Electrical Tester online
May 2008
Putting fault location on the road

Putting fault location on the road

03 May 2008

Allen Joyce - International product manager

By its very nature, cable fault location often needs to be carried out at remote sites, and even the most modern of cable fault locators could hardly be described as lightweight or easily portable. The solution is to install fault location equipment in a suitably adapted road vehicle, so that it can be driven direct to the site where it’s needed, and be ready for immediate use.

To satisfy the need for vehicle-mounted fault location equipment, Megger offers a range of options. Customers can, if they wish, supply their own vehicle and Megger will install equipment to suit individual requirements. Alternatively, Megger can supply equipment for customers to fit themselves. The final option is for Megger to supply a vehicle ready fitted with cable testing equipment.

In every case the cable fault location equipment supplied will be based on products from Megger’s new PFL20 and PFL40 families. These test sets are designed specifically to aid rapid, accurate location of cable faults in a wide range of power distribution cables, thereby cutting costly downtime.

PFL20 testers offer DC proof testing at up to 20 kV with energies up to 1,500J, while the PFL40 models offer proof testing at up to 40 kV and energies up to 2,000J. To ensure fast and convenient operation, the integral power supply can recharge the testers to full energy and voltage in as little as two seconds.

PFL20 and PFL40 cable fault locators feature a high-voltage DC test set, complemented by a time domain reflectometer (TDR). The DC test set can be used to prove the integrity of cable networks or to confirm faults, and an operator-selectable overcurrent trip is incorporated to protect the system under test in the event of a cable breakdown.Fault pre-location can be achieved using the TDR in standard pulse echo mode, or by the arc reflection, impulse current or voltage decay methods. To optimize performance in arc reflection mode, the units incorporate inductive filters that enable maximum energy to be delivered to the fault.

The TDR can also be used as a transient analyzer. It resolves current transients with the aid of the built-in current coupler, and voltage transients by using the external voltage decay coupler. In addition, the testers support acoustic pinpoint fault location, using their high voltage, high energy surge generators.

For intermittent or unstable faults, PFL20 and PFL40 testers offer a choice of fault conditioning features. In proof/burn mode, after cable breakdown has occurred, the units apply a high current that stabilizes the fault, making it much easier to locate. Alternatively, the arc reflection method can be used to establish a temporary bridge to earth, enabling standard pulse echo location techniques to be used.