GE L30, Инструкция по эксплуатации

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CHAPTER 7: COMMANDS AND TARGETS COMMANDS MENU
L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 7-5
7
When enabled, the function continuously compares the present time with the pre-set
PMU ONE-SHOT TIME
. When the two
times match, the function compares the present sequence number of the measured synchrophasors with the pre-set
PMU
ONE-SHOT FRACTIONAL SEC
. When the two numbers match, the function freezes the synchrophasor actual values and the
corresponding protocol data items for 30 seconds. This allows manual read-out of the synchrophasor values for the pre-
set time and pre-set sequence number (via the faceplate display, supported communication protocols such as Modbus or
DNP, and the EnerVista UR Setup software).
When freezing the actual values, the function also asserts a
PMU ONE-SHOT OP
FlexLogic operand. This operand can be
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
operand indicates that the one-shot operation has been executed, and the present time is
at least 30 seconds past the scheduled one-shot time
• The
PMU ONE-SHOT PENDING
operand indicates that the one-shot operation is pending; that is, the present time is
before the scheduled one-shot time
• The
PMU ONE-SHOT OP
operand indicates the one-shot operation and remains asserted for 30 seconds afterwards
When the function is disabled, all three operands are de-asserted.
The one-shot function applies to all logical PMUs of a given L30 relay.
Figure 7-1: PMU one-shot FlexLogic operands
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.