Distance Relay

[yaoyaodes]

Can anyone explain to me the 9.2t. I am so confused about the distance relay topic.

 

[xnuke]

For Relay A, the primary impedances for the required distance settings are:

• the Z1 setting is 80% of impedance 1-2, or 0.8(4 + j20) ohms = 3.2 + j16 ohms.
• the Z2 setting is 120% of impedance 1-2, or 1.2(4+l20) ohms = 4.8 + j24 ohms.
• the Z3 setting is 100% of impedance 1-2 plus 120% impedance 2-3, or 1(4 + j20) ohms + 1.2(6 + j24) ohms, for a total of 11.2 + j48.8 ohms.

Since the question asks for the result for each setting in secondary impedance, not primary impedance, you need to divide each of these by the primary-to-secondary impedance ratio, which is the VT ratio/CT ratio, or (600/1)/(200/5), or 15.

Thus, the answer is B