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7.2.1: Loss Compensation in Three Element Installations
Loss compensation is based on the loss and impedance values provided on the transformer
manufacturer's test report. A typical test report will include at least the following information:
•
Manufacturer
•
Unit Serial Number
•
Transformer MVA Rating (Self-Cooled)
•
Test Voltage
•
No Load Loss Watts
•
Load Loss Watts (or Full Load Loss Watts)
•
% Exciting Current @ 100% voltage
•
% Impedance
The transformer MVA rating is generally the lowest MVA rating (the self-cooled or OA rating) of the
transformer winding. The test voltage is generally the nominal voltage of the secondary or low
voltage winding. For three phase transformers these values will typically be the three-phase rating
and the phase-to-phase voltage. All of the test measurements are based on these two numbers. Part of
the process of calculating the loss compensation percentages is converting the transformer loss
values based on the transformer ratings to the base used by the meter.
Correct calculation of loss compensation also requires knowledge of the meter installation. In order
to calculate the loss compensation settings you will need the following information regarding the
meter and the installation:
•
Number of meter elements
•
Potential Transformer Ratio (PTR)
•
Current Transformer Ratio (CTR)
•
Meter Base Voltage
•
Meter Base Current
This section is limited to application of Nexus meters to three-element metering installations. As a
result, we know that:
•
Number of metering elements = 3
•
Meter Base Voltage = 120 Volts
•
Meter Base Current = 5 amps
The loss compensation values can be calculated by clicking the TLC Calculator button on the
Transformer Loss screen of the Nexus Device Profile (MS Excel Spreadsheet) or by completing the
worksheet "Three Element Loss Compensation Worksheet" below. In order to activate the Excel
Spreadsheet, you must have MS Excel installed on your computer.
NOTE: A copy of the Excel Spreadsheet with Example Numbers can be found in Appendix A of this
manual.
Electro Industries/GaugeTech
Doc # E107706 V1.25
7-4
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