should be carried out in the smallest operating mode that may occur when the power grid is normally powered, and should be carried out during a period when the amount of harmonics generated in the working cycle of the harmonic source is large (for example: arc steelmaking The furnace should be measured during the melting period).

D1.2 When a capacitor bank is installed near the measurement point, measurements should be made in various operating modes of the capacitor bank.

scope

The harmonic order measured by D2 is generally from the 2nd to the 19th order. According to the characteristics of the harmonic source or the test analysis results, the range of the harmonic order measurement can be appropriately changed.

D3.1 For harmonic sources with rapid load changes (such as steelmaking electric arc furnaces, rolling mills powered by thyristor converter equipment, electric locomotives, etc.), the measurement interval should not exceed 2 minutes, and the number of measurements should meet the requirements of mathematical statistics. Generally No less than 30 times.

D3.2 For harmonic sources with slow load changes (such as chemical rectifiers, DC transmission converter stations, etc.), the measurement interval and duration are not specified.

Data value

D4.1 The harmonic measurement data should be taken as the largest phase value among the 95% probability values of the actual measured values of each phase during the measurement period, as a basis for judging whether the harmonics exceed Basis for allowed values.

D4.2 However, for harmonic sources with slow load changes, five close actual measured values can be selected and their arithmetic mean value should be taken.

Harmonic measuring instruments

D5.1 The functions of the instrument should meet the measurement requirements of this standard.

D5.2 In order to distinguish transient phenomena and harmonics, for harmonics with rapid load changes, each measurement result can be the average value of the measured values within 3 seconds.

D5.3 Instrument accuracy The allowable error of the harmonic measuring instrument is shown in Table D1.

D5.4 The instrument has a certain ability to resist electromagnetic interference and is easy to use on site. The instrument should ensure that its power supply can operate normally under the condition that the nominal voltage is ±15%, the frequency is in the range of 49 to 51Hz, and the total harmonic distortion rate of the voltage does not exceed 8%.

D7 Within the frequency range of measurement, harmonic sensing equipment such as instrument transformers and capacitive voltage dividers should have good frequency characteristics. The amplitude error introduced by them should not be greater than 5%, and the phase angle error should not be greater than 5°. . In the absence of exact frequency response error characteristics, current transformers and low-voltage voltage transformers are used for harmonic measurement at frequencies of 2500Hz and below; 6-110kV electromagnetic voltage transformers can be used for frequency measurements at 1000Hz and below; capacitive voltage transformers cannot Used for harmonic measurements. In harmonic voltage measurement, when there is a higher need for harmonic order or measurement accuracy, a resistive voltage divider (UN<1kV= or a capacitive voltage divider (UN≥1kV) should be used.

9 Harmonics between voltages

GB/T 24437-2009 "Power Quality Harmonics between Public Grids"

4 limits

4.1 The harmonic voltage content rate between each order at the public connection point (PCC) of the power system of 220kV and below should not be greater than the limit value in Table 1;

4.2 The content rate of each inter-harmonic voltage caused by a single user connected to the PCC shall generally not exceed the limit in Table 2.

4.3 On the same node, the interharmonic voltages of multiple interharmonic sources of the same order can be synthesized.

5 Measurement values and measurement conditions

5.2 The frequency resolution of interharmonic measurement is 5Hz, and the measurement sampling window width is 10 power frequency cycles.

5.3 Method for determining the value of interharmonics

5.4 The measurement of interharmonics can be based on the 3s measurement results, and the measurement values of 3min, 10min, or 2 hours can be synthesized.

5.5 Evaluation and measurement of inter-harmonics requires measurement in the minimum mode of normal operation of the system and the maximum occurrence of inter-harmonics; when the system conditions do not meet the requirements (greater than the normal minimum mode), the results can be converted according to the short-circuit capacity (to be measured) The result is multiplied by the ratio of the actual short-circuit capacity and the minimum short-circuit capacity).

5.6 The evaluation time period for interharmonics is generally at least 24 hours, and the larger one-phase value among the 95% probability of the three-phase comprehensive value within the evaluation time period is used as the basis for evaluation.

6 Measuring instrument accuracy

The requirements are shown in Table 3