Vanguard Tri-Phase - Manual (Page 12)

TRI-PHASE OPERATING™ INSTRUCTIONS
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3.0 Functional Description (continued)
• The TTRA software application is compatible with Microsoft Windows XP, and Microsoft
Windows Vista (see section 11.3 for more details).
• Capable of raising or lowering the Load Tap Changer (LTC) tap position from the TRI-
PHASE™ front panel with the built-in LTC controller (see section 24.0 for more details).
4.0 Principles of Operation
The TRI-PHASE™ measures transformer turns-ratios (using the ANSI/IEEE C57.12.90 method) by
applying a test voltage across the primary (H) winding and sensing the induced voltage on the
secondary (X) side. For safety, testing is always done in a step-down transfer, regardless of the
transformer’s actual use. Since there is no load on the windings during testing, the measured voltage
ratio is virtually the same as the winding turns-ratio.
The TRI-PHASE™ checks for test cable hook-up errors before each test. It applies a low-level test
voltage (300 mV) across the winding being tested and senses the induced secondary voltage. If the
induced voltage is greater than the applied excitation voltage, a hookup error is assumed. If a
connection error is detected, the TRI-PHASE™ aborts the test and displays “Hook-Up Error” on the
LCD. If no hookup error is detected, the TRI-PHASE™ applies a full test voltage to the transformer
winding being tested and the turns-ratio (or voltage ratio) is displayed on the LCD.
The winding polarity and phase-angle are determined by comparing the induced voltage waveform
to the test voltage waveform (which is used as the reference). In-phase waveforms (+) measure a
phase angle centered about 0 degrees. Out-of-phase waveforms (
−) measure a phase angle centered
about 180 degrees.
The TRI-PHASE™ measures turns-ratios in the range from 0.8 to 15,000. Excitation current
(flowing in the H leads) is measured for reference and ranges from 0 to 2,000mA. Winding polarity
is displayed as a “+” or “
−”sign in front of the measured ratio. The phase angle is measured in
degrees with a resolution of
±0.2 degrees.
NOTE:
The phase angle measurement is not displayed on the LCD.
The phase angle measurement will be printed when the detail print format is selected
and displayed with a PC running the TTRA software application.