With the continuous expansion of the scale of urban rail transit construction in China, the impact of urban rail transit on the power quality of urban power grid has become increasingly apparent. Researchers and institutions in the industry focus on the following:
The test analysis and comprehensive evaluation method of power quality of urban rail transit, the influence of the operation mode of power supply and distribution system on power quality, the power quality problems existing in the actual operation system and their solutions. Design institutes, urban rail transit owners and power quality control device manufacturers focus on the charging power of 35kV power supply cables for urban rail transit users, which can easily cause capacitive reactive power reversal, and may also lead to serious harmonic amplification, affecting the safe and reliable operation of urban rail power supply and distribution system.
Common power quality problems.
The following diagram is a schematic diagram of various loads in the power supply and distribution system of a rail transit.
35kV under normal and fault operating conditions of power supply cables in 110kV and 35kV systems.
Harmonic problems caused by traction station negative 35kV traction station under normal and fault operating conditions.
Capacitive reactive power reversal caused by 110KV power factor caused by reactive power.
110KV power factor problem caused by load reactive power of 35kV traction station under normal and fault operating conditions.
Harmonic amplification caused by 110kV and 35kV power supply cables under normal and fault operating conditions.
The problem of High failure rate of Shunt Capacitor reactive Power compensation device.
Harmonic and reactive power problems of frequency conversion equipment such as air conditioners, escalators, fans and so on.
The problem of Harmonic and reactive Power produced by switching Power supply of computer equipment.
Harmonic and reactive Power problems of nonlinear Lighting equipment.
Harmonic and reactive Power of UPS Power supply.
Means of power quality monitoring.
In July 2016, the handheld PQ6300 power quality analyzer independently developed by Guangzhou Xuantong Electric was used to monitor the 11th harmonic voltage of a rail transit during the peak period of power consumption. The maximum value of 11th harmonic current content of 35kV in traction station is 4.26A, and that of 110kV in main substation and 35kV outlet are 19.48A and 62.98A, respectively.
According to the investigation, there are at most six traction stations in the 35kV I section of the main substation. Assuming that the maximum harmonic generation occurs synchronously, the 11th harmonic current generated by the six rectifiers does not exceed 4.26x6mm 25.56A, and the 11th harmonic current of the 35kV outlet of the main substation is all generated by the traction station rectifier and flows into the system. The 11th harmonic current injected into the input line of the 35kV I section of the main substation is magnified by 2.5 times (the maximum simultaneous rate is not taken into account). The actual magnification is much greater than 2.5).
Figure 1: harmonic voltage coefficient of 35kV distribution network at peak power consumption of a metro branch line
Figure 2: harmonic amplification solution