EWWD440~850AAYNNO**
Packaged water-cooled water chillers
4PW25558-1B
Installation and operation manual
23
Namely,
1.
If the operating time of the compressor immediately before stop is
420 seconds or more: ON-OFF limiting time is 180 seconds.
2.
If the operating time of the compressor immediately before stop is
less than 420 seconds: ON-OFF limiting time becomes [600–
operating time of the compressor immediately before stop] seconds.
■
ON-OFF limiting time immediately after power-up to the control
circuit of the unit becomes 180 seconds.
■
Do not try to shorten the ON-OFF limiting time by turning the
circuit breaker of the control circuit ON and OFF after stop of the
unit.
Current limiting function
When the condenser water temperature is high or adhesion of
contamination to the inside of the condenser heat exchanger tubes is
large, the operating current of the unit increases.
This function is for optimization of the cooling capacity in relation to
protection of electrical components such as the compressor motor,
even under conditions of high current values.
If the operating current of the individual compressor exceeds the
Maximum Load Amps, this function forcedly performs the capacity
control of the compressor until the operating current reaches the
Maximum Load Amps or less.
If only one compressor out of 2 exceeds the Maximum Load Amps,
the capacity control is performed on the compressor that exceeds the
Maximum Load Amps only.
Because the unit shifts to partial load operation due to working of this
function, the cooling capacity reduces. Abnormal stops however, due
to activation of safety devices such as overcurrent relays, do not
occur and continuous operation of the unit is available. See
Current limiting function/Current demand function" on page 23
Current demand function
For sites where you want to benefit from the capacity of an entire
system (=with several units), it is possible to limit and to control the
operation current of each unit individually.
For automatic capacity control of the entire system, this function
enables you to set the upper limit value of the compressor operation
current to a predetermined current value, instead of to the Maximum
Load Amps of the compressors.
Set the demand value (% relative to the reference current
value) on the graphic panel display
["MENU"
➞
"SETTING"
➞
"SETTING (1/2)"]
This function takes effect only when the remote signal for current
demand stays ON. See
"Figure: Current limiting function/Current
Table 3
Figure: Current limiting function/Current demand function
CAUTION
Do not try to shorten the ON-OFF limiting time by
turning the circuit breaker of the control circuit ON and
OFF.
It may lead to abnormal stops due to overheat of the motor.
Reference current value per
compressor (A)
Model
Hz
Standard
EWWD440
50
91
EWWD600
50
128
EWWD850
50
173
NOTE
■
Standard voltage of this model is 400 V.
■
Because this model has 2 compressors, the
actual maximum operating current of the unit is
the value in table above x2.
1
Forced load up area (to stabilize the motor cooling)
2
Reference current A1
3
Demand current A2=A1xB (current demand setpoint B (%))
4
Operating current
Automatic capacity control range when current demand function is
ON
Automatic capacity control range when current demand function is
OFF
Current limiting function is active
5
The operating current of the compressor increases (before
activation of the current limiting function or the current demand
function)
6
The operating current of the compressor increases (after
activation of the current limiting function or the current demand
function)
7
Reference current A1 or Demand current A2 (=A1xB)
8
Reference current A1x0.95 or Demand current A2x0.95
9
Operating current per compressor
Automatic capacity control (up/down/stop)
Load up not allowed
Forced load down
NOTE
■
In the current demand function, setting of the
value between 0 and 100% is available.
■
For obtaining a state motor cooling, capacity
control only starts when a certain operating
current of compressors is reached (after forced
load up).
■
For this reason, it is possible that in case of a too
low current demand setpoint B, the actual current
value does not decrease to the level of the
calculated current demand but remains above A2.
Be aware that, depending on the operation
condition, the minimum operating current value
must be 30 to 40% of the current at full load
operation.
0(A)
1
4
B(%)
3
2
5
6
8
7
9
