Gas Gap
Coaxial cylinder gap The DC breakdown voltage of a 80/200mm diameter coaxial cylinder gap of Fig.2(b) B related to DC application time and inside gas pressure is shown in Fig.3. The effect of voltage holding time is scarecely observed. Voltagepolarity effect is prominent at the pressure abcve 1 kg/cm1 abs.
The 'positive DC breakdown occurs' at slightly below the theoretical limiting breakdown voltage Ulim, while the negative breakdown occurs at much lower voltage than Ulim,especially at higher pressure. The negative DC breakdown voltage at 3.5 kg/cm1 pressure is approximately
80 percent of the AC breakdown value.
Marked effect of electrode covering at negative polarity is found as given in Fig.4. In this case the inner conductor of 80mm diameter is insulated wilth doubly wound half lapped polyethylene terephthalate tape.
The covering of