## 4 Discussion  
The generated process of the positive and negative ion and free electron is illustrated in Figure 5. In the case of a low external electric field, the bonding energy between the free electron and positively charged ion in air insulation is larger than that of the external electric field. Therefore, many neutral molecules remain in air. However, in high external electric fields, collisions occur between neutral molecules and then free electrons are accelerated in the high electric field [12]. The newly generated free electron from the surface of the ionizer conductor and air insulation can play a role as new electron avalanches under a high electric field condition. Some of these secondary electrons will again strike the air insulation, producing tertiary electron [13]. The possibility of early corona discharge caused by the presence of an ionizer conductor was reviewed in the viewpoint of CTS. In the case of a positive strike occurrence, the surface of the current collector is induced with a negative charge, and the ionizer conductor is positively charged. The electric field between the current collector and the ionizer conductor is distorted, caused by the presence of an ionizer conductor and the ionized free electron emitted from sharp tip of the ionizer conductor under high electric field. Thus, it might be possible that the electric field concentration occurs at the sharp tip of ionizer conductor and it could be the starting point of early corona discharge inception. \begin{table}
\begin{tabular}{c c c c} \hline
**Air Space [mm]** & **Time [\(\mu\)s]** & **Electric Field [V/m]** & **Electron Density [mol/m\({}^{3}\)]** & **Negative Ion Density [mol/m\({}^{3}\)]** \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._Some studies have investigated the early corona discharge between the floating conductor and conducting brushes in terms of experimental results and computer simulation studies according to the presence or absence of a floating conductor [5,6]. The experimental results show that a floating conductor system can generate more electrons than without a floating electrode, and the corona discharge can be controlled using a floating conductor [6]. In our research work, we have focused on the air space over the presence or absence of a floating conductor to control the inception and occurrence position of corona discharge. In the 0.0005 mm air space, the electric field and electron density are concentrated between ionizer conductor and current collector; it could be a starting point of the corona discharge inception. However, when the air space is increased, the electric field concentration and high electron density occurs at the SK-AOR380 tip part. The reason for the inception and occurrence position of the corona discharge according to the air space in the simulation results can possibly be explained by the following empirical factor:  
* The behavior of the electric field and electron density according to air space is related with the electron mean free path (MFP)  
If the air space is too far, the generated free electron could not excite another free electron for the electron avalanche between ionizer conductor and current collector. In other words, the first free electron cannot play a role as the seed of the secondary and tertiary electron avalanches. [PERSON] et al. [14] have reported the dependences of the length of exponential enhancement of the runaway electron avalanche on the electric field strength in air insulation, calculated using the Monte Carlo method. [PERSON] et al. [15] investigated the distance to first ionization under 30 kV/cm, \(\rho=1\)_bar_; a minimum distance for first ionization is required for several \(\upmu\)m. In this research work, we found the optimized air space using a numerical analysis method while considering relational equations from the above reference papers [14,15]. However, the above discussion is just one possibility reviewed from the simulation results as a basic research work.