GIS Partial Discharge Test And Hipot Test

THE 

The AC withstand voltage test for GIS is a critical procedure in the field of electrical engineering. GIS, which stands for Gas-Insulated Switchgear, is a type of high-voltage electrical equipment that is commonly used in substations to control the flow of electricity. To ensure the reliability and safety of GIS equipment, it is essential to conduct AC withstand voltage test. AC withstand voltage test is performed by applying a high voltage AC signal to the GIS equipment and measuring its ability to withstand the voltage without breaking down. This test is crucial as it simulates the conditions that the equipment may face during operation, such as lightning strikes or high voltage surges.

The partial discharge (PD) test is another very important test for gas-insulated switchgear (GIS) systems to ensure their reliability and performance. Partial discharge is a phenomenon that can occur in GIS systems due to insulation defects and can lead to the deterioration of insulation and, ultimately, to failure of the system. Therefore, conducting PD tests is essential to detect any possible defects early on and prevent potential issues in the future.

There are several methods of performing PD tests for GIS systems, including electrical, acoustic, and optical methods. One common method is the electrical method, which involves applying a voltage stress to the GIS system and measuring any partial discharges that may occur. By analyzing the data collected from these tests, engineers can evaluate the condition of the insulation and identify any potential issues that need to be addressed.

Test equipment

1. The variable frequency series resonant test system is used for testing GIS. The working principle is adopted to make the circuit reach the resonant state by adjusting the frequency and reducing the power capacity requirement. It includes a Variable frequency power supply,  excitation transformer,  resonant reactor, and capacitance divider. 

2. The Partial discharge detector uses the worldwide standard Windows operating system and an intuitive control and display panel to allow even inexperienced operators to learn quickly with minimal training. In addition, advanced features such as higher accuracy, automated calibration, data analysis, and customized test recording are standard. It has full program-controlled automatic calibration, automatic synchronization, automatic voltage recording, automatic measurement & save & playback features. Comply with IEC-270 such as the discharge repetition rate n, the average discharge current I. Various display styles of the PD waveform form, such as a sine map, dot matrix, and so on, make it easier to get the result. New digital filtering and interference suppression combined with a rich and dynamic statistical analysis of patterns. The detection method, measurement loop, and technical performance parameters comply with the latest GB7354 and IEC-270 "partial discharge measurement" standards. Applicable to all types of high voltage electrical equipment, covering the full voltage and capacity levels, on behalf of the domestic digital PD instruments of the most advanced technology

Critical test procedure: 

Before test, the preparation should be finished to ensure the test's safety and efficacy

1. Ensure the GIS installation and gas status meet requirements.
2. Perform other necessary tests (e.g., resistance, moisture, and leak detection).
3. Isolate devices that do not participate in the test.
4. Plan the application of the test voltage and the staging test.
5. Safety measures, such as grounding and protection.

The main test steps are as follows; 

1. Prepressure treatment: Apply 30% rated voltage for 5 minutes to eliminate residual charge
2. Step voltage boost: Boost voltage by 25%, 50%, 75%, and 100%, and hold each stage for 1 minute
3. Synchronous monitoring of local discharge: at 100% test voltage for 30 minutes, record local discharge (≤5pC is qualified)

IEC standard

FAQ

 

 

01.How to calculate the test voltage for GIS ac withstand voltage test?

Based on IEC 62271-203, Utest=1.1×Umax3Utest​=1.1×3​Umax​​, and the UmaxUmax​ is the Max working voltage of equipment. 

02. How to calculate the capacity of AC resonant test system?

Normally, we need to confirm the suitable capacity or current for the test system. It is usually calculated based on the test method and test object like busbar. 

03. Which kind of reactors for the PD-free AC resonant test system?

The PD-free AC resonant test system is normally used of dry type reactor and exciting transformer. As the PD value is less, insulation performance is better than oil type. 

04. When do we prefer oil type reactor?

The oil-type reactor is normally used for a huge capacity ＞500kVA for a single reactor. PD free test systems pay more attention to partial discharge control and lightweight design, so the oil structure is usually not chosen

05. How to choose the online PD detector and the offline PD detector?

The online PD detector is normally used for routine tests. For smaller  GIS, we can use an online PD detector and UHF sensor. For the offline PD detector, we need to use a PD-free resonant test system, combined with a partial discharge detector to analyse the PD value.  

06. Why is the test method sometimes needed for phasing test?

If the overall power capacity of the GIS is too large (for example, a long bus bar or a complex structure), perform voltage withstand tests in different sections to avoid device overload