The Megger DLRO10HDX micro-ohmmeter measures low resistance values in applications ranging from railways and aircraft to resistance of components in industry. It provides five test modes: bidirectional (current reversal with averaging cancels thermal EMFs), unidirectional, automatic, continuous and inductive. Each test mode is selected by a simple rotary dial on the Mode selection rotary switch. All memory functions, the ability to delete, download to PowerDB, and test results recall are also accessible via the Range Selection rotary switch.
The DLRO10HDX is well suited to measuring thick conductors, bonds, and quality of welding because of its 10Amp range for resistance values up to 250mΩ. It can measure any metallic joint, but users must be aware of measurement limitations depending on the application. For example, if a cable manufacturer plans to make resistive measurements on a thin wire, a low test current should be selected to prevent heating the wire and thereby changing its resistance.
These units are powered from either rechargeable battery or mains power making it suitable for continuous testing in production line or repetitive use environments.
The Background: Our customer is an independent power producer that maintains a number of small windfarms and seeks a reliable means of testing that each windmill is protected from lightning strikes.
The Problem: Due to their size and the materials from which they’re made, windmills are highly susceptible to lightning strikes. Lightning is, in fact, the leading cause of downtime and catastrophic damage can occur if there’s not a good path from blade tips to the ground.
Due to the large distance between blade tips and ground as well as potential damage to conductors from blade flex, there isn’t an easy way to make sure that lightning travels through the lightning protection system rather than into the sensitive electronics.
Necessary periodic testing of the lightning protection system requires extra-long, high integrity test leads, but even the best leads with such length have such high resistance that they need to be used in conjunction with a high wattage, low-resistance ohmmeter.
The Solution: We recommended the Megger DLRO10HDX micro-ohmmeter which provides 25W of power which can supply the required 1A test current over the large distances required by this application and which can test in accordance with IEC61400-24 standards for low-resistance ohmmeters.
The DLRO10HDX was paired with Megger KC series leads which have been developed with turbine manufactures to create a Megger system solution. The leads are designed to test from blade tip to root of a grounding system and are fitted to a reel for ease of use.
Earth test connections to ground should also be completed to make sure complete system resistance is within appropriate guidelines.
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