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

EEEB Electrical Engineers Experience Building

17 Nov 201911:38

Summary

TLDRThis 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.

Outlines

00:00

🔌 Tap Changers in Power Transformers

This paragraph introduces the concept of tap changers in power transformers and their necessity due to varying loading conditions in power networks. It explains that to maintain consumer voltage within acceptable limits, transformers are equipped with additional windings and taps. The arrangement for a three-phase transformer is described, with each phase on a separate limb and the order of components from inside to outside being the core, low voltage winding, high voltage winding, and high voltage tap winding. Two types of tap changers are discussed: on-load tap changers (OLTC) that can change taps while the transformer is energized and loaded, and off-circuit tap changers that require the transformer to be de-energized. The paragraph also differentiates between oil and vacuum tap changers, with oil used for insulation, lubrication, cooling, and arc interruption, and vacuum used in vacuum interrupter caps for arc interruption.

05:02

🛠️ Operation and Components of Tap Changers

This section delves into the components and operation sequence of tap changers, particularly focusing on moving contacts, transition contacts, and transition resistors. The process of tap changing is detailed, explaining the steps involved when shifting from one tap to another, including the arcing that occurs and how it is managed. The paragraph also contrasts oil and vacuum types of OLTC, highlighting the vacuum interrupter capsules unique to vacuum tap changers. An example of a BB vacuum tap changer model, VUBB, is provided to illustrate the switching sequence, emphasizing the role of resistors and vacuum interrupters in controlling the load current and managing arc interruption during the tap changing process.

10:02

📚 Further Exploration of Vacuum OLTC and Closing Remarks

The final paragraph suggests further viewing of videos on the channel for more information on vacuum OLTC, hinting at upcoming topics such as regulating winding switching types and tap changer testing. The video is concluded with thanks to the viewers and an invitation for suggestions or discussions, providing contact information for the presenter, Engineer Hanny Camel. A reminder is given to subscribe to the channel for notifications on the next video, ensuring viewers stay updated with the series.

Mindmap

Keywords

💡Power Transformer

A power transformer is a type of electrical device that transfers electrical energy between two or more windings. In the context of the video, it is used to maintain voltage levels within a certain range despite varying load conditions. The script mentions that power transformers have fixed tap windings to offer variation in the turns ratio, which is essential for maintaining voltage stability.

💡Tap Changer

A tap changer is a mechanism used in transformers to adjust the voltage levels by changing the number of turns in the transformer windings. The video script discusses the importance of tap changers in power networks due to varying loading conditions, which can cause consumer voltage to fluctuate. The tap changer helps to maintain the voltage within acceptable limits.

💡Loading Conditions

Loading conditions refer to the demand for electrical power in a network at a given time. The script explains that due to these varying conditions, the consumer voltage can change out of the acceptable limits, necessitating the use of a tap changer to adjust the voltage levels accordingly.

💡On Load Tap Changer (OLTC)

An On Load Tap Changer (OLTC) is a type of tap changer that allows for the changing of transformer taps while the transformer is energized and under load. The video script describes two types of OLTCs: oil and vacuum, each using different arc interruption mediums. OLTCs are crucial for maintaining voltage levels without interrupting the power supply.

💡Off Circuit Tap Changer

An Off Circuit Tap Changer is a type of tap changer that requires the transformer to be de-energized before tap changing can occur. The script contrasts this with the OLTC, which can operate with the transformer energized and loaded. The off circuit tap changer is typically used in simpler applications where continuous operation is not critical.

💡Vacuum Tap Changer

A vacuum tap changer is a specific type of OLTC that uses a vacuum as the arc interruption medium. The script explains that this type of tap changer operates similarly to a vacuum circuit breaker, with the arc occurring inside a vacuum capsule, which is essential for safe and efficient tap changing.

💡Oil Tap Changer

An oil tap changer is another type of OLTC that uses oil as the arc interruption medium. The script mentions that oil is also used for insulation and lubrication within the tap changer compartment, as well as for cooling and arc interruption during tap changing operations.

💡Transition Resistor

A transition resistor is used in the tap changing sequence to limit the short-circuit current when two taps are shorted during the changeover process. The script describes how the transition resistor helps to maintain the load and limit the current during the tap changing sequence, which is crucial for the safe operation of the tap changer.

💡Moving Contacts

Moving contacts are a critical component of the tap changer mechanism, responsible for selecting the desired tap of the fixed contacts. The script details the role of moving contacts in both oil and vacuum OLTCs, including their involvement in the transition process and the arcing that occurs during tap changing.

💡Regulating Winding

A regulating winding is an additional winding in a transformer that is used in conjunction with the tap changer to offer variation in the turns ratio. The script mentions that the regulating winding is connected to the tap changer, allowing for adjustments to maintain the correct voltage level under varying load conditions.

💡Arc Interrupting Facility

The arc interrupting facility is a feature of the OLTC that allows for the safe interruption of electrical arcs during tap changing. The script explains that this facility is provided in the OLTC to ensure that the tap changing process can be done safely and efficiently, preventing damage to the transformer and ensuring continuous power supply.

Highlights

Introduction to the importance of tap changers in power transformers for maintaining voltage levels under varying load conditions.

Explanation of how tap changers offer variation in transformer turns ratio to accommodate different power network loading conditions.

Description of the winding arrangement for three-phase transformers, including the sequence from core to high voltage tap winding.

Illustration of the taps connections in a three-phase transformer setup.

Classification of tap changers into two types: on-load tap changers (OLTC) and off-circuit tap changers.

Details on on-load tap changers, which allow tap changing with the transformer energized and loaded.

Differentiation between oil and vacuum as arc interruption mediums in OLTC, leading to oil tap changers and vacuum tap changers.

Overview of off-circuit tap changers, which require the transformer to be de-energized for tap changing.

Introduction to ABB oil tap changer model UBV as an example of an on-load tap changer.

Description of the main parts of an on-load tap changer, including fixed and moving contacts, changeover selector, and transition resistor.

Explanation of the tap changing sequence and the role of the drive spring in minimizing arcing time.

Role of oil in air LTC for insulation, lubrication, cooling, and arc interruption during tap changing.

Introduction to vacuum OLTC, highlighting the vacuum interrupter caps and their function.

Description of the tap changing sequence for vacuum OLTC, using model VUBB as an example.

Discussion on the importance of the transition resistor in limiting short-circuit current during tap changing.

Note on the presence of oil in vacuum OLTC for insulation and cooling, despite arc interruption occurring inside vacuum capsules.

Conclusion and invitation to watch further videos on vacuum OLTC and upcoming topics on regulating winding switching types.