Symmetrical Components Example Problem
Symmetrical Components Example Problem
(OP)
Hello,
I'm trying to teach myself a little about symmetrical components, and am in the middle of a problem. To any who has a copy of the Westinghouse Transmission and Distribution Reference Book (or would like a pdf http:// www.scribd .com/doc/7 010747/Ele ctrical-Tr ansmission -and-Distr ibution-Re ference-Bo ok-of-We-S ting-House), please refer to the example problem at the end of Chapter 2: Symmetrical Components (From previous posts it seems many out there have this book).
"It should be remembered that unit I_0 is one ampere in each of the three line conductors with three amperes returning to ground; unit Ig is 3/2 amperes in each of the two ground wires with three amperes returning in the ground; unit I'0 is one ampere in each of the three line conductors with three amperes returning in the ground; and unit I'g is three amperes in the ground wire with three amperes returning to ground"
Where did those numbers come from?
Also, in order to determine the zero-sequence self reactance in the presence of all zero-sequence circuits, E0/I0 = 2.05 ohms/mile, E'0/I'0 = 2.25 ohms/mile, and E'0/I0 = 0.87 ohms per mile from the 110kV self, 66kV self, and mutual impedances, respectively. I don't understand how these numbers were found.
If anyone has worked through this problem before or has any immediate thoughts as to the solution, I'd appreciate the help.
I'm trying to teach myself a little about symmetrical components, and am in the middle of a problem. To any who has a copy of the Westinghouse Transmission and Distribution Reference Book (or would like a pdf http://
"It should be remembered that unit I_0 is one ampere in each of the three line conductors with three amperes returning to ground; unit Ig is 3/2 amperes in each of the two ground wires with three amperes returning in the ground; unit I'0 is one ampere in each of the three line conductors with three amperes returning in the ground; and unit I'g is three amperes in the ground wire with three amperes returning to ground"
Where did those numbers come from?
Also, in order to determine the zero-sequence self reactance in the presence of all zero-sequence circuits, E0/I0 = 2.05 ohms/mile, E'0/I'0 = 2.25 ohms/mile, and E'0/I0 = 0.87 ohms per mile from the 110kV self, 66kV self, and mutual impedances, respectively. I don't understand how these numbers were found.
If anyone has worked through this problem before or has any immediate thoughts as to the solution, I'd appreciate the help.






RE: Symmetrical Components Example Problem
Solving for Ia, you get Ia = I1 + I2 + I0 or Ia = 3 * I0, a result that is common to most relay engineers. This gives you the 3:1 ratio that the Westinghouse authors (Hobson and Whitehead) mentions.
Because you have 2 ground wires, each ground wire carries half of the fault current (Ia/2) or 3/2 * I0.