def calculate_z_base(v_base, s_base):
    """Calculate base impedance from voltage and system base apparent power.

    :param int/float v_base: base voltage (kV).
    :param int/float s_base: base apparent power (MVA).
    :return: (*float*) -- base impedance (ohms).
    """
    return (v_base**2) / s_base