In a power system, voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 at various buses

Electrical bus

Electric bus is a bus powered by electric energy. "Electric bus" can also refer to:* Bus , used for connecting components of a computer or communication between computers* Busbars, thick conductors acting as nodes in electrical substations...

 tends to increase or decrease during its daily operation. To ensure constant voltage to consumers, various techniques are utilized.

When the voltage is below the required level, reactive power produced by inductance needs to be offset by capacitance.

• Synchronous condenser
  Synchronous condenser
  In electrical engineering, a synchronous condenser is adevice identical to a synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid...
  
  s—can be used to generate reactive power, when they are operated as a motor.
• Shunt Capacitance—Capacitor
  Capacitor
  A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
  
   banks can be connected in parallel to the transmission lines.
• Series Capacitance—Capacitors connected in series, especially for long lines can be used to raise the voltage.
• Tap Changing Transformers—Transformer tappings can be automatically changed, to alter the voltage accordingly.

When the voltage is above the required level, reactive power produced by capacitance needs to be offset by inductance.

• Shunt Reactors—Inductor
  Inductor
  An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
  
   banks can be connected in parallel to the transmission lines also known as reactors.
• Static VAr Compensator
  Static VAr compensator
  A static var compensator is an electrical device for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage and stabilising the system...
  
  s—
• Tap Changing Transformers—Transformer tappings can be automatically changed, to alter the voltage accordingly.