Why is a selectable capacitance thumper preferable to a single-stage capacitance thumper?
- October 1, 2019
- Posted by: Dominique
- Category: Cable Fault Location
A quick and efficient location of cable faults is imperative for the utility or electric power delivery company to conduct repairs and resupply customers with much needed power. Most cable fault location equipment, such as the Syscompact series of equipment, combine high voltage surge generators, or thumpers, with TDR measuring devices to locate the fault. An overview of the different fault location methods available with this type of equipment is given in Cable Fault Location with Syscompact Series and also in Cable Fault Location Measuring Methods.
A HV surge generator or thumper is a capacitive discharge device that can produce sufficient voltage and energy to breakdown a fault for pre-location purposes and generate an audible thump for pin-pointing purposes. The energy that a thumper can produce is according to the equation E = 1/2CU2, in which E is the energy of the thumper in J or Ws, C is the internal capacitance of the thumper in F, and U is the voltage of the thumper in V. Depending on the voltage range selector (0-8 kV, 0-16 kV, or 0-32 kV) the internal capacitor bank within the SSG surge generator of the Syscompact equipment will switch from all 4 capacitors being in parallel (highest capacitance in 0-8 kV range) to 2 capacitors in series and 2 in parallel (0-16 kV range) to all 4 capacitors in series (lowest capacitance in 0-32 kV).
The ability to select the voltage range, and therefore also the internal capacitance of the thumper, reduces the use of unnecessary high voltage during fault location which could possibly damage healthy parts of the cable, while also still producing a thump with sufficient surge energy for the cable fault to breakdown and produce a significant audible signal. The below image shows the available energy associated with the three selectable voltage ranges with different SSG surge generators.
The above graph shows that in order to get the maximum amount of surge energy the surge generator should be within the correct selected voltage range of the cable fault. For example, using the SSG 3000, if the cable fault breaks down at 6 kV, then the surge energy provided to the fault in the 0-8 kV range would be much higher (1500 J) than when in the 0-16 kV range (500 J) or 0-32 kV range (200 J). The ability to select the most appropriate voltage range allows for the most available energy and audible signal at a minimum of voltage than when thumping a fault with only a single-stage capacitive thumper.
Increasing the amount of energy of a surge pulse is also important in terms of the pulse duration. By increasing the internal capacitance provided by the thumper, the higher the energy of the pulse and the longer the duration of the pulse. In the example shown below, you will see that a surge pulse at a higher voltage level may not follow the ignition curve of the fault and cause it to break down. The greatest chance to have the fault break down is when choosing to be within the 0-8 kV range of the voltage selector. The additional capacitance in this lower voltage range allows the surge pulse to have sufficient energy and duration for the fault to break down, which would not have been possible in a higher voltage range.
Increasing the surge energy is especially helpful when pin-pointing the fault as a more audible and easily detectable breakdown can be detected. The acoustic fault pin-pointing method can be used while thumping the cable with the Protrac Fault Pin-Pointing System. During the flashover an acoustic signal is generated that can be detected on the ground surface by using a ground microphone, receiver, and headphone. The closer the distance to the fault, the higher the amplitude of the flashover sound. The flashover will also produce an electromagnetic signal. The detection of this signal allows for a distance calculation to be conducted, guiding a user to the exact fault location.
HVT’s Range of Selectable Capacitance Fault Locators and Fault Pin-pointers
|Syscompact 2000 M Pro||
|Syscompact 2000 Portable||