How does a vault 4kv vib type oil breaker work?

What does 200kb volts get reduced to when it gos through a substation?

There are at least two fundamental problems with this question. First, and assuming that the subject is electrical power transmission, the generated power will always be expressed in killovolts or "kv", which indicates "thousands of volts". The 200kb that is given is a computer expression indicating killobytes, which indicates a factor of 1,024 bytes. Second, the 200k value given in this question is not familiar. A real-world value will be closer to 230kv, and depending on the area served, this value may very well rise toward a million killovolts, or may be less. In answering the "question apparent", we can now assume that 230kv is transmitted from a power generator to a distribution network where there should be several, if not many, substations. Such a network is typically located within a large geographic area. The substations and their outputs (reduced voltages) are designed specifically to meet the needs of the area served. Some examples of output voltages are 26kv, 13kv, and 4kv.