16
A typical metering circuit showing ATPOL II connected is shown in figure 9.
This circuit has three CTs and, if higher voltage is present, may have three
PTs. It is typical for metering a three-phase four-wire wye type service. The
currents flowing to the load are considered the “primary currents”. Those
currents are
“stepped down” by each CT to a “secondary current” according
to the ratio of the CT printed on its rating plate. A typical value would be
600:5 (120:1). The output of each CT must have some burden across it for
the secondary current to flow. The current probes of ATPOL II are clamped
around the secondary of each CT. Make sure to use current probes that are
suited for accurate measurement in the 0-5 amp range. The AT6003 is best
for this. The AT6001 or AT6002 may be acceptable, depending on the
current level.
Once the current probes are attached, it is best to set the input ratios for each
of the current probes (see the
Setting Input Ratios
section). This will allow
the displayed values and logged values to reflect the primary current level
instead of the secondary current level. This in turn allows accurate power and cost readings without
having to multiply the results times some ratio. Remember that these ratios are reset to 1:1 whenever
ATPOL II is turned off.
Similarly, the PTs take a primary voltage and step it down to a secondary value. If the primary voltage
is below 600Vrms, you will not need to hook up to the PTs (in fact, there will probably be none present).
The ratio of the stepping down of the voltage will be printed on the rating plate of the PT. Typically this
would be 2400:120 (20:1). As with the CTs, this ratio should be entered into ATPOL II (see the
section) to simplify interpreting the results.
Connections To a 2 CT / 2 PT Metering Circuit
Figure 10 shows recommended connections to a metering circuit with only 2
CTs or 2 PTs. This type of metering circuit may be preferable when cost is an
issue (less instrument transformers are used) or when metering a delta service
with no reference to neutral. The discussion of the previous section
(
Connections To a 3 CT / 3 PT Metering Circuit
) applies to this circuit as well,
with one important exception. If you clamp onto the CTs, rather than clamping
onto each of the primary currents directly, ATPOL II must be operating in the 2
Current Probe mode of operation (see the
Phase-Neutral vs. Phase-Phase vs. 2
Current Mode
section).
Connections To an Open Delta (3CT / 2PT) Metering Circuit
In the open delta configuration, two PTs and 3 CTs are available. Make the
voltage connections as shown in figure 10 of the
Connections to a 2CT / 2PT
Metering Circuit
section. For current connections, connect the phase 1 and phase 3 probes as shown
in figure 10 and attach the phase 2 current probe to the phase 2 CT. You will not need to operate in the
2 Current Probe mode of power measurement since there are 3 currents being monitored.
ATPOL II
ATPOL II
Содержание ATPOL II
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