The DMOM-200 S3 is Vanguard’s fourth generation, microprocessor-based,true DC micro-ohmmeter. It is designed for testing EHV circuit-breaker contact resistances, bushing contact joints, welding joints, or for any low-resistance measuring application. This high current and very lightweight (19.8 lbs/ 8.9Kg) micro-ohmmeter is designed to meet the IEEE C57.09-1999 (5.15)requirement for testing circuit breaker contact resistance.The DMOM-200 S3 can accurately measure resistance values from 1 micro-ohmto 5 ohms. A 0.1 micro-ohm resolution is possible with current greater than 5A.The DMOM-200 S3 applies a selectable true DC test current from 1A to 200A to the resistance load to be tested. The DMOM-200 S3 controls the test current’s rise and fall rates. The test current rise and fall rate can be selected from 5 seconds to 10 seconds. An “Auto Test” mode is also available and can be initiated simply by applying the sense cables’ leads across the two points of interest in the current path. This feature is very convenient when measuring a sequence of several resistance values in a circuit breaker contact. The DMOM-200 S3 can also compare test results against preset limits and determine if a test passed or failed, and a “Pass” or “Fail” flag is displayed accordingly.Since a true DC current (with controlled rise/fall time) is passed through the circuit breaker contact, no magnetic transient is induced into the breaker’s current transformers. This feature greatly reduces the risk of inductively tripping a breaker control (bus differential relay).With the Dual Ground option, the DMOM-200 S3 can also measure the circuit breaker contact resistance with both sides of the breaker bushing being grounded.When a test current is applied to a circuit breaker with both sides grounded,some of the test current flows through the safety ground cables. Using an external current sensor, the DMOM-200 S3 measures and eliminates this current from the total test current. The DMOM-200 S3 then calculates the actual resistance value of the circuit breaker.The DMOM-200 S3 features a back-lit 128 x 64 pixel LCD screen that is viewable in both direct sunlight and low light levels. The resistance readings are displayed on the LCD screen in micro-ohms or milliohms. The unit is operated via a convenient44-key “QWERTY” keypad on the front panel. The DMOM-200 S3 can store 128 records of 64 readings internally, and up 999 test records on an external USB Flash drive. Test header information (Company, Substation, circuit breaker ID’s) can also be entered using the 44-key keypad and is stored with each test record. The DMOM-200 S3 also features a built-in 2.5” wide thermal printer that can be used to print test reports in the field.Windows® based (XP/Vista/7) analysis software is provided with each unit and can be used to remotely control the DMOM-200 S3 via the RS-232C port. Using this software, the user can retrieve test records (from the unit’s memory or a USB Flash drive), analyze test results, and print test results on a desktop printer.Test results can also be exported to PDF, Excel, and XML formats.The DMOM-200 S3 is furnished with a 30-ft test cable set. A 15-ft test cable set is also available as an option. Test cables are terminated with heavy duty welding type clamps. The test current and voltage sense cables are isolated and fastened to the clamp jaws. This feature allows for a simple connection to the circuit breaker bushing. An optional voltage sense cable and probe can be used to measure resistance in small access locations. Optional heavy-duty, welding typeC-clamps are also available allowing the user to connect the test leads to a wide variety of bushing sizes, bus-bars, or large conductors.
