Voltage Dips-Voltage Surges/Spikes-Over Voltages:
Prolonged over voltage occurance is a rare event in the power system. Some of the causes of over-voltages is due to mal-adjustment or mal-operation of the voltage regulators or tap changers of the sychronous generators or alternators, in correct settings of the fixed tap positions of the transformers. Over voltages in the system cause insulation failure of the equipment. In many cases, performance of the operating equipment degrade significantly due to over-voltages when persists for prolonged duration resulting in the failure of the equipment. Therefore over-voltage sensitive equipment should be taken out by protection system during over-voltages.
Harmonics in power system:
Generation of harmonics in the power system is one of the major problem associated with the power quality. The main cause of harmonics in the power system is due to the non-linear load in the power system. Loads such as computers, power electronic devices, UPS systems, rectifiers, static VAR systems etc..Some other sources includes arc furnace, arc lamps and welders, electrical discharge lamps etc.. Harmonic sources in the power system causes:
- Over-heating in rotor equipment of electrical machines (motors, transformers and generators)
- Interference with the communication lines due to harmonics
- Mal operation of the protective devices.
- Increase in the core losses in electrical machines
- Capacitor failures
Frequency Variations in power systems:
Frequency in the power system varies when there is mis-match between the generated electrical power and electrical power demand. When the demand for electrical power is more frequency drops and when demand for electrical power is less (during light load conditions) frequency in the system increases. Frequency variations can also occur in the power system due to generator governor failures and during fault conditions where frequency falls down in the system. When the frequency in the power system starts deteriorating, electrical grid is divided into number of islands (each island consists of group of generating stations and load centers receiving the load).
Some of the effects or impact of frequency fluctuations in the power system are:
Speeds of the motors will vary which results in the variation in the process system associated with the electrical motors.
Reduction in the frequency increases the flux (flux is proportional to voltage / frequency) which drives the magnetic circuits in the machines (transformers, motors and generators) to saturation
Voltage Fluctuations in power system:
When in a three phase system, unbalanced load exist on the networks, voltage unbalances arises. Un-transposed transmission lines (unbalanced impedances) also can cause the unbalanced voltage conditions
Unbalanced voltages in the power system results in heating of the machine rotor which inturn damage the insulation of the rotor of the machine.