Protection & Absorption of Reactive Power

I. Introduction

In power systems, the protection and absorption of reactive power play a crucial role in maintaining system stability and efficiency. Reactive power is an essential component of alternating current (AC) power systems and is responsible for voltage control and power factor correction. This topic explores the fundamentals of reactive power, its impact on power system stability and efficiency, and the methods used for voltage control.

A. Importance of Protection & Absorption of Reactive Power in power systems

The protection and absorption of reactive power are essential for the following reasons:

• Ensuring voltage stability: Reactive power control helps maintain the voltage within acceptable limits, preventing voltage collapse and instability in the power system.
• Improving power system efficiency: By controlling reactive power flow, power losses can be minimized, leading to improved overall system efficiency.
• Enhancing power quality: Proper reactive power control helps reduce voltage fluctuations and harmonics, ensuring a stable and reliable power supply.

B. Fundamentals of Reactive Power

Reactive power is the power component that oscillates between the source and the load without being consumed. It is measured in volt-amperes reactive (VAR) and is denoted by Q. Reactive power is essential for the operation of inductive and capacitive loads and is necessary for maintaining the power factor of the system.

Reactive power has both leading and lagging components. Leading reactive power is associated with capacitive loads, while lagging reactive power is associated with inductive loads. The power factor of a system is the ratio of real power (measured in watts) to apparent power (measured in volt-amperes). A power factor of 1 indicates a purely resistive load, while a power factor less than 1 indicates the presence of reactive power.

II. Method of Voltage Control

Voltage control is crucial in power systems to maintain a stable and reliable power supply. Various methods are employed to control reactive power and regulate system voltage. The following are the commonly used voltage control methods:

A. Definition and purpose of voltage control in power systems

Voltage control refers to the regulation of system voltage within acceptable limits. It involves the adjustment of reactive power flow to maintain voltage stability and ensure optimal system performance. Voltage control is necessary to compensate for voltage drops and fluctuations caused by load variations and system disturbances.

B. Reactive power control methods

1. On-load tap changers (OLTC): On-load tap changers are used in transformers to adjust the turns ratio and regulate the voltage output. By changing the tap position, the reactive power flow can be controlled to maintain the desired voltage level.

2. Shunt capacitors and reactors: Shunt capacitors and reactors are connected in parallel with the load to supply or absorb reactive power. Capacitors are used to supply reactive power, while reactors are used to absorb reactive power, depending on the system requirements.

3. Synchronous condensers: Synchronous condensers are rotating machines that operate without a mechanical load. They are connected to the power system and provide or absorb reactive power as needed. Synchronous condensers are particularly effective in voltage control and improving system stability.

4. Static VAR compensators (SVC): SVCs are solid-state devices that provide fast and precise control of reactive power. They consist of thyristor-controlled reactors (TCR) and thyristor-switched capacitors (TSC) that can be switched on or off to supply or absorb reactive power.

5. Unified Power Flow Controllers (UPFC): UPFCs are advanced devices that combine the functionalities of SVCs and phase-shifting transformers. They provide simultaneous control of voltage magnitude, phase angle, and impedance, allowing for precise control of reactive power flow.

C. Advantages and disadvantages of each voltage control method

• On-load tap changers (OLTC):

  • Advantages: Allows continuous adjustment of voltage, suitable for large power transformers.
  • Disadvantages: Mechanical wear and tear, limited control range.

• Shunt capacitors and reactors:

  • Advantages: Cost-effective, simple design, suitable for low and medium voltage systems.
  • Disadvantages: Fixed reactive power compensation, requires manual switching.

• Synchronous condensers:

  • Advantages: Fast response, excellent voltage control, improves system stability.
  • Disadvantages: High capital cost, requires maintenance.

• Static VAR compensators (SVC):

  • Advantages: Fast and precise control, suitable for high voltage systems.
  • Disadvantages: High capital cost, requires complex control algorithms.

• Unified Power Flow Controllers (UPFC):

  • Advantages: Simultaneous control of multiple parameters, enhances power system controllability.
  • Disadvantages: High capital cost, complex installation and operation.

III. Static VAR Systems

Static VAR Systems (SVS) are widely used for reactive power control and voltage regulation in power systems. SVS consists of various components that work together to supply or absorb reactive power as needed.

A. Definition and function of Static VAR Systems (SVS)

Static VAR Systems (SVS) are power electronic devices used for reactive power compensation and voltage control. They are capable of supplying or absorbing reactive power to maintain the desired voltage level and improve system performance.

B. Components of SVS

1. Thyristor-controlled reactors (TCR): TCRs are used to control the flow of reactive power by adjusting the impedance in the circuit. They consist of thyristor switches that can be turned on or off to vary the reactor impedance and regulate the reactive power flow.

2. Thyristor-switched capacitors (TSC): TSCs are used to supply or absorb reactive power by switching capacitors in or out of the circuit. They provide fast and precise control of reactive power and are commonly used in SVS.

3. Thyristor-switched reactors (TSR): TSRs are similar to TCRs but with the addition of capacitors. They provide a combination of reactive power control and voltage regulation, making them suitable for a wide range of applications.

C. Operation and control of SVS

SVS operates by monitoring the system voltage and adjusting the reactive power flow accordingly. The control system continuously measures the voltage and compares it to the desired setpoint. Based on the deviation, the control system activates the appropriate components (TCRs, TSCs, or TSRs) to supply or absorb reactive power and regulate the voltage.

D. Real-world applications and examples of SVS in power systems

SVS is widely used in power systems for various applications, including:

• Voltage control in transmission and distribution networks
• Power factor correction in industrial plants
• Reactive power compensation in renewable energy systems

SVS provides an effective and flexible solution for reactive power control, improving system stability and efficiency.

IV. Protection of Reactive Power

The protection of reactive power equipment is crucial to ensure its safe and reliable operation. Reactive power equipment, such as capacitors, reactors, and SVCs, can be subjected to various faults and abnormal conditions that may result in damage or failure. Therefore, proper protection schemes are implemented to detect and mitigate these issues.

A. Importance of protecting reactive power equipment

Protecting reactive power equipment is essential for the following reasons:

• Preventing equipment damage: Reactive power equipment is susceptible to faults and abnormal conditions that can lead to damage or failure. Protection schemes help detect these issues and isolate the faulty equipment to prevent further damage.
• Ensuring system reliability: Reactive power equipment plays a critical role in maintaining system stability and voltage control. Protecting this equipment ensures the reliable operation of the power system.

B. Common protection schemes for reactive power equipment

1. Overcurrent protection: Overcurrent protection is used to detect excessive current flow in reactive power equipment. It involves the use of current sensors and protective relays that trip the circuit breaker when the current exceeds a predetermined threshold.

2. Overvoltage protection: Overvoltage protection is employed to safeguard reactive power equipment from voltage surges. It typically involves the use of voltage sensors and protective relays that disconnect the equipment when the voltage exceeds a specified limit.

3. Underfrequency protection: Underfrequency protection is used to detect low-frequency conditions that can affect the operation of reactive power equipment. It involves monitoring the system frequency and tripping the circuit breaker when the frequency drops below a certain threshold.

4. Overtemperature protection: Overtemperature protection is essential for reactive power equipment that generates heat during operation. It involves the use of temperature sensors and protective relays that disconnect the equipment when the temperature exceeds a safe limit.

C. Step-by-step walkthrough of typical problems and their solutions in reactive power protection

1. Problem: Overcurrent in a shunt capacitor bank

   • Cause: Excessive current flow due to a short circuit or capacitor failure.
   • Solution: Install overcurrent protection relays that trip the circuit breaker when the current exceeds a predetermined threshold.

2. Problem: Overvoltage in a static VAR compensator (SVC)

   • Cause: Voltage surge due to a lightning strike or system fault.
   • Solution: Implement overvoltage protection relays that disconnect the SVC when the voltage exceeds a specified limit.

3. Problem: Underfrequency in a synchronous condenser

   • Cause: Low-frequency conditions due to a system disturbance or generator tripping.
   • Solution: Use underfrequency protection relays that trip the circuit breaker when the frequency drops below a certain threshold.

4. Problem: Overtemperature in a thyristor-controlled reactor (TCR)

   • Cause: Excessive heat generation due to high ambient temperature or overload.
   • Solution: Employ temperature sensors and protective relays that disconnect the TCR when the temperature exceeds a safe limit.

V. Absorption of Reactive Power

Absorbing reactive power is necessary in power systems to maintain the desired voltage level and improve system performance. Various methods are employed to absorb reactive power, depending on the system requirements.

A. Definition and purpose of absorbing reactive power in power systems

Absorbing reactive power involves the consumption of excess reactive power in the system. The purpose of absorbing reactive power is to maintain the voltage within acceptable limits, improve power factor, and reduce system losses.

B. Methods of absorbing reactive power

1. Synchronous condensers: Synchronous condensers are rotating machines that operate without a mechanical load. They are connected to the power system and absorb reactive power as needed. Synchronous condensers provide fast response and excellent voltage control.

2. Static VAR compensators (SVC): SVCs can both supply and absorb reactive power. They consist of thyristor-controlled reactors (TCR) and thyristor-switched capacitors (TSC) that can be switched on or off to regulate the reactive power flow.

3. Unified Power Flow Controllers (UPFC): UPFCs are advanced devices that can absorb or supply reactive power. They provide simultaneous control of voltage magnitude, phase angle, and impedance, allowing for precise control of reactive power flow.

C. Advantages and disadvantages of each method of absorbing reactive power

• Synchronous condensers:

  • Advantages: Fast response, excellent voltage control, improves system stability.
  • Disadvantages: High capital cost, requires maintenance.

• Static VAR compensators (SVC):

  • Advantages: Fast and precise control, suitable for high voltage systems.
  • Disadvantages: High capital cost, requires complex control algorithms.

• Unified Power Flow Controllers (UPFC):

  • Advantages: Simultaneous control of multiple parameters, enhances power system controllability.
  • Disadvantages: High capital cost, complex installation and operation.

VI. Conclusion

In conclusion, the protection and absorption of reactive power are vital for maintaining power system stability and efficiency. Various methods, such as voltage control techniques and static VAR systems, are employed to regulate reactive power flow and ensure optimal system performance. Additionally, proper protection schemes are implemented to safeguard reactive power equipment from faults and abnormal conditions. The absorption of reactive power is necessary to maintain voltage stability and improve power factor. Synchronous condensers, SVCs, and UPFCs are commonly used methods for absorbing reactive power. Understanding the importance and key concepts of protection and absorption of reactive power is crucial for power system engineers and operators. Future developments and advancements in reactive power control and protection will continue to enhance power system reliability and efficiency.

Summary

The protection and absorption of reactive power are crucial in power systems to maintain system stability and efficiency. Reactive power is responsible for voltage control and power factor correction. Various methods, such as voltage control techniques and static VAR systems, are used to regulate reactive power flow. Protection schemes are implemented to safeguard reactive power equipment from faults and abnormal conditions. The absorption of reactive power is necessary to maintain voltage stability and improve power factor. Synchronous condensers, SVCs, and UPFCs are commonly used methods for absorbing reactive power. Understanding the importance and key concepts of protection and absorption of reactive power is essential for power system engineers and operators.

Analogy

Reactive power can be compared to the water in a water tank. Just as water stored in a tank can be used to maintain a constant water pressure in a plumbing system, reactive power is stored and utilized to maintain a stable voltage level in a power system. The protection and absorption of reactive power can be likened to the control and regulation of water flow in and out of the tank to ensure a consistent water pressure throughout the plumbing system.