Lightning protection Seminar

Power System – Causes for Over Voltage and Prevention: 

Power System – Causes for Over Voltage and Prevention Seminar Presented by: S Murali Krishnan 5050910061 – BTech EEE SRM University, Chennai

Power System – Causes for Over Voltage and Prevention: 

Power System – Causes for Over Voltage and Prevention Terminology Normal

Power System – Abnormalities: 

Power System – Abnormalities 1. Voltage Drop/ Shot interruptions 2.Harmonic waves due to voltage changes 3.Temporary voltage increases 4.Switching surges 5. Lightning surges

Slide 4: 

1.The voltage falls below normal: Sag 2.The reverse of a sag: Swell 3.Increase in voltage above 110% of nominal for more than one minute - Over-voltage . Power System – Abnormalities

Slide 5: 

4.Noise - used to describe very small and persistent disturbances. These do not have damaging effects but can be a nuisance 5.Harmonics are a recurring distortion of the waveform that can be caused by various devices including variable frequency drives, non-linear power supplies and electronic ballasts. Power System – Abnormalities

Slide 6: 

6. When the voltage drops below 10% of its nominal value it is called an interruption or a blackout . 7. Transients are very short duration (sub-cycle) events of varying amplitude.  Often referred to as "surges", transients are probably most dangerous power abnormally Power System – Abnormalities

Slide 7: 

External Causes: Lightning - Direct hit Distant Lightning - Transients on Utility lines Brownouts/Blackouts - Sags & Recovery Grid Switching - Utility switching Other Users - Adding/Removing loads line Power System – Causes for Transients

Slide 8: 

Internal Causes: Switching of: Electrical motors Elevator Motors Compressors Welding or heavy machinery Power Overloads Power System – Causes for Transients

Slide 9: 

Power System – Lightning types Stepped Leader Streamer

Slide 10: 

A strike can average 100 million volts of electricity Current of up to 100,000 amperes Can generate 54,000 o F Lightning strikes somewhere on the Earth every second Kills 100 US residents per year Power System-Facts -Lightning

Slide 11: 

Direct strike Side Flash Power System-Lightning Effects

Slide 12: 

Once the building is struck, lightning current can cause damage either by spark over or intrusion through service lines Power System-Lightning Effects

Slide 13: 

Lightning generates strong electromagnetic radiation in a broad band of frequencies Power System-Lightning Effects

Slide 14: 

Once entered into nearby structures, these radiation may damage sophisticated electronics irrespective of whether they are in operation or not Power System-Lightning Effects

Slide 15: 

A service line may directly encountered with lightning or a nearby hit may induced large voltage pulses in the service line Power System-Lightning Effects

Slide 16: 

Safe Zone Degradation Catastrophe Failure Power System-Transient Effects

Slide 17: 

Random faults (Annoying) Memory Loss Data Errors Random System Halts Degradation (Un-noticed Damage) Break-Down of ICs Loss of Circuit Traces, or Insulation Shortening of Component Thermal Runaway of Semi-Conductors Burn-Out (Catastrophic Failure) Board Damage & Failure System Down System Failure Power System-Transient Effects

Slide 18: 

Damage to a modem card The surge has come through the communication line. In this case the damage to the modem has prevented further damage to the computer Power System-Transient Effects

Slide 19: 

Power System-Lightning types Two types of Lightning – Direct & Indirect Direct – Stroke A-Cloud to tall object – protection is possible, Stroke B-Between clouds-protection not possible

Slide 20: 

Power System-Lightning types Indirect – Line directly below the cloud gets electrostatically charged. When the cloud discharges to earth thro lighhtning, -ve charge on the line gets isolated and it travels fast on the line in both directions in the form of waves. Indirect lightning is the major cause for transients in elec lines

Slide 21: 

Power System-Lightning Protection OH grounding wire Lightning arrester Earthing screen

Slide 22: 

Power System-Lightning Protection OH grounding wire

Slide 23: 

Power System-Lightning Protection Lightning arrester

Slide 24: 

Power System-Lightning Protection Earthing screen – A grid of earthed copper conductors criss crossing the Substation provide a low resistance path for lightnings. They do not guard against travelling waves

Slide 25: 

Power System-Lightning Arresters Rod gap Horn gap Multigap Expulsion type Valve type Rod gap

Slide 26: 

Power System-Lightning Protection Horn gap Multigap

Slide 27: 

Power System-Lightning Protection Expulsion Type

Slide 28: 

Power System-Lightning Protection Valve Type

Susceptibility of components to damage.: 

Susceptibility of components to damage . Motors & Transform. Relays Valves Passive components Diodes Transistors (power) Integrated circuit ICs Semi-conductor diodes 10 10 10 10 10 10 10 10 10 -8 -6 -4 -2 0 2 4 6 8 J No damage Possible damage Destruction

Protecting Equipment Against Transients: 

Protecting Equipment Against Transients

Lightning Current: Peak Value: 

Lightning Current: Peak Value Typical value for the first stroke is 30 kA Typical value for the subsequent stroke is 15 kA Values over 250 kA has been recorded

Power System-Peterson Coil: 

Power System-Peterson Coil

Power System-Peterson Coil: 

Power System-Peterson Coil

Power System-Peterson Coil - sample: 

Power System-Peterson Coil - sample

Principles of Surge Protection Devices: 

Diverting surge current to earth Principles of Surge Protection Devices Does NOT prevent lightning but protects against effects Clamping output voltage to a safe level

Slide 36: 

A protector performs like a switch controlled by voltage. If the voltage is higher than the rated voltage of the electrical line to be protected, then the protector changes its state to low impedance and derives current to earth. The usual state of the protector is being in high impedance, so that the protector is transparent for the installation. Principle of Power Protection

Slide 37: 

Examples for typical U p values

Surge protection devices: 

Surge protection devices Spark gaps (air gaps) Gas discharge tubes (GDTs) Zener diodes (avalanche diodes) Metal oxide varistors (MOVs) Transobers Relays Fuses PTCR (Positive Temperature Coefficient Resistor) TBU (Transient Blocking Unit)

MOV/GDT/SAD: 

MOV/GDT/SAD MOV GDT SILICON DIODE

Earthing for lightning protection - principles: 

Earthing for lightning protection - principles Divert current as soon as possible Use dedicated low impedance connection Make sure other systems are bonded to it, once!

Slide 43: 

Clean and unclean lines should not be placed together

Slide 45: 

Bundled wires introduce much less voltage drop than unbundled wires

Details of SPDs: 

Details of SPDs

Gas Discharge Arresters: 

Two electrodes, close together, enclosed in a tube filled with gas When the voltage rises, a low impedance arc is formed between the two electrodes Symbol: Also called gas-filled surge arrester Gas Discharge Arresters

Gas Discharge Arresters: 

Gas Discharge Arresters

Metal Oxide Varistor: 

Variable resistor – resistance depends on voltage Symbol: The most common type of varistor is the M etal O xide V aristor, or MOV Metal Oxide Varistor

MOVs: 

MOVs

Silicon Avalanche Diodes: 

Semiconductor devices with similar characteristics to varistors Symbol: Also called “transorbs” and “clamping diodes” Silicon Avalanche Diodes

Silicon Avalanche Diodes: 

Silicon Avalanche Diodes

Surge Arrester Characteristics: 

Surge Arrester Characteristics MOV SAD GDA Let-through voltage Good Best Bad Surge rating Good Bad Best Lifespan Good Best Good Current sharing Good Fair Bad Leakage current Fair Good Best Capacitance Bad Good Best

Slide 54: 

Thank You