Measurement Methods Of High Voltage Generator

A high voltage generator, also known as a DC high voltage generator or direct-current high voltage generator, is widely used to evaluate the insulation condition of electrical equipment.

During a high voltage test, the generator applies a controlled DC voltage to the test object while the measuring system monitors leakage current, insulation behavior, and possible defects. These measurements help identify insulation aging, moisture, contamination, and other conditions that may affect the reliability of high voltage equipment.

Typical test objects include:

Zinc oxide surge arresters

Power cables

Power transformers

Generators

Motors

Bushings and other high voltage apparatus

DC voltage testing falls under IEC 60060‑1 high‑voltage test specifications. Always set test voltage, test duration, measurement configuration and acceptance criteria in accordance with applicable industry standards and original‑equipment‑manufacturer instructions.

Weshine Electric Manufacturing Co., Ltd. is a specialized manufacturer of DC high‑voltage generators and high‑voltage test accessories. Its R&D team follows IEC standards and accumulates rich practical experience from numerous on‑site power testing projects worldwide.

Safety Notice: The procedures below are general technical guidance, not a substitute for the equipment manufacturer's manual, site-specific risk assessment, or applicable electrical safety regulations. High-voltage testing and discharge operations must only be performed by trained and authorized personnel.

1. Measurement with a Microammeter

A microammeter is commonly used to measure the leakage current of high voltage equipment. Because the current under test may be extremely small, correct shielding and wiring are essential for obtaining reliable results.

Instrument Requirements

The microammeter should have a metal shielding structure and be specifically designed for high voltage testing.

A properly shielded instrument helps reduce:

External electric field interference

Stray current

Electromagnetic coupling

Unstable readings caused by the test environment

A standard, unshielded current meter may produce inaccurate or fluctuating readings and should not be used as a substitute for a dedicated high voltage measuring instrument.

Shielded Wiring Method

The test object should be connected to the microammeter using a suitable shielded cable. The shielding outlet of the high voltage lead must be firmly connected to the shielding terminal of the measuring instrument.

Before energizing the test circuit, check the following points:

1.The shielded cable is securely connected to the test object.

2.The high voltage lead shield is correctly connected to the instrument shield.

3.The shielding layer has no damage or loose connection.

4.The measuring circuit is separate from control and communication cables.

5.The grounding arrangement complies with the test equipment manual.

The purpose of the shield is to provide a controlled path for interference and surface leakage current, preventing these currents from entering the effective measuring circuit.

Dealing with a Contaminated Test Surface

Dust, moisture, oil, and salt contamination on the surface of a test object can create a surface leakage current. This current may flow across the insulation surface and cause the microammeter to display a value higher than the actual internal leakage current.

When necessary, a bare metal flexible wire can be wound around the contaminated surface area and connected to the shield of the high voltage lead. This arrangement helps divert surface leakage current away from the measuring circuit.

The wire should be installed carefully:

Make sure it is in continuous contact with the intended surface area.

Avoid damaging the insulation.

Keep the shielding connection secure.

Prevent accidental contact with the wrong terminal.

Clean and dry the test object whenever possible.

Shielding is intended to reduce measurement interference. It is not a replacement for cleaning, drying, or repairing contaminated insulation.

2. Measurement of Zinc Oxide Surge Arresters

Zinc oxide surge arresters are commonly tested by measuring their DC leakage current. Changes in leakage current may indicate moisture, contamination, aging, or deterioration of the metal oxide varistors.

The test result should not be judged by a single value alone. Temperature, humidity, rated voltage, test voltage, arrester type, and previous test records should also be considered. IEC 60099-5 provides application guidance for metal-oxide surge arresters used in high voltage systems. IEC 60099-5

Microammeter Installation Position

When the grounding terminal of the surge arrester can be disconnected, the microammeter is generally installed on the grounding-potential side.

This arrangement provides a clearer measuring circuit and keeps the instrument at a relatively lower potential during the test. Before making the connection, ensure that the surge arrester is completely isolated from the operating system.

The test team should verify:

The arrester model and rated voltage

The correct test voltage

The isolation of all connected equipment

The polarity and wiring of the test circuit

The condition of the grounding system

Reducing Surface Leakage Current

If the arrester surface is wet or contaminated, surface leakage current may flow toward the grounding terminal and interfere with the measurement.

To reduce this effect, a bare copper wire can be wound around the grounding end of the arrester and connected to the shield wire. This allows surface leakage current to bypass the microammeter and improves the accuracy of the body leakage current measurement.

For proper analysis, record the following information:

Test voltage

Leakage current

Ambient temperature

Relative humidity

Arrester identification and rated parameters

Differences between phases or individual units

Comparison with previous test results

A significant difference between similar arresters should lead to a further inspection of the connections, surface condition, measuring instrument, and arrester itself.

3. Safe Discharge After Testing

A high voltage test is not complete when the generator stops producing voltage. The test object and high voltage cables may still retain dangerous electrical energy.

Small-Capacitance Equipment

Small-capacitance equipment, such as zinc oxide surge arresters, can normally be discharged through the voltage-measuring resistance or the discharge resistance built into the test system.

After the initial discharge, use an approved discharge rod to confirm that no hazardous residual voltage remains. The equipment should then be grounded before the test leads are touched or removed.

Large-Capacitance Equipment

Large-capacitance equipment, such as power cables, should not normally be discharged suddenly at full test voltage.

The equipment should first be allowed to self-discharge until the residual voltage falls below approximately 20% of the test voltage. A suitable discharge rod can then be used for the remaining charge.

The general sequence is:

1.Stop the high voltage output.

2.Allow the test object to discharge through the designated circuit.

3.Confirm that the voltage has fallen to a safe level.

4.Discharge the equipment with a correctly rated discharge rod.

5.Verify the absence of hazardous voltage.

6.Apply the grounding cable completely and securely.

7.Remove the high voltage leads only after grounding is confirmed.

The discharge time and method depend on the capacitance of the equipment, test voltage, discharge resistance, and test equipment design. Always follow the manufacturer’s instructions and site safety procedures.

4. Essential Safety Requirements

High voltage generator testing must only be performed by trained and authorized professionals. Operators should hold the required high voltage testing certificate or equivalent qualification recognized in their region.

High voltage test work requires knowledge of:

Electrical insulation systems

High voltage test equipment

Grounding and discharge procedures

Electric shock and arc flash hazards

Safe approach distances

Emergency shutdown procedures

Before testing, the team should inspect the test area, establish barriers, display warning signs, and prevent unauthorized personnel from entering. High voltage testing procedures should also include test-area protection, safe grounding, secure measuring and control circuits, and periodic safety checks. OSHA Testing and Test Facilities

Only qualified personnel should enter the controlled test area or work with high voltage test connections. Training requirements should cover electrical hazards, equipment operation, voltage identification, and the procedures needed to control or avoid exposure. OSHA Qualified Person Requirements

Frequently Asked Questions

Q：What is a high voltage generator used for?

A：A high voltage generator is used to apply a controlled high voltage to electrical equipment and measure insulation performance, leakage current, and dielectric strength.

Q：Why is a shielded microammeter necessary?

A：Leakage current is often very small and can be affected by external electric fields and stray currents. A shielded microammeter helps reduce interference and improve measurement stability.

Q：How is a zinc oxide surge arrester tested?

A：The arrester is isolated from the system, connected to a DC high voltage generator, and tested by measuring leakage current from the grounding-potential side. The surface condition and shielding arrangement must also be considered.

Q：Why must a power cable be discharged gradually?

A：A power cable has relatively high capacitance and can store a dangerous amount of electrical energy. Gradual discharge reduces the risk of equipment damage, flashover, and electric shock.

Q：Does a lower leakage current always mean better insulation?

A：Not necessarily. Leakage current must be evaluated together with test voltage, temperature, humidity, equipment specifications, and historical test data.

Conclusion

Accurate high voltage generator measurement depends on more than applying the correct test voltage. Proper microammeter shielding, reliable wiring, surface leakage control, correct surge arrester connections, and complete discharge procedures are all essential.

Whether testing surge arresters, power cables, transformers or rotating machinery, strictly execute tests complying with relevant IEC standards, manufacturer specifications and local electrical‑safety regulations. High‑voltage testing must never be performed by untrained personnel.

Weshine Electric Manufacturing Co., Ltd. develops and manufactures a full portfolio of high‑voltage test instruments complying with international IEC standards. If you are looking for reliable DC high‑voltage generators and supporting measuring accessories for your power‑testing tasks, feel free to contact our technical team for further support.

For field‑work convenience, use matched high‑voltage test accessories including shielded measuring cables and certified discharge rods to reduce on‑site measurement errors and safety risks.