change docs

Signed-off-by: Tony Xiang <19280867+TonyXiang8787@users.noreply.github.com>

Author: TonyXiang8787

docs/user_manual/components.md

@@ -614,9 +614,9 @@ The impedance is specified by convention as short circuit power.
 |---------------|-----------|------------------|----------------------------------------------------|:----------------------------:|:--------:|:------------:|
 | `u_ref`       | `double`  | -                | reference voltage in per-unit                      | ✨ only for power flow | ✔ |    `> 0`     |
 | `u_ref_angle` | `double`  | rad              | reference voltage angle                            |    ❌ default `0.0`    | ✔ |              |
-| `sk`          | `double`  | volt-ampere (VA) | short circuit power                                |   ❌ default `1e10`    | ❌ |    `> 0`     |
-| `rx_ratio`    | `double`  | -                | R to X ratio                                       |    ❌ default `0.1`    | ❌ |    `>= 0`    |
-| `z01_ratio`   | `double`  | -                | zero-sequence to positive sequence impedance ratio |    ❌ default `1.0`    | ❌ |    `> 0`     |
+| `sk`          | `double`  | volt-ampere (VA) | short circuit power                                |   ❌ default `1e10`    | ✔ |    `> 0`     |
+| `rx_ratio`    | `double`  | -                | R to X ratio                                       |    ❌ default `0.1`    | ✔ |    `>= 0`    |
+| `z01_ratio`   | `double`  | -                | zero-sequence to positive sequence impedance ratio |    ❌ default `1.0`    | ✔ |    `> 0`     |
 
 #### Electric Model