ADE7752BARW AD [Analog Devices], ADE7752BARW Datasheet - Page 16

• Manufacturer Part Number: ADE7752BARW
• Description: Polyphase Energy Metering IC with Pulsed Output
• Manufacturer: AD [Analog Devices]

ADE7752B
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.
In theory it is better to center tap Rb; however, this requires
very careful attention to the layout and matching of the resistors
to ensure that the channels have the same resistance. A single
resistor may be more practical and is a valid design choice.
VOLTAGE CHANNELS CONNECTION
Figure 20 shows two typical connections for the voltage chan-
nel. The first option uses a potential transformer (PT) to pro-
vide complete isolation from the main voltage. In the second
option, the ADE7752B 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 a
convenient way of carrying out a gain calibration on the meter.
VR can be implemented using either a potentiometer or a
binary weighted series of resistors. Either configuration works,
however, the potentiometer is subject to noise over time. Two
fixed value resistors can be used in place of VR to minimize the
noise.
IP
PHASE
PHASE
PHASE
NEUTRAL
NEUTRAL
NEUTRAL
Figure 20. Typical Connections for Voltage Channels
Figure 19. Typical Connection for Current Channels
Ra
VR
*
Rb
*
*
PT
CT
*
Ra >> Rf + VR;
±500mV
AGND
Cf
R
±500mV
b
*
Rf
Rf
Rb + VR = Rf
±500mV
Rf
Rf
Rf
Cf
Cf
Cf
Cf
Cf
IAP
IAN
VAP
VAP
VN
VN
Rev. PrA | Page 16 of 27
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 6).
where V
different phases.
The current inputs are represented by
where:
I
phase.
φ
voltage channel of each phase.
The instantaneous powers can then be calculated as follows:
Then:
As shown in Equation 8, in the ADE7752B, the active power
calculation 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 active power calcula-
tion gives the total active power information, P(t) = P
P
A
A
B
, I
, φ
(t) + P
B
, and I
B
P
P
P
V
V
V
P
P
P
I
I
I
, and φ
A
B
C
C
C
A
B
A
B
A
B
C
(t) = V
(t) = V
(t) = V
( )
( )
( )
( )
( )
( )
t
t
( )
A
t
( )
t
t
C
t
t
( )
t
, V
(t).
t
=
=
=
C
=
=
=
=
=
V
V
=
V
B
represent the rms value of the current of each
C
, and V
B
C
A
B
C
represent the phase difference of the current and
A
(t) × I
2
2
2
2
(t) × I
(t) × I
×
2
×
×
2
I
I
I
I
I
I
×
×
×
B
C
C
A
A
B
V
V
V
×
×
×
×
Preliminary Technical Data
×
×
C
A
B
B
C
A
cos
C
cos
cos
(t)
represent the voltage rms values of the
cos
cos
(t)
cos
(t)
×
×
×
( )
( )
( )
cos
φ
φ
cos
φ
cos
⎧
⎨
⎩
⎧
⎨
⎩
C
B
A
(
ω
ω
ω
−
−
( )
⎛
⎜
⎝
l
−
l
l
⎛
⎜
⎝
ω
t
t
t
ω
V
V
ω
V
+
l
+
+
B
C
l
t
A
l
t
t
φ
×
×
2
4
×
+
3
3
+
A
π
π
I
I
I
C
B
2
A
)
4
3
+
+
3
×
π
×
π
×
cos
φ
cos
φ
⎞
⎟
⎠
cos
⎞
⎟
⎠
B
C
⎫
⎬
⎭
⎫
⎬
⎭
⎛
⎜
⎝
⎛
⎜
⎝
(
2
2
2
ω
ω
ω
l
l
l
t
t
t
+
+
+
φ
4
8
3
3
π
π
A
)
+
+
A
φ
φ
(t) +
C
B
⎞
⎟
⎠
⎞
⎟
⎠
(6)
(7)
(8)