e-lesson #1 – On-load tap changers basics
Key focus
To understand the operating principles, construction concepts, and voltage-regulation role of on-load tap changers in power transformers operating under dynamic load conditions.
Lesson description
This lesson introduces the fundamentals of on-load tap changers (OLTCs) and explains their role in maintaining voltage stability in modern power systems. It reviews the principles of voltage regulation through transformer taps and explains how OLTCs perform tap changes while the transformer remains energized and under full load. The session compares resistor- and reactor-type tap changers, discusses make-before-break switching principles, and introduces key construction elements such as diverter switches, selectors, reversing switches, and series transformers. Particular attention is also given to OLTC placement, switching technologies, regulation arrangements, maintenance considerations, and the operational challenges associated with reliability, diagnostics, and transformer protection.
Learning outputs
- Explain why on-load tap changers are required for voltage regulation under varying system-load conditions. • Distinguish resistor-type and reactor-type OLTC designs and explain their operating principles and switching characteristics. • Identify the main OLTC components, including diverter switches, selectors, reversing switches, and series transformers. • Describe the make-before-break switching principle and explain how circulating-current limitation is achieved during tap transitions. • Assess the main operational, diagnostic, and maintenance challenges associated with OLTC reliability and transformer performance.
