Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Utility Patent
1999-04-09
2001-01-02
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C361S027000, C361S103000, C361S106000
Utility Patent
active
06169648
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electric motors and more particularly to systems for protecting such motors from adverse conditions such as over-temperature of the windings.
BACKGROUND OF THE INVENTION
Electronic motor protection systems have been in wide use for a number of years. Typically, such systems have temperature sensors, such as positive temperature coefficient of resistivity (PTC) thermistors embedded in the windings of a motor to be protected with the thermistors electrically connected to a circuit which is arranged to de-energize the motor whenever a winding heats up to a selected level, occasioned by overcurrent or the like, thereby causing the PTC thermistors to go into a high resistance state. A system of this type is the subject of U.S. Pat. No. 4,281,358, assigned to the assignee of the instant invention. This system employs a transformer for an isolated power supply with different transformers used for different input voltage levels such as 115 and 240 volts. Subsequently a new electronic circuit, the subject of U.S. Pat. No. 5,585,990 also assigned to the assignee of the present invention, was developed which employs an integrated power supply in which an integrated circuit reduces the voltage to a selected level, e.g., 24 volts, providing a lower cost circuit, however, in some applications, particularly in some parts of the world where step down transformers to attenuate line voltage are not used and where power is connected across a phase to neutral, the IC power supply is vulnerable to transients, electrical noise and the like thereby resulting in premature failure in some cases.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved motor protection system which is low in cost yet robust in design, one in which the temperature sensors are electrically isolated from line voltage and one in which there is greater commonality in parts among all voltage ratings, without the need for jumpers or additional circuit connections.
Briefly, in accordance with the invention, an electronic motor protection system employs temperature responsive thermistors, i.e., sensors, which are adapted to be embedded into respective windings of a motor. An electrical signal is fed from the sensors to a comparator circuit which controls the energization of a transistor switch serially connected to the coil of a low current relay which in turn controls the energization of a contactor which switches current to the motor being protected. According to a feature of the invention, a transformer is used to provide an isolated power supply which is compatible with either 120 or 240 VAC input voltage. In one embodiment, line voltage is inputted to a transformer and the combination of a zener follower network and a series regulation network are used to simultaneously provide independent DC voltage supply levels for control circuitry, thereby allowing for logic operation and voltage detection over a wide range of input AC voltage. According to a second embodiment, line voltage is input to a dual-primary transformer whose coil orientation is controlled by a double pole, double throw relay which switches the primary from a 240 volt series connection to a parallel connection when exposed to 120 VAC line input. The relay is controlled on the secondary side of the transformer by a comparator circuit. On the secondary side, after the transformer, a full wave bridge is followed by a simple regulation arrangement, such as a zener follower regulation network, to provide DC voltage to the logic circuitry. According to a feature of the invention, the protection system includes comparator circuits to detect whenever the AC input voltage drops a selected amount below nominal and thereupon turn off the output relay. According to another feature, a dead-band voltage range is provided between the 120 and 240 VAC modes of operation so that when in the dead-band voltage range the output relay contacts will not close to thereby prevent the possibility of excessive voltage being applied to 120 volt motors. According to yet another feature of the invention, an adjustment circuit is provided to compensate for the change in load conditions whenever the output relay is de-energized to thereby stabilize current in the circuit.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 4281358 (1981-07-01), Plouffe et al.
patent: 5548464 (1996-08-01), Manning
Denvir Kerry J.
Nield, Jr. Joseph G.
Baumann Russell E.
Jackson Stephen W.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
LandOfFree
Electronic motor protection system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electronic motor protection system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electronic motor protection system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2469451