US3912976A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Multilevel current sensing detector system for overcurrent protection of multispeed ac motors
Assignee: Detprotector Inc
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Filing: 1973-11-05
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Granted: 1975-10-14
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Expires: 1993-11-05
Abstract
Abstract The specification discloses a system for preventing current overload in a three phase dual speed motor in both low and high speed modes. The system includes current transformers for sensing the current level in each of the three phases applied to the motor. A divider network is connected to each of the current transformers. Each of the divider networks has a first configuration for converting the sensed current in the low speed mode into a proportional voltage and further includes a second configuration for converting the sensed current in the high speed mode into a proportional voltage. Circuitry is responsive to the proportional voltages generated from the divider network in both first and second configurations in order to generate an overload signal when the voltages from the divider networks exceed a predetermined magnitude. The overload signal operates a relay in order to terminate current flow through the three phases in order to protect the motor.
Inventors
- 👤 James E Sons
- 👤 Wayne C Starnes
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 20:07
CPC Classifications
H; H02; H02H; H02H7/00; H02H7/08; H02H7/085; H02H3/00; H02H3/08; H02H3/093
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
131 words
A system for protecting an alternating current phase multispeed motor for current above each of a plurality of predetermined current levels comprising: means for sensing the current level on said phase, circuitry connected in different configurations in response to different speeds of said motor for detecting the occurrence of a current level above each of said plurality of levels and for generating an electrical overload signal in response thereto, and a semiconductor switch responsive to said overload signal for terminating current flow through said phase upon detection of current level above any one of said plurality of levels, the time interval between detecting of the occurrence of a current level above said predetermined levels and the termination of current flow being inversely proportional to the magnitude of the sensed current level.
Claim 2
Independent Claim
131 words
A system for protecting an alternating current phase multispeed motor for current above each of a plurality of predetermined current levels comprising: means for sensing the current level on said phase, circuitry connected in different configurations in response to different speeds of said motor for detecting the occurrence of a current level above each of said plurality of levels and for generating an electrical overload signal in response thereto, and a semiconductor switch responsive to said overload signal for terminating current flow through said phase upon detection of current level above any one of said plurality of levels, the time interval between detecting of the occurrence of a current level above said predetermined levels and the termination of current flow being inversely proportional to the magnitude of the sensed current level.
Claim 3
Independent Claim
116 words
A system for protecting a multispeed motor in both low and high speed modes comprising: means for sensing the current on an input phase of said motor, divider circuitry operable during said low speed mode for converting the sensed current to a first voltage proportional to said sensed current, means operable during said high speed mode for varying said divider circuitry for converting the sensed current to a second proportional voltage, means responsive to both said first and second voltages for generating an electrical overload signal upon the occurrence of a voltage above a single predetermined magnitude, and means responsive to said electrical overload signal for terminating current flow to said input phase of said motor.
Claim 4
Independent Claim
116 words
A system for protecting a multispeed motor in both low and high speed modes comprising: means for sensing the current on an input phase of said motor, divider circuitry operable during said low speed mode for converting the sensed current to a first voltage proportional to said sensed current, means operable during said high speed mode for varying said divider circuitry for converting the sensed current to a second proportional voltage, means responsive to both said first and second voltages for generating an electrical overload signal upon the occurrence of a voltage above a single predetermined magnitude, and means responsive to said electrical overload signal for terminating current flow to said input phase of said motor.
Claim 5
Dependent Claim
13 words
The system of claim 2 wherein said sensing means comprises a current transformer.
Claim 6
Dependent Claim
44 words
The system of claim 2 wherein said divider circuitry includes a resistor network for converting the sensed current to said first voltage and further including means for removing a portion of said resistor network during operation of the high speed mode of said motor.
Claim 7
Dependent Claim
33 words
The system of claim 4 and further comprising: relay contacts connected across a portion of said resistor network, said contacts open during said low speed mode and closed during said high speed mode.
Claim 8
Dependent Claim
21 words
The system of claim 5 wherein said relay contacts are automatically opened and closed in response to a motor speed sensor.
Claim 9
Dependent Claim
37 words
The system of claim 2 wherein said overload signal generating means comprises: means for generating a predetermined reference voltage, and means for generating said overload signal when either said first or second voltage exceeds said reference voltage.
Claim 10
Dependent Claim
23 words
The system of claim 7 and further comprising: a normally nonconductive transistor which is rendered conductive in order to generate said overload signal.
Claim 11
Dependent Claim
37 words
The system of claim 2 wherein said means for terminating current flow comprises: a triac device which is conductive during normal operation of said system and which is rendered nonconductive by the generation of said overload signal.
Claim 12
Dependent Claim
22 words
The system of claim 9 and further comprising: a relay responsive to nonconduction of said triac device for terminating said current flow.
Claim 13
Dependent Claim
17 words
The system of claim 10 and further comprising reset means for again rendering said triac device conductive.
Claim 14
Independent Claim
114 words
A system for preventing current overload in a three phase multispeed motor in low and high speed modes comprising: means for seNsing the current level in each of said phases, a divider network connected to each of said sensing means and having a first configuration for converting the sensed current in the low speed mode into a voltage and further having a second configuration for converting the sensed current in the high speed mode into a voltage, means responsive to said voltages for generating an electrical overload signal when said voltages exceed a predetermined magnitude, and means responsive to said electrical overload signal for controlling the current flow through the phases of said motor.
Claim 15
Independent Claim
114 words
A system for preventing current overload in a three phase multispeed motor in low and high speed modes comprising: means for seNsing the current level in each of said phases, a divider network connected to each of said sensing means and having a first configuration for converting the sensed current in the low speed mode into a voltage and further having a second configuration for converting the sensed current in the high speed mode into a voltage, means responsive to said voltages for generating an electrical overload signal when said voltages exceed a predetermined magnitude, and means responsive to said electrical overload signal for controlling the current flow through the phases of said motor.
Claim 16
Dependent Claim
39 words
The system of claim 12 wherein said divider network includes a plurality of resistors, each of said resistors being connected in said first configuration and ones of said resistors being electrically removed from said network in said second configuration.
Claim 17
Dependent Claim
20 words
The system of claim 12 and further comprising a capacitor for storing the voltage appearing across each said divider network.
Claim 18
Dependent Claim
30 words
The system of claim 12 wherein said voltages from all of said divider networks are summed, and said overload signal being generated when said summed voltages exceed said predetermined magnitude.
Claim 19
Dependent Claim
26 words
The system of claim 12 wherein said means for controlling comprises: a normally conductive triac device which is rendered nonconductive in response to said overload signal.
Claim 20
Dependent Claim
32 words
The system of claim 16 and further comprising normally closed relays connected in series with each of said phases, said relays being opened in response to said triac device being rendered nonconductive.
Claim 21
Independent Claim
70 words
The method of protecting a multiple phase multispeed motor from overcurrent comprising: sensing the current level on each of said motor phases, converting each of said sensed current levels to proportional voltages with a first resistive network in a first motor speed mode and with a second resistive network in a second motor speed mode, and generating an electrical overload signal when said proportional voltages exceed a predetermined voltage level.
Claim 22
Independent Claim
70 words
The method of protecting a multiple phase multispeed motor from overcurrent comprising: sensing the current level on each of said motor phases, converting each of said sensed current levels to proportional voltages with a first resistive network in a first motor speed mode and with a second resistive network in a second motor speed mode, and generating an electrical overload signal when said proportional voltages exceed a predetermined voltage level.
Claim 23
Dependent Claim
22 words
The method of claim 18 and further comprising: terminating flow of current in said motor phases in response to said overload signal.
Claim 24
Dependent Claim
43 words
The method of claim 19 wherein said motor drives an air conditioning system and further comprising: means responsive to the ambient temperature adjacent said motor for changing the speed of said motor and for interconnecting one of said first or second resistive networks.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-10-13 | 1979-04-14 | 1979-10-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-10-13 | 1983-04-14 | 1983-10-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-10-13 | 1987-04-14 | 1987-10-14 | $7700.00 | Window Closed / Lapsed |