If a transformer rated at 100 MVA has 80 MW flowing through it, how many MVARS could it support before reaching its limit?

To determine how many MVARS a transformer can support before reaching its limit, it's important to understand the relationship between the real power (measured in MW) and the apparent power (measured in MVA) expressed in the formula:

Apparent Power (S) = √(Real Power (P)² + Reactive Power (Q)²)

In this scenario, the transformer has a rating of 100 MVA and is currently carrying 80 MW (real power). To find the maximum reactive power (Q) the transformer can handle, we can rearrange the formula:

Q = √(S² - P²)

Substituting the known values:

S = 100 MVA

P = 80 MW

Calculating Q:

Q = √(100² - 80²)

Q = √(10000 - 6400)

Q = √3600

Q = 60 MVAR

This result indicates that the transformer can support an additional 60 MVAR of reactive power before reaching its apparent power limit of 100 MVA. Therefore, the correct answer is that the transformer can support 60 MVAR before it reaches its limit, confirming that option B is the accurate choice.