Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1998-10-02
2001-02-06
Lefkowitz, Edward (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S649000, C318S490000, C318S729000, C361S023000
Reexamination Certificate
active
06184795
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to motor controllers, and more particularly, to a controller for a delta motor that automatically detects when the two leads of a single motor winding are connected to the supply lines for a single phase of a three phase power source.
BACKGROUND OF THE INVENTION
A delta motor system typically includes a delta motor, a three phase power source and a motor controller. During start up, delta motors often experience potentially damaging high inrush currents and starting torques. This can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. In addition, current peaks during motor startup can also cause voltage disturbances in the power supply.
Motor controllers are typically used to restrict the motor torque and reduce the high starting currents by controlling the application of voltage from the three phase power source to the delta motor. The motor controller generally includes a set of three control switches that are connected between the line voltage terminals of the three phase power source and each of the windings of the delta motor. The motor controller regulates the voltage from the three phase power source to the delta motor by selectively opening and closing the three control switches. The proper operation of the delta motor is dependent on the proper regulation of the control switches.
The motor controller's internal timing mechanisms are specifically designed to regulate the application of specific line voltages from the three phase power source to specific delta motor windings based on a predesignated wiring configuration. Conventional electrical leads are typically used to connect the delta motor windings to the control switches and to the line voltage terminals. Since the electrical leads providing connection to the delta motor terminals are not always clearly marked, mistakes in wiring the delta motor system are not uncommon.
A common wiring error where the two leads providing connection to a single winding are electrically coupled to a single line voltage terminal while the other two windings are connected in parallel across the remaining two line voltages terminals, is known as a single dead ended winding wiring configuration. In this configuration, the dead ended winding does not have any current flowing through it while the other two windings are subjected to lower motor torque and significantly higher current conditions. The lower motor torque in combination with the higher operating current can potentially damage both the delta motor and the motor controller.
Clearly it would be desirable to use a motor controller that automatically detects a single dead ended winding configuration so that the faulty wiring can be corrected prior to subjecting the delta motor and motor controller to the potentially damaging combination of low motor torque and high operating currents. The present invention seeks to achieve these objectives.
SUMMARY OF THE INVENTION
It is a principal object of this invention to provide a new and improved motor controller that automatically detects a fault condition when the two leads of a single motor winding have been connected to the supply lines of a single phase of a three phase power source. More specifically, it is an object of the invention to provide a motor controller that detects the fault condition prior to starting the delta motor so that the faulty wiring can be corrected prior to subjecting the delta motor and the motor controller to the potentially damaging combination of low motor torque and high operating currents.
An exemplary embodiment of the invention achieves the foregoing object in a motor controller for use in a motor system that includes a multiphase power source having three supply lines and a delta motor having three windings, each winding having a first lead and a second lead, where the first lead of each winding is intended for connection to a selected supply line.
The motor controller includes a plurality of switching means and an error detecting means. Each of the switching means is intended for connection between selected supply lines and the second leads of selected windings. The error detecting means is connected across each of the switching means and is operable to detect a fault condition if both the first and second leads of one of the windings are connected to a single one of the supply lines. An indicating means may be connected to the error detecting means for generating an indication in response to the fault condition.
In one embodiment, the plurality of switching means comprise solid state devices.
In another embodiment, the plurality of switching mean comprise SCRs or triacs.
In another form of the invention, the error detecting means may include a sensing means that is operably connected across each of the switching means and is operable to generate a plurality of outputs representative of the voltages across each of the switching means.
The error detecting means may also include a decoding means, connected to the sensing means, for detecting the fault condition. The decoding means identifies the fault condition if the voltages across the second and third switching means are synchronously both greater than or less than zero and the voltage across the first switching means is equal to zero; or if the voltages across the first and third switching means are synchronously both greater than or less than zero and the voltage across the second switching means is equal to zero; or if the voltage across the first and second switching means are synchronously both greater than or less than zero and the voltage across the third switching means is equal to zero.
Other objects and advantages of the invention will become apparent from the following specification taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4384243 (1983-05-01), Mskovac
patent: 5153489 (1992-10-01), Unsworth et al.
patent: 5574346 (1996-11-01), Chavan et al.
patent: 5945797 (1999-08-01), Johnson
Goins Davetta W.
Lefkowitz Edward
Siemens Energy & Automation Inc.
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