Severe Phase Unbalance RTAA

Issue: 

Severe Phase Unbalance

Resolution:

Phase Unbalance in excess of 30%, not defeatable, has been detected.  This diagnostic occurs if the default 15% Phase Unbalance criteria has been defeated/disabled.

Items to check:

• CTs (Current Transformers)
  • Part Numbers should all match
  • CTs resistances should be equal within ±10%
  • If changing out the CT, it is a good idea to replace the wiring from the CT all the way back to the compressor module if there is any evidence that wiring may be brittle or show any signs of corrosion
  • Investigate the (MTA) connector that plugs into the compressor module and consider replacing it
• Line Voltages should be close, with a 2% or less unbalance
• Power wiring and connections from the incoming point, any terminal blocks, to the contactors, and to the compressor motor should all be verified
• Conductors not damaged
• Contactor Poles (if able verify) should be in good condition
• MCSP (Compressor Module) may need to be replaced if everything listed above has been verified

Notes:

Changes:

Other Question/Problem/Cause Statements:

• Severe phase unbalance

Facts:

• Only on one circuit
• Swapped compressor modules with the same result
• Actual measured CT resistance is within 1 ohm of each other
• Replaced CT and spliced to existing wiring.
• Problem is very intermittent
• Actual unbalance measured using amp probe is less than 5% on worst leg
• Air-Cooled Chiller (Pueblo) (RTAA 130-400 Ton)
• Air-Cooled Chiller (Pueblo) (RTAA 70-125 Ton)
• Compressor Chiller (Pueblo) (RTUA)
• Water-Cooled Chiller (Pueblo) (RTWA)

Document Identifier: DOC-83399