Cures for Low Frequency Disturbances |Power Quality & Management|

Summary

In this video lecture, the focus is on addressing low or power frequency disturbances in power systems, which are slow phenomena caused by switching events. The video explains how isolation transformers, though not effective for voltage sags or swells, can minimize common mode noise and prevent it from converting into troublesome transverse mode noise. It also delves into the role of voltage regulators, including switching and ferro-resonant types, in maintaining constant voltage levels. The video highlights how these devices help power systems remain stable and protect sensitive data and signal circuits from disturbances.

Takeaways

• 😀 Power frequency disturbances are slow phenomena caused by switching events, which dissipate once the incident causing them is removed.
• 😀 Isolation transformers help minimize common mode noise but do not cure voltage sags or swells.
• 😀 Common mode noise is present equally in the line and neutral circuit and can be converted into troublesome transverse mode noise.
• 😀 Shielded isolation transformers reduce the conversion of common mode noise into transverse mode noise by limiting noise coupling.
• 😀 The effectiveness of a shielded isolation transformer in reducing common mode noise is measured as attenuation in decibels.
• 😀 The formula for attenuation is A = 20 log(v1/v2), where v1 is the common mode noise voltage at the transformer primary and v2 is the differential mode noise at the secondary.
• 😀 Voltage regulators maintain a constant voltage within a predetermined tolerance by adjusting the voltage as needed.
• 😀 A switching-type voltage regulator uses an electronic switch to respond to voltage sensing signals and maintain a constant output voltage.
• 😀 Ferro-resonant voltage regulators operate on the principle of decoupling the secondary winding from the primary by operating in the saturation region of the magnetic core.
• 😀 Ferro-resonant voltage regulators are static devices with no moving parts and are more resilient to voltage changes in the primary circuit.

Q & A

What are power frequency disturbances, and what causes them?

Power frequency disturbances are slow phenomena caused by switching events related to power frequency. These disturbances disperse over time once the event causing them is removed, allowing the power system to return to normal operation.

How do isolation transformers work to minimize noise?

Isolation transformers have primary and secondary windings separated by an insulating medium. They do not cure voltage sags or swells but help minimize common mode noise by limiting the coupling of noise between the primary and secondary windings.

What is common mode noise, and why is it problematic?

Common mode noise is the noise that appears equally in both the line and neutral circuits with respect to ground. It can be converted into troublesome transverse mode noise, which can affect sensitive data and signal circuits.

What is attenuation in the context of shielded isolation transformers?

Attenuation refers to the effectiveness of a shielded isolation transformer in limiting common mode noise. It is indicated in decibels and is calculated using the formula: A = 20 log(v1/v2), where v1 is the common mode noise voltage at the transformer primary, and v2 is the differential mode noise at the secondary.

How does a shielded isolation transformer help reduce noise?

A shielded isolation transformer reduces noise by decoupling the primary and secondary windings using a shield between them, which decreases interwinding capacitance and minimizes noise coupling.

What is the function of a voltage regulator?

A voltage regulator is a device designed to maintain a constant voltage within a predetermined tolerance, compensating for voltage changes above and below the nominal value.

How does a switching type voltage regulator work?

A switching type voltage regulator uses an electronic switch that responds to a voltage sensing circuit. The switch adjusts the connection to maintain a constant output voltage, typically within half of a cycle, which is quick enough for sensitive devices.

What is a ferroresonant voltage regulator, and how does it work?

A ferroresonant voltage regulator is a static device with no moving parts. It operates on the principle that when a transformer’s secondary magnetic circuit is in the saturation region, the secondary winding decouples from the primary, making it less sensitive to primary voltage changes.

What role does the capacitor across the secondary winding play in a ferroresonant voltage regulator?

The capacitor connected across the secondary winding in a ferroresonant voltage regulator forms a parallel resonant circuit with the inductance of the secondary winding. This setup helps decouple the secondary winding from the primary, stabilizing the voltage.

What happens when the secondary winding of a ferroresonant voltage regulator is decoupled from the primary?

When the secondary winding is decoupled from the primary, it becomes less sensitive to voltage changes in the primary circuit, which allows the voltage regulator to maintain a more stable output voltage despite fluctuations in the input voltage.