begin{equation}
label{eqn_33}
UR_i=DR_i=dfrac{P_i^{max}}{2} qquad textrm{(MW/min)} quadforall i\
end{equation}

% arara: pdflatex

documentclass{IEEEtran}
usepackage[fleqn]{mathtools}
setlength{mathindent}{0pt}
usepackage{blindtext} % for demo only
usepackage[per-mode=symbol-or-fraction]{siunitx}

begin{document}
blindtext
begin{equation}
label{eqn_33}
UR_i=DR_i=frac{P_i^text{max}}{2},si{megawattperminute}qquadforall i
end{equation}
Which results in SI{42}{megawattperminute} blindtext
end{document}