With the increasing use of electrified locomotives, a large amount of harmonics and negative-sequence pollution will occur in the power grid. If it cannot be timely treated in a traction substation, it will be injected into the power grid to reduce the power quality, along with the development of urban railways and subways. This contradiction has become increasingly prominent. The precondition for improving the power quality is to carry out reasonable monitoring and detailed analysis of power quality under different operating conditions, and most of the domestic power supply stations do not have relevant analytical instruments and equipment. To solve this problem, according to the characteristics of our country's electrified railways, it is necessary to develop a portable, multi-functional, portable power quality detection and analysis device that is portable, powerful, and meets the railway work habits and requirements.
"Clean" opportunityAccording to the definition of power quality, we must first analyze and measure parameters such as frequency, reactive power, negative sequence current, and harmonics. At the beginning of the design, the traction power supply power quality analysis system performs a fixed period of time on the traction load harmonics, negative sequence, and voltage quality of the electrified railway passenger dedicated line AT, the direct supply substation, the AT, the subarea, and the opening and closing station. Statistical analysis of the maximum, minimum, average, 95% probability values.
Electrified railway passenger dedicated line AT, direct supply substation, AT, substation, opening and closing traction load harmonics, negative sequence test other test requirements determined by the nature of the load:
(1) The testing of the power supply system for passenger dedicated lines, especially during the joint debugging joint test, takes a long time, and often there are all power cuts including the electricity used in the middle. The test system needs to have a virtual instrument, namely, start and test, and threshold value. Stop, scheduled start and stop functions.
(2) The requirements for harmonics analysis and THD calculation to different harmonic orders determined by EMU performance, electric locomotive performance and SVC, suppression of resonance filter performance, etc., and whether to calculate even harmonic requirements.
(3) The power supply system of the passenger dedicated line test needs to calculate the correlative relationship (power, phase difference) between the current of each feeder and its associated voltage.
In terms of hardware, voltage and current need to meet certain standards. The sampling rate and accuracy of the system must be very high. ADLINK data acquisition card (PCI-9846), DVDI series transformers, and current clamp are used to select the FLUKEi200s AC current clamp.
Figure 1 overall design
The software portion of the system is written by the LabVIEW Development Platform. The power quality inspection system based on virtual instruments is divided into two parts: detection and analysis. The task of the monitoring part is to collect and convert the original voltage and current signals into digital signals, then display waveforms and spectrums, and store and output data files. The functional modules include data transmission module, data analysis module, graphic display module, and data file. The output module, etc.; analysis part is a systematic and in-depth analysis of the data file output from the monitoring part, and the statistical results and trend of the parameters of the power quality are obtained, and the power quality analysis report of the traction power supply system is printed according to need.
Measure effectAccording to the characteristics of the traction power supply system, LabVIEW software is used to design the traction power supply system parameter settings, station transformation ratio, real-time waveform data, real-time data analysis, historical data, historical data analysis, traction-side current and related calculation statistics Controls.
Using soft-phase-locked FFT harmonic detection and combined wavelet detection of harmonics, the measured data of electrified railway harmonics are analyzed. Harmonic data comes from a substation of Beijing-Guangzhou Line in Shijiazhuang Power Supply Section of Beijing Railway Bureau Substations and a transformer substation in Shide. The number of harmonics processed is 2~63 times, and the sampling frequency is 256 points/cycle. The time for recording data is 24 hours. The voltage and current data of the traction power supply system are based on the different types of vehicle loads and there are inorganic vehicle loads in the power supply section of the traction substation. The harmonic content also has its differences. This paper mainly aims at the different types of vehicle load brought to the traction power supply system. Harmonic analysis.
(1) Test of a Substation at Beijing-Guangzhou Line
The transformer substation adopts a 110/27.5kV impedance-matching balance transformer. The traction transformer adopts a three-phase Vv junction line, the 110kV side voltage transformer has a transformation ratio of 110kV/100V, the current transformer is 300/5A, and the traction side voltage transformer changes. The ratio is 27.5kV/100V, the current transformer ratio is 1000/5A, and the power supply section is powered by DC plus return current. The CRH series, SS series locomotives, and Harmony series freight locomotives are used for the models operating in this power supply section.
(2) Test of a substation at Shiteke
The transformer substation adopts a 110/27.5kV impedance matching balance transformer. The traction transformer adopts a three-phase Vv junction line, the 110kV side voltage transformer has a transformation ratio of 110kV/100V, the current transformer has a voltage of 400/5A, and the traction side voltage mutual inductance. The transformer ratio is 27.5kV/100V, the current transformer ratio is 1200/5A, and the power supply section is powered by DC plus return current. The traction substation only supplies power for this passenger dedicated line. The vehicle model is relatively single, mainly CRH. Series trains.
CRH series of the locomotive take the waveform shown in Figure 2:
Figure 2 CRH series take off waveform of this locomotive
CRH series of the locomotive taken after analysis of the harmonic content histogram shown in Figure 3. According to Fig. 3, the CRH series locomotive electric locomotive takes almost sinusoidal current, and the harmonic content of the current taken is mainly concentrated on the third harmonic.
Fig. 3 The histogram of the harmonic content of the CRH series taken from this type of locomotive
(3) Test of a Substation at Shide Line
The transformer substation adopts a 110/27.5kV impedance matching balance transformer. The traction transformer adopts a three-phase Vv junction line, the 110kV side voltage transformer has a transformation ratio of 110kV/100V, the current transformer has a voltage of 400/5A, and the traction side voltage mutual inductance. The transformer ratio is 27.5kV/100V, and the current transformer ratio is 600/5A, and the power supply section is powered by DC plus return current. The main locomotives operated in the power supply section of Yucheng Substation are mostly SS4 freight locomotives. More diesel locomotives are the mainstay.
SS takes the waveform of the locomotive as shown in Figure 4:
Figure 4SS Take-off waveform of this type of electric locomotive
The histogram of the harmonic content of this type locomotive taken from the SS is shown in Fig. 5. The currents taken by the SS electric locomotive are mainly distributed on the 3rd, 5th, 7th, 9th, and 11th orders. With the increase of the harmonic frequency, the harmonic content also decreases.
Figure 5SS Harmonic content histogram of this type of locomotive
It is easy to see that for the characteristics of traction power supply on the serious pollution of the power grid, the traction power supply power quality detection system designed can detect such parameters as frequency, negative sequence current, reactive power, and harmonics. The hardware data card uses ADLINK high-speed data acquisition card to ensure the speed and accuracy of data acquisition. At present, the detection system has been applied to a number of passenger dedicated lines with stable and reliable performance.
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