Rockwell Automation 1402-LSM Line Synchronization Module Installation Instructions - Manual (Page 13)

Chapter 2
Installation
2–3
For proper monitoring and synchronization, correct selection of current
transformers (CT’s) and potential transformers (PT’s) is critical. The
following paragraphs provide the information required to choose these
transformers. Also refer to transformer operational characteristics Pages 3–2
and “Factory Configuration Parameters” listed on Page B–2.
PT Selection
The LSM is designed for a nominal full scale input voltage of 120V AC. The
user must supply transformers to scale down the system L–N (Wye) or L–L
(Delta) voltage to the full scale input rating of the module. The PT’s should
be selected as follows:
•
Wye (Star) Configuration – PT primary rating = L–N voltage or nearest
higher standard size. PT secondary rating = 120 Volts.
•
Delta or Open–Delta Configuration – PT primary rating = system L–L
voltage. PT secondary rating = 120 Volts.
PT quality directly affects system accuracy. The PT’s must provide accurate
linearity and maintain the proper phase relationship between voltage and
current in order for the Phase Error, Volts, kW, and Power Factor readings to
be valid. Instrument accuracy Class 1 or better is recommended. The LSM
PT inputs represent a
O.O2 VA burden.
CT Selection
The LSM uses current transformers (CT’s) to sense the current in each phase
of the power feed from the synchronizing voltage source, and may optionally
be included in the ground or neutral conductor. The precision of the selected
CT’s will directly affect the device accuracy.
The CT secondary should have a rating of 5A full scale and a burden
capacity greater than 3VA. The LSM Module CT Inputs represent a burden
of 0.0025VA.
!
ATTENTION: The CT primary rating is normally selected to be
equal to the current rating of the power feed protection device.
However, if the peak anticipated load is much less than the rated
system capacity, then improved accuracy and resolution can be
obtained by selecting a lower rated CT. Generally, the CT size
should be the maximum expected peak current +25%, rounded
up to the nearest standard CT size.
PT and CT Transformer
Selection