Vanguard DMOM‐600 - Manual (Page 10)

Auto‐Ohm 200 S3 / DMOM‐200 S3 / DMOM‐600 USER’S MANUAL REV 2
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1.3 DMOM-600 General Description and Features
The DMOM‐600 is specifically 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 (33 lbs/ 15 Kg) micro‐ohmmeter is designed to meet the IEEE
C57.09‐1999 (5.15) requirement for testing circuit breaker contact resistance.
The DMOM‐600 can accurately measure resistance values from 1 micro‐ohm to 450 milliohms.
A 0.1 micro‐ohm resolution is possible with current greater than 10A. The DMOM‐600 applies a
selectable true DC test current from 10A to 600A to the resistance load to be tested. The
DMOM‐600 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‐600 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‐600 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‐600 measures and
eliminates this current from the total test current. It then calculates the actual resistance value
of the circuit breaker.
The DMOM‐600 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 in a large font 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‐600 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‐600 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‐600 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‐600 is furnished with a 15‐ft (#1/0 AWG) test cable set. Custom test cable lengths
are optionally available. Optional heavy‐duty, welding type C‐clamps are also available allowing
the user to connect the test leads to a wide variety of bushing sizes, bus‐bars, or large
conductors.