1. Transformer with conservator tank (WCT),
2. Hermetically sealed type (HST),

 Below table will help to engineers to select the best option according to environmental conditions which transformer works in:

 Meanwhile here is the advantage-disadvantage of the WCT-HST types:

• In HST type, tank pressure is more than WCT type. WCT type generally works under low pressure due to its open to atmosphere,
• In HST type, cooling/insulation oil does not contact to the air (theoretically). Therefore oil maintenance period is longer than WCT type,
• HST type transformers and their related parts generally work under higher temperature (If we evaluate WCT-HST work under same conditions).