GE T60 Instruction Manual page 589

CHAPTER 7: COMMANDS AND TARGETS
When freezing the actual values, the function also asserts a
configured to drive an output contact and trigger an external measuring device such as a digital scope with the intent to
verify the accuracy of the PMU under test.
With reference to the following figure, the PMU one-shot function (when enabled) controls three FlexLogic operands:
• The
PMU ONE-SHOT EXPIRED
at least 30 seconds past the scheduled one-shot time
• The
PMU ONE-SHOT PENDING
before the scheduled one-shot time
• The operand indicates the one-shot operation and remains asserted for 30 seconds afterwards
PMU ONE-SHOT OP
When the function is disabled, all three operands are de-asserted.
The one-shot function applies to all logical PMUs of a given T60 relay.
7.1.5.1 Testing accuracy of the PMU
The one-shot feature is used to test accuracy of the synchrophasor measurement. GPS-synchronized tests sets perform a
similar function to PMUs; instead of measuring the phasor from physical signals with respect to the externally provided
time reference, they produce the physical signals with respect to the externally provided time reference, given the desired
phasor values. Therefore the GPS-synchronized test sets cannot be automatically assumed more accurate than the PMUs
under test. This calls for a method to verify both the measuring device (PMU) and the source of signal (test set).
With reference to the following figure, the one-shot feature can be configured to trigger a high-accuracy scope to capture
both the time reference signal (rising edge of the 1 pps signal of the IRIG-B time reference) and the measured waveform.
The high-accuracy high-sampling rate record of the two signals captured by the scope can be processed using digital
tools to verify the magnitude and phase angle with respect to the time reference signal. As both the time reference and the
measured signals are raw inputs to the PMU under test, their independently captured record, processed using third-party
software, is a good reference point for accuracy calculations. Such a record proves useful when discussing the test results,
and can be retained as a part of the testing documentation.
T60 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
PMU ONE-SHOT OP
operand indicates that the one-shot operation has been executed, and the present time is
operand indicates that the one-shot operation is pending; that is, the present time is
Figure 7-1: PMU one-shot FlexLogic operands
COMMANDS MENU
FlexLogic operand. This operand can be
7
7-5