ADE7753
–24–REV. PrC 01/02
PRELIMINARY TECHNICAL DATA
NO LOAD THRESHOLDNO LOAD THRESHOLD
NO LOAD THRESHOLDNO LOAD THRESHOLD
NO LOAD THRESHOLD
The ADE7753 includes a "no load threshold" feature that will
eliminate any creep effects in the meter. The ADE7753
accomplishes this by not accumulating energy if the multi-
plier output is below the "no load threshold". This threshold
is 0.001% of the full-scale output frequency of the multiplier.
Compare this value to the IEC1036 specification which states
that the meter must start up with a load equal to or less than
0.4% Ib. This standard translates to .0167% of the full-scale
output frequency of the multiplier.
REACTIVE POWER CALCULATIONREACTIVE POWER CALCULATION
REACTIVE POWER CALCULATIONREACTIVE POWER CALCULATION
REACTIVE POWER CALCULATION
Reactive power is defined as the product of the voltage and
current waveforms when one of this signal is phase shifted by
90º. The resulting waveform is called the instantaneous
reactive power signal. Equation 17 gives an expression for the
instantaneous reactive power signal in an ac system when the
phase of the current channel is shifted by +90º.

)sin(2)(

θω

+= tVtv

(15)
)tsin(I)t('i)tsin(I)t(i 2
22 p
+w=w=
(16)
Where θ is the phase difference between the voltage and
current channel, V = rms voltage and I = rms current.
)(')()( titvtRp ×=)2sin()sin()(θωθ++= tVIVItRp
(17)
The average power over an integral number of line cycles (n)
is given by the expression in Equation 18.
∫==
nT
VIdttRpnTRP
0
)sin()(1θ
(18)
where T is the line cycle period.
RP is referred to as the Reactive Power. Note that the reactive
power is equal to the DC component of the instantaneous
reactive power signal Rp(t) in Equation 17. This is the
relationship used to calculate reactive power in the ADE7753.
The instantaneous reactive power signal Rp(t) is generated by
multiplying the channel 1 and channel 2. In this case, the
phase of the channel 1 is shifted by +90º. The DC component
of the instantaneous reactive power signal is then extracted by
a low pass filter to obtain the reactive power information.
Figure 41 shows the signal processing in the Reactive Power
calculation in the ADE7753.
++
Σ
CALIBRATION
CONTROL
LINECYC[15:0]
LPF1
FROM
CHANNEL 2
ADC
ZERO CROSS
DETECTION
ACCUMULATE ACTIVE
ENERGY IN INTERNAL
REGISTER AND UPDATE
THE LVARENERGY
REGISTER AT THE END OF
LINECYC HALF-CYCLES
53 0
LVARENERGY[23:0]
23 0
Instantaneous Reactive
Power Signal - Rp(t)
MULTIPLIER
90 DEGREE
PHASE SHIFT
I
Π
2
V
Figure 41 - Reactive Power Signal Processing
The features of the Reactive Energy accumulation are the
same as the Line Active Energy accumulation. The number
of half line cycles is specified in the LINECYC register.
LINECYC is an unsigned 16-bit register. The ADE7754 can
accumulate Reactive Power for up to 65535 combined half
cycles. At the end of an energy calibration cycle the LINCYC
flag in the Interrupt Status register is set. If the LINCYC
mask bit in the Interrupt Mask register is enabled, the IRQ
output will also go active low. Thus the IRQ line can also be
used to signal the end of a calibration. The ADE7753
accumulates the Reactive Power signal in the LVARENERGY
register for an integer number of half cycles, as shown in
Figure 41.
The Reactive Energy accumulation in the ADE7753 not only
provides the reactive energy calculated using the phase shift
method, it is also useful to provide the sign of the reactive
power if it is desirable to use triangular method to calculate
reactive power. The ADE7753 also provides an accurate
measurement of the apparent power. The user can choose to
determine reactive energy through the mathematical rela-
tionship between apparent, active and reactive power. The
sign of the reactive energy can be found by reading the result
from the LVARENERGY register at the end of a reactive
energy accumulation cycle.
22
)(Re
Re
EnergyActiveEnergyApparentEnergyactivesign
Energyactive
−×=
APPARENT POWER CALCULATIONAPPARENT POWER CALCULATION
APPARENT POWER CALCULATIONAPPARENT POWER CALCULATION
APPARENT POWER CALCULATION
Apparent power is defined as the amplitude of the vector sum
of the Active and Reactive powers -see Figure 42. The angle
θ between the Active Power and the Apparent Power generally
represents the phase shift due to non-resistive loads. For
single phase applications, θ represents the angle between the
voltage and the current signals. Equation 20 gives an expres-
sion of the instantaneous power signal in an ac system with a
phase shift.