A conductor is rated for 180 MVA, a current transformer at one end is rated at 160 MVA, and the bus is rated at 200 MVA. What is the MVA limit for this transmission line?

• A. 160 MVA
• B. 100 MVA
• C. 180 MVA
• D. 200 MVA

Answer: (A)

In determining the MVA limit for a transmission line, it is essential to identify the component with the lowest capacity, as this will ultimately govern the maximum power flow through the line without risking equipment damage or system instability.

In this scenario, the conductor is rated for 180 MVA, which indicates that it can safely carry loads up to that amount. The bus, rated at 200 MVA, is capable of handling a higher capacity; thus, it does not limit the transmission line's ability to operate at a high level.

However, the current transformer, which is rated at 160 MVA, is the component that imposes the most restrictive limit. Current transformers are crucial for accurate current measurement and protection functions in the transmission system. If the current transformer is exceeded by the load, it may not accurately replicate the current, leading to potential protection relay malfunctions and safety hazards.

Since the current transformer has the lowest rating of 160 MVA, this value becomes the limiting factor for the entire transmission line. Therefore, the MVA limit for this transmission line is set at 160 MVA, which aligns with the rating of the current transformer, ensuring safe and effective operation of the system.