Control; Electrical Connections; Motor Design - Emerson Copeland Screw SCH2 Applications Manual

Thermostatic expansion valves Thermostatic expansion valves
Thermostatic expansion valves Thermostatic expansion valves Thermostatic expansion valves
• Valve layout for liquid sub-cooler:
- Basis is the sub-cooling capacity
- Evaporating temperature corresponds to the
ECO intermediate temperature.
- Valves with a superheat adjustment of about 10
K should be used in order to avoid unstable
operation when switching on the sub-cooling
circuit and in connection with load fluctuations.
- If the sub-cooling circuit is also operated under
part-load conditions, this must be given due
consideration when designing the valves.
• Valve layout for evaporator:
Due to the high degree of liquid sub-cooling suction
mass flow is much lower than with systems with
similar capacity and no sub-cooler (see software
data). This requires a modified layout. In this
context the lower vapor content after expansion
must also be taken into consideration. For further
hints on the layout of expansion valves and evapora-
tors see Section 4.2.

5.7 Control

5.7 Control
5.7 Control 5.7 Control 5.7 Control
Between that start and the stabilization of operating
conditions, the solenoid valve of the sub-cooling circuit
is switched on time delayed or depending on suction
pressure. For further hints and a schematic layout
diagram see Section 6.4.
6 Electrical connection 6 Electrical connection 6 Electrical connection 6 Electrical connection 6 Electrical connection

6.1 Motor design

6.1 Motor design 6.1 Motor design 6.1 Motor design 6.1 Motor design
Figure 14
© 2002 Copeland Corporation
Issued 4-2002
Printed in U.S.A.
Figure 15
15
The compressors are supplied as standard with part
winding motors of connection (Part Winding "PW").
Start delta motors are available as special design.
Part winding motors Part winding motors Part winding motors Part winding motors Part winding motors
Starting methods (connections according to figures 14
and 15):
• Part winding start to reduce the starting current
• Direct on line start (DOL)
Start delta motors Start delta motors Start delta motors Start delta motors Start delta motors
Starting methods (connections according to figures 16
and 17).
The start current value in star mode (1/3 of The start current value in star mode (1/3 of The start current value in star mode (1/3 of The start current value in star mode (1/3 of The start current value in star mode (1/3 of
the direct on line value) is generally stated the direct on line value) is generally stated
the direct on line value) is generally stated the direct on line value) is generally stated the direct on line value) is generally stated
according to standard locked rotor condi- according to standard locked rotor condi- according to standard locked rotor condi- according to standard locked rotor condi- according to standard locked rotor condi-
tions. In reality, however tions. In reality tions. In reality , however , however , however, approx. 50% are
tions. In reality tions. In reality , however
obtained during the start. Moreover obtained during the start. Moreover, when obtained during the start. Moreover obtained during the start. Moreover obtained during the start. Moreover
switching from start to delta mode there is a switching from start to delta mode there is a switching from start to delta mode there is a switching from start to delta mode there is a switching from start to delta mode there is a
current peak as high as the direct start value. current peak as high as the direct start value.
current peak as high as the direct start value. current peak as high as the direct start value. current peak as high as the direct start value.
This is caused by the voltage interruption This is caused by the voltage interruption This is caused by the voltage interruption This is caused by the voltage interruption This is caused by the voltage interruption
during switch-over of the contactors, which during switch-over of the contactors, which during switch-over of the contactors, which
during switch-over of the contactors, which during switch-over of the contactors, which
results in a speed drop due to the results in a speed drop due to the results in a speed drop due to the results in a speed drop due to the results in a speed drop due to the
compressor' ' ' ' ' s small rotating masses. compressor compressor s small rotating masses. s small rotating masses. s small rotating masses.
compressor compressor s small rotating masses.
Figure 16
AE4-1322
, approx. 50% are , approx. 50% are , approx. 50% are
, approx. 50% are
, when , when , when , when
Figure 17