The Core Transformer Construction The closed-core transformer and the shell-core transformer are the two most frequent and fundamental transformer designs. The primary and secondary windings of a "closed-core" transformer (core form) are coiled outside and around the core ring. A "shell-core" transformer (shell form) has an outer shell containing the coil wire that surrounds the core inside the shell. Both types of transformer have plastic or metal cases to hold them together and provide some degree of insulation between the primary and secondary sides. These cases usually have openings on either end for connecting the wires into the circuit.
The third type of transformer core is called a "hybrid", or "sandwich" core. It consists of multiple layers of magnetic material with thin sheets of non-magnetic material in between. The hybrid core is used mainly when very high frequency signals need to be transmitted through the transformer, or if large amounts of power need to be transferred efficiently over long distances.
Closed-Core Transformers: These transformers use a core form consisting of one or more rings of magnetic material wrapped around an iron bobbin. The primary and secondary coils are wound around the exterior of the core ring(s). Closed-core transformers are very efficient at transferring energy from one voltage level to another. They also have low inductance, which means that much current can flow through them without significant loss.
Transformer cores are typically of one of two types: core type or shell type. The primary and secondary coils are positioned around the steel core in different ways, which distinguishes these two kinds. The primary kind is: The windings of this form encircle the laminated core. These are most commonly used in power transformers.
The secondary kind is: The windings of this type are wound on a cylindrical shell. These are common in low voltage transformers.
A third type of transformer core is called "laminated", which means that it is made up of multiple sheets of magnetic material bonded together. These are used in high voltage transformers because they are able to carry more current than core types or shells without getting too hot to the touch. They also tend to be more efficient than other types of cores when converting electrical energy into thermal energy (heat).
Laminated cores are usually constructed by stacking thin disks of iron or steel with copper wire inserted between each layer. The number of layers used to construct the core determines its height and weight. A large transformer might have 20 layers while a small one could have just four. The manufacturer then needs to choose how to connect the various stacks of magnetic discs and coil windings to provide enough space for the primary and secondary circuits. These connections are called "tap points".
A transformer's core size is based on the voltage it will be handling; larger cores are used for higher voltages.
Cores are made out of magnetic material because electricity is a form of magnetism. Transformers use electromagnets to pull wires through their holes to create a circuit with each other. When alternating current (AC) is applied to a transformer, the coil creates a magnetic field that pulls the wires through its center, creating a loop from both ends of the coil. This completes the circuit with the opposite coil on the other side of the core. The amount of current flowing through each wire depends on how much power is being transferred by the transformer.
Because magnetic fields leak away from their source, there must be some way for the magnetic field of one side of the transformer to reach the other side. This is where the core comes into play. The inside surface of the core is wrapped with wire just like the outside is, but instead of moving in a circular pattern, these wires move in straight lines toward the center, then back out to the edge of the core.
The transformer is in core form when the windings encircle the core; the transformer is in shell form when the windings surround the core. Because of the convenience of stacking the core around winding coils, shell form design may be more common in distribution transformer applications than core form design. Core form transformers are generally smaller because they do not require as much space around the coil for insulation. Shell form transformers are usually larger because more wire can be wrapped around the outside of the case without breaking the circuit.
In low voltage power transmission systems, transmission transformers are usually large, heavy, and ironclad devices located near the substation. They transmit voltage from the generating station to the distribution substations and on to consumer centers. Transmission transformers regulate the amount of current flowing into their cores so that specific voltages are maintained at all times. This prevents excessive heating of any one conductor or component within the transformer. Transmission transformers also protect against short circuits by opening their circuits if anything causes a voltage drop across them to fall below a certain level. This level depends on the type of transformer but it's usually well above what would cause damage to other components on the line.
Transmission transformers must be able to withstand high voltages while maintaining the integrity of their magnetic field. These factors determine how much material they contain inside the tank walls. The thicker the wall plates, the greater the capacity of the transformer.
Concentric cylindrical winding is used in core type transformers, whereas sandwiched winding is used in shell type transformers. It should also be noted that the winding surrounds the core in a core-type transformer, whereas the core surrounds the winding in a shell-type transformer. These are very basic differences between these two types of transformers. There are many other differences as well; for example, core type transformers have more surface area exposed to the magnetic field than shell type transformers. This provides more conductivity and thus less resistance against the flow of current through the windings of the transformer.
Another difference is that core type transformers require more precise winding techniques because of their small size. Winding irregularities such as skew (an angle between adjacent turns of the coil) must be avoided because they can cause points of low resistance that will reduce the effectiveness of the transformer.
Finally, core type transformers are generally more expensive than shell type transformers because they require special manufacturing processes and/or materials that allow them to be made smaller while still providing effective operation. For example, core type transformers usually contain silicon steel cores instead of iron cores because silicon steel has higher permeability than iron. This means that they can be wound with fewer turns to achieve the same amount of magnetism from the transformer.