Transformer Off Circuit and On Load Tap Changer function, components, installation, operation part1

Summary

This video script delves into the intricacies of power transformers, focusing on the tap changer—a crucial component that adjusts voltage levels to maintain stability under varying load conditions. It explains the tap changer's role, its types (on-load and off-circuit), and the distinction between oil and vacuum interrupters. The script provides a detailed look at the construction and operation of ABB's oil and vacuum tap changers, highlighting their components and the sequence of tap changing. Engineer Hanny Camel's presentation is aimed at educating viewers on the importance of tap changers in power systems and their technical aspects, encouraging further exploration of the topic through additional resources.

Takeaways

• 🔌 Tap Changers are essential in power transformers to maintain voltage levels under varying load conditions.
• 🌐 Transformers have additional windings with taps to allow for changes in the turns ratio, which helps in maintaining constant voltage.
• 👷‍♂️ For three-phase transformers, each phase has a limb with a specific arrangement: core, low voltage winding, high voltage winding, and high voltage tap winding.
• 🔧 Tap Changers can be classified into two types based on operation: On Load Tap Changers (OLTC) and Off Circuit Tap Changers.
• ⚡ OLTC allows for tap changing while the transformer is energized and loaded, equipped with an arc interrupting facility.
• 🛠 Off Circuit Tap Changers require the transformer to be de-energized before tap changing and have a fixed number of taps.
• 🛡️ OLTC can use different arc interruption mediums such as oil or vacuum, leading to the terms oil tap changer and vacuum tap changer.
• 🏭 OLTCs are predominantly used in power transformers, while Low Current Tap Changers (LCTC) are used additionally for special customer requirements.
• 🔩 The main parts of an OLTC include fixed contacts, moving contacts, changeover selector, transition resistor, and drive spring.
• 🛢️ Oil is used in air LTFCs for insulation, lubrication, cooling, and arc interruption during tap changing.
• 🔄 The tap changing sequence involves stages of arcing, transition contact engagement, resistor use for short-circuit current limitation, and main contact movement.
• 🔬 Vacuum type OLTCs function similarly to oil types but with the arc interruption happening inside vacuum capsules, providing a different mechanism for tap changing.

Q & A

What is the purpose of a tap changer in a power transformer?

A tap changer is used to maintain the consumer voltage within limits by offering variation in the transformer's turns ratio under various loading conditions.

How does a tap changer help in maintaining voltage levels?

A tap changer maintains voltage levels by adjusting the turns ratio of the transformer through additional windings with taps, compensating for changes in the power network's loading conditions.

What are the two main types of tap changers based on operation?

The two main types of tap changers are on-load tap changers (OLTC) and off-circuit tap changers. OLTC allows tap changing while the transformer is energized and loaded, whereas off-circuit tap changers require the transformer to be de-energized.

What are the different components of an on-load tap changer?

The main components of an on-load tap changer include fixed contacts, moving contacts, a changeover selector, a transition resistor, and a drive spring.

How does an oil-type on-load tap changer (OLTC) differ from a vacuum-type OLTC?

An oil-type OLTC uses oil as an arc interruption medium, while a vacuum-type OLTC uses vacuum interrupter caps similar to vacuum circuit breakers, with the arc occurring inside the vacuum capsule.

What is the role of the transition resistor in an OLTC?

The transition resistor limits the short-circuit current during the tap changing sequence when two taps are shorted before breaking.

What is the total time taken by an OLTC to change taps?

An OLTC takes around 4.5 seconds to change taps, which includes the drive spring charging time, the time for the actual tap changing, and the mechanism normalizing time.

What are the functions of oil in an air OLTC?

In an air OLTC, oil is used for insulation, lubrication of the moving parts inside the tap changer compartment, cooling, and arc interruption during tap changing.

How does the tap changing sequence work in a vacuum-type OLTC?

In a vacuum-type OLTC, the sequence involves stages where the main contact moves between taps, the resistor auxiliary contact engages and disengages, and the main vacuum interrupter opens and closes to manage the load current and arc interruption.

What is the arrangement of windings for a three-phase transformer with a tap changer?

For a three-phase transformer with a tap changer, each phase is on a separate limb. From inside to outside, the arrangement is core, low voltage winding, high voltage winding, and high voltage tap winding or cold regulating winding.

What is the significance of the moving contacts in a tap changer?

Moving contacts in a tap changer are crucial for selecting the desired tap of the fixed contacts, ensuring the correct turns ratio is maintained for voltage regulation.