Hi @Ye Zaw, the parameters used to model a surge arrester—specifically the protection voltage (Vref), reference current (Iref), and number of columns—depend on the electrical system’s characteristics and the specific arrester being modeled. MATLAB examples may use default values for demonstration purposes, which is why the parameters may vary across different models.1. Protection Voltage (Vref)
Vref is the voltage across the arrester at a specified reference current (typically 500 A or 1 kA, depending on manufacturer specification). It represents the clamping voltage during a surge and must be:
- Higher than the system’s maximum continuous operating voltage (MCOV) to avoid false triggering,
- Lower than the system’s Basic Insulation Level (BIL) to provide effective protection.
The appropriate value should be selected based on equipment insulation ratings and expected surge conditions.2. Reference Current (Iref)
Iref is the current at which Vref is defined. Manufacturers typically use a standard value (e.g., 500 A) for this reference. It does not vary arbitrarily; it serves to anchor the V-I characteristic of the arrester. This ensures consistent behavior across simulation tools and test standards.
3. Number of Columns
The "number of columns" in a surge arrester model refers to how many stacks of MOV (metal-oxide varistor) elements are used in series. This value scales the total protection voltage and energy handling capability. To determine this:
- Decide the required total protection voltage (e.g., based on your line-to-ground or line-to-line voltage).
- Divide the required voltage by the per-column Vref.
- Round up to the nearest whole number.
For example, if a total protection voltage of 200 kV is needed and each column provides 100 kV at the specified Iref, then 2 columns would be required.Why MATLAB Examples Differ
MATLAB's examples (such as the ones in Simscape Electrical) use generic, illustrative values—such as Vref = 500 kV, Iref = 500 A, and 2 columns—to demonstrate modeling techniques. These values are not intended to represent a specific device or standard. For actual system modeling, these parameters must be determined from:
- Equipment datasheets,
- System voltage levels,
- Surge analysis requirements,
- Manufacturer guidelines.
Hope this helps!
