Application of automatic compensation of arc suppr

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Application of automatic compensation of arc suppression coil

the system with ungrounded neutral point or grounded through arc suppression coil is adopted. When a phase has grounding fault, the grounding fault current is often much smaller than the load current because it can not form a short-circuit circuit circuit, so this system is called small grounding current system. The automatic compensation device of arc suppression coil introduced in this paper is mainly used in 10 kV system with ungrounded neutral point. In case of single-phase grounding fault in 10 kV system, the grounding current forms a loop through the grounding capacitance of the outgoing line. Therefore, when the power develops to a certain scale, the total length of 10kV outgoing line increases and the capacitance to ground is large, the single-phase grounding current can not be ignored. Electric operation experience shows that when the single-phase grounding current is greater than 10 A, the arc will develop into phase to phase fault and cause accident tripping. At present, according to the calculation and measured results, the single-phase grounding current of 10 kV System in most substations in Chengdu is far greater than 10 A, so reducing the capacitive current of single-phase grounding has become an important topic to ensure the reliability of power supply. Using arc suppression coil to compensate capacitive current is a mature and common method, but the method of fixed compensation or manual adjustment of tap obviously can not meet the system requirements. In recent years, with the rapid development of computer technology, the application of microcomputer control for automatic compensation of arc suppression coil has become a new trend

1 solution

1.1 system wiring

use the arc suppression coil to compensate the capacitive current, that is, use the inductive current flowing into the grounding arc channel of the arc suppression coil to offset the structural principle current of the capacitive wear-resistant friction experimental machine flowing into the place through the sound phase. Arc suppression coil has two functions: one is to greatly reduce the grounding current at the fault point; The second is to slow down the rising speed of recovery voltage at the instantaneous fault point of arc extinction. The arc suppression coil shall be connected to the neutral point of the system. The 10 kV side of the main transformer of the substation adopts triangular connection, and the 10 kV system has no neutral point. The solution is to connect the arc suppression coil to the neutral point of the 10 kV station grounding transformer with star connection. In this way, the zero sequence circuit of the system is equivalent to the LC series circuit composed of ground capacitance and arc suppression coil. In order to avoid resonance and overvoltage of LC series circuit, the arc suppression coil is also provided with damping resistance in series or parallel to ensure that the displacement voltage UN of neutral point is less than 15% of phase voltage. When single-phase grounding occurs in the system, a large current flows through the neutral point. At this time, the damping resistance must be short circuited or disconnected. In addition, the neutral point of the grounding transformer is also equipped with TV for measuring the neutral point voltage UN and TA for measuring the neutral point current

1.2 device principle

at present, there are many such devices, but their principles are similar and their structures are similar. The general composition is shown in Figure 1

the central processing unit usually adopts an industrial computer with strong processing capacity and high reliability, equipped with relevant peripheral interface equipment. Provide interface with integrated automation equipment and support constant value and real-time state display. Analog and switching values to be collected by the device mainly include neutral point voltage and current of grounding transformer; Arc suppression coil gear, parallel operation contact, etc. The main function of the device is to properly compensate the capacitive current during normal operation or grounding of the system by adjusting the gear of arc suppression coil and switching damping resistance according to the collected neutral point voltage and current

The two most important indicators of

compensation are that managers take the lead in changing style: detuning degree V and grounding residual current Ig. Where, v = (ic-il)/IC is calculated by the device in real time. The degree of detuning determines the residual current in the arc channel; The second is the time when the recovery voltage rises to the maximum value; The third is the rising speed of recovery voltage, which is the main factor affecting arc extinguishing. According to the operation experience and relevant regulations, the minimum detuning degree shall be less than 5%, and the minimum residual current value shall be less than 5 a. Generally, the detuning degree and residual current range can be set on the device

2 important issues

1) select the appropriate on load regulating arc suppression coil according to the actual situation of the system. Firstly, the compensation range of arc suppression coil, that is, capacity, should be determined according to the capacitance current of the system. If the arc suppression coil operates at the maximum compensation current gear and the detuning degree is still greater than 5%, it indicates that the capacity of arc suppression coil Jinan gold testing machine in low price sales can not meet the requirements. Secondly, it is necessary to determine the adjustment step of arc suppression coil, that is, the number of taps. Theoretically, it is better to use continuously adjustable arc suppression coil. However, due to technical reasons, the use of turn adjustable arc suppression coil with tap is more common. The number of taps determines the minimum detuning degree that can be achieved, so the total number of taps can be determined according to the detuning degree index: n = 1 + ln (IMAX/Imin)/ln (1 + 2V). IMAX and Imin are the maximum and minimum current corresponding to the tap of arc suppression coil respectively

2) two grounding transformers operate in parallel. Generally, two grounding transformers of a substation are connected to two sections of bus, and the device shall consider their parallel and separate conditions. During parallel operation, two arc suppression coils shall be adjusted at the same time to obtain appropriate compensation and ensure the consistency of the two neutral points. At present, the devices produced by some manufacturers need to be improved in this regard

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