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ADE7752 数据表(PDF) 15 Page - Analog Devices |
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ADE7752 数据表(HTML) 15 Page - Analog Devices |
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15 / 24 page  ADE7752/ADE7752A Rev. C | Page 15 of 24 TYPICAL CONNECTION DIAGRAMS CURRENT CHANNEL CONNECTION METER CONNECTIONS 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 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. () () () () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × × = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + × × = × × = 3 π 4 cos 2 3 π 2 cos 2 cos 2 t ω V t V t ω V t V t ω V t V l C C l B B l A A (5) IAP ±500mV Rb Rf Rf CT NEUTRAL PHASE IP IAN Cf Cf where V 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. ±500mV Ra * Rb * VR * VAP AGND Rf Rf PT NEUTRAL PHASE VN Cf Cf VAP Rf NEUTRAL PHASE VN Cf Cf * Ra >> Rf + VR; * Rb + VR = Rf ±500mV Figure 20. Typical Connections for Voltage Channels A , VB, and VC B represent the voltage rms values of the different phases. The current inputs are represented by Equation 6. () ( ) () () ⎭ ⎬ ⎫ ⎩ ⎨ ⎧ + + × = ⎭ ⎬ ⎫ ⎩ ⎨ ⎧ + + × = + × = C l C C B l B B A l A A φ t ω I t I φ t ω I t I φ t ω I t I 3 π 4 cos 2 3 π 2 cos 2 cos 2 (6) where IA, IB, and IC B represent the rms value of the current of each phase and ϕA, ϕB B , 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 B (t) × I B B (t) P B C (t) = VC(t) × IC(t) Then: ( ) () ( ) () () () () ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + + × × − × × = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + + × × − × × = + × × − × × = C l C C C C C C B l B B B B B B A l A A A A A A φ t ω I V φ I V t P φ t ω I V φ I V t P φ t ω I V φ I V t P 3 π 8 2 cos cos 3 π 4 2 cos cos 2 cos cos (7) 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(t) + PC(t). B |
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