Vanguard DMOM‐600 - Manual (Page 6)

Auto‐Ohm 200 S3 / DMOM‐200 S3 / DMOM‐600 USER’S MANUAL REV 2
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1.0 INTRODUCTION
1.1 Auto-Ohm 200 S3 General Description and Features
The Auto‐Ohm‐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 (16.8 lbs/ 7.6 Kg) micro‐ohmmeter is designed to meet the IEEE
C57.09‐1999 (5.15) requirement for testing circuit breaker contact resistance.
The Auto‐Ohm‐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 Auto‐Ohm‐200 S3
applies a selectable true DC test current from 1A to 200A to the resistance load to be tested.
The Auto‐Ohm‐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 Auto‐Ohm 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 trip‐ping a breaker control (bus differential relay).
With the Dual Ground option, the Auto‐Ohm‐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 Auto‐Ohm‐200 S3 measures and
eliminates this current from the total test current. The Auto‐Ohm then calculates the actual
resistance value of the circuit breaker.
The Auto‐Ohm‐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 Auto‐Ohm 200 S3 can store 128 records of 64 readings internally, and up to
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.
Windows® based (XP/Vista/7) analysis software is provided with each unit and can be used to
remotely control the Auto‐Ohm 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 records can also be exported to PDF, Excel, and XML
formats.