Here is a detailed explanation of the working principle of an On-Load Tap Changing (OLTC) transformer.We are a Chinese manufacturer specializing in producing various types of transformers. If you need any, please contact us directly.

Core Purpose: Why OLTC is Needed

The primary purpose of a power transformer is to step up or step down voltage for efficient transmission and distribution. However, the voltage level on a power network is not constant; it fluctuates due to changes in load (e.g., factories turning on/off) and generation (e.g., solar power dropping at sunset).

If the transformer's turns ratio is fixed, these fluctuations would cause the output voltage to deviate from the required level, leading to:

Poor power quality for consumers.

Potential damage to sensitive equipment.

Inefficient system operation.

An On-Load Tap Changer (OLTC) is the device that allows the transformer's turns ratio to be adjusted while the transformer is energized and supplying load, thereby maintaining a stable output (or secondary) voltage regardless of input variations or load changes.

The Fundamental Challenge

You cannot simply slide a contact along the winding. Breaking the circuit under full load current would create a massive arc, destroying the contacts and the transformer insulation. The OLTC's ingenious design is entirely focused on solving this problem of making a switching transition without interrupting the load current.

Working Principle: The Resistor Transition Method (Most Common)

The most widely used modern design is the resistor-type transition OLTC. Its operation is based on temporarily connecting transition resistors to bridge taps during the switching process, limiting the circulating current.

Let's break it down step-by-step:

Key Components:

1. Tap Winding: A part of the main transformer winding with multiple taps (connection points) providing different turns ratios.

2. Selector Switches (S1, S2): These switches select the next tap to be used. They operate slowly and do not break current. They move when the diverter switch is in a neutral position.

3. Diverter Switch: This is the fast-acting switch that actually makes and breaks the current. It operates very rapidly to extinguish the arc quickly.

4. Transition Impedances (Resistors R1, R2): These resistors limit the circulating current between two adjacent taps when both are temporarily connected.