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Meeting CMT

The document discusses measuring line-to-line voltages on a Y-connected system using a NI 9225 device. It notes that each channel of the NI 9225 can measure up to 240Vrms between the AI+ and AI- terminals, and it is rated to withstand up to 300Vrms from channel to earth. For a balanced three-phase system with 120 degree phase separation, the line-to-line voltage can be calculated as 1.732 times the line-to-neutral voltage, which would be 416Vrms for a 240Vrms line-to-neutral voltage. This voltage is within the NI 9225's 600V channel-to-channel isolation rating.

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Brett Hendricks
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44 views1 page

Meeting CMT

The document discusses measuring line-to-line voltages on a Y-connected system using a NI 9225 device. It notes that each channel of the NI 9225 can measure up to 240Vrms between the AI+ and AI- terminals, and it is rated to withstand up to 300Vrms from channel to earth. For a balanced three-phase system with 120 degree phase separation, the line-to-line voltage can be calculated as 1.732 times the line-to-neutral voltage, which would be 416Vrms for a 240Vrms line-to-neutral voltage. This voltage is within the NI 9225's 600V channel-to-channel isolation rating.

Uploaded by

Brett Hendricks
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Meeting cmt

Each channel in the NI 9225 will nominally have 240Vrms between the AI+ and AI- terminal. The
NI 9225 is rated to 300Vrms from channel to earth, so the measurement is within the safety
specifications. Assuming a perfectly balanced system, each phase is separated by 120 degrees
and the line-to-neutral voltage on each phase is the same. As long as these two assumptions
hold true, then the magnitude of the line to line voltage is 1.732 * Vp , where Vp is the line-to-
neutral voltage. If the line-to-neutral voltage is 240Vrms, then the line-to-line voltage will be
416Vrms. The NI 9225 is rated for 600V ch-ch isolation, so this voltage is within the safety
specifications.
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2. Measuring line-to-line Voltages - The Most General Case


The connection scheme shown above in figure 1 can be used to indirectly measure the line-to-
line voltages on a Y-connected systems. The line-to-line voltage is the vector sum of the line to
neutral voltages. So, for example, if we know Van, Vbn, and Vcn (defined as in the diagram below),
we can find the line to line voltages as follows:

The following phasor diagram (diagram 1) will help visualize the phasor math required to
convert from line-to-neutral voltages to line-to-line voltages.

Diagram 1. Line-to-line calculation phasors

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