The Lightning Impulse Withstand Voltage
1. What's the lightning impulse withstand voltage?
Definition:
LIWV is the maximum lightning impulse voltage that an insulator or electrical equipment can withstand without experiencing flashover or breakdown. It simulates the effect of a lightning strike on the equipment.
Waveform: Typically a 1.2/50 μs standard impulse wave
1.2 μs = rise time (time from 10% to peak)
50 μs = half-peak time (time from peak to half value)
Unit: kV (kilovolts)
| Test metrics | Purpose |
| LIWV(Lightning Impulse Withstand Voltage) | The insulator is designed to withstand voltage under lightning strikes to prevent flashover. |
| CFO(Critical Flashover Voltage) | Statistical analysis of flashover voltage to verify safety margin |
| BIL(Basic Insulation Level) | System Design and Insulation Coordination Reference |
2. What's the purpose of lightning impulse withstand voltage?
(1) Verifying the Insulator's Withstand Capability to Lightning Strike
Lightning impulse is one of the most common and intense transient overvoltages in high-voltage lines.
The transient voltage waveform of a lightning strike is steep (1.2/50μs), much higher than the peak value of the power frequency voltage.
Through testing, it was determined that the insulator will not flashover or break down under actual lightning strike conditions.
(2) Ensure the safety of the power transmission system
Prevent lightning strikes from causing line flashovers or power outages.
Reduce the risk of equipment damage and improve the reliability and stability of the power transmission system.
Coordinate with system insulation coordination design to ensure that equipment ratings match the system voltage.
(3) Evaluating the rationality of insulator design
Testing lightning impulse withstand voltage can verify the insulator's:
Material selection (silicone rubber/EPDM bushing, etc.)
Geometric design (creepage distance, streamlined design)
Whether the mechanical strength meets design requirements
If the insulator's performance under impulse voltage is substandard, the materials or structure need to be optimized.
(4) Provide standardized parameters
Obtain Impulse Withstand Voltage / LIWV
Obtain Critical Flashover Voltage (CFO)
Used for classifying insulators, preparing technical documents, and providing quotations to customers.
3. Test Procedure
Install the insulator on a test frame.
Apply positive and negative lightning impulse voltages using a high-voltage impulse generator.
Record the voltage at which flashover occurs (Critical Flashover Voltage, CFO).
LIWV is usually the specified voltage the insulator must withstand without flashover during the test.
4.The Testing Standard
IEC 61109 - Composite insulators for AC overhead lines with a nominal voltage ≥ 1000 V
Content:
Specifies the design, performance, and test methods for composite insulators
Includes Lightning Impulse Withstand Voltage (LIWV) test
Considers both positive and negative lightning impulses during testing
Waveform: Standard 1.2/50 μs
Judgment: Record the voltage after flashover or breakdown; passing is within the specified withstand voltage range.