JP2011102668A - Surge detector and surge detecting method of turbo refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surge detector and a surge detecting method of a turbo refrigerator accurately detecting a surge while monitoring the operating current to a motor that drives a turbo compressor in the variable speed turbo refrigerator. <P>SOLUTION: The surge detector of the turbo refrigerator provided with the turbo compressor driven by the motor includes: a rate of change of current detecting means (a differentiation circuit 31) detecting the rate of change of the operating current to the motor; and a surge detecting means (a comparing circuit 33, an off-delay circuit 34, and an on-delay circuit 36) detecting a surge from the rate of change of current detected by the rate of change of current detecting means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surging detection device and a surging detection method for a turbo refrigerator, and more particularly to a surging detection device and a surging detection method suitable for a turbo refrigerator including a variable speed drive turbo compressor.

  Turbo chillers compress refrigerant gas by centrifugal force, and in the case of high head / low airflow operation due to factors such as ingress of non-condensable gas, abnormal rise in cooling water temperature, extreme low load operation, etc. Surging may occur. Further, in the case of a refrigerator equipped with a variable speed drive turbo compressor, surging may occur in the case of a decrease in rotational speed due to a malfunction in rotational speed control or the like. When the surging phenomenon occurs, various problems such as a decrease in bearing life and damage due to excessive noise, excessive thrust load, etc., and sudden fluctuations in the chilled water temperature occur. For this reason, when surging occurs, it is essential to promptly detect it and take necessary protective measures such as issuing an alarm, stopping the device, and correcting the rotation speed.

  In a conventional centrifugal chiller, there is a method for detecting surging based on a change in the current value of an electric motor that drives a turbo compressor. That is, it is known that when the turbo chiller generates surging, the torque of the turbo compressor changes periodically, and therefore the current value of the electric motor that drives the turbo compressor changes periodically. For this reason, an allowable range of fluctuation of the operating current of the electric motor is determined in advance, and an alarm is issued when the operating current fluctuates more than a specified number of times exceeding this range.

Japanese Patent Publication No.8-16563

  However, in a centrifugal chiller equipped with a variable speed turbo compressor that has been generalized in recent years, the operating current greatly changes even during normal operation due to changes in the operating speed of the turbo compressor. It is difficult to determine. For this reason, a surging detecting means capable of detecting surging with high accuracy is required.

  The present invention has been made in view of the above points, and a surging detection device for a turbo chiller capable of accurately detecting surging by monitoring the operating current of an electric motor that drives the turbo compressor of the variable speed turbo chiller, and the surging An object is to provide a detection method.

  In order to solve the above problems, the present invention provides a surging detection device for a turbo chiller including a turbo compressor driven by an electric motor, and a current change rate detecting means for detecting a change rate of an operating current of the electric motor. And surging detection means for detecting surging from the current change rate detected by the current change rate detection means.

  Further, in the surging detection device for a turbo chiller according to the present invention, surging occurs when the current change rate detected by the current change rate detecting means is out of a specified range, and the frequency exceeds a specified value. Surging judgment means for judging that is provided.

  Further, the present invention is characterized in that, in the surging detection device for a turbo chiller, a value obtained by differentiating an operating current detection signal of an electric motor with a differentiator is used as a current change rate.

  Further, the present invention is characterized in that, in the surging detection device for a turbo chiller, the current change rate detecting means detects the current change rate based on a current value ratio or difference of the operating current of the motor measured at a specified time. To do.

  According to the present invention, in the surging detection apparatus for a turbo chiller, the current change rate detection means is configured to determine a current change rate based on a ratio or difference between a maximum value and a minimum value of the motor operating current detected within a specified time. Is detected.

  Further, in the surging detection device for a turbo chiller according to the present invention, the current change rate detecting means is a ratio or difference between a start point of increase or decrease of the operating current of the motor and a current value at the end point of increase or decrease. In this case, the current change rate is detected.

  The present invention is also a surging detection method for a turbo chiller equipped with the above turbo compressor, characterized in that a rate of change in operating current of the motor is detected and surging is detected from the rate of change in current.

  Further, the present invention is characterized in that, in the surging detection method for a turbo chiller described above, it is determined that surging has occurred when the rate of change in current is out of a specified range and the frequency exceeds a specified value. .

  Further, the present invention is characterized in that, in the surging detection method for a turbo refrigerator, a value obtained by differentiating an operating current detection signal of an electric motor with a differentiator is used as a current change rate.

  Further, the present invention is characterized in that, in the turbo chiller surging detection method, the current change rate is detected by a current value ratio or a difference in operating current of the electric motor measured every specified time.

  Also, in the surging detection method for a turbo chiller according to the present invention, the current change rate is detected by a ratio or difference between a maximum value and a minimum value of the motor operating current detected within a specified time. And

  In the turbo chiller surging detection method according to the present invention, the current change rate is detected by a ratio or difference between a current value at the start or rise of the operating current of the motor and a current value at the end of the rise or fall. It is characterized by doing.

  According to the present invention, surging is detected from the current change rate of the operating current of the electric motor that drives the turbo compressor, so that surging of the variable speed turbo refrigerator can be accurately detected.

FIG. 1 is a diagram showing a schematic configuration example of a turbo chiller to which a surging detection apparatus and a surging detection method according to the present invention are applied. FIG. 2 is a block diagram showing a configuration example of a surging detection device for a turbo refrigerator according to the present invention. FIG. 3 is a diagram for explaining a surging detection method for a turbo refrigerator according to the present invention. FIG. 4 is a diagram showing a current value and a current change rate of an electric motor during surging for explaining a surging detection method for a turbo refrigerator according to the present invention. FIG. 5 is a diagram showing fluctuations in the electric current of the electric motor during the occurrence of surging of the centrifugal chiller. FIG. 6 is a diagram showing current fluctuations (load fluctuations, etc.) other than surging of the centrifugal chiller.

  Hereinafter, embodiments of the present invention will be described in detail. The surging detection apparatus according to the present invention detects the surging by monitoring the operating current of the electric motor that drives the turbo compressor and detecting a sudden change (abrupt decrease and rapid increase) of the operating current. Here, the detection of a sudden change is preferably determined as a sudden change when the change rate of the operating current measured at each specified time is outside the range of the predetermined change rate. Also, the surging detection device counts how many times this sudden change has occurred within a specified time, and determines that surging has occurred when this number exceeds a predetermined number of times.

  In practice, it is preferable to determine that the rate of change is out of the specified range when the absolute value of the rate of change is equal to or greater than the specified value. Hereinafter, the fact that the rate of change is outside the specified range and the absolute value of the rate of change exceeding the specified value are treated as synonymous. When surging occurs in the turbo chiller and the surging detection device detects it, the surging detection device should first issue an alarm. Accordingly, the turbo chiller (the electric motor that drives the turbo compressor) may be stopped. When the turbo compressor is a variable speed machine, surging may be eliminated by increasing the rotation speed.

Hereinafter, the surging detection method will be specifically described.
[First Surging Detection Method]
In the first surging detection method, the surging detection device differentiates the operating current of the electric motor that drives the turbo compressor by a differentiator (differential circuit) provided in the apparatus, and monitors the rate of change of the current. When the differentiated current value falls outside the specified range, the sudden change detector in the surging detection device sets this as a “sudden change” of the current, and generates a pulse signal for a specified time. Although this pulse signal depends on the characteristics of the turbo compressor, it is usually several tens of seconds to several minutes.

  If a sudden change in the operating current of the motor that drives the turbo compressor is transient due to the start of operation or temperature change, etc., the pulse does not occur continuously, so the pulse signal disappears after the specified time has elapsed. . However, when surging occurs, sudden changes in current occur periodically, so that pulse signals are generated continuously and do not disappear.

  Here, the surging detection device detects this as surging when the pulse continues for a specified time or more. As a result, it is possible to detect that a sudden current change occurs at a certain frequency within a specified time, and to determine that surging has occurred.

[Second Surging Detection Method]
In the second surging detection method, the surging detector detects the current value of the motor that drives the turbo compressor every second specified time (test time) for the first specified time (detection period) after the start of detection. And calculate the rate of change. If this rate of change falls outside the specified range, the test result within this test time is true, and if it is within the range, it is false. This test is repeated continuously during the detection period, and the number of times that the test result is true is counted. When the count result exceeds the specified number, the surging detection device can determine that surging has occurred. If the detection result is no surging, the counter of the surging detection device is reset and detection is started again.

  In the second surging detection method, the test for each test time plays the role of a differentiator (differential circuit) in the first surging detection method.

[Third Surging Detection Method]
In the third surging detection method, the surging detection device detects the current of the motor driving the turbo compressor during the first specified time (detection period) and the second specified time (test time) after the start of detection. Observe the minimum and maximum values. Here, the ratio between the maximum value and the minimum value of the current is taken, and this is taken as the rate of change of the current. The subsequent detection method is the same as the second surging detection method.

[Fourth Surging Detection Method]
In the fourth surging detection method, the surging detection device constantly monitors the current value of the electric motor that drives the turbo compressor. When the current starts to increase or decrease, the current value is recorded and the current increases. Alternatively, the current value at the time when the decrease is completed is recorded, and the ratio is obtained and used as the current change rate. At this time, the current change rate may be obtained by gradually reducing the amount of fluctuation of the current over the time required for the fluctuation. Here, even if the current continues to increase or decrease, if the predetermined “maximum verification time” (1 to 10 seconds is good) has elapsed, it is assumed that the current change has ended once, The current change rate is calculated using the current value at the time, and this is set as the start value of the next change. The subsequent detection method is the same as the second surging detection method.

  Hereinafter, a specific example of the surging detection device for a turbo refrigerator according to the present invention will be described. FIG. 1 is a diagram showing an example of a schematic configuration of a turbo refrigerator to which a surging detection apparatus according to the present invention is applied. As shown in the figure, the turbo refrigerator 10 includes an evaporator / condenser 11 and a turbo compressor 12. Reference numeral 14 denotes a main motor for driving the turbo compressor 12, and the rotation shaft of the main motor 14 is connected to the impeller 16 via the speed increaser 15. By starting the main motor 14, the rotational force of the rotating shaft of the main motor 14 is transmitted to the impeller 16 through the speed increaser 15, the impeller 16 of the turbo compressor 12 rotates, and the turbo refrigerator 10 It becomes a driving state.

  Refrigerant vapor evaporated by removing heat from the cold water flowing into the evaporator in the evaporator of the evaporator / condenser 11 flows into the turbo compressor 12, is compressed, and flows into the condenser of the evaporator / condenser 11. And it cools with the cooling water which flows in into a condensation part, is condensed and becomes a refrigerant | coolant liquid, this refrigerant | coolant liquid flows in into an evaporation part, and a refrigeration cycle is performed. Further, the current value I supplied from the power source 18 to the main motor 14 is detected by a current detector 20, and the current value I is input to a differentiation circuit of a surging detection device described later.

  FIG. 2 is a block diagram showing the configuration of a surging detection apparatus that implements the first surging detection method. As shown in the figure, the surging detection device 30 includes a differentiation circuit 31, a comparison circuit 33, an off-delay circuit 34, an on-delay circuit 36, and a self-holding circuit 37, and these are connected in series. The self-holding circuit 37 is provided as necessary. A current value I supplied from the power source 18 to the main motor 14 detected by the current detector 20 (see FIG. 1) is supplied to the differentiation circuit 31. The circuit may be constituted by an electronic circuit and a sequence circuit, or may be virtually provided by an electronic computer. In particular, it is preferable in practice to define a logic circuit in a so-called programmable controller.

  In the surging detection device 30 having the above configuration, when surging occurs in the turbo chiller 10, the operation is as follows. First, the differentiating circuit 31 differentiates the current value I signal detected by the current detector 20 and outputs a change rate signal (differential output). Since the current value I increases or decreases, the signal becomes a positive or negative signal. Here, the absolute value of the differentiated signal is output, and both the increase and decrease of the current value I are output as positive signals.

  FIG. 3A is a diagram showing an example of the signal A of the actual current value I of the main motor 14 of the turbo refrigerator 10 generating surging and the change rate signal (differential output) B obtained by differentiating it. . A signal B obtained by differentiating the current value I of the main motor 14 of the turbo chiller 10 generating surging is input to the comparison circuit 33. The comparison circuit 33 outputs a true logic signal when the signal B exceeds the detection level L (specified value). As a result, a “comparison output C” in the form of a pulse signal as shown in FIG. When this comparison output C is input to the off-delay circuit 34, the width of the pulse signal widens only for the holding time of the off-delay circuit 34, and when the fluctuation of the current signal occurs at a certain frequency or more, the signal continues as shown in the figure. Delay output D.

  Here, when this delay output D is input to the on-delay circuit 36, if this continues for a specified time or more (that is, when a sudden change in the current value I exceeding the specified frequency occurs more than the specified frequency), the output becomes true and surging occurs. A detection output E for detecting the signal is output from the on-delay circuit 36. When the self-holding circuit 37 is provided, the detection output E is output to the self-holding circuit 37, and the detection output E is self-held by the self-holding circuit 37.

  FIG. 4 is a diagram for explaining an example of surging detection by the second surging detection method. In this example, the surge detector is operated at the main motor every set “validation time” (preferably about 0.1 to 10 seconds) during the set “detection period” (preferably about 1 to 10 minutes). 14 current values I are measured. Then, the ratio between the measured current value and the previously measured current value recorded is calculated. Here, the change rate is preferably divided by the smaller one of the two, and the larger one is divided. In this case, all the change rates can be detected as positive values. When this ratio exceeds a specified value (preferably about 1.02 to 1.2), the surge detection device accumulates the number of times during the detection period.

  If the number of detections exceeds a specified number (preferably about 1 to 10 times) during the detection period, the surging detection device determines that surging has occurred. If the specified number of times is not exceeded during the detection period, the accumulated number is reset and detection is started again. In the example of FIG. 4, the detection level is 1.06 times, the detection period is 180 seconds, the verification time is 1 second, and the specified number of times is 2. In the first verification period of FIG. 4, since the number of integrations is 2, the specified number is 2, and the specified number is not exceeded, surging is not detected, and in the next detection period, the number of integrations is 3. Therefore, it is determined that surging is detected. The number of times and the time are set optimally according to the characteristics of each turbo compressor.

  In the case of the third surging detection method, instead of calculating the ratio of the current values measured for each detection time in the second surging detection method, a separately determined test period (1 to 10 seconds) The ratio between the maximum value and the minimum value of the current value of the main motor 14 measured within a good degree is defined as the rate of change. Otherwise, follow the same procedure.

  FIGS. 5 and 6 are diagrams for explaining an example of a surging detection device according to the fourth surging detection method. FIG. 5 shows fluctuations in the current value I of the main motor 14 during surging, and FIG. The fluctuation of the current value I of the main motor 14 of load fluctuation or the like) is shown. In FIG. 5, the surging detector records the change in current between the time when the current value starts to rise and ends, or the time when the current value starts to drop and ends, and takes the ratio to obtain the current. Change ratio. Alternatively, the changed amount of change is divided by the time required for change, and this is used as the current change ratio. Other procedures are the same as those described with reference to FIG. 3 or FIG.

  Here, the case of defining the test time will be supplemented with reference to FIG. When specifying the test time, when the specified test time (about 1 to 10 seconds) has elapsed from the time when the increase (or decrease) in the current value is detected, it is assumed that the increase (or decrease) has ended here, Calculate the rate of change. Then, the detection is started again with this point of time as the starting point of rising (or falling). In this way, a gradual and wide current value fluctuation as shown in FIG. 6 is not erroneously detected as surging or the like.

In addition, when surging is detected, it is better to respond as follows.
An alarm is issued and the inspection of the turbo chiller is encouraged.
Open the throttle valve.
If there is a situation where the turbo chiller cannot be stopped, the so-called hot gas bypass valve is opened to increase the air flow of the turbo compressor.
If the turbo compressor is a variable speed machine, the rotational speed is increased.
Stop the refrigerator.

  By making the surging detection device and the surging detection method of the turbo chiller as described above, a turbo in which the current of the main motor that drives the turbo compressor during a steady operation, such as a variable speed turbo compressor, varies greatly. Even in a refrigerator, it is possible to accurately detect surging and take appropriate measures.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea described in the claims and the specification and drawings. Can be modified. Note that any shape or structure not directly described in the specification and drawings is within the technical scope of the present invention as long as the effects of the present invention are achieved.

  Since the present invention detects surging from the current change rate of the operating current of the electric motor that drives the turbo compressor, the surging detecting device of the turbo chiller and the surging detecting method capable of accurately detecting the surging of the variable speed turbo chiller Can be used as

DESCRIPTION OF SYMBOLS 10 Turbo refrigerator 11 Evaporation / condenser 12 Turbo compressor 14 Main motor 16 Impeller 18 Power supply 20 Current detector 30 Surging detection device 31 Differentiation circuit 33 Comparison circuit 34 Off-delay circuit 36 On-delay circuit 37 Self-holding circuit 37

Claims (12)

A turbo chiller surging detection device comprising a turbo compressor driven by an electric motor,
Current change rate detecting means for detecting the change rate of the operating current of the motor;
A surging detection device for a turbo refrigerator, comprising surging detection means for detecting surging from the current change rate detected by the current change rate detection means. The surging detection device for a turbo refrigerator according to claim 1,
A turbo comprising: surging determining means for determining that surging has occurred when the current change rate detected by the current change rate detecting means falls outside a specified range when the frequency exceeds a specified range. Surging detection device for refrigerator. In the surging detection device for a turbo refrigerator according to claim 1 or 2,
The turbo chiller surging detection device, wherein a value obtained by differentiating an operating current detection signal of the electric motor with a differentiator is used for the current change rate. The surging detection device for a turbo refrigerator according to claim 1,
The turbo chiller surging detection device, wherein the current change rate detection means detects a current change rate based on a current value ratio or a difference in operating current of the motor measured every specified time. The surging detection device for a turbo refrigerator according to claim 1,
Surging detection of a turbo chiller, wherein the current change rate detecting means detects a current change rate based on a ratio or difference between a maximum value and a minimum value of the operating current of the motor detected within a specified time. apparatus. The surging detection device for a turbo refrigerator according to claim 1,
The turbo refrigeration is characterized in that the current change rate detection means detects a current change rate based on a ratio or difference between a start point of an increase or decrease in operating current of the motor and a current value at the end point of increase or decrease. Machine surging detection device. A surging detection method for a turbo refrigerator equipped with a turbo compressor driven by an electric motor,
A surging detection method for a turbo chiller, characterized in that a rate of change in operating current of the electric motor is detected and surging is detected from the rate of change in current. The surging detection method for a turbo refrigerator according to claim 7,
A surging detection method for a turbo chiller, wherein surging is determined to occur when the current change rate is out of a specified range and the frequency exceeds a specified range. In the turbo refrigerator refrigerator surging detection method according to claim 7 or 8,
A surging detection method for a turbo refrigerator, wherein a value obtained by differentiating an operating current detection signal of the electric motor with a differentiator is used for the current change rate. The surging detection method for a turbo refrigerator according to claim 7,
The surging detection method for a turbo chiller, wherein the current change rate is detected by a current value ratio or a difference of operating currents of the electric motor measured at specified time intervals. The surging detection method for a turbo refrigerator according to claim 7,
The surging detection method for a turbo chiller, wherein the current change rate is detected by a ratio or difference between a maximum value and a minimum value of the operating current of the motor detected within a specified time. The surging detection method for a turbo refrigerator according to claim 7,
A surging detection method for a turbo chiller, characterized in that the current change rate is detected by a ratio or difference between a start point of an increase or decrease in operating current of the electric motor and a current value at the end point of increase or decrease.

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