GE Multilin g60, Instruction Manual

Page: 522 / 780

7-4 G60 Generator Protection System GE Multilin
7.1 COMMANDS 7 COMMANDS AND TARGETS
7
7.1.6 PHASOR MEASUREMENT UNIT ONE-SHOT
PATH: COMMANDS

PMU ONE-SHOT
This feature allows pre-scheduling a PMU measurement at a specific point in time. This functionality can be used to test for
accuracy of the PMU, and for manual collection of synchronized measurements through the system, as explained below.
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 SEQUENCE NUMBER
. 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 may be
configured to drive an output contact and trigger an external measuring device such as a digital scope with the intent to ver-
ify the accuracy of the PMU under test.
With reference to the figure below, 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 G60 relay.
Figure 7–1: PMU ONE-SHOT FLEXLOGIC OPERANDS
TESTING ACCURACY OF THE PMU:
The one-shot feature can be used to test accuracy of the synchrophasor measurement. GPS-synchronized tests sets per-
form a similar function to PMUs: instead of measuring the phasor from physical signals with respect to the externally pro-
vided 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 figure below, the one-shot feature could 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 mea-

COMMANDS

PMU ONE-SHOT
PMU ONE-SHOT
FUNCTION: Disabled
Range: Enabled, Disabled
PMU ONE-SHOT
SEQUENCE NUMBER: 0
Range: 0 to nominal frequency – 1 in steps of 1
PMU ONE-SHOT TIME:
2005/06/14 7:58:35
Range: 24h time format