RTHD and RTAC - Trane
RTHD and RTAC - Trane
RTHD and RTAC - Trane
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Current Transformers<br />
Each compressor motor has all three of its line currents monitored by toroid<br />
(doughnut) current transformers. These currents are normalized with respect to<br />
the Rated Load Amps of the respective compressor <strong>and</strong> thus are expressed in<br />
terms of % RLA <strong>and</strong> in Amps. The currents are “normalized” through the proper<br />
selection of the Current Transformer <strong>and</strong> the unit configuration. CTs are selected<br />
based on the motor RLA. Refer to Table 5.<br />
The current transformers provide the input for five basic functions of the starter<br />
module:<br />
1 Current overload protection using a programmed % of Rated Load Amps<br />
versus time to trip characteristic. The steady state “must trip” value is 140%<br />
RLA <strong>and</strong> the “must hold” value is 125% RLA. The starter Module will trip out<br />
the compressor, <strong>and</strong> the Main Processor (MP) will then shut down the other<br />
compressor on the same refrigerant circuit (if applicable). The appropriate<br />
diagnostic codes will be displayed.<br />
2 Loss of Phase Current. A phase loss due specifically to lack of Current<br />
Transformer inputs is not looked for during transition (which lasts for 3<br />
seconds in software) <strong>and</strong> is additionally delayed 2.8 seconds. As such, the<br />
diagnostic will not be called out any sooner than 5.8 seconds after transition<br />
even if it occurs immediately at start. Additional, two of the three current<br />
inputs also serve the Phase Rotation circuits. If this circuit (monitored<br />
immediately after start), outputs an inconsistent value to the module (due to<br />
loss of one or both of its inputs), a diagnostic of either Phase Loss (steady<br />
output) or Phase Reversal Protection Lost (varying output) will occur with a<br />
maximum delay of 1.2 seconds after start.<br />
3 Phase Rotation. Screw compressors cannot be allowed to run in reverse<br />
direction. To protect the compressors, the phase rotation is detected by the<br />
current transformers immediately at start up. If improper phasing is detected,<br />
within 1 second of startup, the Starter Module will trip out the compressor,<br />
<strong>and</strong> the MP will then shut down the other compressor on the same refrigerant<br />
circuit (if applicable). The Phase Rotation diagnostic codes will be displayed.<br />
Phase Rotation is only active for the first second of operation.<br />
4 Phase Unbalance. The Starter Module will shut down the compressor if a<br />
phase current unbalance is detected by the current transformers while the<br />
compressor is running. A 30% unbalance will cause the Starter Module to trip<br />
out the compressor, <strong>and</strong> the MP will then shut down the other compressor on<br />
the same refrigeration circuit (if applicable). Phase unbalance is based on the<br />
following calculation:<br />
% unbalance = (I0x-Iave) x 100<br />
26 RLC-SVD05A-EN<br />
Iave