Frequency measurement, Power measurement – Basler Electric BE1-11t User Manual
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9424200995 Rev H
VT Connections
When four-wire VT connections are used, the BE1-11t measures the three-phase to neutral voltages and
calculates the phase voltage quantities. Overvoltage and undervoltage functions (27/59) can be set to
operate on either the phase-to-neutral (PN) or phase-to-phase (PP) quantities. Three-wire VT
connections limit 27/59 operation to PP quantities. When single-phase VT connections are used, the
27/59 elements operate as appropriate for the single-phase voltage applied.
Neutral-Shift Voltage
When four-wire VT connections are used, the BE1-11t calculates the neutral-shift voltage (3V0). Neutral-
shift voltage measurement is not available when single-phase or three-wire VT connections are used. The
27X and 59X can be set to monitor the neutral-shift voltage.
Negative-Sequence Voltage
Negative-sequence voltage (V2) is calculated from the fundamental component of the three-phase
voltage inputs. It is available only on three-phase, three-wire, or three-phase, four-wire systems. V2 is
calibrated to the phase-to-neutral base. Negative-sequence measurements accommodate either an ABC
or ACB phase-sequence.
Positive-Sequence Voltage
Positive-sequence voltage (V1) is calculated from the fundamental component of the three-phase voltage
inputs. It is available only on three-phase, three-wire, or three-phase, four-wire systems. V1 is calibrated
to the phase-to-neutral base. Positive-sequence measurements can accommodate either ABC or ACB
phase-sequence.
Frequency Measurement
Power system frequency is monitored on the A-phase voltage input or the AB voltage input when in three-
wire mode. When the applied voltage is greater than 10 volts, the BE1-11t measures the frequency. The
measured frequency is used by the 81 function and applies to all measurements and calculations.
Frequency Compensation
After measuring the frequency, the BE1-11t varies the sampling rate to maintain 32 samples per cycle
over a frequency of 10 to 75 hertz. If the voltage is too low for accurate frequency measurement or if the
measured frequency is out of range, the ADC defaults to a sampling rate appropriate for the BE1-11t
nominal frequency setting. The sampling rate is adjusted every 50 milliseconds (3 cycles).
Nominal Frequency
Nominal frequency (F
nom
) can be set for 25-, 50-, or 60-hertz power systems. When the voltage and
current are too low for reliable frequency measurement, the ADC sample rate defaults to operation at the
nominal frequency setting. Nominal frequency is also used in the volts/hertz (24) overexcitation
calculation.
Power Measurement
The measured fundamental component of current and voltage as described previously in this chapter is
used to calculate the power per the equations following:
For Sensing Type: Four-wire
)
cos(
I
V
Watts
A
A
AN
A
φ
=
)
cos(
I
V
Watts
B
B
BN
B
φ
=
)
cos(
I
V
Watts
C
C
CN
C
φ
=
C
B
A
3
W
W
W
Watts
+
+
=
φ
)
sin(
I
V
Vars
A
A
AN
A
φ
=
)
sin(
I
V
Vars
B
B
BN
B
φ
=
)
sin(
I
V
Vars
C
C
CN
CA
φ
=
Configuration
BE1-11t