ADE7752B_15 datasheet(14/24 Pages) AD

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ADE7752B

Rev. 0 | Page 14 of 24

TYPICAL CONNECTION DIAGRAMS

CURRENT CHANNEL CONNECTION

Figure 15 shows a typical connection diagram for the current

channel (IA). A current transformer (CT) is the current trans-

ducer selected for this example. Notice that 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.

IAP

±500mV

NEUTRAL

PHASE

IAN

Figure 15. Typical Connection for Current Channels

VOLTAGE CHANNEL CONNECTION

Figure 16 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 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.

±500mV

Ra*

Rb*

VR*

VAP

AGND

NEUTRAL

PHASE

VAP

NEUTRAL

PHASE

*Ra >> Rf + VR; *Rb + VR = Rf

±500mV

Figure 16. Typical Connections for Voltage Channels

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 7).

()

( )t

cos

()

⎟

⎠

⎞

⎜

⎝

⎛

cos

(7)

()

⎟

⎠

⎞

⎜

⎝

⎛

cos

where VA, VB, and VC represent the voltage rms values of the

different phases.

The current inputs are represented by

()

(

)

cos

()

⎟

⎠

⎞

⎜

⎝

⎛

cos

(8)

()

⎟

⎠

⎞

⎜

⎝

⎛

cos

where:

IA, IB, and IC represent the rms value of the current of each phase.

φA, φB, 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(t) = VB(t) × IB(t)

PC(t) = VC(t) × IC(t)

Then:

( )

(

)

−

cos

( ) =

()

⎟

⎠

⎞

⎜

⎝

⎛

−

cos

(9)

()

⎟

⎠

⎞

⎜

⎝

⎛

−

cos

As shown in Equation 9, 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 calculation gives the

total active power information, P(t) = PA(t) + PB(t) + PC(t).

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