The approximate _________ of the major components of a transformer normally included are core and coil, main tank or case, radiator, and ______.

The approximate weight of the major components of a transformer is an important consideration in substation maintenance. These components, which include the core and coil, main tank or case, and radiator, each contribute significantly to the overall weight of the transformer. Understanding the weight helps in planning for transport, installation, and maintenance of the equipment.

Additionally, the reference to oil is pertinent, as transformers rely on insulating oil not only for electrical insulation but also for cooling the internal components. The oil's presence is crucial because it absorbs heat generated during operation, thus maintaining efficient function and protecting against overheating.

In the context of the other choices, "size" or "volume" may not provide the same level of operationally relevant detail as weight when it comes to transformer maintenance and logistics. "Cost" and "gas" do not directly relate to these core components and their operational functions within the transformer system. Thus, the focus on weight and oil encapsulates key factors in a transformer's operational integrity and maintenance requirements.