Why do I need to do shock test before putting the transformer into operation?
In fact, impact test is not a power system terminology. It is generally to determine the military, civilian equipment in the impact or role of external forces when the product safety, reliability and effectiveness of a test method. The impact test in electrical engineering, on the other hand, generally includes operational impact test, lightning impact test, and steep wave front impact test, which aims to test the insulation strength of electrical equipment.
The impact test of electric power system is divided into three kinds:
1）The prescribed impulse test method, the use of sinusoidal wave for the test. Such as sine wave vibration testing machine, widely used in national defense, aerospace, aviation, communications and other industries, adapted to the discovery of early failure, simulation of actual working conditions assessment and structural strength test.
2）Impact spectrum test method. Such as impact test bench, it can be controlled to simulate the size of the impact force, duration, etc., used to accurately test the adaptability of the product to the environment, is also often used to test the packaging of the product whether the product can play a protective role, to avoid damage to the product in the process of transportation loading and unloading.
3）The provisions of the test machine test method. Such as gravel impact testing machine, is specially designed for automotive materials and surface coatings to resist gravel impact test.
This impulse voltage generator has the following main features：
1. Complete sets, full voltage classes.
2. Small loop inductance, take the band elimination filter measures, still produce standard impulse wave in the large-capacity load, large load capacity, high voltage utilization, convenient to adjust wave.
3. Simple operation, excellent synchronization performance, reliable action.
4. Constant current charging technology, high automation, strong anti-interference performance.
5. Digital measurement and analysis system and computer on line processing system for impulse test data, greatly improve the test technology and efficiency.
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And according to the temperature to points, impact test is divided into: room temperature impact test, test at room temperature, generally in the range of 23 ± 5 degrees Celsius; low-temperature impact test; in the low-temperature medium to save a certain amount of time, so that the temperature reaches the requirements of the rapid removal after the completion of the impact test.
In the grid system, the new put into operation of the transformer, in addition to the handover test standards to do some of the necessary tests and protection, secondary aspects of the test, in the formal put into the former, usually have to do no-load full-voltage impact test, and the transformer for the purpose of impact test has two purposes.
First, not charged, pull open the no-load transformer, there may be operational overvoltage, in the power system neutral ungrounded or grounded by the arcing coil, overvoltage amplitude can be up to 4 ~ 4.5 times the phase voltage; in the neutral directly grounded, up to 3 times the phase voltage. So in order to check the transformer insulation strength can withstand the full voltage or operating overvoltage, need to do impact test.
Secondly, in the case of charged, into the no-load transformer, will produce excitation current, its value can be up to 6 ~ 8 times the rated current, due to the excitation current generates a lot of electric power, in order to assess the mechanical strength of the transformer, while assessing the excitation current attenuation of the initial period can cause relay protection device malfunction, need to do impact test.
Usually, the newly installed transformer is generally required to no-load closing five times to comprehensively test the transformer insulation, mechanical strength and differential protection action. Because each time the closing moment of the closing angle is different, the corresponding excitation current is also different, sometimes large, sometimes small, the first shock to continue to run for more than 10 minutes after the impact, after the impact to wait for more than 5 minutes before the next impact, a complete impact test usually takes 1 hour.
