Radio Interference Measurement
Due to various reasons the noise voltage is produced such as :
- Over head conductors subjected to high voltage stresses and abrupt changes in the climatic conditions.
- Bonding between the porcelain body of the solid insulator fitted on the metallic-pin.
- Binding of H.V. conductor to the body (grove) of the insulator body surface.
- Surface of insulator polluted.
- Electrical apparatus such as rotating machines, static-machine like transformers produce unwanted electrical signals in radio and high frequency bands (These signals arise due to corona discharges in the air).
- Sparking at the brushes and commutators in rotating machines. These noise voltages affect the television band and radio bands and microwave bands.
Hence it becomes necessary to measure these interference voltages to check whether they are within the acceptable limits or not.
Measurement of radio frequency interference
The noise generated in the radio-frequency band due to corona or partial discharges in H.V. apparatus is measured by radio frequency line to ground voltage (i.e. Radio Influence Voltage RIV).
Following important main parts connected together forms a circuit for this purpose :
Radio noise meter with
- Portable radio receiver
- Local oscillator
- Radio frequency amplifier
- Detector
- Mixer
- Intermediate frequency amplifier
- Multi input circuit (to accommodate pick up devices attenuators calibrators etc.)
- Output circuit having detectors and meters.
Capacitors and resistances and inductors such as
- Radio frequencies inductor choke
- Tuning inductor choke
- Meter input resistance (impedance)
- Measuring resistance (impedance)
- Stray capacitances
- Coupling capacitor
The detector circuit with measuring device is for measuring average value of peak value or quasi peak value. The voltmeter at detector and has 50 to 752 as an input impedance.