Lightning Arrester Connection Calculator – IEC, IEEE

Lightning arresters are critical devices designed to protect electrical systems from transient overvoltages. Calculating their connection parameters ensures optimal performance and safety.

This article explores lightning arrester connection calculations based on IEC and IEEE standards. It covers formulas, tables, and real-world examples for engineers.

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• Calculate arrester energy absorption for a 33 kV distribution line.
• Determine maximum continuous operating voltage (MCOV) for a 11 kV system.
• Compute protective level voltage for a 132 kV substation arrester.
• Find arrester residual voltage for a 66 kV transmission line.

Common Values for Lightning Arrester Connection – IEC and IEEE Standards

Fundamental Formulas for Lightning Arrester Connection Calculations

Lightning arrester calculations involve several key parameters to ensure proper protection and coordination with the electrical system. Below are the essential formulas used in IEC and IEEE standards.

1. Maximum Continuous Operating Voltage (MCOV)

The MCOV is the highest RMS voltage the arrester can continuously withstand without degradation.

• V_system: System RMS voltage (line-to-ground for single-phase systems)
• Typically, MCOV is set 5% above the system voltage to accommodate voltage fluctuations.

2. Protective Level Voltage (Up)

The protective level voltage is the maximum voltage that appears across the arrester terminals during a discharge current.

• k: Protective factor, typically between 1.3 and 1.5 depending on arrester design and system requirements.
• Up must be lower than the insulation level of the protected equipment.

3. Residual Voltage (Ur)

Residual voltage is the voltage across the arrester during the flow of surge current.

• ΔV: Additional voltage drop due to arrester internal resistance, typically 5-10% of Up.
• Ur must be less than the equipment’s withstand voltage to prevent damage.

4. Energy Absorption (W)

Energy absorbed by the arrester during a surge is calculated as:

• v(t): Voltage across arrester as a function of time.
• i(t): Surge current through arrester as a function of time.
• For practical purposes, energy is often approximated using standard surge waveforms (e.g., 8/20 µs current wave).

5. Residual Voltage for Specific Surge Current (Ir)

Residual voltage at a given surge current is often provided by manufacturer curves or approximated by:

• R: Dynamic resistance of arrester during surge (Ω).
• I_r: Surge current (kA).
• This formula helps estimate voltage stress on equipment during surges.

6. Coordination of Arrester with System Insulation

To ensure proper coordination, the arrester’s protective level voltage must be less than the equipment’s insulation level:

• V_insulation: Equipment insulation withstand voltage.
• Safety margin typically ranges from 5% to 15% depending on system criticality.

Real-World Application Examples of Lightning Arrester Connection Calculations

Example 1: Selecting a Lightning Arrester for a 33 kV Distribution Line (IEC Standard)

A 33 kV distribution line requires a lightning arrester to protect a transformer. The system RMS voltage is 33 kV line-to-line. The transformer insulation withstand voltage is 75 kV peak. Calculate the MCOV, protective level voltage, and verify if the arrester is suitable.

• Step 1: Calculate system line-to-ground voltage (V_system):

• Step 2: Calculate MCOV:

• Step 3: Calculate protective level voltage (assuming k = 1.4):

• Step 4: Check if Up is less than transformer insulation voltage:

The selected arrester with MCOV 20 kV and protective level 28 kV is suitable for protecting the transformer.

Example 2: Calculating Residual Voltage for a 132 kV Substation Arrester (IEEE Standard)

A 132 kV substation arrester has an MCOV of 132 kV. The dynamic resistance during surge is 0.5 Ω. Calculate the residual voltage when the arrester discharges a surge current of 10 kA.

• Step 1: Calculate protective level voltage (assuming k = 1.35):

• Step 2: Calculate residual voltage:

• Step 3: Verify if residual voltage is within equipment insulation limits (assumed 200 kV):

The arrester’s residual voltage during surge is within safe limits, ensuring equipment protection.

Additional Technical Considerations for Lightning Arrester Connections

• Surge Current Waveforms: IEC and IEEE recommend using 8/20 µs current waveforms for nominal discharge current ratings, while 10/350 µs waveforms are used for maximum discharge current ratings.
• Arrester Installation Location: Proper placement near equipment terminals minimizes lead length and reduces voltage stress.
• Coordination with Insulation Levels: Arrester protective level must be coordinated with system insulation to prevent flashovers.
• Temperature Effects: Arrester characteristics vary with temperature; derating may be necessary in extreme conditions.
• Multiple Arrester Configurations: For high voltage systems, series or parallel arrangements may be used to achieve desired voltage ratings and energy absorption.
• Maintenance and Testing: Regular testing per IEC 60099-5 or IEEE C62.11 ensures arrester reliability.

References and Further Reading

• IEC 60099-4: Surge Arresters – Part 4: Selection and Application Recommendations
• IEEE C62.11-2012: IEEE Standard for Metal-Oxide Surge Arresters for AC Power Circuits
• NEMA Surge Arrester Standards and Guidelines
• DOE Lightning Protection Guide