According to definitions given by IEEE, voltage stability refers to the ability of a power system to maintain steady voltages at all buses in the system after being subjected to a disturbance from a given initial operating condition. By definition, voltage collapse is the process by which the sequence of events accompanying voltage instability leads to abnormally low voltages in a significant part of the power system and consequently leads to a system blackout.
As a result, the voltage problems can be divided to two main categories namely, under-voltage problem and overvoltage problem. There are two types of overvoltage; one is transient overvoltage or voltage spike (voltage surges) which has short duration and high magnitude, and the other one is long-term overvoltage. Both under and overvoltage have some negative effects.
Some negative effects of under-voltage condition are:
Large-disturbance voltage stability: refers to the system’s ability to maintain steady voltages following large disturbances such as system faults, loss of generation, or circuit contingencies.
Small-disturbance voltage stability: refers to the system’s ability to maintain steady voltages when subjected to small disturbances such as incremental changes in system load.
At the same time, there are also short-term and long-term voltage stabilities. Short-term voltage stability includes dynamics of fast acting load components such as induction motors, electronically controlled loads, and HVDC converters. However, long-term voltage stability is related to slower acting equipment such as tap-changing transformers, thermostatically controlled loads, and generator current limiters.
Voltage instability is the inability of the power system to meet demand for reactive power and as mentioned before, it could result in voltage collapse. The contributing factors resulting voltage instability are as follows:
As a result, the voltage problems can be divided to two main categories namely, under-voltage problem and overvoltage problem. There are two types of overvoltage; one is transient overvoltage or voltage spike (voltage surges) which has short duration and high magnitude, and the other one is long-term overvoltage. Both under and overvoltage have some negative effects.
Some negative effects of under-voltage condition are:
- Lamps start to dim because they are constant impedance loads
- Dimming or shrinking television or computer images
- Flashing of digital clocks and electronic equipments
- Data loss, processing errors
- Poor quality or loss of radio and television reception
- Overheating of electrical motors
- Insulation breakdown
- Over-fluxing
- Saturation, and
- Harmonics
Large-disturbance voltage stability: refers to the system’s ability to maintain steady voltages following large disturbances such as system faults, loss of generation, or circuit contingencies.
Small-disturbance voltage stability: refers to the system’s ability to maintain steady voltages when subjected to small disturbances such as incremental changes in system load.
At the same time, there are also short-term and long-term voltage stabilities. Short-term voltage stability includes dynamics of fast acting load components such as induction motors, electronically controlled loads, and HVDC converters. However, long-term voltage stability is related to slower acting equipment such as tap-changing transformers, thermostatically controlled loads, and generator current limiters.
Voltage instability is the inability of the power system to meet demand for reactive power and as mentioned before, it could result in voltage collapse. The contributing factors resulting voltage instability are as follows:
- Generator Q/V control limit
- Load characteristics
- Characteristics of reactive power compensation devices (Shunt Reactors, Shunt Capacitors, and generally FACTS devices)
- Action of On Load Tap Changer (OLTC)