What are power resistors? How are they made? What type of applications are they used in?
Well as the name suggests high power resistors are designed to dissipate large amounts of power, it is a common trait amongst all high-power resistors that they dissipate as much power as possible whilst keeping the form factor as small as possible. Power Resistors typically generate a lot of heat when functioning and to compensate they are made from materials with high thermal conductivity as well as some specifically designed to allow for easy heat sink coupling. In extreme cases the resistors may require forced air cooling or liquid cooling when under maximum load to help remove the additional heat generated.
There are a lot of variations on power resistors each are made using different techniques which give each variation slightly different properties. Here is a quick overview of the types and some of their key properties, Water type high power resistors (yes, they exist) are typically suited for <500MW (30 second pulses), normal a medium-large form factor and have an average vibration resistance. Chip/SMD are a small component that look like integrated circuit chips, typically dissipate <5 W and a very resistant to vibration. Grid type resistors are capable of dissipating large amount of power <100kW, typically have an average size form factor and are very resistant to vibration.
There are also wire wound resistors which have a few different methods of manufacture, there is Helical Wound which typically dissipate <50 W however are susceptible to vibration. This type of winding is very standard and just a wire wrapped in a helix around a cylindrical core, this also causes the resistor to have a certain inductance since the wire is coil shaped. There is also bifilar winding which is very similar to helical winding however they minimise the impact on other devices with electromagnetic fields etc by winding in two directions, this reduces the electromagnetic fields created. There is also edge wound resistors which utilize a strip of metal and winding it on its wider edge, these are typically coreless and are air cooled thus allowing them to dissipate more power (<3.5kW) than typical helical types.
The most typical application of a high-power resistor is to safely convert large amounts of energy into heat and are used as protective devices and allow for controllable power dissipation. Engine braking is one application for high power resistors, this braking requires a large amount of energy to be dissipated.