What are the protective measures taken against lightning overvoltages?
The most commonly used devices for protection against lightning surges are : (i) Earthing screen (ii) Overhead ground wires (iii) Lightning arresters or surge diverters Earthing screen provides protection to power stations and sub-stations against direct strokes whereas overhead ground wires protect the transmission …
What are the causes for switching and power frequency overvoltages?
The main cause of these voltage surges in power system are due to lightning impulses and switching impulses of the system. But over voltage in the power system may also be caused by, insulation failure, arcing ground and resonance etc.
What is Unit protection?
Unit protection is designed to operate for abnormal conditions inside the protected zone while remaining stable for abnormal conditions outside the protected zone. This scheme requires current to be measured at each end of the zone.
Which of the following is the protective device against lightning over voltages Mcq?
Surge arresters are also called lightning arresters. They are applied to electric systems to protect equipment such as transformers, rotating machines, etc., against the effects of overvoltages resulting from lightning, switching surges, or other disturbances.
Which devices are used for overvoltage protection?
Overvoltage protection devices
- Arcing horns.
- Avalanche diode.
- Gas-filled tube.
- Lightning rod.
- Metal-oxide varistor.
- Spark gap.
- Transient-voltage-suppression diode.
- Trisil.
What are switching overvoltages?
Switching overvoltages are the primary dimensioning parameter for air-clearances in EHV and UHV systems. All network switching operations result in a certain level of transient overvoltages that propagate through the system.
Which type of protection scheme is a unit protection scheme?
Unit and Non-Unit Protection Scheme. a) Unit Protection Scheme: Unit type schemes protect a specific area of the system i.e. a transformer, transmission line, generator or bus bar. The unit protection schemes are based on Kirchhoff’s Current Law – the sum of the currents entering an area of the system must be zero.
What is the difference between unit and non-unit protection?
Non-unit protection consists of circuits that measure and compare the voltages and currents at the relaying point. It is able to determine the location of the fault from these values. This contrasts with unit protection which will not operate for a fault outside its zone.
Which devices are used for over voltage protection?
How to protect power system from over voltage surges?
But over voltage surges appear in the system due to lightning impulses are very high in amplitude and highly destructive. The affect of lightning impulse hence must be avoided for over voltage protection of power system. These are mainly three main methods generally used for protection against lightning. They are Earthing screen.
What is overvoltage protection?
Overvoltage Protection. There are always a chance of suffering an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc.
How to protect equipment in substations from transient overvoltages?
The classical device to protect equipment in substations against the effects of transient overvoltages is the surge arrester. The most frequent transient overvoltage in substations comes from switching operations, and the most fearful is lightning, which introduces large disturbances.
What happens if over voltage protection is not provided to power system?
If over voltage protection is not provided to the power system, there may be high chance of severe damage. Hence all over voltage protection devices used in power system mainly due to lightning surges. Let us discuss different causes of over voltages one by one.