5.2
SEL-700G Relay
Instruction Manual
Date Code 20170814
Metering and Monitoring
Power Measurement Conventions
Power Measurement Conventions
The SEL-700G uses the IEEE convention for power measurement. The
implications of this convention are depicted in Figure 5.1.
Figure 5.1
Complex Power Measurement Conventions
Delta-Connected CTs
The relay displays currents, voltages, and power in primary values as part of
most metering and monitoring reports. If the winding phase CTs are wye
connected, the relay can accurately derive the primary currents from the
secondary values through multiplying them by the corresponding CT ratio.
Delta-connected CTs, in general, remove zero-sequence current and introduce
a phase shift. They also increase magnitude by
under balanced system
conditions and as high as two times under unbalanced conditions. As a result,
the relay cannot derive the primary currents/quantities accurately. The relay
performs the following under all system conditions in the case of delta-
connected CTs. The primary currents displayed are derived from the
secondary values through multiplying them by the corresponding CT ratio and
dividing them by
. The phase angles are not compensated and reflect the
same values as measured on the secondary.
Metering
The SEL-700G meter data fall into the following categories:
➤
Fundamental metering
➤
Thermal metering: RTD metering (with the external SEL-2600
RTD Module or an internal RTD option) and generator thermal
capacity
➤
Energy metering
➤
Maximum and minimum metering
➤
Math variable metering
➤
RMS metering
➤
Analog transducer input metering
Q+ (VAR)
I leads V
W = —
VAR = —
PF = LAG
I lags V
W = —
VAR = +
PF = LEAD
P+ (W)
I leads V
W = +
VAR = —
PF = LEAD
I lags V
W = +
VAR = +
PF = LAG
Generator
SEL-700G
Relay
Source
Bus
Direction of
Positive Real Power
3
3
Содержание SEL-700G Series
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