Pre-location
Impulse Current Method

The surge generator ignites an arc at the fault which creates a travelling wave between the fault and the surge generator. The TDR Teleflex displays this transient wave which indicates the distance to the fault. A linear coupler for the impulse current method is installed in all surge generators with an output energy of 1000 J or more. This method can be useful for all high resitance faults, on wet cables and splices as well as on long paper-lead cables.
ARM Arc Reflection Method

High resistive faults and intermittent faults can easily be located with the ARM Method. If the fault resistance is too high for direct measurement with a TDR Teleflex, a surge generator provides a low resistance arc at the fault which is then clearly located by the Teleflex like a low resistance fault via an ARM Filter. The Teleflex shows a comparison of the traces with and without the arc. It is an easy, clear and precise method and therefore the most commonly used fault locating procedure today and even often replaces burning (fault conditioning) on cables at all. ARM Filters are also available as separate instruments. Available are passive filters M 219 (inductive) and LSG 300 (resistive). An active Arc Reflection Filter LSG 3-E provides an extra 2 kV power supply and capacitor. The SPG 32-series features a built-in LSG 300 filter.

Pinpointing For a precise location of the fault it is essential to confirm its position along the cable after pre-location with TDR measurement or any HV-fault locating methods.

All SebaKMT surge generators have a time controlled surge output. It allows a periodical discharge into the cable for acoustic locating of the flash-over at the fault with an adequate ground microphone and receiver.
Combined Acoustic and Magnetic Method

The Digiphone (see leaflet, backside) measures the time difference between the magnetic signal of the surge current and the slower acoustic sound of the flash-over traveling through the ground. The display shows the time delay as indication of fault distance and the magnetic field strength as indication of the cable position. This means that a low number showing a short time delay indicates a short distance to the fault. This will also work in noisy environment, cable ducts and for faults under paved surfaces.

M 219

The ARM® Filter M 219 is the coupling unit for connection of the Teleflex M or the Teleflex T 01/6 Time Domain Reflectometer and a Surge Generator for pre-location of high resistive and intermittent faults.

By means of the Surge Generator and the choke in the M 219 Filter at the fault point a flash-over is created. This flash-over converts the high resistive fault temporarily in a low resistive fault. Now the fault causes a reflection that can easily stored in the Teleflex.

The comparison of the traces before the flash-over and during the flash-over clearly shows the fault distance. The connection circuit is shown on the cover of the ARM^® Filter M 219.

LSG 300

The Arc Stabilisation Unit LSG 300

Pulse echo is by far the simplest method of fault location, but its use is severely limited, not being suitable for flashing or high impedance faults. To overcome these limitations and still use pulse echo techniques a new method known as arc stabilisation can be used. As the name suggests the aim is to stabilise an arc at the point of fault, this arc then being seen and recorded by a suitable pulse echo set. Such an instrument capable of stabilising an arc at the point of fault is the LSG 300 available from Seba KMT. The LSG 300 is a compact, easy to use Arc Stabilisation Unit suitable for use in a modular system or a cable test van. The LSG 300 is an effective aid to pre-locating the majority of cable faults, quickly and accurately and is suitable for use by operators of all experiences.

Test Method

The energy pulse of a shock discharge generator is applied to the faulty cable through the arc stabilising unit LSG 300. This pulse ignites the fault and generates a short-term arc at the fault. Simultaneously, the LSG 300 triggers the pulse echo set and takes a standard pulse reflection measurement into what is seen as a short circuit. A typical configuration is shown in figure 1. The pulse reflected back by the stabilised arc at the point of fault reaches the pulse echo set via the high voltage separating filter "F" and is stored in the internal memory. This trace is then compared with a previously recorded trace of the same core, the fault position is clearly identifiable as the point of divergence between the two traces. This is shown in figure 2. All switching elements necessary for the triggering and the coupling of the pulse, are contained in the LSG 300. After the pre-location using the arc reflection method, the decoupling element is bypassed using a manual switch and the shock discharge generator is ready for use on its own for acoustic pin-point fault location.

PowerFuse

The Powerfuse is used in the low voltage distribution network. It maintains continuous power supply on cables with intermittent faults on a temporary basis replacing the fuse until the fault is located and the cable is repaired. It switches the supply on again automatically after a fault occurs. The number of faults is stored and limited.

Applications of the Powerfuse are:

• Switching of LV cables without arc
• Check of the cable condition after fuse tripping
• Reconnection after maintenance
• Commissioning after assembling
• Self-acting reconnection of critical cables
• After short circuit of intermittent cable faults
• After overload
• Cable fault pre-location in connection with pulse reflection instrument (Teleflex)