Automatic Voltage Regulators (AVRs) and On-Load Tap Changers (OLTCs) play an important role in voltage regulation for generators and transformers, each designed to cater to specific operational requirements.
AVRs in Generators:-
AVRs in generators are responsible for regulating excitation current to maintain a stable output voltage.
These systems typically source power from auxiliary windings or the generator’s main output, converting AC supply to DC for controlling the field winding.
OLTCs in Transformers:-
In high-voltage transformers, such as a 132 kV unit, OLTCs adjust the turns ratio to compensate for voltage fluctuations.
The supply for the OLTC’s motor drive and control system is generally derived from the transformer’s tertiary winding (if available) or an auxiliary transformer connected to the lower voltage side.
For example, in a 132/33 kV transformer, the OLTC mechanism may be powered by an AC supply stepped down from the 33 kV side to a usable level, such as 400V.
Key Differences:-
While generator AVRs focus on maintaining output voltage by managing excitation with a DC supply, transformer OLTCs adjust the physical configuration of windings under load, driven by an AC-powered motor system. These devices differ in design and implementation, reflecting the unique challenges of their applications.
Example Application: In a 132/33 kV transformer, theOLTC supply could come from a dedicated auxiliary transformer stepping down voltage from the 33 kV side. The motor mechanism then uses this supply to adjust the tap changer based on load conditions, ensuring stable voltage delivery to the grid.
