5.2
SEL-751A Relay
Instruction Manual
Date Code 20100129
Metering and Monitoring
Power Measurement Conventions
Power Measurement Conventions
The SEL-751A uses the IEEE convention for power measurement. The
implications of this convention are depicted in
.
Figure 5.1
Complex Power Measurement Conventions
Metering
The SEL-751A 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)
➤
Energy metering
➤
Maximum and minimum metering
➤
Math variable metering
➤
RMS metering
➤
Analog transducer input metering
➤
Demand and peak demand metering
➤
Synchrophasor metering
➤
Light metering for arc-flash detection (AFD)
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
Feeder
SEL-751A
Relay
Source
Bus
Direction of
Positive Real Power
Summary of Contents for 751A
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