The 110 kV system wiring is characterized by radial, with 220 kV substation as the power point, and radiated to the terminal substations through the 110 kV line. The 110kV terminal substation uses internal bridge wiring or line-inverter group wiring, and there is no power supply on the low voltage side.
In the inner bridge wiring substation, in the normal operation mode, the 100 female branch switch is not used as the contact element of the 103 and 104 lines. Therefore, the internal bridge wiring substation usually only has two modes of operation: one line with two main transformers or two lines with one transformer. In the 1 line with 2 variable operation mode, it is only necessary to have one neutral point grounded for the two main transformers, but it must be grounded by the neutral point of the transformer on the 110kV power supply line side. This is very important. The current transformer zero sequence protection configuration of the inner bridge wiring substation is: neutral point zero sequence current protection first time limit jump 100 and 900 mother points; second time limit jumper transformer; at the same time, the transformer neutral point is equipped with rod gap, but there is no Configure the gap TA and open delta voltage protection.
In order to save investment, land occupation, and save 110kV line air corridor, etc., the newly constructed 110kV substation uses line-transformer group wiring, and one line can be connected with 2 or even 3 transformers with "T". Neutral point zero-sequence overcurrent protection, no neutral point gap current protection and 110kV TV open triangle zero-sequence voltage protection (only single-phase line TV on the 110kV side of the main transformer). Since the zero sequence protection configuration is not complete enough, in the line-transformer wiring of multiple "T" connections, the neutral points of each transformer are still all grounded. However, all neutral grounding of the transformer has a certain negative impact on the system.
1 When part of the line or transformer is repaired, shut down, and the system operation mode changes, the zero-sequence network and the zero-sequence impedance value change greatly, and the magnitude and distribution of the zero-sequence current of each branch will also change greatly. Starting from the protection and setting, it is required to keep the zero sequence impedance of the substation basically unchanged.
2 During the operation of the transformer or the line reclosing, sometimes the neutral point grounding transformer running on the same line will be caused by the magnetizing inrush current, the amplitude is larger and the attenuation is slower, and the DC component is larger. Zero sequence current. It is easier to cause unsuccessful power transmission or unsuccessful reclosing.
3 The neutral point of the transformer is grounded completely, so that the zero-sequence impedance of the system is greatly reduced, resulting in a significant increase in the short-circuit current of the asymmetric ground fault. Because lightning strikes and asymmetric ground faults interfere with the secondary equipment, accidents that cause the protection device to malfunction and damage the communication equipment still occur. Therefore, part of the transformer neutral grounding method should be used in the effective grounding system to limit the single-phase grounding short-circuit current and reduce the interference to the communication system.
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