The RN-120U carbon voltage regulator is designed to automatically maintain the voltage of the starter-generators and the GS-24B generator within the specified limits when changing their rotation speed and load in the generator mode. At the same time, the regulator maintains an even load distribution when the starter-generators operate in parallel. 
 
The voltage regulator is a rheostat-type electromagnetic regulator with a smooth change in the resistance of the coal column.

The main parts of the regulator are the regulator itself, a plate with shock absorbers, a base, a plug connector, three resistors and a block with a germanium diode. 
 
The regulation process proceeds as follows: when the generator voltage increases, the current in the working winding l1 regulator 704, which is energized by the generator. Consequently, the force of the electromagnet increases due to which the armature, overcoming the resistance of the spring, begins to be attracted to the core.

The pressure on the carbon column, connected in series with the excitation winding, decreases, and its resistance increases, which leads to a decrease in the current in the excitation circuit of the generator. The generator voltage is reduced to the nominal value. When the generator voltage decreases, the regulation process is reversed. 
 
To prevent temperature changes from affecting the operation of the regulator, it has a temperature compensation winding l3 and constantan resistances R1 and R2.

To increase the stability of the regulator, diodes and a stabilizing resistance R3 are provided in its circuit, which helps to reduce voltage fluctuations and their damping. 
 
Parallel winding ensures normal operation of parallel generators. The windings of the regulators operating with parallel-connected generators are connected towards each other and serve to equalize the loads of the generators by automatically adjusting their voltages. 
 
The voltage value maintained by the regulator can be adjusted using external resistances set to power industry control panel.