Power system resonance? Wuhan UHV specializes in the production of series resonance, with a wide range of product selection and professional electrical testing. To find series resonance, choose Wuhan UHV. 

Overvoltage phenomenon is quite common in the power system. The main causes of overvoltage in the power grid include resonance overvoltage, operating overvoltage, lightning overvoltage, and sudden changes in system operation mode, as well as system overvoltage caused by severe load fluctuations. Among them, resonance overvoltage occurs frequently and its harm is significant. 

Ferroresonance is a resonance condition formed by iron core inductive components such as generators, transformers, voltage transformers, reactors, arc suppression coils, and system capacitive components such as transmission lines and capacitance compensators, which excite sustained ferromagnetic resonance and generate resonant overvoltage in the system. 

Reason for series resonance: When performing knife switch operation, the circuit breaker isolation switch is connected to the busbar, causing the coupling of the circuit breaker port capacitance and the transformer on the busbar to meet the resonance condition

The power system is a complex power network, in which there are many inductive and capacitive components. Especially in ungrounded systems, ferromagnetic resonance often occurs, posing a hidden danger to the safe operation of equipment. 

The conditions for the generation of ferromagnetic resonance in the power system

Many components in the power system are inductive or capacitive, such as power transformers, transformers, generators, and arc suppression coils as inductive elements, parallel or series capacitors used for compensation, and parasitic capacitors of high-voltage equipment as capacitive elements. However, there are both longitudinal and transverse inductances between the wires of the line and the ground, and these components form complex LC oscillation circuits. Under certain energy sources, resonance phenomena will occur in circuits with specific parameter combinations. Due to the nonlinear relationship between the magnetic flux and current of the iron core inductor, an increase in voltage can cause the iron core inductor to become saturated, which can easily lead to ferromagnetic resonance in the voltage transformer. In a neutral ungrounded system, if the active losses and phase capacitance of the line are not considered, and only the inductance L of the voltage transformer and the ground capacitance Co of the line are considered, when C reaches a certain value and the voltage transformer is not saturated, the inductance XL is greater than the capacitance XCo. When the voltage on the voltage transformer rises to a certain value, the iron core of the voltage transformer saturates, and the inductive reactance XL is smaller than the capacitive reactance XCo, which constitutes the resonance condition. The following excitation conditions can cause ferromagnetic resonance:

a. Sudden activation of voltage transformers; 

b. Single phase grounding of the line; 

c. Sudden changes in system operation mode or switching of electrical equipment;

d. Significant fluctuations in system load; 

e. Fluctuations in grid frequency; 

f. Unbalanced changes in load, etc. 

Prevent resonance from occurring:

1. Control the ratio of XcE/XL and try to avoid the resonance zone as much as possible. 

2. When XCo/XL ≤ 0.01 or XCo/XL ≥ 3, no ferromagnetic resonance occurs

3. When the operating phase voltage Up divided by the rated voltage Un equals 0.58, it is highly prone to frequency division or fundamental ferromagnetic resonance. 

4. Change the operating mode to modify network parameters and eliminate resonance

5. When the XL of the voltage transformer is constant, increasing the capacitance Co to ground will decrease XCo, and the ratio of XCo/XL will also decrease, which is an effective method to prevent ferromagnetic resonance from occurring. The methods for adding Co in the switching operation generally include external capacitors, intervening in no-load lines or transformers, intervening in cable lines, pulling busbars or segmented circuit breakers, etc.