Vanguard DMOM‐600 - Manual (Page 8)

Auto‐Ohm 200 S3 / DMOM‐200 S3 / DMOM‐600 USER’S MANUAL REV 2
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1.2 DMOM-200 S3 General Description and Features
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/ 8.9 Kg) 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‐ohm to 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 convenient 44‐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.