What is the function of the shunt reactor in a substation?

To reduce the short circuit current or starting currents.
For compensation of long lines.
To provide reactive power compensation during low loads.
To provide compensations to reactive loads of lagging power factors.

Answer: 3. To provide reactive power compensation during low loads.

Explanation:

What is the function of the shunt reactor in a substation?

A shunt reactor is an electrical device that is used in high voltage power transmission systems to stabilize the voltage during load variations. It is connected in parallel with the electrical system or circuit, allowing it to pass current. Shunt reactors are also known as current absorbers, as they are designed to absorb excess reactive power that can cause voltage instability in the electrical system.

One of the primary functions of a shunt reactor is to allow or pass low-frequency signals or alternating current. This is because shunt reactors have high internal resistance, which blocks current in normal conditions but passes current in abnormal conditions. This helps to maintain voltage stability in the electrical system during load variations, by absorbing excess reactive power and reducing voltage fluctuations.

Shunt reactors are generally used for capacitive reactive power compensation of the power system, and to control dynamic over-voltage occurring in the system due to load rejection. A three-phase shunt reactor is typically connected to a 400 kV or higher electrical bus system, and is designed to compensate for the capacitive reactive power in the power system. This helps to improve the stability and reliability of the electrical system, by reducing voltage fluctuations and maintaining a stable voltage profile.

It is important for the shunt reactor to be capable of withstanding maximum continuous operating voltage under normal power frequency variation without exceeding the top spot temperature of 150°C at any part of the shunt reactor. This ensures that the shunt reactor operates safely and reliably under all operating conditions, without overheating or causing damage to the electrical system.

Some of the common applications and uses of shunt reactors are:

Suppressing high capacitance effect: In transmission and distribution systems, the presence of high capacitance in the cables and lines can lead to high transient voltages, which can cause damage to the equipment and affect the performance of the system. Shunt reactors are used to suppress these high capacitance effects by absorbing the excess reactive power and maintaining a stable voltage profile.
Adjusting transient voltage: Shunt reactors are used to adjust the transient voltage in transmission and distribution systems. Transient voltage is a voltage that varies rapidly over time, and can be caused by lightning strikes, switching operations, and other disturbances in the system. Shunt reactors help to stabilize the transient voltage by absorbing excess reactive power and maintaining a stable voltage profile.
Excessive Reactive Power Absorber: Shunt reactors are used as excessive Reactive Power Absorbers or compensators during low loads. During periods of low load, the system may have excess reactive power that can cause voltage instability and affect the performance of the system. Shunt reactors absorb this excess reactive power, helping to stabilize the voltage and maintain a stable voltage profile.
Voltage balancing and power factor improvement: Shunt reactors are used in electrical substations for voltage balancing, power factor maintenance, and improvement. By absorbing excess reactive power, shunt reactors help to improve the power factor of the system, which in turn reduces losses and improves the efficiency of the system. Shunt reactors are also used to maintain a balanced voltage profile across the system, ensuring that all equipment operates safely and efficiently.