10kV High Voltage Power Equipment Preventive Maintenance

In modern society, electricity flows like blood through the veins of our cities, powering every aspect of our lives. Behind this vast power system, the stable operation of 10kV power equipment is crucial. To ensure the safety and reliability of these devices, a series of rigorous and often hidden tests are conducted. Today, we will unveil this process.

Preventive testing is a vital component of the operation and maintenance of electrical equipment. It is one of the most effective means to ensure safe operation. During use, electrical equipment is subjected to various factors such as electric field forces, operating temperatures, humidity, and corrosive gases, which can gradually deteriorate insulation conditions. This deterioration is a normal phenomenon; as long as it remains within the operating parameters set by the manufacturer, the equipment can be safely used. However, specific adverse conditions may prevent the equipment from reaching its normal operational lifespan, making regular testing and inspections essential.

These tests help analyze the extent of insulation aging in electrical equipment to ensure compliance with operational requirements. Based on the results of these inspections and tests, appropriate maintenance measures and operational protocols are implemented to maintain equipment performance, ensuring safe, economical, and reliable operation.

The testing requirements include conducting preventive tests and maintenance, along with insulation performance tests annually, in accordance with preventive testing regulations. Relevant test reports must be issued, with two reports provided for inspection and testing results.

High voltage switchgear, Current transformer and voltage transformer, circuit breakers, busbars, transformers, 10kV cables, switchgear, lightning arresters, grounding systems, relay protection devices, and 10kV high voltage busbar tests are all common components in power systems. Regular preventive testing is essential to ensure the safe operation of this equipment. Next, we will discuss the preventive power tests for these common components.

1）High Voltage switchgear Testing

1. Insulation Resistance Test

• Measure the insulation resistance of the switchgear main circuit between phases and to ground.
• Measure the insulation resistance of the control circuit.

2. AC Voltage Withstand Test

• Conduct an AC voltage withstand test on the main circuit to assess its insulation strength.
• Perform an AC withstand voltage test for the secondary circuit.

3. Contact Resistance Test

• Measure the circuit resistance of the main circuit to determine the quality of the contacts.

4.Mechanical Characteristic Test (for Circuit Breakers)

• Measure the opening and closing times and speeds of the circuit breaker.

5. Relay Protection Calibration

• Calibrate the action values, response times, and other parameters of the relay protection device.

6. Grounding Resistance Test

• Measure the grounding resistance of the switchgear to ensure effective grounding.

7. Five Switchgear Prevention Performance Check

• Verify measures to prevent incorrect opening and closing of circuit breakers.
• Ensure that loaded disconnect switches do not open or close inadvertently.
• Prevent grounding wires (grounding switches) from being energized during operation.
• Ensure circuit breakers (disconnect switches) are not closed while grounding wires (grounding switches) are connected.
• Prevent accidental access to energized areas.

8. Instrument Calibration

• Calibrate the accuracy of measuring instruments, such as voltmeters and ammeters.

9. Voltage Transformer and Current Transformer Tests

• Conduct insulation resistance tests.
• Perform variable ratio tests.
• Check polarity.

10. Discharge Counter Operation Test (for Lightning Arresters)

These tests ensure the safe and reliable operation of high voltage switchgear and facilitate the timely detection of potential faults and defects.

2)Current transformer and voltage transformer test

1.Insulation resistance test

• Measure the insulation resistance of primary winding, secondary winding to ground and between windings of the transformer to check whether the insulation performance is good.

2.DC resistance measurement of windings

• To check the conductivity of the windings and whether the resistance value meets the requirements.

3. Ratio test

• To determine whether the actual ratio of the transformer and the nominal ratio is consistent.

4. Polarity check

• To determine whether the polarity of the primary and secondary transformer windings is correct.

5.Excitation characteristic test (only for current transformer)

• Depict the relationship between the excitation current and the induced electromotive force of the secondary winding of the current transformer to check the performance and saturation characteristics of the transformer.

6.Dielectric loss factor (tanδ) test (voltage transformer only)

• Measure the dielectric loss factor of the voltage transformer windings to assess the condition of the insulation.

7.AC voltage withstand test

• Apply the specified AC voltage to the transformer to check the insulation’s ability to withstand the AC voltage.

8. Partial discharge test (for important or large – capacity transformers)

• To detect the existence of local discharge phenomenon inside the transformer and assess the quality of insulation.

The purpose of these tests is to ensure that the transformer can accurately transform the voltage or current in operation, to ensure the normal realization of the functions of measurement, protection and control of the power system, and to guarantee the safe and stable operation of the equipment and system.

3) Circuit Breaker Testing

1. Insulation Resistance Test

• Measure the insulation resistance of the circuit breaker, including phase to phase, phase to ground, and inter break insulation resistance, to assess insulation performance.

2.Contact Resistance Test

• Measure the resistance of the circuit breaker’s conductive loop to determine the quality of the contacts.

3.Breaking Time and Simultaneity Test

• Measure the breaking time of the circuit breaker and the simultaneity of three – phase breaking and closing operations.

4.Tripping Speed Test

• Determine the speed characteristics of the circuit breaker during the opening and closing process.

5.Operating Mechanism Action Characteristics Test

• Evaluate the performance of the operating mechanism, including energy storage, closing, and splitting actions.

6.Low Voltage Action Test

• Assess whether the circuit breaker can operate reliably under low voltage conditions, measuring the timing of opening and closing actions and the synchronization of three phase operations.

7.AC Voltage Withstand Test

• Evaluate the circuit breaker’s ability to withstand AC voltage, checking its insulation integrity.

8.Vacuum Degree Test of Interrupter Chamber (for Vacuum Circuit Breakers)

• Verify that the vacuum level in the interrupter chamber meets specified requirements.

9.Gas Leakage and Water Content Test (for SF6 Circuit Breakers)

• Check for gas leakage and assess the moisture content in SF6 gas.

Through these tests, the performance and reliability of the circuit breaker can be evaluated to ensure its proper operation within the power system.

4) Busbar test

1.Insulation resistance test

• Measure the insulation resistance between phases and to the ground of the busbar to determine whether the insulation is in good condition.

2.AC voltage withstand test

• Apply AC voltage of certain frequency and amplitude to the busbar for a certain period of time to check its insulation resistance under AC voltage.

3.DC resistance test

• Detect the DC resistance of the busbar, used to judge the conductivity of the busbar and whether the contact is good.

4.Temperature rise test

• Measure the temperature rise of the busbar under a certain current load to verify its heat dissipation performance and current carrying capacity.

5.Appearance inspection

• Check whether the surface of the busbar has damage, deformation, corrosion and other defects.

6.Connection part inspection

• Check whether the connection bolts of the busbar are tight, and whether there are abnormal phenomena such as overheating and discoloration at the connection.

These tests and inspection contents help to ensure that the busbar operates safely and reliably in the power system.

5)Transformer Testing

1. Insulation resistance test

• Measure the insulation resistance of transformer windings to ground and between windings to judge the insulation condition.

2.DC Resistance Measurement

• Measure the DC resistance of each winding of the transformer to determine whether there is any short circuit, disconnection or poor contact in the windings.

3.Ratio test

• To determine whether the actual ratio of the transformer matches the nominal value.

4.Polarity and group test

• Check whether the polarity of the transformer and the group of winding connection is correct.

5.No load test

• Apply rated voltage to the primary side of the transformer, measure no load current and no load loss, assess the quality of the iron core and the reasonableness of the magnetic circuit.

6.Short circuit test

• Short circuit the secondary side of the transformer, apply voltage to the primary side, measure the short circuit current and short circuit loss, and calculate the short circuit impedance and other parameters.

7.AC withstand voltage test

• Apply AC voltage to the transformer for a certain time and amplitude to check the ability of its insulation to withstand AC voltage.

8.Partial discharge test

• Detect whether there is partial discharge phenomenon inside the transformer, assess the integrity of insulation.

9.Dielectric loss factor (tanδ) test of windings and bushings

• Used to judge the moisture and deterioration of insulation.

10. On load tap changer test

• To check whether the action sequence, switching time, transition resistance and other parameters of the on load tap changer meet the requirements.

These test items help to ensure the performance and quality of the transformer and guarantee its safe and reliable operation in the power system.

6) 10kV Cable Test

1.Insulation resistance test

• Use megohmmeter to measure the insulation resistance of the cable, including phase – to – phase insulation resistance and phase – to – ground insulation resistance, in order to judge the insulation condition of the cable.

2.DC withstand voltage test and leakage current measurement

• Apply DC voltage to detect the leakage current of the cable under withstand voltage to evaluate the strength of cable insulation.

3.AC withstand voltage test

• It can more effectively find out the local defects in cable insulation.

4.Insulation resistance test of cable outer sheath

• To check the insulation performance of cable outer sheath.

5.Cable main insulation and outer sheath grounding system check

• To ensure good grounding, to ensure safety.

6.Cable phase check

• To ensure the correct phase correspondence between the two ends of the cable.

7.Partial discharge test

• Helps to find out the local defects of insulation in the early stage of the cable.

These tests can effectively evaluate the performance and insulation condition of 10kV cables to ensure their safety and reliability in operation.

7) 10kV Switch Cabinet

1. Insulation Resistance Test

• Measure the insulation resistance of the main circuit of the switchgear between phases and ground, ensuring it is not less than 1000 MΩ.
• The insulation resistance of the secondary circuit should be no less than 1 MΩ.

2. AC Voltage Withstand Test

• Conduct an AC withstand voltage test on the main circuit, typically using a test voltage of 28 kV for 1 minute.
• Perform an AC withstand voltage test for the secondary circuit, with a test voltage of 2 kV for 1 minute.

3.Circuit Breaker Characteristic Test

• Measure the opening and closing times, as well as the simultaneity of the circuit breaker.
• Assess the opening and closing speeds of the circuit breaker.
• Measure the DC resistance and insulation resistance of the switching coil.

4.Circuit Resistance Test

• Measure the circuit resistance of the main circuit, ensuring it meets the product’s technical specifications.

5.Relay Protection Calibration

• Calibrate over – current, quick – break, zero – sequence, and other protection devices to ensure their action values and response times are accurate and reliable.

6. CT and PT Test

• For Voltage Transformers: conduct insulation resistance tests, ratio tests, polarity checks, and no – load current tests.
• For Current Transformers: perform insulation resistance tests, ratio tests, polarity checks, and volt – ampere characteristic tests.

7. Lightning Arrester Test

• Conduct an insulation resistance test.
• Measure leakage current with a DC reference voltage of 1 mA and 0.75 times the DC 1 mA reference voltage.

8.Earth Resistance Test

• Test the grounding resistance of the switchgear to ensure it meets design requirements.

9.Five Prevention Function Check

• Verify that the switchgear includes functions to prevent incorrect opening and closing of circuit breakers, prevent opening and closing of disconnect switches under load, prevent grounding wires (grounding switches) from being energized, prevent circuit breakers (disconnect switches) from closing with grounding wires (grounding switches), and prevent accidental access to electrically energized areas.

10.Switchgear Mechanical Operation and Interlocking Test

• Perform manual and electrical opening and closing operations to assess the flexibility and reliability of the operating mechanism.
• Check the reliability of both mechanical and electrical interlocking systems.

8) Lightning Arrester Test

1.Insulation Resistance Test

• Use a megohmmeter to measure the insulation resistance of the surge arrester, ensuring it demonstrates good insulation performance.

2.Leakage Current Measurement

• Measure the leakage current under a DC reference voltage of 1 mA and at 0.75 times this voltage to determine the operating voltage of the arrester and verify that the leakage current meets the requirements.

3.AC Leakage Current Measurement Under Operating Voltage

• Monitor the leakage current of the arrester during normal operating conditions.

4.Discharge Counter Action Check

• Verify the functionality of the discharge counter and record the number of times the arrester operates.

These tests help assess the performance and condition of the arrester, ensuring it can effectively protect electrical equipment from lightning overvoltage and operational overvoltage damage in the power system.

9) Grounding Test

1.Grounding Resistance Measurement

• This is the core aspect of the grounding test. Use a specialized grounding resistance tester to measure the resistance of the grounding device, ensuring it meets design and specification requirements.

2.Grounding Conductivity Test

• Evaluate the conductivity of connections within the grounding system to ensure that current can pass through smoothly.

3.Soil Resistivity Measurement

• Assess the soil characteristics surrounding the grounding device to provide a basis for grounding design and evaluation.

4.Contact Potential Difference and Step Potential Difference Measurements

• For large grounding systems, especially in areas where personnel may be close, measure contact potential differences and step potential differences to ensure safety.

5.Grounding Device Integrity Check

• Inspect the grounding lead wire for corrosion or breakage and ensure that the grounding electrode is secure.

6.Connection Reliability Test of the Grounding System

• Verify the firmness and reliability of connections between the grounding pole and the grounding network.

By conducting these grounding tests, you can comprehensively assess the performance and safety of the grounding system, allowing for timely detection and resolution of potential issues, thereby ensuring the grounding system effectively supports the normal operation of electrical equipment and personnel safety.

10) Relay Protection Test

1.Appearance Inspection

• Check the device for any damage, deformation, and ensure that the terminals are secure.

2.Insulation Resistance Test

• Measure the insulation resistance of the relay protection device to confirm its insulation performance.

3.Inverter Power Supply Check

• Test the stability and precision of the output voltage from the inverter power supply.

4.Preliminary Energization Check

• Power the device and verify that its display, indicator lights, and other functionalities are operating normally.

5.Switching Input Circuit Check

• Confirm the correctness and responsiveness of the switching input.

6.Output Contact and Signal Check

• Ensure the output contacts function accurately and that the output signals are normal.

7.Analog to Digital Conversion System Check

• Test the accuracy and linearity of the analog input.

8.Calibration of Setting Values

• Input analog fault quantities according to the set values and check whether the protective device’s response meets specifications.

9.Action Time Test

• Measure the response time of the protective device during a fault condition to ensure it meets specified time requirements.

10.Longitudinal Protection Channel Test (if applicable)

• For devices using longitudinal protection, check the performance of the communication channel.

11.Cooperation Test with Other Protection Devices

• Verify that this device coordinates effectively with related protection devices.

These tests are designed to ensure that the relay protection device operates accurately and reliably, contributing to the safety and stability of the power system.

11) 10kV High Voltage Busbar Test

1.Insulation Resistance Test

• Use a megger tester to measure the insulation resistance of the busbar to assess its insulation performance.

2.AC Withstand Voltage Test

• Apply an AC test voltage of a specified frequency and voltage to check if the busbar can withstand the specified voltage without breakdown or flashover.

3.Busbar Connection Point Contact Resistance Test

• Verify the quality of contact at the busbar connection points, ensuring the contact resistance is within normal ranges.

4. Partial Discharge Test (if necessary)

• Detect any local discharge phenomena in the busbar under operating voltage.

These tests ensure that the 10kV high – voltage busbar operates safely and reliably, allowing for timely identification and resolution of potential issues.

With the continuous advancement of science and technology, testing methods for 10kV power equipment are continually innovating and developing. I believe that in the future, more advanced and efficient testing methods and technologies will emerge to support the safe and stable operation of power systems.