Monday, February 15, 2010
Causes of Power Surges.
Lightning – This is the most common and most severe. It may increase the system voltage by several times the normal value causing considerable damage in the system. Lightning discharge may have currents in the range of 10kA to 90kA.
Switching Surges – This happens when an unloaded line (line having no load e.g. Resistor, Inductor) is connected to a voltage source. A voltage wave is set-up along the line and when it reaches the end of the line, it is reflected back without changing the sign therefore doubling the voltage in the line.
Insulation Failure – Takes place when a line conductor is grounded which may cause over voltages in the system.
Effects of Power Surges.
Since lighting is the most common cause of power surges, I am going to focus on its effects. Switching surges and Insulation failure effects are minimal and can be handled by protective equipments installed. A lighting strike on a transmission line produces a steep-fronted wave and this wave may cause a rise in line voltage to a maximum value of 2000kV in just 1microsecond, and reduce to half the maximum value in just 5microseconds. The travelling wave will cause:
1. Shattering of the insulators and even wreck poles
2. Extreme damage to transformers.
3. Set up oscillations that will damage any equipments connected to the line.
The effects mentioned above sound devastating to the consumer but worry not because power engineers have installed protective devices to stop this harmful current from finding its way to our homes.
Protection Against Power Surges
1. Surge Diverter
This is a protective device which conducts the high voltage surge on the power system to the ground. During normal operation, the surge diverter is off the line, i.e. it is not conducting because of the spark gap. When an overvoltage or power surge occurs the gap breaks down and the surge is harmlessly conducted to the ground. Being grounded and therefore providing a less resistance path to the ground, current will opt to use this path other than flowing on the line conductor. After the surge is over, the resistor offers high resistance to make the gap non-conducting.
2. Surge Absorber.
3. Rod Gap Arrestor.
Fires caused by unnecessary power surges are started by either faulty equipment or negligence of people concerned.
When a power surge takes place and the surge diverter or any other equipment, successfully manages to eliminate it, that equipment needs maintenance or replacement to enable another successful operation in future. However this is not done. It is not until another surge that will result in a fire, only then it will be replaced or maintained.
In developing countries, illegal connections are a common sight. This dangerous act is carried out mostly in slums. If one connects his/her house directly to the line above, the appliance using this current is not protected from surges in any way. Should a surge occur on the line (due to a lighting strike) the result is unimaginable. The appliance would blow up resulting in an electric fire therefore destroying property and lives.
Conduct routine maintenance on all equipments on the line in relation to power surge protection.
Educate persons on the effects of power surges and how they can be minimized.
Install more power surge protection equipments especially at commercial and residential levels
at 7:48 PM