2.6.2 CT POLARITY
NOTE: Take care to ensure correct polarity of the CT primary as shown above. If in doubt,
check with the CT supplier.
Take care to ensure the correct polarity of the CTs. Incorrect CT orientation leads to negative kW
readings when the set is supplying power. Take note that paper stick-on labels on CTs that show the
orientation are often incorrectly placed on the CT. It is more reliable to use the labelling in the case
moulding as an indicator to orientation (if available).
To test orientation, run the generator in island mode (not in parallel with any other supply) and load
the generator to around 10 % of the set rating. Ensure the DSE module shows positive kW for all
three individual phase readings.
To Generator
To Load
Polarity of CT Primary
2.6.3 CT PHASING
Take particular care that the CTs are connected to the correct phases. For instance, ensure that the
CT on phase 1 is connected to the terminal on the DSE module intended for connection to the CT for
phase 1.
Additionally ensure that the voltage sensing for phase 1 is actually connected to generator phase 1.
Incorrect connection of the phases as described above results in incorrect power factor (pf)
measurements, which in turn results in incorrect kW measurements.
One way to check for this is to make use of a single-phase load. Place the load on each phase in turn,
run the generator and ensure the kW value appears in the correct phase. For instance if the load is
connected to phase 3, ensure the kW figure appears in phase 3 display and not in the display for
phase 1 or 2.
2.6.4 CT CLASS
Ensure the correct CT type is chosen. For instance if the DSE module is providing over current
protection, ensure the CT is capable of measuring the overload level required to protect against, and
at the accuracy level required.
For instance, this may mean fitting a protection class CT (P15 type) to maintain high accuracy while
the CT is measuring overload currents.
Conversely, if the DSE module is using the CT for instrumentation only (current protection is disabled
or not fitted to the controller), then measurement class CTs can be used. Again, bear in mind the
accuracy required. The DSE module is accurate to better than 1% of the full-scale current reading. To
maintain this accuracy, fit a Class 0.5 or Class 1 CT.
Check with the CT manufacturer for further advice on selecting CTs.
Labelled as
p1,
k
or K
Labelled as
p2,
l
or L
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