Cable Fault Locator TDR RI-407 “SWIFT+”
for Power Lines applications

Overview

TDR RI-407 cable fault locator implements the following measurement methods:

• Time Domain Reflectometry (TDR)
• Arc Reflection Method(ARM or SIM )*
• Impulse Current Method (ICM)*
• DECAY  travelling wave method*

* when used in complex with high-voltage pulse generators (HVPG), for example: ADG-200-2 “STINGRAY-M”

Time Domain Reflectometry (TDR)

the most accurate and safe mode – effective for diagnosing low-resistance faults (less than 1 kOhm) and short circuits, searching for cable line breaks, joints/splices, parallel branches, etc.

More about this method:

Time Domain Reflectometry (TDR). Theoretical basis.

Time Domain Reflectometry (TDR). Practical techniques.

The method allows you to perform the following works:
• cable length measurement;
• measurement of distances to impedance inhomogeneities or faults;
• measurement VoP (v/2) of the line at its known length;
• determination of the nature of cable fault.

The TDR method is based on the phenomenon of partial reflection of electromagnetic waves in places where the impedance of a line changes. When measuring by the TDR method, a short voltage probe pulse is sent to the line, which, partially reflected from the impedance inhomogeneities, returns back. The reflected pulses return to the TDR-device some time after the sending of the probe pulse. Knowing the signal velocity of propagation in the line and the delay time of the reflected signal, it is possible to calculate the distance to the impedance inhomogeneity (fault). Reflections from the probe pulse are observed on a range-scaled screen, and by their form can be determined the nature of inhomogeneity.
Inhomogeneities of the impedance are the result of a violation of the cable production technology, as well as a consequence of mechanical and electrical damage during the construction and operation of the cable. Inhomogeneity also occurs in the points where any devices are connected to the cable line (coupling, branch, cable splice/joint, Pupin coil, etc.), or in points of faults (open circuit, short circuit, wetting of the cable core, leakage to earth, leakage to an adjacent wire, broken pairs, etc.). The TDR method makes it possible to see multiple inhomogeneities, both discrete and distributed, depending on the ratio of their length and the minimum wavelength of the probe pulse spectrum.

TDR RI-407 reflectogram examples:

Arc Reflection Method (ARM)

in combination with a High-Voltage Pulse Generator (HVPG), for example ADG-200-2 “STINGRAY-M”, allows to detect High-Resistance faults (> 1 kOhm) with the accuracy of the TDR method.

You can read more about this method at the link:

Arc Reflection Method (ARM) for high-resistance faults prelocation

Localization of high-resistance faults at the site of a defect is usually difficult when using a low-voltage pulse measurement method. One of the ways to localize such defects on power cables is the Arc Reflection Method (ARM).

The essence of the ARM method is that a short-term electric arc is created (with the help of High-Voltage Pulse Generator ) at the place of cable damage. A burning electric arc has a low resistance, so it is well detected by an TDR.

The method does not require preliminary burning of the insulation and is especially effective when working on cables with a polyethylene sheath.

An example of reflectogram of a cable line obtained by a ARM method:

Impulse Current Method (ICM), DECAY  travelling wave method

in combination with a High-Voltage Pulse Generator (HVPG), for example ADG-200-2 “STINGRAY-M”, it allows to determine the location of high-resistance defects in cases where the fault is distributed in nature and electrical breakdown occurs without ARC ignition (respectively, ARM is not applicable)

You can read more about this method at the link:

Impulse Current Method (ICM), DECAY  travelling wave method for determining high resistance faults

Locating faults caused by a floating breakdown of insulation is usually difficult when using a low-voltage TDR measurement method. One of the ways to localize such defects on power cables is the oscillatory discharge method (ICM / Decay).

The method of oscillatory discharge (wave) is based on measuring the duration of the period of the oscillatory process that occurs during the breakdown of a charged cable.

To create an oscillatory process in the cable, with the help of HVPG, the voltage in the cable is smoothly raised to breakdown, but not higher than the value determined by the norms of preventive tests, or with the help of HVPG, the built-in high-voltage capacitor is charged and then discharged into the cable.

The reflectometer in this case acts as an oscilloscope that records the oscillatory process in the cable (using a current sensor – ICM method or voltage sensor – Decay method).

An insulation defect causes a breakdown at the place of damage, a and an oscillatory discharge occurs in the cable. Knowing the speed of propagation of the electromagnetic wave along the line and the period of the oscillatory process, it is possible to calculate the distance to the breakdown: