Pumps – Condition responsive control of pump drive motor – Single motor control element responsive to means sensing...
Reexamination Certificate
1998-06-05
2001-04-03
Freay, Charles G. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
Single motor control element responsive to means sensing...
C019S032000, C019S044000, C019S044000
Reexamination Certificate
active
06210119
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and system for detecting reverse rotation of a compressor due to improper wiring.
Compressors are a major component in air conditioning and refrigeration systems. One popular type of compressors is a scroll compressor. In a scroll compressor, a pair of wraps interfit to define a plurality of compression chambers. One of the wraps is driven through an orbit relative to the other, and the compression chambers are reduced in volume such that they compress an entrapped fluid. Scroll compressors are designed to rotate in a forward direction for fluid compression. They are not intended to rotate in the reverse direction during normal operation.
However, if the compressor is improperly wired, or under certain operational conditions, it is possible for the compressor to operate in reverse. Scroll compressors include a motor received in a sealed compressor shell. The refrigerant leading into the compression chambers passes over the motor on its way to the compressor, cooling the motor.
During reverse rotation, little or no refrigerant is pumped through the compressor, and thus the motor can quickly overheat. At the same time, refrigerant is not driven through the compression chambers. Thus the pair of interfitting scroll wraps can also quickly overheat due to heat generated by internal friction between the fixed and orbiting wrap. If reverse rotation is permitted to continue for a long period of time, there is the possibility of damage to the scroll compressor wraps or the motor.
The prior art placed motor protection sensors or line breaks, which would cut off power to the compressor if the motor is overheated. However, this can result in continuous compressor cycling as the motor cools off and compression comes back on line. Then the motor overheats again and the compressor is cycled off.
This of course prevents the compressor from performing its duty of compressing refrigerant, and can lead to potential compressor damage due to continuous cycling. Also the compressor wraps can be damaged due to overheating before the compressor is cycled off.
For residential or commercial applications, it is sometimes possible to detect reverse rotation since it typically results in loud undesirable noise. Since the compressor in a residential or commercial application is typically near occupants, the sound may be noted and corrective measures can take place. However, in typical container refrigeration applications, such as refrigerated transport containers, the compressor and refrigerant system are not mounted near any operator who could hear the sound. Further, such systems include large fans which also generate substantial noise. This noise often masks any increase in the compressor noise.
A three phase compressor is driven by a motor receiving three phase power. Such a compressor can run in reverse, if the connections are miswired at the main power supply or at the connection to the compressor.
The problem of miswiring is especially acute if the connections must be repeatedly made. This is particularly true with three phase compressors in transport container refrigeration where electrical reconnections are frequently made thus increasing the risks of miswiring.
The present invention discloses methods and apparatus for detecting and responding to the detection of compressors running in reverse.
SUMMARY OF THE INVENTION
The present invention detects the occurrence of reverse rotation by comparing the suction and discharge of the compressor to the expected pressures. As an example, the system could look at the pressure differential between the compressor suction and compressor discharge. If the pressure differential is below a minimum value, then a control for the system can identify reverse rotation. If rotation were in the proper direction, then the pressure differential across the compressor will be much greater. Alternatively, the system may only look at the compressor discharge pressure, and determine whether the discharge pressure increases after start-up within a set period of time to a given minimum value. Again, if the pressure does not increase, drops, or stays the same then a determination can be made that the compressor must be running in reverse.
In a first embodiment, if reverse rotation is detected, the system may be shut down and/or an alarm generated. An operator then knows to correct the problem.
In a second embodiment, the system responds by switching the phase on any two of the three wires in the three-phase power supply. By switching these two wires, the system reverses the polarity of the power supply leading to the compressor. This will cause the compressor to begin running in the opposite direction. If the problem that caused the reverse rotation was a miswiring at the compressor, then this reversal may result in other three-phase components in the system connected to the power supply to start running in reverse. Often there are no other three-phase components, thus, it becomes a non-issue. If other three-phase components are present, such as three-phase fans, their operation in reverse is not as detrimental to system and component reliability as compressor operation in a reverse direction. Further, if the problem that caused the compressor to run in reverse has originated at the main power supply, this phase switching will universally correct that problem.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
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patent: 5713724 (1998-02-01), Centers et al.
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Karpman Boris
Lamb John Douglas
Lifson Alexander
Carlson & Gaskey & Olds
Carrier Corporation
Freay Charles G.
Tyler Cheryl J.
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