Study on Vibration Characteristics of Power Transformer under No-load Condition

Transformer winding core deformation directly or indirectly damages the transformer, this fault hazard general conventional electrical test can not diagnose the transformer and similar structure of power equipment vibration online monitoring method, the first foreign application in the shunt reactor by online monitoring of transformer body vibration to reflect the winding and core condition is a matter of recent years, compared with FRALVI and online or offline measurement of short-circuit reactance and other methods, vibration method can not only detect the fault winding, but also detect the core condition, and the method and the power system is not electrically connected, safe and reliable, so it should be studied to understand the power transformer in the no-load load condition and subjected to short circuit when the body vibration characteristics, which no-load vibration characteristics is the basis of 1 principle power transformer in stable operation, silicon steel core, winding vibration under the action of electromagnetic field and through the transformer oil The vibration of the transformer body surface is closely related to the displacement and deformation of the winding and the core, so the winding and the core can be monitored by measuring the vibration of the body online.

The main magnetic flux generated by the excitation current at the same tap position of the transformer in the core remains basically unchanged when the load, load and load change, so the vibration of the core caused by magnetostriction also remains basically unchanged. In order to obtain the vibration characteristics of the transformer core at different tap positions, it is only necessary to measure the vibration of the transformer body under no-load conditions. Because the vibration of the transformer body under load conditions also includes the vibration of the winding under the action of the load current, the winding vibration signal can be obtained by measuring the vibration signal under the load of the transformer. Compared with the vibration signal under no-load, the vibration signal measured when the transformer core or winding is displaced or deformed will have a higher frequency component, and the amplitude at the original frequency will also change. The larger the displacement deformation, the higher the frequency component and The larger the amplitude change, because the vibration characteristics at each position of the transformer body are most closely related to the nearest vibration source, according to the degree of change in the vibration signal measured around the transformer body, it is convenient to determine which part of the winding or core is faulty, that is, using the vibration method to monitor the power transformer online can achieve fault location. Therefore, when the vibration method is used to monitor the power transformer online, the vibration signal of the body must be measured under no-load conditions to obtain the vibration status of the core, so as to determine whether the core is faulty. The winding vibration signal must be removed from the vibration signal of the body under load to determine whether the winding is faulty. 2 Tests and results 2.1 Test objects and test wiring Simulation experiments show that the transformer body vibration signal test system can correctly measure the transformer body The acceleration signal of vibration (converted into a voltage signal proportional to it by the charge amplifier), so the test system is used to conduct vibration test on the low-high-voltage side of a power transformer in a long-term no-load test. When the transformer cooling system is turned off during the test, the parameters of the transformer are as follows: Model: OSFPSZI2.2 Test results and analysis The vibration sensor is attached with double-sided tape under the neck of the exit of the high and low voltage arms respectively. Because the low-voltage side of the C phase is connected with the test power supply, the vibration test test wiring phase of the transformer body has not been measured. The vibration signal spectrum of each phase on the high and low voltage sides is shown in 3 respectively. After the test, it is considered that the fundamental frequency of the vibration of the transformer body during the no-load test is 100Hz, and there are other high-order harmonic components. The harmonics after 1000Hz are basically attenuated to 0, which is consistent with the results of theoretical analysis.

The amplitude of the vibration signal in the frequency domain of the three-phase high-pressure side at the same position appears at the same frequency position, that is, the high-pressure side is at 400Hz; while the amplitude of the vibration signal in the frequency domain of the low-pressure side is at 100Hz. The fundamental frequency and the amplitude of each harmonic of the vibration signal at the same position on the high and low voltage sides are on an order of magnitude, that is, the frequency domain characteristics are basically the same. However, from the slight difference in the amplitude and frequency characteristics of each phase on the high-voltage side, it can be seen that if the amplitude of the main frequency is relatively large, the harmonic test of the no-load vibration characteristics of another 300MVA power transformer found that except for the main frequency of the high-voltage side at 300Hz, other vibration characteristics are the same as the above-mentioned transformer3 Conclusion The vibration signal of the transformer body is based on 100Hz and has other harmonic components. After 1000Hz, the harmonic amplitude is basically attenuated to 0. For the same position on the high-voltage side or the low-voltage side, the vibration signal of the body has a common law, that is, the main frequency of the vibration is the same, and the amplitude and frequency characteristics of each phase vibration signal are basically similar, but the main frequency of different types of transformers may be different. Due to the influence of factors such as the transformer structure, the core and winding compression of each phase, and the structure of the transformer box, the vibration amplitude of each phase on the same side of the transformer has certain differences, but when the main frequency amplitude is relatively large, the amplitude of its harmonic components is also slightly higher, and vice versa.