InfraRed	UltraViolet
	ΔT - Hot Spots – Not Corona!(Internal Phenomenon)	Detects Corona, Partial Discharge & Arcing(External Phenomenon)
	Current Dependent (Heavy Line Loading)	Voltage Dependent Only (No Line Loading)
	Solar Radiation and Hot environment set a problem	All Lighting & Weather Conditions (humidity is an advantage)
	Detection Usually at Progressive Stage of Degradation	Detection at Earlier of Degradation (i.e. Commissioning)

Here are some facts...

• Infra Red (IR) thermography detects hot spots and indicates temperature difference
  
• The IR technology does not locate corona
  
  
• Some severe corona and arcing activity cases in transmission may generate enough heat so it can be located with IR equipment but these may be revealed in advanced stages of degradation where corrective action may be too late
  
  
• In distribution usually heavy line loading is requested which makes it inconvenient and sometimes even impractical procedure for inspection of distribution lines
  
  
• Corona and arcing occur by stress of the electric field and is not current dependent and therefore can be revealed by UV inspection and not by thermographic equipment
  
  
• In cases where severe corona or arcing evolves temperature gradient lighting and weather conditions may set limitation to the inspection
  
  
• Bright light and humid or foggy conditions may obscure the visibility of the thermal gradient
  
  
• Partial discharges in motor and dry transformer coils and windings will be located by UV inspection and not by the IR camera.
  
  
• Internal defects in the transmission and distribution cables, components and insulators will be mainly exhibited as hot spots and thermal gradients and will not be revealed by UV inspection.
  
  
• Strong arcing emits both UV and IR.
  
  
• Corona is a blinking flickering event and to capture it a video camera is a must. IR can do with stills camera.
  
  
  
  therefore...

The IR thermographic technology and the UV inspection technology are complementary and both are therefore required in a well established predictive maintenance procedure in transmission distribution and substations and in commissioning stages of new installations