By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as power frequency withstand voltage test equipment). Next, we will share with you the application of 220kV series resonance.
In the power system, series resonance is a testing device used for preventive testing of electrical equipment, consisting of a control part, a boosting part, and an acquisition part. It is mainly used to detect the insulation performance of high voltage and large capacity electrical equipment. In the series resonance circuit composed of the test object, the series resonance test device generates different combinations according to its testing technology and specifications, and resonates with the test object to achieve the purpose of resonance testing. Therefore, the capacity of series resonance has the most direct relationship with the capacity of the test object. Series resonance can be divided into AC voltage withstand test device for substation electrical equipment, cable voltage withstand test device, generator voltage withstand test, etc. according to the application scenario.
Introduction to the Application of Series Resonance Test in 220kV System
In the following introduction, I will take 540kvA/270kv variable frequency series resonance as an example to talk about the series resonance test of 100000kVA main transformer. Firstly, we need to mention the power preventive standard. According to the document, in the 220kv system handover test, the standard value of AC withstand voltage for the neutral point grounding of the main transformer is 58kv. When the neutral point is not directly grounded, the standard value of AC withstand voltage is 160kv. For the algorithm of the standard value, please click on the resonance voltage calculation method and standard for reference.
Neutral point grounding measurement method
Based on the existing design capacity, neutral point grounding usually refers to considering the resonant voltage, using a series connection of 27kV * 3 reactors, selecting the middle voltage value for the excitation transformer tap, parallel connecting A, B, C and the neutral point on the transformer body and directly connecting them to the measurement circuit of the series resonant device, ensuring good grounding on the low voltage side, and finally cross checking, taking measures for civil defense isolation, starting the power supply, selecting automatic testing, and the series resonant device automatically finding the resonant frequency, automatically raising the voltage and calculating the time until the test is completed. It should be noted that during the experiment, if you have requirements for the resonant frequency, you can adjust the configuration of the reactor or add compensation capacitors.
Neutral point ungrounded measurement method
Taking the maximum voltage of 160kv as an example, the 540kvA/270kv variable frequency series resonance is composed of 10 reactors, with a single reactor of 27kv and a maximum voltage of 270kv. When measuring, a combination of at least 6 reactors in series can be used, and the excitation transformer can choose either the middle tap or the maximum tap.
Whether it is a 220kV system or a 110kV system, the measurement method is the same. Whether the neutral point is grounded or not depends on the design requirements and the structure of the transformer. The withstand time required for the voltage to rise to a certain level is ultimately determined by the customer’s requirements.