High-pressure Mercury-Vapour Lamp (HPMVL):
Working:
* Whenever 1-ph, 230V, AC Supply is provided to the discharge tube of MVL, initially the current flows from Phase to the choke to the starting electrode to neutral.
* The starting electrode or resistance is made of tungsten filament having more resistance ( 5 to 10 kOhm), so that whenever current flows through the tungsten filament, as per the thermal emission, the light is emitted through the filament. The initial colour of light is therefore blue.
* At the same time the rated voltages is applied in between the main electrode No.1 & main electrode no. 2. Due to this voltage, there will be collision of neon gas particles & current will start to flow through the discharge tube,
* Whenever temperature surrounding the inner tube increases up to 600 degree C the mercury powder will start vaporizing & the continuous collision process of all inert gases takes place so that full light is emitted through the discharge tube.
* The colour of light is bluish white. The full light is emitted after 10-15 min.
OR
The construction & connection diagram is as shown in figure. As per this construction there are following components.
* Choke: The choke is acting as the ballast. At the time of supply voltage variation, the current flowing through the inner tube is maintained constant to keep uniform light intensity. Sometimes choke can be designed to get the higher voltages, to apply to the inner tube of mercury vapour lamp.
* Starting resistance/limiting resistance: Whenever current flows through the starting resistance, there is a I2R loss which is converted into heat. If the temperature of this heat goes near about 600 degree C then inert gases ionization starts.
* Auxiliary electrode & Main electrode: It is made by high resistive element. The ionization is takes place through the inert gases whenever current flows from auxiliary electrode to main electrode. * Inner Tube: The various inert gases e.g. Argon, Nitrogen etc with mercury powder are filled in the inner tube at 5 to 7 times of the atmospheric pressure.
* Outer Tube: The function of outer tube is to make the vacuum surrounding the inner tube to avoid thermal dissipation or to maintain 600 degree C surrounding the inner tube. Power factor improvement Capacitor: The function of power factor improvement capacitor is to improve the power factor from 0.5 to 0.95.