Before we understand the role of the voltage transformer's neutral harmonics, we may first discuss the neutral operating mode of the power system. In the three-phase AC power system, as the neutral point of the generator and transformer of the power supply, there are three modes of operation: one is that the neutral point of the power supply is not grounded; the function and principle of installing the harmonic elimination device for the voltage transformer are Before we understand the role of the voltage transformer's neutral harmonics, let's explore the neutral operation of the power system. In the three-phase AC power system, as the neutral point of the generator and transformer of the power supply, there are three modes of operation: one is that the neutral point of the power supply is not grounded; the other is that the neutral point of the power supply is grounded via the arc suppression coil; This is a direct neutral grounding of the power supply. The first two are collectively referred to as the neutral point non-effective grounding, or the small current grounding system. The latter neutral point is directly grounded as the neutral point effective grounding, or the large current grounding.
1 The power system is grounded by the arc suppression coil of the neutral point. This system has considered the arc suppression grounding (as described in the second section above). In the voltage transformer of the system, the Yo wiring can be considered without adding a harmonic elimination device.
2 We generally refer to the PT cabinet with harmonic elimination device, which refers to a non-linear resistor installed between the neutral point of the Yo-junction and the ground of the 6-35kV electromagnetic voltage transformer (referred to as pressure change). With the role of current limiting. In the 6-35kV power generation and substation, we often encounter the fact that the neutral point of the grid is not grounded, and the electromagnetically-variable primary winding of the Yo line on the busbar becomes the only metal channel for the neutral point ungrounded grid to the ground. The charging and discharging paths of the relative capacitance must pass through the voltage-variable primary winding. This slow change process makes the pressure-changing iron core deeply saturated. When the grounding of the power grid disappears, a surge of several ampere amplitude will appear in the primary winding of the pressure change, and the 0.5A high-voltage fuse will be melted. Even if this inrush current has not reached the fuse's fuse value, it still exceeds the voltage transformer's rated current. The voltage transformer operating under the overcurrent condition for a long time will be burned, which will cause other accidents. This phenomenon does not occur when a harmonic elimination device is selected. When the single-phase grounding capacitor current is less than a certain value, it will not generate a large inrush current in the voltage-variable primary winding, and has no influence on the pressure change and the high-voltage fuse. From the perspective of economy and product cost, it may not be eliminated. Harmonic device. If the customer requests, adding a harmonic eliminator on the primary side of the voltage transformer will add a layer of protection to the operation of the equipment.
3 When it comes to pressure change, add a harmonic elimination device. Don't mistake it for the PT cabinet. Because the voltage transformer is VV wiring in the 2PT cabinet, it is mainly used for measurement, measurement and insulation monitoring. The problem of grounding the ground (it is impossible to have the charging and discharging paths of the capacitor relative to the ground), and there is no need to install a harmonic elimination device.
4 In some engineering designs, the user has connected a certain size of capacitor on the bus side according to the actual situation of the site power grid, so that the ratio of the capacitive impedance (Xc) and the inductive impedance (XL) of the line is less than 0.01, which can avoid resonance. In this power distribution system, there is no need to install a harmonic eliminator for the neutral point of the voltage transformer.
In short, the harmonic elimination device installed in the PT neutral point should be treated differently according to the specific conditions and operation mode of the power grid. Do not blindly increase it. Design to add a harmonic elimination device to distinguish between semi-insulated voltage transformers and fully insulated voltage transformers. The selected one type of harmonic elimination device is different.
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1 The power system is grounded by the arc suppression coil of the neutral point. This system has considered the arc suppression grounding (as described in the second section above). In the voltage transformer of the system, the Yo wiring can be considered without adding a harmonic elimination device.
2 We generally refer to the PT cabinet with harmonic elimination device, which refers to a non-linear resistor installed between the neutral point of the Yo-junction and the ground of the 6-35kV electromagnetic voltage transformer (referred to as pressure change). With the role of current limiting. In the 6-35kV power generation and substation, we often encounter the fact that the neutral point of the grid is not grounded, and the electromagnetically-variable primary winding of the Yo line on the busbar becomes the only metal channel for the neutral point ungrounded grid to the ground. The charging and discharging paths of the relative capacitance must pass through the voltage-variable primary winding. This slow change process makes the pressure-changing iron core deeply saturated. When the grounding of the power grid disappears, a surge of several ampere amplitude will appear in the primary winding of the pressure change, and the 0.5A high-voltage fuse will be melted. Even if this inrush current has not reached the fuse's fuse value, it still exceeds the voltage transformer's rated current. The voltage transformer operating under the overcurrent condition for a long time will be burned, which will cause other accidents. This phenomenon does not occur when a harmonic elimination device is selected. When the single-phase grounding capacitor current is less than a certain value, it will not generate a large inrush current in the voltage-variable primary winding, and has no influence on the pressure change and the high-voltage fuse. From the perspective of economy and product cost, it may not be eliminated. Harmonic device. If the customer requests, adding a harmonic eliminator on the primary side of the voltage transformer will add a layer of protection to the operation of the equipment.
3 When it comes to pressure change, add a harmonic elimination device. Don't mistake it for the PT cabinet. Because the voltage transformer is VV wiring in the 2PT cabinet, it is mainly used for measurement, measurement and insulation monitoring. The problem of grounding the ground (it is impossible to have the charging and discharging paths of the capacitor relative to the ground), and there is no need to install a harmonic elimination device.
4 In some engineering designs, the user has connected a certain size of capacitor on the bus side according to the actual situation of the site power grid, so that the ratio of the capacitive impedance (Xc) and the inductive impedance (XL) of the line is less than 0.01, which can avoid resonance. In this power distribution system, there is no need to install a harmonic eliminator for the neutral point of the voltage transformer.
In short, the harmonic elimination device installed in the PT neutral point should be treated differently according to the specific conditions and operation mode of the power grid. Do not blindly increase it. Design to add a harmonic elimination device to distinguish between semi-insulated voltage transformers and fully insulated voltage transformers. The selected one type of harmonic elimination device is different.
Source of information: Harmonic Elimination Device http://?class_id=2http://news.chinawj.com.cn Submission:
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