Modelica model:

model Resistor "Ideal linear electrical resistor" 
  extends Modelica.Electrical.Analog.Interfaces.OnePort;
  parameter SIunits.Resistance R=1 "Resistance";
equation 
  R*i = v;
end Resistor;

;;; OnePort is a primitive which defines i, v, ...

(defmetamodel modelica-Resistor
    :external-terminals (p n)
    :includes Modelica.Electrical.Analog.Interfaces.OnePort
    :description "Ideal linear electrical resistor" 
    :source <complete modelica model as a string>
    :parameters ((R 1 SIunits.Resistance "Resistance"))
    :equations (= (* R i) v))


model Capacitor "Ideal linear electrical capacitor" 
  extends Modelica.Electrical.Analog.Interfaces.OnePort;
  parameter SIunits.Capacitance C=1 "Capacitance";
equation 
  i = C*der(v);
end Capacitor;

(defmetamodel modelica-Capacitor
    :external-terminals (p n)
    :description "Ideal linear electrical capacitor" 
    :includes Modelica.Electrical.Analog.Interfaces.OnePort
    :source <complete modelica model as a string>
    :parameters ((C 1 SIunits.Capacitance "Capacitance"))
    :equations (= i (* C (deriv v 1 t))))

model EMF "Electromotoric force (electric/mechanic transformer)" 
  parameter Real k(final unit="N.m/A") = 1 
    "Transformation coefficient";
  
  SIunits.Voltage v "Voltage drop between the two pins";
  SIunits.Current i "Current flowing from positive to negative pin";
  SIunits.AngularVelocity w "Angular velocity of flange_b";
  Modelica.Electrical.Analog.Interfaces.PositivePin p;
  Modelica.Electrical.Analog.Interfaces.NegativePin n;
  Modelica.Mechanics.Rotational.Interfaces.Flange_b flange_b;
equation 
  v = p.v - n.v;
  0 = p.i + n.i;
  i = p.i;
  
  w = der(flange_b.phi);
  k*w = v;
  flange_b.tau = -k*i;
end EMF;

(defmetamodel EMF
    :external-terminals (p n flange_a flange_b)
    :description "Electromotoric force (electric/mechanic transformer)" 
    :source <...>
    :parameters ((k 1 ??? "Transformation coefficient"))
    :includes (Modelica.Electrical.Analog.Interfaces Modelica.Mechanics.Rotational.Interfaces)
    :variables ((v (voltage))
		(w (angular-velocity))
		(i (current))
		(p.v (voltage p ground))
		(p.n (voltage n ground))
		(p.i (current p))
		(n.i (current n))
		(phi (angular-position flange_b))
		(tau (torque flange_a)))
    :equations
    ((= v (- p.v n.v))
     (= 0 (+ p.i n.i))
     (= i p.i)
     (= w (deriv phi 1 t))
     (= (* k w) v)
     (= tau (* k i))))


(defmetamodel EMF
    :external-terminals (p n flange_a flange_b)
    :description "Electromotoric force (electric/mechanic transformer)" 
    :source <...>
    :parameters ((k 1 ??? "Transformation coefficient"))
    :variables ((v (voltage p n)) 
		(i (current p))
		(w (angular-velocity flange_b flange_a))
		(tau (torque flange_a)))
    :equations
    ((= (* k w) v)
     (= tau (* k i))))