Off Load Tap Changer in transformer || English

Summary

In this video, the focus is on understanding offload tap changers in transformers. The video delves into the role of tap changers in maintaining voltage levels, explaining the differences between onload and offload tap changers. While onload tap changers allow voltage adjustments while the transformer is live, offload tap changers require the transformer to be switched off before adjustments are made. The video also covers the internal workings of offload tap changers, demonstrating how the tap positions are adjusted to maintain the desired output voltage while ensuring the safety and functionality of the transformer.

Takeaways

• 😀 Offload tap changers in transformers are used to change the tap settings when the transformer is off.
• 😀 Onload tap changers allow tap settings to be changed while the transformer is live and in operation.
• 😀 Offload tap changers are typically found in transformers with smaller capacities (up to 500 MVA), but cannot be used in continuous power supply scenarios.
• 😀 The primary purpose of a tap changer is to maintain the output voltage within the rated value by adjusting the transformer winding's tap positions.
• 😀 The voltage output on the LV side of a transformer remains constant at 440 volts, regardless of the tap position on the HV side.
• 😀 Different tap positions (from 1 to 5) adjust the transformer voltage on the HV side, based on the system's voltage level.
• 😀 A transformer’s winding is divided into sections, with taps allowing different voltage levels by either increasing or decreasing the number of turns in the primary winding.
• 😀 When adjusting tap positions, a short-circuiting arrangement is used to connect different sections of the winding, which effectively alters the voltage output.
• 😀 Offload tap changers require turning off the transformer first because an open circuit in the winding during a tap change can lead to faults or high current surges.
• 😀 The tap changing mechanism can include a wheel arrangement for manual adjustment, where the tap position is moved by rotating the wheel to select the desired voltage level.

Q & A

What is a tap changer in a transformer?

A tap changer in a transformer is a device that allows for the adjustment of the voltage levels by selecting different tap positions, ensuring the transformer operates within the desired voltage range.

What are the two types of tap changers discussed in the video?

The two types of tap changers are the On-Load Tap Changer (OLTC) and the Off-Load Tap Changer. OLTC can be adjusted while the transformer is live, whereas Off-Load Tap Changer requires the transformer to be turned off before adjustments can be made.

Why is it important to use tap changers in transformers?

Tap changers are crucial for maintaining stable voltage levels in transformers by adjusting the input voltage according to the system's needs, ensuring that the secondary voltage remains constant, typically 440V.

What is the main difference between an on-load tap changer and an off-load tap changer?

The main difference is that an On-Load Tap Changer allows voltage adjustment while the transformer is operational (live), while an Off-Load Tap Changer requires the transformer to be turned off before adjustments can be made.

In what situations would an off-load tap changer be used?

An off-load tap changer is used in transformers that can be temporarily powered down for maintenance or voltage adjustments, typically in situations where the transformer does not need to operate continuously, such as in industries with intermittent power needs.

What voltage levels are typically associated with off-load tap changers?

Off-load tap changers are often found in transformers with voltage ratings between 100kV to 500kV, although they can sometimes be used in larger transformers, provided the transformer can be easily turned off for adjustments.

How does the voltage adjustment work in a transformer with an off-load tap changer?

The voltage adjustment in a transformer with an off-load tap changer is done by selecting different tap positions, which alters the number of windings in the transformer’s primary coil, thereby changing the voltage level. For example, fewer windings reduce the voltage.

Why must the transformer be turned off when using an off-load tap changer?

The transformer must be turned off because when tap positions are changed, an open circuit may be created in the windings, which could lead to high fault currents or cause damage to the transformer. Therefore, the transformer is de-energized before adjustments are made.

What happens when the tap positions are changed in the off-load tap changer?

When the tap positions are changed, the number of turns in the primary winding is altered. Connecting different taps shortens or increases the winding turns, which directly changes the voltage input, while the output voltage (e.g., 440V) remains constant.

What are the potential risks of adjusting the tap positions while the transformer is energized?

Adjusting the tap positions while the transformer is energized can cause an open circuit in the winding, potentially leading to high fault currents, voltage flux imbalances, and transformer damage. This is why adjustments are made only when the transformer is off in the case of off-load tap changers.