[Abstract] This paper mainly discusses the main reasons for the ferroresonance in the power system, the phenomena when the resonance occurs, the harm and the way to eliminate the resonance 0 Foreword In recent years due to the rapid development of Luzhou power grid, coupled with this year is the power grid construction year, Luzhou Power Grid also carried out a large number of transformation and expansion project, as large as 500kV, as small as 10kV distribution network have a greater change, making the entire network change To be more complex, flexible and strong. But it is because of the large changes in the grid structure (such as the expansion of medium and low voltage networks, the number of outgoing circuits, line growth, the gradual increase in cable lines, medium and low voltage power grid capacitance to ground has also increased significantly, etc.) Of the ferromagnetic resonance phenomenon, but now and again have occurred, because the resonance will have over-voltage, resulting in a huge threat to grid security, if not taken effective measures to eliminate, may cause damage to equipment, and even induce more Serious power system accident. Below on the ferroelectric resonance in the power network to talk about my personal understanding, opinion. 1 Overview Ferromagnetic resonance is formed by the core inductance components, such as generators, transformers , voltage transformers , reactors, arc suppression coils and other capacitive components of the system, such as transmission lines, capacitance compensators, etc. to form a co-harmonic condition, Resonance, the system resonant over-voltage. Ferro-resonance of power system can be divided into two categories: one is in 66kV and below the neutral point of the insulated grid, due to the capacitive reactance and electromagnetic induction transformer excitation inductance adverse combination, the system voltage disturbance (Such as lightning, single-phase ground fault disappears and switching operations, etc.) under the excitation and the resulting ferromagnetic resonance phenomenon; the other is occurred in the 220kV (or 110kV) substation bus without load, when using 220kV, 110kV belt Fracture equalizing capacitor of the main switch or busbar switch with electromagnetic voltage transformer empty bus charging process, or cut off (including the protection of the entire group of transmission line jump) empty with electromagnetic voltage transformer bus, the operation temporarily State process connected to the empty bus in the electromagnetic voltage transformer group of one phase, two-phase or three-phase excitation of the ferromagnetic resonance phenomenon, that is, series resonance, simply by the high-voltage circuit breaker capacitor and the bus voltage mutual inductance Resonance coupling induces resonance Resonance waves are confined to the no-load bus range of the substation and are also referred to as the null bus resonance of the substation. Ferromagnetic resonance phenomenon 2.1 Ferromagnetic resonance forms and symbols 2.1.1 fundamental resonance: a relative reduction of voltage, the other two relative voltage rise exceeds the line voltage; or two-phase voltage decreases, a phase voltage increases over the line voltage, a ground signal is issued. 2.1.2 Graded harmonics: three relative voltage while rising, low frequency changes 2.1.3 Higher harmonics: three relative voltage while rising above the line voltage 2.2 The phenomenon of series resonance: line voltage increases, the meter swing, the voltage transformer opening triangular voltage exceeds 100V 3. Ferromagnetic resonance causes and analysis 3.1 ferromagnetic resonance causes: 3.1.1 there is a line ground, disconnection, circuit breaker non-contemporaneous closing caused by system impact 3.1.2 cut, together empty bus or system disturbance excitation resonance 3.1.3 The system in a special mode of operation, the parameters match, reached the resonance conditions 3.2 series resonance causes: knife operation, the circuit breaker disconnector connected to the bus, causing the circuit breaker port capacitance and transformer bus coupler to meet the resonant conditions 3.3 Power System Ferromagnetic Resonance Analysis Power system is a complex power network. In this complex power network, there are many inductance and capacitance components. Especially in ungrounded systems, the phenomenon of ferromagnetic resonance frequently occurs, which brings hidden dangers to the safe operation of the equipment. The reason of ferromagnetic resonance is analyzed from the simple ferromagnetic resonance circuit. 3.4 Simple ferromagnetic resonance circuit resonance analysis In a simple R, C and iron core inductor L circuit, assuming that under normal operating conditions, the initial state is the inductive reactance is greater than the capacitive reactance, that ωL> (1 / ωC), then do not have the linear resonant conditions, the loop Maintain a steady state. However, when the power supply voltage rises or the inrush current appears in the inductor, it is possible to saturate the core and reduce the inductance. When ωL = (1 / ωC), the series resonant condition is satisfied, Over-voltage occurs at both ends of the inductor and capacitor, and the phase and amplitude of the loop current will change suddenly to cause magnetic resonance. Once the resonance is formed, the resonance state may be "self-sustained" for a long time without attenuation until a new The disturbance that has changed its resonant condition can be eliminated. 3.5 power system ferroresonance conditions Many components in the power system are inductive or capacitive, such as power transformers, transformers, generators, arc suppression coil inductance components, compensation and or capacitor banks in series, the parasitic capacitance of high-voltage equipment for the capacitive components, However, there are both longitudinal inductances and lateral capacitances between the conductors of the lines and the conductors. These components form a complex LC tank circuit. Under the action of a certain energy source, the resonance phenomenon occurs in the circuit with certain parameters. Due to the non-linear relationship between the flux and the current of the core inductor, the voltage rise causes the core inductor to saturate, which makes it very easy to make the voltage transformer produce ferroresonance. In the neutral ungrounded system, if we do not consider the active loss of the line and the phase-to-phase capacitance, only consider the capacitance L of the voltage transformer inductance L and the capacitance of the line to ground Co, when C reaches a certain value and the voltage transformer is not saturated, Sensitivity XL is greater than capacitive XCo. When the voltage on the voltage transformer rises to a certain value, the core of the voltage transformer is saturated, and the inductive reactance XL is less than the capacitive reactance XCo, thus forming a resonance condition. The following excitation conditions can cause ferromagnetic resonance: 3.5.
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August 06, 2024