US5386183A — Method and apparatus for sensing a ground fault i…

Claim 1

Independent Claim 120 words

A method for sensing a ground fault in a motor control system including a motor coupled to at least two conductors, the method comprising the steps of: generating a first unrectified signal indicative of the current level in a first conductor; generating a second unrectified signal indicative of the current level in a second conductor; summing the first and second unrectified signals to generate an unrectified sum signal indicative of the sum of the current levels; rectifying the sum signal to produce a rectified sum signal and data representative thereof; comparing the data to a predetermined limit; and generating indicia of a ground fault in response to the data exceeding the predetermined limit for more than a predetermined time period.

Claim 2

Independent Claim 120 words

A method for sensing a ground fault in a motor control system including a motor coupled to at least two conductors, the method comprising the steps of: generating a first unrectified signal indicative of the current level in a first conductor; generating a second unrectified signal indicative of the current level in a second conductor; summing the first and second unrectified signals to generate an unrectified sum signal indicative of the sum of the current levels; rectifying the sum signal to produce a rectified sum signal and data representative thereof; comparing the data to a predetermined limit; and generating indicia of a ground fault in response to the data exceeding the predetermined limit for more than a predetermined time period.

Claim 3

Dependent Claim 26 words

The method of claim 1, further comprising the step of disengaging the motor from the conductors in response to the generation of indicia of ground fault.

Claim 4

Dependent Claim 69 words

The method of claim 2, further comprising the steps of: rectifying the first unrectified signal; rectifying the second unrectified signal; determining the greater of the first and second rectified signals; comparing the greater rectified signal to a designated trip limit; generating a trip signal upon the greater rectified signal exceeding the trip limit; and disengaging the motor from the conductors in response to the generation of a trip signal.

Claim 5

Dependent Claim 74 words

The method of claim 2, further comprising the steps of: rectifying the first unrectified signal; rectifying the second unrectified signal; comparing the rectified first and second signals to a designated trip limit; generating a trip signal upon the first rectified signal exceeding the trip limit; generating a trip signal upon the second rectified signal exceeding the trip limit; and disengaging the motor from the conductors in response to the generation of a trip signal.

Claim 6

Independent Claim 138 words

An apparatus for sensing a ground fault in a motor control system, the apparatus comprising: means for generating a first unrectified signal indicative of the current level in a first conductor coupled to the motor; means for generating a second unrectified signal indicative of the current level in a second conductor coupled to the motor; means for summing the first and second unrectified signals to generate an unrectified sum signal indicative of the sum of the current levels; means for rectifying the sum signal to produce a rectified sum signal; means for generating data representative of the rectified sum signal; means for comparing the data representative of the rectified sum signal to a predetermined limit; and means for generating indicia of a ground fault upon the data exceeding the predetermined limit for more than a predetermined time period.

Claim 7

Independent Claim 138 words

An apparatus for sensing a ground fault in a motor control system, the apparatus comprising: means for generating a first unrectified signal indicative of the current level in a first conductor coupled to the motor; means for generating a second unrectified signal indicative of the current level in a second conductor coupled to the motor; means for summing the first and second unrectified signals to generate an unrectified sum signal indicative of the sum of the current levels; means for rectifying the sum signal to produce a rectified sum signal; means for generating data representative of the rectified sum signal; means for comparing the data representative of the rectified sum signal to a predetermined limit; and means for generating indicia of a ground fault upon the data exceeding the predetermined limit for more than a predetermined time period.

Claim 8

Dependent Claim 26 words

The apparatus of claim 5, further comprising means for disengaging the motor from the conductors in response to the generation of indicia of a ground fault.

Claim 9

Dependent Claim 13 words

The apparatus of claim 5, wherein the first conductor is a neutral conductor.

Claim 10

Dependent Claim 41 words

The apparatus of claim 5, wherein the means for generating a first unrectified signal comprises a current transformer coupled to the first conductor, and the means for generating a second unrectified signal comprises a current transformer coupled to the second conductor.

Claim 11

Dependent Claim 46 words

The apparatus of claim 5, wherein the means for rectifying the sum signal comprises a first operational amplifier and a second operational amplifier, the sum signal being applied to the non-inverting input of the first operational amplifier and the inverting input of the second operational amplifier.

Claim 12

Dependent Claim 29 words

The apparatus of claim 5, wherein the means for comparing and the means for generating comprise a microprocessor including an analog-to-digital convertor to which the sum signal is applied.

Claim 13

Dependent Claim 46 words

The apparatus of claim 6, wherein the means for disengaging comprises a contactor including a pair of contacts associated with each conductor of the system, the contactor separating the contacts of each pair of contacts in response to the generation of indicia of a ground fault.

Claim 14

Dependent Claim 83 words

The apparatus of claim 6, further comprising: means for rectifying the first unrectified signal; means for rectifying the second unrectified signal; means for determining the greater of the first and second rectified signals; means for comparing the greater rectified signal to a designated trip limit; and means for generating a trip signal upon the greater rectified signal exceeding the trip limit, wherein the means for disengaging the motor, disengages the motor from the conductors in response to the generation of a trip signal.

Claim 15

Dependent Claim 88 words

The apparatus of claim 6, further comprising: means for rectifying the first unrectified signal; means for rectifying the second unrectified signal; means for comparing the rectified first and second signals to a designated trip limit; means for generating a trip signal upon the first rectified signal exceeding the trip limit; and means for generating a trip signal upon the second rectified signal exceeding the trip limit; wherein the means for disengaging the motor, disengages the motor from the conductors in response to the generation of a trip signal.

Claim 16

Dependent Claim 252 words

A motor control for sensing a ground fault in an electric motor coupled to a three phase system, comprising: a first current transformer disposed to generate an unrectified first voltage substantially proportional to the current level in a first phase; a second current transformer disposed to generate an unrectified second voltage substantially proportional to the current level in a second phase; a third current transformer disposed to generate an unrectified third voltage substantially proportional to the current level in a third phase; means for generating, from the first, second and third unrectified signals, an unrectified sum signal indicative of the sum of the current levels; means for rectifying the sum signal so as to produce a rectified sum signal; means for generating data representative of the rectified sum signal; means for storing data representative of a sum limit and data representative of a predetermined time period; means for comparing the data representative of the rectified sum signal to the data representative of the sum; and means for generating indicia of a ground fault upon the data representative of the rectified sum signal exceeding the data representative of the sum for more than the predetermined time period as defined by the data representative of the predetermined time period; means responsive to a control signal applied thereto, for selectively engaging and disengaging the motor from the first, second and third phases; and means, responsive to the generation of indicia of a ground fault, for applying a control signal to the means for selectively engaging.

Claim 17

Dependent Claim 252 words

A motor control for sensing a ground fault in an electric motor coupled to a three phase system, comprising: a first current transformer disposed to generate an unrectified first voltage substantially proportional to the current level in a first phase; a second current transformer disposed to generate an unrectified second voltage substantially proportional to the current level in a second phase; a third current transformer disposed to generate an unrectified third voltage substantially proportional to the current level in a third phase; means for generating, from the first, second and third unrectified signals, an unrectified sum signal indicative of the sum of the current levels; means for rectifying the sum signal so as to produce a rectified sum signal; means for generating data representative of the rectified sum signal; means for storing data representative of a sum limit and data representative of a predetermined time period; means for comparing the data representative of the rectified sum signal to the data representative of the sum; and means for generating indicia of a ground fault upon the data representative of the rectified sum signal exceeding the data representative of the sum for more than the predetermined time period as defined by the data representative of the predetermined time period; means responsive to a control signal applied thereto, for selectively engaging and disengaging the motor from the first, second and third phases; and means, responsive to the generation of indicia of a ground fault, for applying a control signal to the means for selectively engaging.

Claim 18

Dependent Claim 39 words

The apparatus of claim 14, wherein the means for disengaging comprises a contactor including a pair of contacts associated with each phase of the system, the contactor separating the contacts of each pair in response to the control signal.

Claim 19

Dependent Claim 46 words

The apparatus of claim 14, wherein the means for rectifying the sum signal comprises a first operational amplifier and a second operational amplifier, the sum signal being applied to the non-inverting input of the first operational amplifier and the inverting input of the second operational amplifier.

Claim 20

Dependent Claim 29 words

The apparatus of claim 14, wherein the means for comparing and the means for generating comprise a microprocessor including an analog-to-digital convertor to which the sum signal is applied.

Claim 21

Dependent Claim 91 words

The apparatus of claim 14, further comprising: means for rectifying the unrectified first voltage; means for rectifying the unrectified second voltage; means for rectifying the unrectified third voltage; means for determining the greater of the rectified first, second and third voltages; means for comparing the greater rectified voltage to a designated trip limit; and means for generating a trip signal upon the greater rectified signal exceeding the trip limit, wherein the means for disengaging the motor, disengages the motor from the phases in response to the generation of a trip signal.

Claim 22

Dependent Claim 111 words

The apparatus of claim 14, further comprising: means for rectifying the unrectified first voltage; means for rectifying the unrectified second voltage; means for rectifying the unrectified third voltage; means for comparing the rectified first, second and third voltages to a designated trip limit; means for generating a trip signal upon the first rectified voltage exceeding the trip limit; means for generating a trip signal upon the second rectified voltage exceeding the trip limit; and means for generating a trip signal upon the third rectified voltage exceeding the trip limit; wherein the means for disengaging the motor, disengages the motor from the phases in response to the generation of a trip signal.

Claim 23

Independent Claim 160 words

An apparatus for sensing a ground fault in a motor control system, the apparatus comprising: a plurality of current transformers, each of which is disposed to generate a signal indicative of the current level in one of a plurality of conductors; means for generating, from the signals generated by the current transformers, a sum signal indicative of the sum of the current levels in the conductors; a microprocessor coupled to the means for generating, the microprocessor being programmed to determine whether the sum signal falls within a range defined by at least one designated limit, the microprocessor further comprising means for storing data representative of a predetermined time period based upon a digital model of a motor being controlled by the motor control system; and means, coupled to the microprocessor, for generating indicia of a ground fault upon the sum signal falling outside the designated limit for more than the predetermined time period as defined by the data representative thereof.

Claim 24

Independent Claim 160 words

An apparatus for sensing a ground fault in a motor control system, the apparatus comprising: a plurality of current transformers, each of which is disposed to generate a signal indicative of the current level in one of a plurality of conductors; means for generating, from the signals generated by the current transformers, a sum signal indicative of the sum of the current levels in the conductors; a microprocessor coupled to the means for generating, the microprocessor being programmed to determine whether the sum signal falls within a range defined by at least one designated limit, the microprocessor further comprising means for storing data representative of a predetermined time period based upon a digital model of a motor being controlled by the motor control system; and means, coupled to the microprocessor, for generating indicia of a ground fault upon the sum signal falling outside the designated limit for more than the predetermined time period as defined by the data representative thereof.

Claim 25

Dependent Claim 26 words

The apparatus of claim 20 wherein the sum signal is rectified and the microprocessor is programmed to compare the sum signal to a single designated limit.

Claim 26

Dependent Claim 24 words

The method of claim 1 further comprising the step of generalizing data representative of the root mean square value of the rectified sum signal.

Claim 27

Dependent Claim 23 words

The apparatus of claim 5 further comprising means for generating data representative of the root mean square value of the rectified sum signal.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1998-01-30	1998-08-01	1999-01-31	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2002-01-30	2002-08-01	2003-01-31	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2006-01-30	2006-08-01	2007-01-31	$7700.00	Window Closed / Lapsed

Method and apparatus for sensing a ground fault in a motor control system

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