# Transmission line current magnitude

I want to compute the current magnitude in a transmission line. The line has properties b (total line charging susceptance, p.u.), x (reactance, p.u.), and r (resistance, p.u.). I'm confused about what value of resistance I need to use in Ohm's law and the difference between b, x, and r parameters.

When I compute the flow magnitude (section 4.1.1) as

$$\ |y_{\text{snd},\text{rec}}| \times |V_{\text{snd}} e^{jA_{\text{snd}}} - V_{\text{rec}} e^{jA_{\text{rec}}}| \$$

where $$\V_{\text{snd}}\$$ is the voltage magnitude at the "sending" bus and $$\A_{\text{snd}}\$$ is the voltage angle at the "sending" bus (and rec denotes "receiving" bus), how do I compute the magnitude of the branch admittance, $$\|y_{\text{snd},\text{rec}}|\$$, from b, x, and r?

I'm confused because if $$\y_{\text{snd},\text{rec}}\$$= r / (r^2 + x^2) - j x / (r^2 + x^2), then what is the purpose of the line charging b? Or is $$\y_{\text{snd},\text{rec}}\$$= 1/b?

• This site supports limited TeX (I believe specifically Mathjax), which would help make your equations more readable. – Hearth May 27 '20 at 17:00
• Your notation: from/to etc, is confusing. Also, the two ends of a transmission line are normally referred to as the 'sending end', SE, and 'receiving end', RE. – Chu May 27 '20 at 17:23
• @Chu: ok, i replace from/to with send/receive – rrrrr May 27 '20 at 17:55