Megger's DLRO10HD ohmmeter combines ultimate simplicity of operation with a rugged IP65 case and is designed for stable ground and bench operation. The unit is powered from either its rechargeable battery or line power making it suitable for continuous testing in production line/repetitive use environments. Rotary switch controls are simple and easy to operate in all weather conditions and with gloved hands. A large, clear, backlit LCD display is easy to read from a distance.
The DLRO10HD provides significantly enhanced compliance and is capable of delivering 10A into measurements up to 250mΩ and 1A into measurements up to 2.5Ω. The duration of each test may be up to 60 seconds.
The DLRO10HD is rated CAT III 300V. A range of test leads is available to suit the application.
The DLRO10HD provides five test modes each of which is selected through a simple rotary control: Rotary mode switch with bidirectional (current reversal with averaging cancels thermal EMFs), unidirectional, automatic, continuous and inductive modes.
Automatic unidirectional mode applies current in one direction only to speed up the measurement process. However thermal EMF resulting from dissimilar metal bonds can cause lower accuracy. Test starts automatically when probes are connected.
Continuous mode allows repeated measurements to be made on the same sample. Simply connect the test leads and press the test button. The measurement is updated every three seconds until the circuit is broken.
Inductive mode is selected when measuring resistance on, for example, motors and generators. When measuring inductive loads it is necessary to wait for the voltage to stabilize as the inductive element is charged. Test leads are firmly connected to the device under test and the ‘Test' button pressed. The instrument will pass the selected current through the sample continuously in one direction only and take repetitive readings that will gradually decrease to the true value as the voltage stabilizes. The operator decides when the result is stable and presses the ‘Test' button to terminate the test.
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 DLRO10HD 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 DLRO10HD 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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