The correct answer is D. Voltaire transformers.
Exciters are used to control the voltage and current of a generator. Series capacitors are used to improve the power factor of a transmission line. Shunt reactors are used to limit the current flow in a transmission line. Voltaire transformers are not used in substations.
Exciters are devices that are used to control the voltage and current of a generator. They do this by providing a magnetic field that interacts with the rotor of the generator. This interaction causes the rotor to turn, which in turn generates electricity. Exciters are essential for the proper operation of generators, and they are typically located in the same substation as the generator.
Series capacitors are devices that are used to improve the power factor of a transmission line. Power factor is a measure of how efficiently electricity is being used. A low power factor indicates that the electricity is being wasted, and this can lead to increased costs for the utility company. Series capacitors help to improve the power factor by providing a reactive component to the current flow. This reactive component helps to cancel out the inductive component of the current flow, which in turn improves the power factor.
Shunt reactors are devices that are used to limit the current flow in a transmission line. They do this by providing a magnetic field that opposes the current flow. This opposition causes the current to decrease, which in turn helps to protect the transmission line from damage. Shunt reactors are typically located near the end of a transmission line, where the current is highest.
Voltaire transformers are a type of transformer that is used to convert high-voltage electricity to low-voltage electricity. They are typically used in power distribution systems, and they are not typically found in substations.