Integral sign is not showing in beamer

Question

The integral sign is not showing when I generate my slides using beamer, any idea how to resolve this matter. Thanks in advance,

The minimal code

\documentclass{beamer}
\usepackage[capitalise]{cleveref}
\usepackage{textpos}
 \usepackage{pbox}
 \newcommand<>{\itemarrow}{\mbox{}\visible#1{\llap{\color{structure}$\rightarrow$\hspace{1.5em}}}}
 \usepackage{xcolor}
\usepackage[english]{babel}
\usepackage[american voltages,siunitx]{circuitikz}
\newcommand*{\equal}{=}
\usepackage{multicol}
\newcommand{\tikzmark}[1]{\tikz[overlay,remember picture] \node (#1) {};}
\usepackage[latin1]{inputenc}
\usepackage{amsmath,amsthm, amssymb, latexsym}
\usepackage{makecell, multirow, booktabs}
\usepackage[libertine,cmintegrals,cmbraces,vvarbb]{newtxmath}
\usepackage[scaled=0.95]{inconsolata}
\usepackage{IEEEtrantools}
\usepackage{relsize}
\usepackage{smartdiagram}
\usepackage{booktabs}
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\usepackage{xcolor}
\usepackage{tcolorbox}
\usepackage{smartdiagram}
\definecolor{darkred}{rgb}{0.55, 0.0, 0.0}
\setbeamertemplate{navigation symbols}{}
 \usepackage{relsize}
\definecolor{myblue}{rgb}{0.0, 0.18, 0.39}
\definecolor{lava}{rgb}{0.81, 0.06, 0.13}
\definecolor{mordantred19}{rgb}{0.68, 0.05, 0.0}
\usecolortheme[named=myblue]{structure}
\setbeamerfont{block body}{size=\scriptsize}
\newcommand\Fontvi{\scriptsize\selectfont}
\titlegraphic{}
\usepackage{xcolor,soul}
\definecolor{lightblue}{rgb}{.90,.95,1}
\sethlcolor{lava}
\renewcommand<>{\hl}[1]{\only#2{\beameroriginal{\hl}}{#1}}
\newenvironment{squareenv}{\only{\setbeamertemplate{items}[square]}}{}
% https://tex.stackexchange.com/questions/41683/why-is-it-that-coloring-in-soul-in-beamer-is-not-visible
\makeatletter
\newcommand\SoulColor{%
  \let\set@color\beamerorig@set@color
  \let\reset@color\beamerorig@reset@color}
\makeatother
\SoulColor
\mode<presentation>{\usetheme{Singapore}}
 \useinnertheme{circles}
 \usepackage{tikz}
 \usepackage{pst-sigsys}
\usetikzlibrary{shapes,arrows,positioning,calc}
\usesmartdiagramlibrary{additions}
\usepackage{tikz}
\usetikzlibrary{overlay-beamer-styles}
 \tikzset{
    highlight on/.style={alt={#1{fill=red!80!black,color=red!80!black}{fill=gray!30!white,color=gray!30!white}}},
}
 \usepackage[font=scriptsize, labelfont=bf]{caption}
 \setbeamercolor{block title}{use=structure,fg=white,bg=myblue}
\setbeamercolor{block body}{use=structure,fg=black,bg=white}
\usefonttheme{serif}
\title{ENEC 250 ELECTRIC CIRCUITS II}
\author{Instructor: Dr. Diana Dawoud}
%\institute[ICS]{Institute of Communication Systems (ICS)}
\date{\today}
\setbeamertemplate{footline}{
   \begin{beamercolorbox}[ht=4ex,leftskip=1.4cm,rightskip=.3cm]{author in head/foot}
    \usebeamercolor{myblue}
    \hrule
    \vspace{0.1cm}
      \insertframenumber
   \end{beamercolorbox}
   \vspace*{0.1cm}
} 

 \renewcommand{\familydefault}{\rmdefault}
\setbeamercolor{section number projected}{fg=}





\usetikzlibrary{chains}


\usepackage{animate}


\usepackage{multido}


\usetikzlibrary{calc,intersections}


\newsavebox\myAnim

\usepackage{ifthen}




\newcommand\layera{%
\begin{tikzpicture}[y=0.20pt,x=0.20pt,yscale=-1, inner sep=0pt, outer sep=0pt]
  \path[cm={{0.8028232,-0.59621716,0.59621716,0.8028232,(0.0,0.0)}},draw=black,opacity=0.990,miter
    limit=4.00,line width=0.943pt,rounded corners=0.0000cm] (-99.8372,584.6912)
    rectangle (-30.7483,653.7801);
  \end{tikzpicture}
}

\newcommand\layerb{%
\begin{tikzpicture}[y=0.20pt,x=0.20pt,yscale=-1, inner sep=0pt, outer sep=0pt]
    \fill[blue!40] (0,0) circle (1);
\end{tikzpicture}
}

\newcommand\layerc{%
\begin{tikzpicture}[y=0.20pt,x=0.20pt,yscale=-1, inner sep=0pt, outer sep=0pt]
    \fill[red!40] (0,0) circle (1);
\end{tikzpicture}
}


\usepackage{ifthen}
    \usepackage{xcolor}
    \definecolor{lava}{rgb}{0.81, 0.06, 0.13}
    \definecolor{myblue}{rgb}{0.0, 0.30, 0.60}
     \definecolor{myblue2}{rgb}{0, 0.1, 0.1}
    
    \usepackage{tikz}
    \usepgflibrary{shapes.symbols}
    \usetikzlibrary{mindmap,trees,arrows,shapes.symbols,shapes.misc}
    \usepackage[ampersand]{easylist}
    \usepackage{lmodern}
    \usetikzlibrary{shapes}
\usepackage{gensymb}
\usepackage{nccmath}
\usepackage{tikz-3dplot} %requires 3dplot.sty to be in same directory, or in your LaTeX installation

\usepackage[active,tightpage]{preview}  %generates a tightly fitting border around the work

\setlength\PreviewBorder{2mm}

\makeatletter
\AtBeginPart{%
  \beamer@tocsectionnumber=0\relax
  \setcounter{section}{0}%
}


\usepackage{hyperref}
\hypersetup{pdfpagemode=FullScreen}
\usepackage{ifthen}
\usepackage{animate}
%

%

        
        \usepackage{relsize}
        \usepackage{amsmath,amsthm, amssymb, latexsym}
        \begin{document}
        
        \begin{frame}{RMS Value}
     \onslide<1->{\begin{itemize}
     \item Substitute Eq.1 to Eq.2:
      \begin{align*}
      V_{ms}&=\dfrac{1}{T} \int_{-\tfrac{T}{2}}^{\tfrac{T}{2}}v^2(t)dt \\
      &=\dfrac{1}{T}\int_{-\tfrac{T}{2}}^{\tfrac{T}{2}} \dfrac{V^2_m}{2} dt+ \dfrac{1}{T} \int_{-\tfrac{T}{2}}^{\tfrac{T}{2}}v^2(t)dt \\
      &=\dfrac{1}{T}\mathlarger{\int}_{-\tfrac{T}{2}}^{\tfrac{T}{2}}\dfrac{V^2_m}{2}\cos(2\omega+2\theta_v). 
       \end{align*}
       \onslide<2->{
     \item The root mean square (RMS) value is the square root of the mean square value. For sinusoids, we have
     \begin{center}
     $V_{rms}=\dfrac{V_m}{2}= 0.7071V_m$
    \end{center}}
     \onslide<3->{
     \item  Peak value $V_m$ from RMS value ($V_{rms}$)$\Rightarrow$  $V_m =\sqrt{2}V_{rms} = 1.4142 V_{rms}$
     }
    \end{itemize}
    }
    
    \end{frame}
        \end{document} 

The result

Answer 1

You were right, this is the package that caused the problem

\usepackage[libertine,cmintegrals,cmbraces,vvarbb]{newtxmath}

Answer 2

Very late, but with hope that my answer still may help you or someone else.

You have serious problems with document preamble. It is big mess, many package are loaded twice or more, some packages as xcolor, hyperref, amsmath, are already loaded by by beamer, some packages are sensitive on order of loading (for example, cleveref had to be the last). So, please, clean-up preamble and at this at each package ask yourself, do you really need it (for example IEEEtrantools).

It is expected that in question you provide MWE (Minimal Working Example), i.e. a small but self contained document, which reproduce your problem, something like as is my answer below (which from preamble consider only packages relevant to your problem).

Cause of your problem (not seeing integrals signs) is order of loading packages dedicated to font selections. If you will move lmodern before newtxmath with desired options, you will get desired result.

Off-topic:

• if you have equation in display mode, than fractions are in display mode too, so you not need to use \dfrac, just \frac is sufficient
• I don't see any reason, that integral sign in the last line in the align* equations is bigger.
• to my taste is better to leave to the LaTeX to choose the right size of fraction of integral limits
• instead of \onslide<1->{...}, etc is simpler to use mechanism, which is offered by itemize in beamer: \item<1->, \item<2->, etc

A possible MWE:

\documentclass{beamer}

\usepackage{lmodern}
\usepackage[libertine,cmintegrals,cmbraces,vvarbb]{newtxmath}
\usepackage[scaled=0.95]{inconsolata}
\usepackage{nccmath}            % not used in MWE
\usepackage{amsthm, amssymb, latexsym}
\DeclareMathOperator{\ms}{ms}   % mean square
\DeclareMathOperator{\rms}{rms} % root mean square
\usepackage{relsize}            % not used in MWE, do you really need it?
        
        
\begin{document}

\begin{frame}{RMS Value}
    \begin{itemize}
\item<1-> Substitute Eq.1 to Eq.2:
    \begin{align*}
V_{\ms} & = \frac{1}{T} \int_{-\frac{T}{2}}^{\frac{T}{2}}v^2(t)dt       \\
        & = \frac{1}{T} \int_{-\frac{T}{2}}^{\frac{T}{2}} \frac{V^2_m}{2} dt
                + \frac{1}{T} \int_{-\frac{T}{2}}^{\frac{T}{2}}v^2(t)dt  \\
        & = \frac{1}{T} \int_{-\frac{T}{2}}^{\frac{T}{2}}
                        \frac{V^2_m}{2}\cos(2\omega+2\theta_v).
\end{align*}

\item<2-> The root mean square (RMS) value is the square root of the mean square value. For sinusoids, we have
    \[
V_{rms}=\frac{V_m}{2}= 0.7071V_m
    \]

\item<3->  Peak value from RMS value is: 
    \[
V_m =\sqrt{2}V_{\rms} = 1.4142 V_{\rms}
    \]
\end{itemize}

\end{frame}
\end{document}

which at last slide gives:

I took a liberty and slightly reformat your equations (I'm not sure in its validity, the second line in align* is suspicious to me).