Redundant, dedicated variable speed drive system

Pumps – Condition responsive control of pump drive motor – Plural pumps having separate drive motors – supply sources,...

Reexamination Certificate

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Details

C417S005000, C417S017000, C417S028000

Reexamination Certificate

active

06257833

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to variable speed pump drive systems. More particularly, the invention pertains to such systems wherein a variable speed drive system is coupled to each pump.
BACKGROUND OF THE INVENTION
Multiple pump fluid delivery systems which incorporate a variable speed drive system, switchable between pumps are known. One such system is disclosed in Potter U.S. Pat. No. 5,522,707 entitled “Variable Frequency Drive System for Fluid Delivery System” assigned to the assignee hereof. The disclosure of the Potter patent is hereby incorporated by reference. The benefits of combining pumps being driven at constant speed with one being driven by a variable speed drive are known.
While useful for their intended purpose, known systems suffer from a lack of redundancy with respect to the variable speed drive. In such systems, in the event of a failure in the variable speed drive, all of the pumps must be run at constant speed and the respective pressure regulator valves relied on to deliver fluid at the preset pressure. This is a less energy efficient mode of operation.
For reasons of energy efficieny, it would be desirable, in the event of a failure of a variable speed drive, to be able to continue, in some way to vary the speed of at least some of the pumps. Preferably such functionality could be incorporated into multiple pump systems to provide both redundancy and operational flexibility.
Additionally, multiple pump fluid delivery systems which incorporate multiple variable frequency drive systems and by-pass constant-speed contactors, each dedicated to a particular pump on the system are known. The benefits of combining pumps, each being driven by an independent variable speed drive and by-pass constant-speed contactor are also known. These known systems do not incorporate pressure regulator valves to permit a preselected output pressure to be maintained.
While useful for their intended purpose, known systems suffer from a lack of redundancy with respect to the variable frequency drive. In such systems, in the event of a failure of one of the variable frequency drives, the pump with the failed drive must operate at constant-speed, and because there is no pressure regulating valve, there is then no means of delivery of the pumped fluid at the preset pressure.
It would be desirable, in the event of a variable speed drive failure, to be able in some way to run the pump with the variable speed drive failure in the constant-speed mode, while continuing to deliver the pumped fluid at the preset pressure. Preferably such functionality could be incorporated into multiple pump systems to provide both redundancy and operational flexibility.
SUMMARY OF THE INVENTION
A multi-pump control system includes a plurality of pump modules. Each module includes a variable speed drive and a constant speed drive coupled to a pump. Each module includes a pressure regulating valve which can be disabled by a remotely generated control signal which allows the variable speed drive to operate correctly and efficiently.
The use of standardized modules promotes ease of expansion while at the same time it reduces manufacturing and maintenance overhead.
A control unit is coupled to all of the modules. The control unit also receives output pressure feedback. In response to demand, the control unit actuates one or more of the pumps to provide fluid on demand at a preset pressure.
To minimize wear, the control unit can assign a lead pump function to available pumps on a rotating basis. Each pump can be driven by either the respective variable speed drive or the respective constant speed drive depending on its currently assigned function. Variable speed is preferable. Constant speed operation is intended to be for standby operation.
In the event that the respective variable speed drive fails, that pump can be driven using the constant speed drive. The remaining pumps can be driven by their respective variable speed drives. This redundancy provides continued flexibility and makes possible continued variable response to fluid demand. As a result, in an n pump system, (n−1) variable speed drives can fail, and the system will be able to function with a combination of variable speed and constant speed drives.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.


REFERENCES:
patent: 3511579 (1970-05-01), Gray et al.
patent: 4527681 (1985-07-01), Sommer
patent: 5120201 (1992-06-01), Tuckey et al.
patent: 5522707 (1996-06-01), Potter
patent: 60-263771-A (1985-12-01), None
patent: 63-302199-A (1988-12-01), None
patent: 08-200232-A (1996-08-01), None

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