Nautel NX3, Installation Manual

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NX5/NX3 INSTALLATION MANUAL COMMISSIONING TASKS
VERSION 3.1 2021-04-22 PAGE 2.8.3
4. Check the ac sample voltage using the local front panel UI ( Main Menu-> View Status -> View
Meters -> Rack ). This sample represents the transformer’s secondary voltage. It should be
between 302 V and 326 V. If so, proceed to Step 5 . If not, change the transformer tap setting as
follows:
 If the ac sample voltage is too high, you will need to increase the tap voltage. If the ac sample
voltage is too low, you will need to decrease the tap voltage.
 If the ac sample voltage is more than 4 V outside of the acceptable range (i.e., less than 298 V
or greater than 330 V), a “major tap change” is required. If the ac sample voltage is within
4 V of the acceptable range (i.e., between 298 and 302 V or between 326 and 330 V), a
“minor tap change” is required. See
Figure 2.8.2 on page 2.8.4 for explanations of major and
minor tap changes.
 Estimate the expected ac sample level for a major or minor tap change using the following
formula:
NOTE
: * denotes change only the major tap value or the minor tap value, as applicable.
Example # 1: If the ac sample voltage in Step 4 is 335 V, you require a “major” tap
increase. If the transformer is currently tapped at 380 V (360 - 505 V ac transformer), the
next higher major tap is 400 V (see
Figure 2.8.2 on page 2.8.4 ). Using the equation above
(noting “New Minor Tap” = 0), the “Ac Sample (new)” value is 318.2 V, which is within the
acceptable range.
Example # 2: If the ac sample voltage in Step 4 is 300 V, you require a “minor” tap
decrease (-10 V for the 360 - 505 V ac transformer; -5 V for the 200 - 250 V ac
transformer). If the transformer is currently tapped at 380 V (360 - 505 V ac transformer),
use the equation above (noting “New Major Tap”= “Current Major Tap”; in this example
380 V), the “Ac Sample (new)” value is 308.1 V, which is within the acceptable range.
 If the proposed tap change yields an expected Ac Sample between 302 V and 326 V, perform
the “major” or “minor” tap change, using
Figure 2.8.2 on page 2.8.4 , Figure 2.8.3 on page
2.8.5 and Section 2.4, “Connecting Ac Power” as guides.
 Ensure the ac sample voltage on the front panel UI is between 302 V and 326 V. If not, repeat
Step 4 .
Ac Sample (new) Ac Sample (Step 4)
Current Major Tap
New Major Tap* New Minor Tap* +
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=