Why a Core is used in a transformer?
Before diving into the effects on the transformer when its core is removed, we have to understand why we use the transformer core in the first place.
Can we use a transformer without a core? well... We shall discuss it later in this article.
Basically, we use a transformer core to minimize the reluctance path offered by air. In simple words passing magnetic flux through an iron core is much more efficient than air or any other non-permeable materials like wood, paper, glasses etc.
When the core is removed from an existing transformer then the primary side of the transformer will draw more no-load current and for that higher amount of current copper loss in the transformer increases hence the overall or all-day efficiency of the transformer reduces to a great extent.
Another thing that can happen if we remove the core is the transformer may overheat or may get fire due to higher current in the primary side coils.