How to Choose a GIS High Voltage Withstand and Partial Discharge Test System: 7 Key Factors for Manufacturers

For GIS and GIL manufacturers, selecting a high-voltage test system is an important investment decision.

A test system must do more than generate the required high voltage. It must also provide suitable capacity, low background partial discharge, stable operation, convenient connections, and compatibility with the manufacturer's actual testing procedures.

For example, a GIS manufacturer may need a 500kV test system today but plan to expand production to higher-voltage products in the future.

Another manufacturer may already have a high-voltage test transformer but struggle with background partial discharge during insulation testing.

In both situations, purchasing equipment based only on its rated voltage may lead to an unsuitable configuration.

So, what should manufacturers consider before purchasing GIS high-voltage withstand and partial discharge test equipment?

Here are seven important factors to help you make a better decision.

The first step is to identify the voltage level of the GIS or GIL products to be tested.

Different product ratings and insulation designs require different test voltage configurations.

For high-voltage electrical equipment manufacturers, common test system voltage options include:

• 100kV

• 200kV

• 250kV

• 300kV

• 500kV

• 800kV

• 1000kV

For manufacturers developing ultra-high-voltage products, customized higher-voltage configurations may also be required.

However, one important point should be remembered:

The rated voltage of the test system is not automatically the same as the required withstand test voltage of the product.

The actual selection should be based on the applicable test standards, equipment specifications, test object, and customer requirements.

Before requesting a quotation, prepare the following information:

• Rated voltage of the GIS or GIL.

• Required withstand test voltage.

• Test duration.

• Type of test object.

• Whether partial discharge measurement is required.

This information helps the manufacturer recommend an appropriate system configuration.

Capacity is another critical factor in selecting GIS high-voltage test equipment.

A system may reach the required voltage under no-load conditions, but this does not necessarily mean it can operate properly when connected to a large-capacitance test object.

GIS and GIL products can have considerable capacitive loads, especially when testing long sections or large equipment assemblies.

The test system must provide sufficient capacity to supply the required current during the test.

For capacitive test objects, the approximate reactive power requirement can be calculated using:

Where:

• Q = Required reactive power (VA)

• f = Test frequency (Hz)

• C = Capacitance of the test object (F)

• U = Test voltage (V)

For example, the required capacity increases with test voltage, test frequency, and the capacitance of the test object.

This is why manufacturers should provide the following information before selecting the system:

• Capacitance of the GIS or GIL.

• Maximum test voltage.

• Required test frequency.

• Expected test current.

• Whether the equipment will be tested individually or as a complete assembly.

The Sansion SXGTU system offers configurable capacities from 50kVA to 2000kVA, with higher capacities available for customized applications.

Proper capacity matching helps ensure that the selected system is suitable for the actual testing load.

For GIS and GIL insulation testing, partial discharge performance is one of the most important factors to evaluate.

Why?

Because the test system itself can generate unwanted background discharge signals.

If the background PD level is too high, it may interfere with the measurement of partial discharge from the test object.

This creates several practical problems:

• Difficulty distinguishing system background signals from test object discharge.

• Reduced confidence in measurement results.

• More complicated testing and troubleshooting.

• Increased difficulty in evaluating insulation performance.

When selecting a low-PD test system, manufacturers should pay attention to:

• Shielding structure.

• Insulation design.

• High-voltage connection quality.

• Corona and discharge control.

• Background PD level under specified operating conditions.

The Sansion SXGTU is designed with a sealed and shielded high-voltage structure.

Its background partial discharge level can be controlled within 1–3pC at rated voltage under ordinary environmental conditions, according to the manufacturer's specifications.

This helps reduce interference originating from the test system itself and supports more reliable GIS and GIL partial discharge measurements.

It is important to distinguish between two concepts:

Low background PD of the test system does not mean that the GIS test object has no partial discharge.

The purpose is to minimize interference from the test equipment so that the electrical insulation performance of the test object can be evaluated more effectively.

When comparing different suppliers, always ask how the background PD value is measured, at what voltage, and under which environmental conditions.

Different GIS and GIL testing applications may require different high-voltage generation methods.

Three commonly used configurations include:

A high-voltage transformer generates the required test voltage through electromagnetic induction.

It is suitable for applications where the test voltage and capacity requirements can be met by the selected transformer configuration.

Manufacturers should evaluate the rated voltage, output capacity, insulation structure, and applicable test conditions.

A power-frequency series resonance system uses a reactor and the capacitance of the test object to form a resonant circuit.

When the circuit reaches resonance, the reactive power supplied by the power source can be significantly reduced compared with directly supplying the entire capacitive load.

This makes it useful for testing high-capacitance electrical equipment.

A variable-frequency series resonance system adjusts the output frequency to achieve resonance with the test object's capacitance.

It offers flexibility when testing different capacitive loads and can be configured for various high-voltage test applications.

The best choice depends on the characteristics of the test object, required test frequency, voltage, capacity, and factory testing conditions.

The SXGTU supports high-voltage generation through transformer boosting, power-frequency series resonance, and variable-frequency series resonance.

Its single-stage voltage-boosting arrangement avoids the need for a cascaded voltage-boosting structure.

An ideal high-voltage test system must work well in the customer's actual factory environment.

However, some manufacturers focus only on electrical parameters and overlook installation and operating conditions.

Here are several practical issues worth considering.

Available installation space

A large testing system may require significant space. An integrated, compact design can help optimize the factory testing area.

Transportation and installation

High-voltage equipment may need to be transported over long distances or installed in existing testing facilities.

A robust structure and reasonable component arrangement can simplify transportation and installation planning.

Connection convenience

GIS and GIL products often have specific connection requirements. Suitable high-voltage interfaces and connection arrangements help reduce setup complexity.

Testing safety

The system should incorporate appropriate shielding, grounding, interlocking, and other safety provisions according to its design and applicable requirements.

The SXGTU adopts an integrated shielded structure with a built-in high-voltage disconnect switch to support convenient connection arrangements and high-voltage testing operations.

An additional high-voltage bushing interface can also be provided for testing conventional high-voltage equipment.

For manufacturers producing different categories of high-voltage electrical equipment, testing flexibility can be an important purchasing consideration.

For example, one factory may manufacture:

• Gas Insulated Switchgear (GIS).

• Gas Insulated Transmission Lines (GIL).

• High-voltage bushings.

• Other high-voltage electrical components.

Purchasing separate equipment for every testing application may increase equipment investment and occupy more factory space.

An integrated test system with suitable voltage generation methods and interfaces can offer more application flexibility.

The SXGTU is designed to support different high-voltage testing applications through configurable system arrangements.

With an additional high-voltage bushing interface, it can also be adapted for testing conventional high-voltage equipment.

Before purchasing, manufacturers should confirm the actual test requirements for each product category to ensure the proposed configuration is suitable.

The final factor is often overlooked: the technical capability of the equipment supplier.

A supplier should not simply ask, "What voltage do you need?"

A professional technical evaluation should also consider:

• What type of GIS or GIL will you test?

• What is the rated voltage of the product?

• What is the maximum withstand test voltage?

• What is the capacitance of the test object?

• What is the required test capacity?

• Is partial discharge measurement required?

• What background PD level is expected?

• What testing methods are required?

• What are the installation and environmental conditions?

A manufacturer that understands these details can recommend a more appropriate configuration rather than simply offering a standard product.

For manufacturers looking for an integrated high-voltage testing solution, Sansion offers the SXGTU Inflatable Partial Discharge-Free Combined Electrical Test System.

The system is developed for high-voltage and large-capacity testing applications, particularly GIS and GIL factory testing.

• Integrated sealed and shielded high-voltage structure.

• Low background partial discharge performance.

• Compact structure for more efficient use of testing space.

• Built-in high-voltage disconnect switch.

• Multiple high-voltage generation configurations.

• Additional bushing interface available.

• Customizable voltage and capacity according to project requirements.

A GIS partial discharge test system is used to apply high voltage to gas-insulated switchgear and evaluate its insulation performance through partial discharge measurements.

It can help manufacturers identify potential insulation defects during factory quality inspection.

A low background PD level helps reduce interference from the test equipment itself, making it easier to identify and evaluate discharge signals originating from the test object.

Yes, provided that the selected system has suitable voltage, capacity, interfaces, and test configurations for both products.

The actual requirements should be evaluated based on the electrical characteristics of each test object.

The standard configurable voltage levels include 100kV, 200kV, 250kV, 300kV, 500kV, 800kV, and 1000kV. Higher voltage levels can be customized.

Yes. An additional high-voltage bushing interface can be provided for suitable conventional high-voltage testing applications.

Provide the product type, rated voltage, required withstand voltage, capacitance, test frequency, and partial discharge measurement requirements.

These details allow the technical team to evaluate a suitable voltage and capacity configuration.

Selecting GIS high-voltage withstand and partial discharge test equipment requires more than comparing voltage ratings and prices.

The right system should match the electrical characteristics of your test objects, minimize background partial discharge, provide sufficient capacity, and fit your factory's testing environment.

The Sansion SXGTU provides configurable solutions for GIS, GIL, and other high-voltage electrical equipment testing applications.

Planning a new GIS testing laboratory or upgrading your existing high-voltage test facility?

Contact Sansion and share your test object specifications. We can help evaluate the required voltage, capacity, high-voltage generation method, and system configuration for your project.