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Introduction of Frequency Control | Power Systems - Electrical Engineering (EE) PDF Download

Introduction of Frequency Control 

Objectives
In this lecture you will learn the following

→ Why is maintenance of frequency important?

→ An example of typical load and frequency variation in an Indian grid.

Introduction 
Frequency all over a synchronous power grid is the same in steady state. Maintaining a near-constant frequency (one may allow frequency to vary over a very narrow band) is considered an important requirement of power system operation. Frequency in a power system is intimately related to the electrical speed of synchronous generators. The difference between mechanical and electrical torques govern acceleration of a rotor of a generator. Therefore to maintain a constant speed, mechanical input and electrical output power need to be continually matched. Electrical load can vary randomly, but the total load versus time roughly follows a trend. For example, total load in a grid can vary over twenty four hours as shown in the figure on the right.

There is a distinctive peak at about 8 pm. This is the typical variation for a particular season of the year. For other seasons, the load profile is different. Also, power systems are not immune to sudden large load or generation throw-offs due to contingencies.

Frequency variation is dependent on several factors which includes the load characteristics and generator prime mover controls. We shall study these issues in detail in the following lectures.

Why is maintenance of frequency in a power system important? Frequency needs to be maintained near 50 Hz for the following reasons:

Steam turbine blades are designed to operate in a narrow band of frequencies. Deviation of frequency beyond this band may cause gradual or immediate turbine damage. Consequently, protective and control equipment take corrective action in case of under/over frequency. A 50 Hz steam turbine may not be able to withstand frequency deviation of +2 Hz to -2.5 Hz for more than an hour in its entire life!

Loads and other electrical equipment are usually designed to operate at a particular frequency. Off-nominal frequency operation causes electrical loads to deviate from the desired output. The output of power plant auxiliaries like pumps or fans may reduce, causing reduction in power plant output.

At the present time, grid frequency deviation in some Indian grids is generally between 50.5 and 49.0 Hz under normal operating conditions. The figure below shows the typical frequency variation in the Western Grid of India.

The document Introduction of Frequency Control | Power Systems - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Power Systems.
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FAQs on Introduction of Frequency Control - Power Systems - Electrical Engineering (EE)

1. What is frequency control in electrical engineering?
Ans. Frequency control in electrical engineering refers to the ability to regulate and stabilize the frequency of an electrical signal or power supply. It involves techniques and devices used to maintain a consistent and accurate frequency, typically for applications such as power systems, telecommunications, and electronic devices.
2. Why is frequency control important in electrical engineering?
Ans. Frequency control is crucial in electrical engineering for several reasons. Firstly, it ensures the proper functioning and synchronization of power systems, preventing issues like power outages or equipment damage. Secondly, it allows for reliable communication systems, as different devices need to operate at the same frequency to transmit and receive signals effectively. Lastly, frequency control is essential in electronic devices to maintain accurate timing and synchronization for various operations.
3. What are the common methods used for frequency control in electrical engineering?
Ans. There are several common methods used for frequency control in electrical engineering. One method is through the use of crystal oscillators, which utilize the precise vibrations of a quartz crystal to generate a stable frequency. Another method is through the use of phase-locked loops (PLLs) that compare the input frequency with a reference frequency and adjust accordingly. Additionally, frequency control can be achieved through digital signal processing techniques or by using voltage-controlled oscillators (VCOs).
4. How does frequency control impact power system stability?
Ans. Frequency control plays a vital role in maintaining power system stability. In a power grid, the frequency of the alternating current (AC) needs to be kept within a specific range, usually around 50 or 60 Hz. Any deviation from this desired frequency can lead to imbalances in power generation and consumption, potentially causing instability and system failures. Effective frequency control techniques, such as automatic generation control (AGC) and load shedding, help regulate power supply and maintain stability.
5. What are the challenges in achieving accurate frequency control?
Ans. Achieving accurate frequency control can face several challenges. One challenge is the presence of external factors, such as temperature variations, which can affect the stability of frequency-generating devices like crystal oscillators. Additionally, frequency control in large power systems requires coordination and synchronization of multiple generators and loads, which can be complex. Furthermore, maintaining accurate frequency control over long distances in transmission lines can be challenging due to line losses and impedance effects. Advanced control algorithms and monitoring systems are employed to address these challenges and ensure accurate frequency control.
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