ADE7752 Ver la hoja de datos (PDF) - Analog Devices
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ADE7752 Datasheet PDF : 24 Pages
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TYPICAL CONNECTION DIAGRAMS
CURRENT CHANNEL CONNECTION
Figure 19 shows a typical connection diagram for the current
channel (IA). A current transformer (CT) is the current trans-
ducer selected for this example. Notice the common-mode
voltage for the current channel is AGND and is derived by
center tapping the burden resistor to AGND. This provides the
complementary analog input signals for IAP and IAN. The CT
turns ratio and burden resistor Rb are selected to give a peak
differential voltage of ±500 mV at maximum load.
CT
Rb
Rf
±500mV
IAP
Cf
IAN
IP
PHASE NEUTRAL
Rf
Cf
Figure 19. Typical Connection for Current Channels
VOLTAGE CHANNELS CONNECTION
Figure 20 shows two typical connections for the voltage
channel. The first option uses a potential transformer (PT) to
provide complete isolation from the main voltage. In the second
option, the ADE7752 is biased around the neutral wire, and a
resistor divider is used to provide a voltage signal proportional
to the line voltage. Adjusting the ratio of Ra, Rb, and VR is also
a convenient way of carrying out a gain calibration on the meter.
PT
Rf
PHASE NEUTRAL
±500mV
Rf
AGND
VAP
Cf
VN
Cf
Ra*
Cf
Rb*
VR*
±500mV
Rf
PHASE NEUTRAL
* Ra >> Rf + VR; * Rb + VR = Rf
VAP
VN
Cf
Figure 20. Typical Connections for Voltage Channels
ADE7752/ADE7752A
METER CONNECTIONS
In 3-phase service, two main power distribution services exist:
3-phase 4-wire or 3-phase 3-wire. The additional wire in the
3-phase 4-wire arrangement is the neutral wire. The voltage
lines have a phase difference of ±120° (±2π/3 radians) between
each other. See Equation 5.
VA(t )= 2 × VA × cos (ωlt )
VB (t )=
2
× VB
× cos ⎜⎝⎛ωlt
+
2π
3
⎟⎠⎞
(5)
VC (t )=
2
× VC
×
cos
⎜⎝⎛ ωlt
+
4π
3
⎟⎠⎞
where VA, VB,B and VC represent the voltage rms values of the
different phases.
The current inputs are represented by Equation 6.
( ) IA(t ) = 2 IA ×cos ωlt + φA
IB (t ) =
2
IB
×cos
⎩⎨⎧ωlt
+
2π
3
+
φB ⎭⎬⎫
(6)
IC (t ) =
2
IC
×cos
⎩⎨⎧ωlt
+
4π
3
+
φC
⎭⎬⎫
where IA, IB,B and IC represent the rms value of the current of
each phase and ϕA, ϕBB, and ϕC represent the phase difference of
the current and voltage channel of each phase.
The instantaneous powers can then be calculated as follows:
PA(t) = VA(t) × IA(t)
PB(B t) = VBB(t) × IB(B t)
PC(t) = VC(t) × IC(t)
Then:
( ) PA(t ) = VA × IA × cos(φA ) − VA × IA ×cos 2ωlt + φA
PB (t )
= VB
×
IB
×
cos(φB
)
−
VB
×
IB
×cos
⎜⎝⎛ 2ωlt
+
4π
3
+
φB
⎟⎠⎞
(7)
PC
(t )
=
VC
×
IC
×
cos(φC
)
−
VC
×
IC
×cos
⎜⎝⎛ 2ωlt
+
8π
3
+
φC
⎟⎠⎞
As shown in Equation 7, in the ADE7752, the real power calcu-
lation per phase is made when current and voltage inputs of one
phase are connected to the same channel (A, B, or C). Then the
summation of each individual real power calculation gives the
total real power information, P(t) = PA(t) + PB(B t) + PC(t).
Rev. C | Page 15 of 24
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