Table of Contents
What is electrical VLF test?
Very Low Frequency testing for Medium Voltage and High Voltage cables is a method for verifying the integrity of the cable insulation. VLF testing is a withstand test usually carried out at a frequency of between 0.1 Hz and 0.01 Hz rather than 50/60 Hz.
What is the purpose of VLF?
The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks) and for secure military communication. Since VLF waves can penetrate at least 40 meters (131 ft) into saltwater, they are used for military communication with submarines.
What is the difference between VLF and Hipot?
VLF is the abbreviation, and commonly used name, for Very Low Frequency. VLF AC hipots produce a frequency output of 0.1 Hz and lower rather than the conventional 50 Hz or 60 Hz.
Is VLF testing destructive?
Is the VLF test destructive? VLF hipoting is not destructive to good insulation and does not lead to premature failures like with DC voltage testing. Using VLF does not cause degradation of the insulation. It does cause existing cable defects, like water trees and splice defects, to break through during the test.
What is VLF Tan Delta testing?
Very low frequency (VLF) tan delta testing is a precise and non-destructive method to provide information on the extent of ageing in cable insulation. The test applies an AC sinusoidal waveform at 0.1 Hz frequency and measures the degree of real power dissipation (or losses) in a dielectric material.
What is VLF method?
Basic Concept. The VLF method uses powerful remote radio transmitters set up in different parts of the world for military communications (Klein and Lajoie, 1980). In radio communications terminology, VLF means very low frequency, about 15 to 25 kHz.
What is the frequency range of VLF?
15–30 kHz
VLF electromagnetic technology is used in the frequency range of 15–30 kHz. VLF utilizes the carrier waves of distant powerful communications transmission of military organizations also.
What is a VLF generator?
The very low frequency (VLF) testing equipment has been popular in recent years used for ac withstand voltage testing due to its portability. This paper presents a new type of VLF sinusoidal waveform generator which can generate a sinusoidal waveform at 0.1 Hz.
What is the Megger value of cable?
1. IR Values For Electrical Apparatus & Systems
| Max.Voltage Rating Of Equipment | Megger Size | Min.IR Value |
|---|---|---|
| 25 KV | 5,000 Volts | 20,000 MΩ |
| 35 KV | 15,000 Volts | 100,000 MΩ |
| 46 KV | 15,000 Volts | 100,000 MΩ |
| 69 KV | 15,000 Volts | 100,000 MΩ |
What is sheath test of cable?
Sheath Resistance testing is a key onsite diagnostic test for identifying potential cable faults. Commonly known as a Megger Test, it uses a Megohmmeter to measure the resistance of the cross-linked or thermoplastic compound to an applied DC voltage.
What is VLF geophysics?
Very Low Frequency Electromagnetics (VLF) is a geophysical ground probing technology that utilizes VLF signals in the 15 to 30 kHz range normally used for communication with submarines. The signal generated is suitable for making geophysical measurements globally.
What unit is VLF?
Definition. VLF. Very Low Frequency (3-30 kHz; 100-10km)
Is VLF testing AC or DC?
ac
VLF ac voltage testing methods utilize ac signals at frequencies in the range of 0.01 Hz to 1 Hz. The most commonly used, commercially available VLF ac voltage test frequency is 0.1 Hz. VLF ac test voltages with cosinerectangular and the sinusoidal wave shapes are most commonly used.
What is UST mode?
UST mode is used to measure insulation between two ungrounded terminals of the apparatus, isolate an individual section of insulation and test it without measuring other connected insulation.
What is Megger value of 11KV cable?
11kV and 33kV Cables between Cores and Earth (As per ETSA Standard)
| Application | Test Voltage | Min IR Value |
|---|---|---|
| 11KV New cables – Sheath | 5KV DC | 1000 MΩ |
| 11KV After repairs – Sheath | 5KV DC | 100 MΩ |
| 33KV no TF’s connected | 5KV DC | 1000 MΩ |
| 33KV with TF’s connected. | 5KV DC | 15MΩ |
What is VLF testing for solid dielectric cable?
VLF testing of solid dielectric cable is supported in IEC 60502 (up to 35kV) and in IEEE 400.2 (up to 69 kV). Acceptance test voltages are generally 2.5-3 times the line to ground system voltage. VLF tests should last between 15 and 60 minutes with a recommended minimum duration of 30 minutes.
What is the VLF test?
The VLF test can be used in a number of ways: Apply VLF to cables in a simple withstand approach to detect potential failures ( faults) in the cable insulation during a planned outage. The tested cable must withstand an AC voltage for a specified testing time without flashover.
How long does a VLF cable test take?
The VLF cable testing time varies from 15 to 60 minutes. IEEE 400.2 establishes some suggested test voltages and times. Subsequent work by the CDFI has shown there to be no significant change in the efficacy of a VLF test conducted over the frequency range 0.1 to 0.01 Hz when the IEEE 400.2 voltages and times are used.
What is the voltage level of a VLF cable?
Test voltage levels are either calculated using a multiple of the cable’s nominal phase-phase voltage or via tables in IEEE 400.2; typically they are in the range of 1.5 U0 to 3 U0. The VLF cable testing time varies from 15 to 60 minutes.