Synchronous generators are electrical machines where the rotor rotates at the same speed as the rotating magnetic field that drives it. Most hydroelectric power stations are synchronous generators with multiple pairs of poles. The protection of synchronous generators varies according to the power and the mode of the generator drive. A significant difference stems from the way the synchronous generator is connected to the network. The generator can work in a block with a transformer, a block with a transformer and a cut-off for its own consumption, direct connection to the bus and parallel operation of multiple generators at the same bus. Also in the generator there are two basic relay protection divisions. Protection from internal defects and spare protection from external faults. In addition to the relays that are directly connected to the generator and the associated transformer, there are also relays that measure the temperature, oil flow, transformer oil ... The protectors act on failures in the generator and the block transformer and exclude them quickly and selectively, which means they act quickly to switch off the block switch, Breaking and stopping the aggregate with the corresponding sound and light signals.