Manual 85586V1
AtlasPC Digital Control, Vol. I
Woodward
89
Generator Current Inputs
The CT inputs are designed to sense three phase current inputs. The ‘A’ phase
current inputs of each set are used for phase calculations. The fundamental
magnitude and phase information is calculated, in addition to the magnitude and
phase of each harmonic. All harmonics are calculated, up to the 7th harmonic, as
well as the 9th, 11th, and 13th harmonics. In addition the CT current inputs are
used in conjunction with the PT voltage inputs for load calculation purposes. All
current calculations implement algorithms in accordance with IEEE 1459-2000.
Individual fundamental and harmonic CT inputs are provided. A negative phase
sequence current input and a THD current input are also provided.
The CT inputs are rated at 5A and function down to 50 mA. For optimum
accuracy in the usable range, it is recommended to use 5 A secondary CTs with
PowerSense (not 1A secondary CTs). Take care to avoid secondary currents
greater than 7 Arms, as this will cause damage.
CT ratio and gain inputs are provided, to allow field configuration of the CT
scaling. The CT ratio will scale all three CT inputs by the same ratio. There is a
separate gain input provided for each CT input (3 for the generator and 3 for the
mains) that is provided to allow for compensation of current transformer turns
ratio inaccuracies.
The CT inputs have adjustable software filters. All CT inputs are updated every 3
cycles. With an input of 60 Hz, this equates to 50 ms.
The hardware does not require three phases for current calculations, the
application can configure the module for single phase, and all functionality will be
modified accordingly. The single phase input that must be provided is the A
phase. The application can also configure the module for a “Y” or “delta” line
configuration, and the calculations will compensate appropriately. If the physical
connections are to a wye connected generator or load, the input to PowerSense
should also be wye connected (line-to-neutral). If the physical connections are to
a Delta connected generator or load (no neutral present), the input to
PowerSense should also be Delta connected (line-to-line). ). The “Y” or “delta”
configuration applies to the entire set of PT and CTs, it is not possible to
configure the PTs for “Y”, and the CTs for “delta”, or vice versa. However, the
configuration (line type and single or three-phase) may differ between PT/CT 1
and PT/CT 2 (gen and mains in most systems).
Configuration Notes
•
Refer to Figures 8-9 and 8-10 for CT wiring.
•
When using only one CT, rather than 3, the CT must be phase A, and the
application software must configure the PT/CT block for “single phase”
operation.
•
The application software must configure the PT/CT block for the correct
system frequency 50 Hz, or 60 Hz, as well as for the correct rotation,
clockwise or counterclockwise.
•
See the GAP help, for information on application software configuration
variables.
•
The terminal block screws should be torqued to 8–10 lb-in (0.9–1.1 N
x
m).
Summary of Contents for AtlasPC
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