GEA GSC TP User manual

GSC TP
Sequence Control for Packages
Operating Manual (Translation of the original text)
E_301510_2

COPYRIGHT
All Rights reserved.
No part of this publication may be copied or pub-
lished by means of printing, photocopying, microfilm
or otherwise without prior written consent of
•GEA Refrigeration Germany GmbH
herein after called manufacturer. This restriction
also applies to the corresponding drawings and dia-
grams.
LEGAL NOTICE
This documentation has been written in all con-
science. However, the manufacturer cannot be held
responsible, neither for any errors occurring in this
documentation nor for their consequences.
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SYMBOLS USED IN THIS MANUAL
Danger!
Stands for an immediate danger which
leads to heavy physical injuries or to
the death.
Warning!
Stands for a possibly dangerous situa-
tion which leads to heavy physical
injuries or to the death.
Caution!
Stands for a possibly dangerous situa-
tion which could lead to light physical
injuries or to damages to property.
Hint!
Stands for an important tip whose
attention is important for the designa-
ted use and function of the device.
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TABLE OF CONTENTS
1 PARAMETERS 9
1.1 Explanation of the parameters of local control 9
1.1.1 Screw compressor capacity control 9
1.1.2 Reciprocating compressor capacity control 11
1.2 Explanation of the parameters of sequence control options 12
2 EXAMPLES FOR THE SEQUENCE CONTROL OF PACKAGES 14
2.1 Conditions for capacity increase 15
2.2 Conditions for capacity decrease 16
2.3 Variable capacity demand - example 1 17
2.4 Variable capacity demand - example 2 18
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TABLE OF FIGURES
fig. 1 Hysteresis, Neutral Zone 10
fig. 2 Calculating the step time 12
fig. 3 14
fig. 4 Conditions for capacity increase 15
fig. 5 Conditions for capacity decrease 16
fig. 6 Variable capacity demand - example 1 17
fig. 7 Variable capacity demand - example 2 18
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1 PARAMETERS
This chapter presents the parameters relevant for sequence control system.
The sequence control for packages is set up so that the local control for each unit is active. The sequence mod-
ule overrides the local control on certain units in relation to the current running condition. These units are then
not controlled by their setpoints and process values but by the sequence module.
1.1 Explanation of the parameters of local control
Operation mode Required operation mode
Operation modes 0, 1, 2, 5 and 9 are not permitted.
Process value Process value that should be controlled, e.g. suction pressure,
external temperature, discharge pressure
Setpoint °C Setpoint for capacity control
Neutral zone K
As soon as the process value is within this zone, the compressor
capacity is not changed. Exception is if a capacity limitation
becomes active, then the controller can change the capacity. The
zone lies symmetric around the setpoint.
The value must be less than the value for the proportional zone (see
1.1.2 "Capacity control of reciprocating compressors").
Auto start delay secs Initiated by process value rising above Neutral Zone and compres-
sor not running.
Auto stop delay secs
The auto stop delay occurs only when the relevant compressor in
the sequence is active.
The auto stop delay is initiated by process value falling below Neu-
tral Zone and compressor running with Part Load or less
capacity and only one compressor in the sequence is active.
1.1.1 Screw compressor capacity control
Hysteresis K
Area at the boundary of the neutral zone where in dependence of
the direction of the process value change the capacity control does
not change the compressor capacity.
Load pulse secs Pulse time for capacity increase.
Unload pulse secs Pulse time for capacity decrease.
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Parameters
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Pause secs Pause time between pulses.
Auto stop position %
As soon as the control slide has reached this value or is below this
value the "Auto stop delay" will start (stand alone operation). In
sequence operation the control slide is stopped at this position and
the compressor is allowed to stop if it is allowed by the sequence
module.
fig.1: Hysteresis, Neutral Zone
PV Process value
SP Setpoint
NZ Neutral zone
HYS Hysteresis
A Time characteristic of process value
B Time characteristic of the 3-step-controller outputs
C Time characteristic of the pulse generator
D Time character of the pulsed outputs to the capacity control solenoid valves
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1.1.2 Reciprocating compressor capacity control
Proportional zone K
If the process value lies within this zone the step time is calculated
based on the difference between process value and setpoint. The
zone lies symmetric around the setpoint. Furthermore, this value
must always be greater than the value for the neutral zone.
Correction P Zone K
The "Correction P Zone" value enables the correction of the lower
boundary of the proportional zone in case this boundary lies below
the alarm limit for low suction pressure.
Capazität +min
Capazität +max
Capazität -min
Capazität +min
secs
secs
secs
secs
During increasing or decreasing capacity, the capacity controller
uses a step time to prevent too fast changes in compressor
capacity. This step time is calculated between its maximum and min-
imum value. This calculation is made if the process value is within
the proportional zone only. The larger the difference between proc-
ess value and setpoint the shorter the step time.
Hint!
The minimum step time between capacity steps is always 15 seconds.
The way the step time is calculated illustrated by example in the following diagram.
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Parameters
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fig.2: Calculating the step time
Example: Process value = 8 The step time is derived as shown and is 75 secs.
PV Process value (= 8)
SP Setpoint (=6)
NZ Neutral Zone (=2)
PZ Proportional Zone (=6)
CPZ Correction P Zone (=0.5)
t1 Capacity +min (=50)
t2 Capacity +max (=100)
t3 Capacity -max (=60)
t4 Capacity -min (=30)
1.2 Explanation of the parameters of sequence control options
Operation mode Master/
Slave/ Off
One compressor must be chosen as Master and the other compres-
sors as Slaves. "off" means not under sequence control.
Sequence number 1 to 9 Each compressor must have a different number.
Minimum 1%Compressor must be able to reach this capacity, sequence control
may force compressor to hold this capacity.
Part load 1%
Compressor must be able to reach this capacity, sequence control
may force compressor towards part load and to hold this capacity.
For screw compressors with Vi, the value for the part-load should be
set not higher than 70%.
Maximum 1%Compressor must be able to reach this capacity, sequence control
may force compressor towards maximum and to hold this capacity.
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Fixed sequence yes/ no "yes" means a fixed start sequence, "no" means running hours are
equalised
Master process value yes/ no If "yes" then the Master process value will be sent to all Slaves
Auto start delay secs Used to start next compressor in sequence, initiated by process
value rising above sequence neutral zone
Switch delay secs Delay before switching between compressor forced or held at Part
Load or Maximum position and controlling compressor
Auto stop delay secs Used to stop next compressor in sequence, initiated by process
value falling below sequence neutral zone
Neutral zone K Used to start and stop compressors in sequence, must be larger
than local control neutral zone (see 1.1).
1 The value refers to the combination of active cylinder or the control slide position and speed of compressor
drive motor.
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Parameters
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2 EXAMPLES FOR THE SEQUENCE CONTROL OF PACKAGES
This chapter shows 4 possble and typical situations of compressor operation with sequence control. Other situa-
tions may occur depending on the system configuration and load fluctuations.
Important information about the diagrams
fig.3
"Control" Reference to the explanation of the parameters in Chapter 1.1 (Local control)
"Sequence" Reference to the explanation of the parameters in Chapter 1.2 (Sequence options)
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2.1 Conditions for capacity increase
fig.4: Conditions for capacity increase
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2.2 Conditions for capacity decrease
fig.5: Conditions for capacity decrease
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2.3 Variable capacity demand - example 1
fig.6: Variable capacity demand - example 1
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2.4 Variable capacity demand - example 2
fig.7: Variable capacity demand - example 2
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Operating Manual | Sequence Control for Packages
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Examples for the sequence control of Packages
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