The EZ-Thump 12 kV, model v3, cable fault location system makes fault finding on underground MV power cables easier than ever! This all-in-one fault locator has been designed specifically to be readily transportable – it will fit into an average-sized car – and easy to operate, even for inexperienced users. The EZ-Thump 12 kV is an ideal choice for first responders and its extensive capabilities make it well-suited to more demanding applications.
The EZ-Thump 12 kV incorporates a single-stage capacitor surge discharge system that delivers 500 J at 12 kV. An integrated time-domain reflectometer (TDR) facilitates the pre-location of low resistance faults and, by using the Arc Reflection Method (ARM), high resistance faults. In addition, the EZ-Thump 12 kV can be used in conjunction with an acoustic/electromagnetic receiver, such as the DigiPhone 2, to pinpoint the precise location of faults. Sheath testing and sheath fault location are also supported.
The instrument includes advanced safety features as standard, such as the F-OHM system that automatically checks that earth/ground connections have been made correctly and, if detects a problem, will inhibit testing. It also has an emergency stop function and a key-switch safety interlock.
All of the instrument’s functions are controlled with a single rotary knob and the test results are shown on a bright colour display that is easy to read even in bright sunlight. No settings are needed when the instrument is used in automatic mode; users connect the test set to the cable and switch it on. The cable end and the fault location are then automatically detected and displayed. More experienced users can access expert mode to optimise results in particularly challenging applications.
Lightweight and exceptionally compact, the EZ-Thump 12 kV can be powered either from an AC mains supply or its internal rechargeable battery. These features mean you can use the EZ-Thump in any location, even where access is difficult and no mains supply is available. The internal battery is designed to have a long operating life, but when replacement eventually becomes necessary, you can do so in the field.
There are five stages in determining cable fault locations:
fault classification – identifying the type of fault
pre-location – determining the distance to the fault
route tracing – determining the route of the cable
pinpointing – identifying the exact position of the fault
cable identification – identifying which of several cables is faulty
Perhaps not from a theoretical point of view, but from a real-world point of view, the TDR should fit the cable/application.
Pre-location is used to indicate the distance to the fault. While modifying the fault to create conditions more suitable for a particular pre-location technique may occasionally be necessary, it is always best to pre-locate the fault with conditions as found. Several recognised methods of pre-location assist rapid, accurate, and safe location of faults. These include:
Pulse echo (low voltage pre-location)
Arc reflection (high voltage pre-location)
Arc Reflection Plus (ARP)
Differential Arc Reflection (DART)
Impulse current (high voltage pre-location)
Voltage decay (high voltage pre-location)
The results obtained with these techniques will allow the approximate location of the fault to be determined. Still, the accuracy of the results is affected by many factors, including changes in cable types, cable size, and joints, which affect the velocity factor of the cable under test. The lay of the cable is a vital factor as any results obtained with pre-location relate to the actual length of the physical cable, which may be very different from the length of the cable route!
Pinpointing is the identification of the fault’s exact location. Pinpointing is carried out directly over the cable. The most common technique relies on detecting acoustic and electromagnetic signals emitted at the fault location when the cable is being surged by a surge generator (thumper). A sensitive ground microphone and electromagnetic pickup, used in conjunction with an amplifier, detect these signals.
If you can charge the cable, you can ‘thump’ it, and that’s exactly what the pinpointing function of the EZ-Thump does. Accurate pinpoint fault location of the typical high-resistance/flashover faults is achieved using the ‘thunder and lightning’ method, whereby the 500 J surge generator (thumper) and an acoustic/electromagnetic receiver are used.
There are many techniques, including:
DC test to determine flashover voltage
Sheath fault test
VLF test to determine flashover voltage
Pulse reflection measurements
ARM (arc reflection method)
ARM power burning
Decay plus (ARM – igniting the fault using a dc generator)
High voltage bridge method (pre-locating sheath faults)
Voltage-drop method (pre-locating sheath faults)
Audio frequency generator (twist field and minimum turbidity methods)
Shock discharges (acoustic field method, acoustic pinpointing)
Pinpointing sheath fault
Cable and phase identification
Phase identification earthed
Phase identification and phase determination on live systems
The maximum circuit length that the EZ-Thump can test depends on the cable type, but as a rule of thumb, we generally say 3 km - giving 1.5 km for either end. In some circumstances, it can do more.
The EZ-Thump weighs just 33 kg and is compact enough to fit inside an average-sized car. It’s ideal for difficult-to-reach locations, such as rural and inner city areas, because you can easily transport it.
After you have confirmed the exact fault location by pinpointing, you must excavate the cable so that the fault can be confirmed visually. The fault is sometimes evident because of external signs such as cracks, breaks, burning, and general damage. However, there may often be no visible damage with the fault contained inside an apparently sound cable.