Trane RTWA 70-125 TON - Manual (Page 32)

32 RLC-SVD03A-EN
Under-Over Voltage Transformer
The hardware required for the Under/Over voltage sensing function of the
UCM is standard on the 70-125 Ton RTAA chiller. This feature must be
Enabled in the Service Settings Menu for it to be active. A custom designed
transformer whose primary is connected across the Line Voltage phases A to
B, provides a stepped down and isolated AC voltage to the CPM at input J4.
This secondary voltage is directly proportional to the line voltage applied to
the primary. The Chiller Report on the CLD can directly display the % Line
Voltage and, when so enabled, can cause automatically reset MAR
diagnostics for High and Low Line condition. The % Line Voltage is internally
calculated by dividing the selected nominal voltage rating (only certain
discrete values are selectable in the Service Settings Group) by the actual line
voltage as read and processed by the CPM. With the Under-Over Voltage
Protection Function enabled, an Over Voltage diagnostic will occur if the
calculated % Line Voltage equals or exceeds 114%, or an Under Voltage
diagnostic will occur if it equals or falls below 87% for 15 continuous
seconds. Reset differential is set at 3%.
Under-Over Voltage Transformer Checkout
ƽ WARNING
Live Electrical Components!
During installation, testing, servicing and troubleshooting of this
product, it may be necessary to work with live electrical
components. Have a qualified licensed electrician or other
individual who has been properly trained in handling live
electrical components perform these tasks. Failure to follow all
electrical safety precautions when exposed to live electrical
components could result in death or serious injury.
1. Locate the Under-Over Voltage Transformer [1T2] in the panel by referring
to the Component Location Drawing. Carefully measure the primary volt-
age across the Transformer (Line Voltage Phase A to B) and note the
value in Vac rms.
2. Next disconnect the transformers secondary from J4 on the CPM. Using
voltmeter probes, measure and note the unloaded secondary voltage
(Vac rms). (low voltage class 2 less than 32 Vac).
3. The ratio of the primary or line voltage to the open circuity secondary
voltage should be 20 to 1. If the unloaded turns ratio is not within ±2% of
this value, replace the transformer.
4. Reconnect the secondary back to J4 and remeasure the loaded (con-
nected) secondary voltage. The new loaded ratio should be approximately
20.2 to 1. If not within ±2% of this ratio the transformer's secondary
should be disconnected from the CPM and a 1 Kohm resistor connected
across the secondary. Measuring the voltage across the 1 Kohm resistor
should give us a voltage ratio of 20.17. Ratios more than ±2% in error sug-
gest a bad transformer. If the 1 Kohm loaded ratio is within tolerance, but
the CPM connected ratio is out of tolerance suspect a bad CPM. Before