Application of the automatic compensation of the h

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Application of automatic compensation of arc suppression coil

the system with ungrounded neutral or grounded through arc suppression coil is adopted. When a phase has a ground fault, the ground fault current is often much smaller than the load current because it cannot form a short circuit circuit circuit, so this system is called a small ground current system. The automatic compensation device for arc suppression coil, which basically reaches the expectation of "1025", is mainly used for 10 kV system with ungrounded neutral point. When a single-phase grounding fault occurs in the 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. The electric operation experience shows that when the single-phase grounding current is greater than 10 A, the arc will make the fault 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 issue to ensure the reliability of power supply. Using arc suppression coil to compensate capacitive current is a mature and common method, but 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

the arc suppression coil is used to compensate the capacitive current, that is, the inductive current flowing into the grounding arc channel by the arc suppression coil is used to offset the structural principle current of the capacitive abrasion resistance tester flowing through the sound phase. The 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 instant of arc extinction. The arc suppression coil shall be connected to the neutral point of the system. The 10kV side of the main transformer in the substation adopts triangle connection. The 10kV system has no neutral point. The solution is to connect the arc suppression coil to the neutral point of the 10kV station grounding transformer with star connection. In this way, the zero sequence circuit of the system is equivalent to an LC series circuit composed of a ground capacitance and an arc suppression coil. In order to avoid resonance and overvoltage in LC series circuit, the arc suppression coil is also connected in series or in parallel with a damping resistor to ensure that the displacement voltage UN of the neutral point is less than 15% of the phase voltage. When a 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 the industrial control computer with strong processing capacity and high reliability, and is equipped with relevant peripheral interface equipment. Provide interface with integrated automation equipment to support setting and real-time state display. The analog and switching values to be collected by the device mainly include the 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, switching damping resistance and other control means according to the collected neutral point voltage and current

the two most important indicators of compensation are that the management takes the lead in changing the style: detuning degree V and residual grounding 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 path; 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 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 suitable on load regulating arc suppression coil according to the actual situation of the system. Firstly, the compensation range of the arc suppression coil, that is, the capacity, should be determined according to the capacitance current of the system. If the arc suppression coil operates at the maximum compensation current gear, the detuning degree is still greater than 5%, which indicates that the capacity of the 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, it is more common to use turn adjustable arc suppression coil with tap. 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 respectively the maximum and minimum current corresponding to the tap of arc suppression coil

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 respect

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