Characteristic Impedance:
Characteristic impedance is a parameter that describes the behavior of a transmission line. It is the ratio of voltage to current in a wave that propagates along the line. Characteristic impedance is an important factor in determining the performance and efficiency of a transmission line.

Surge Impedance:
Surge impedance is a measure of the ability of a transmission line to transmit electrical energy without reflection. It is defined as the ratio of the voltage to the current during a transient or surge condition. Surge impedance is particularly relevant in situations where there is a sudden change in voltage or current, such as during a lightning strike or a fault condition.

Differences:

1. Definition:
- Characteristic impedance is the ratio of voltage to current in a wave that propagates along the transmission line.
- Surge impedance is the ratio of voltage to current during a transient or surge condition.

2. Behavior:
- Characteristic impedance determines the behavior of a transmission line under steady-state conditions.
- Surge impedance describes the behavior of a transmission line during transient conditions.

3. Reflection:
- Characteristic impedance minimizes reflections in a transmission line by matching the impedance of the source and load.
- Surge impedance determines the ability of a transmission line to handle sudden changes in voltage or current without reflection.

4. Applications:
- Characteristic impedance is important in designing and analyzing transmission lines for efficient power transfer.
- Surge impedance is relevant in assessing the ability of a transmission line to withstand transient conditions, such as lightning strikes or faults.

5. Calculation:
- Characteristic impedance is calculated using the physical and electrical properties of the transmission line, such as its capacitance, inductance, and resistance.
- Surge impedance is derived from the distributed parameters of the transmission line, including its inductance, capacitance, and resistance.

In summary, characteristic impedance describes the behavior of a transmission line under steady-state conditions, while surge impedance relates to its ability to handle transient conditions. Both parameters play crucial roles in the design and analysis of transmission lines, ensuring efficient power transfer and protection against sudden changes in voltage or current.