Imagine two rivers. One flows calmly along the usual channel, while the other carries five times as much water in a second. If you do not change the channel, the stream will begin to destroy the banks. It's a similar story with electric current: the higher it is, the more stringent the requirements are for the conductor, contacts, and the entire input node.
What does the insulator do?
The IPT insulator is installed where the current-carrying part passes through the transformer equipment housing. The porcelain part separates the conductor from the grounded housing, supports it and provides the necessary leakage path. In this case, the current does not flow through the porcelain, but through the metal part.
The marking of the IPT 20 insulator means a voltage class of 20 kV. The number after the slash indicates the rated current: 250, 400, 630, 1000, 3150 or 5000 A. This is not an arbitrary "margin", but an input parameter.
Why can't you just set the model to 1000A
If the current is increased from 1000 to 5000 A at the same connection resistance, then heat generation will theoretically increase by 25 times, since heating depends on the square of the current. In practice, it is restrained by increasing the cross-section of the conductor, changing the contacts and the design of the node. Therefore, the IPT 1000 insulator is designed for a specific input and does not replace the 5000 A version.
The differences are noticeable in size. The IPT-20/1000 A O1 from the Kontur-M catalog has a height of 415 mm, an outer diameter of 175 mm and a weight of 8.5 kg. The IPT-20/5000 A O1 model is larger: 485 mm, 240 mm and 16 kg, respectively. With the same voltage class and a leakage path of at least 40 cm, these are different products with separate drawings.
Where 5000A is needed
The IPT 20 5000 insulator is used in high-power transformer equipment, where a high operating current must pass through the input for a long time. This is not an enhanced "just in case" option. It requires suitable mounting dimensions, a current-carrying part, contacts and an accurate calculation of the thermal regime.
Therefore, IPT pass-through insulators are not chosen based on external similarity and not only on voltage. Before ordering, it is necessary to check the complete marking, rated current, design, drawing, dimensions and documentation of the equipment.
The Kontur-M catalog lists the characteristics of models for removable transformer inputs. If the label on the old part is damaged, you can send a clear photo of the assembly and its dimensions to the supplier. The main thing to remember is that voltage determines the insulation requirements, and current determines the bandwidth of the entire input. Therefore, 1000 and 5000 A are really different "rivers".