US4472676A — Leakage impedance measuring system including a su…

Claim 1

Independent Claim 167 words

Apparatus for measuring the magnitude of the leakage impedance (Z E tot) of an ungrounded alternating-current power supply system having a given system frequency (f N ), comprising (a) means (18) for applying between the conductors of the system and ground a measurement voltage (V M ) having a measurement frequency (f M ) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i M ) in the system which produces across the total leakage impedance a voltage drop (V EM ) that is superimposed on the system component voltage (V EN ) to produce an interference pattern having an envelope (FIG. 3); (b) detector means (A1, A2, A3) for detecting from the envelope of the interference pattern the total leakage voltage drop (V EM ); and (c) display means (38, 46, 66) connected with said detector means for displaying total impedance (Z E tot) as a function of the total leakage voltage drop.

Claim 2

Dependent Claim 167 words

Apparatus for measuring the magnitude of the leakage impedance (Z E tot) of an ungrounded alternating-current power supply system having a given system frequency (f N ), comprising (a) means (18) for applying between the conductors of the system and ground a measurement voltage (V M ) having a measurement frequency (f M ) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i M ) in the system which produces across the total leakage impedance a voltage drop (V EM ) that is superimposed on the system component voltage (V EN ) to produce an interference pattern having an envelope (FIG. 3); (b) detector means (A1, A2, A3) for detecting from the envelope of the interference pattern the total leakage voltage drop (V EM ); and (c) display means (38, 46, 66) connected with said detector means for displaying total impedance (Z E tot) as a function of the total leakage voltage drop.

Claim 3

Dependent Claim 34 words

Apparatus as defined in claim 1, wherein said detector means (A1, A3) includes rectifier means (32) and filtering means (34) for separating the total leaking impedance voltage (V EM ) from the interference pattern.

Claim 4

Dependent Claim 142 words

Apparatus as defined in claim 2, and further including (d) means (C k1 , 20; C k2 , 22) for producing signals (k 1 V E1 ; k 1 V E2 ) that are a function of the voltage components in the system conductors, respectively; (e) switch means (30) normally having a first condition connecting a first one (C k1 , 20) of said signal producing means with said detector means with said detector means, said switch means being operable to a second condition for connecting another one (C k2 , 22) of said signal producing means with said detector means; and (f) means (24, 26, 28) for operating said switch means from said first condition to said second condition when the magnitude of the voltage component of the conductor associated with said first signal producing means drops below a given value.

Claim 5

Dependent Claim 86 words

Apparatus as defined in claim 3, wherein said switch operating means comprises (1) rectifying and averaging means (24) connected with the output of said first signal conducting means for producing a mean value signal (k 1 V EN1 ) as a measure of the system voltage component in the associated conductor; (2) means (26) producing a reference voltage; and (3) threshold detector means (28) for operating said switch means to said second condition when the voltage of said mean value signal drops below said reference voltage.

Claim 6

Dependent Claim 53 words

Apparatus as defined in claim 4, wherein said power supply system is a single-phase system; and further wherein the magnitude of said reference voltage is selected in accordance with the formula: ##EQU6## where: k 1 =a constant i M =injected measurement current Z E tot min =minimum total impedance V N =system voltage.

Claim 7

Dependent Claim 53 words

Apparatus as defined in claim 4, wherein the power supply system is a three-phase system; and further wherein the magnitude of said reference voltage is selected in accordance with the formula: ##EQU7## where: k 1 =a constant i M =injected measurement current Z E tot min =minimum total impedance V N =system voltage.

Claim 8

Dependent Claim 92 words

Apparatus as defined in claim 4, wherein the rectifier means (32) of said detector means comprises (1) a diode (D 32 ) connected in series with the output of said switch means; and (2) a resistor-capacitor branch (R 32 , C 32 ) connected between the output of said diode and ground, the time constant of said resistor-capacitor branch being selected in accordance with the formula: ##EQU8## where C 32 =capacitance of capacitor C 32 R 32 =resistance of resistor R 32 f N =system voltage frequency f M =measurement voltage frequency.

Claim 9

Dependent Claim 138 words

Apparatus as defined in claim 1, wherein said measurement voltage supply means includes first switch means (S 1 ) operable to apply said measurement voltage to said system periodically; and further wherein said detector means (A2) includes (1) peak voltage detector means (40) for detecting from the interference pattern envelope the peak envelope amplitude (V E max); (2) charge storage means (42) including a pair of storage capacitors (C 2 , C 3 ) for storing voltages the maximum envelope value (V E tot) and the system voltage component (V EN ), respectively, and (3) means (44) for subtracting said maximum envelope value (V E tot) from the system voltage component (V EN ), thereby to produce the measurement voltage (V EM ) for display by said display means as a function of total impedance (Z E tot).

Claim 10

Dependent Claim 105 words

Apparatus as defined in claim 8, wherein said measurement voltage supply means includes a balanced bridge circuit connected across each conductor pair of said supply system, the arms of said bridge circuit including balanced resistor pairs (R1, R2; R3, R4), and a measurement voltage source (18) connected with said first switch means and with a measurement resistor (R M ) to define a series path connected diagonally across said bridge circuit, the junction between said measurement voltage source and said measurement resistor being connected with ground; and further including coupling means (C k , R k ) connecting said bridge circuit with said detector means.

Claim 11

Dependent Claim 62 words

Apparatus as defined in claim 9, wherein said peak voltage detector means (40) comprises a rectifying diode D connected in series with said coupling capacitor, and peak voltage capacitor (C 1 ) connected between the output of said diode and ground, whereby said peak voltage capacitor is charged to the peak value of the rectified voltage at any given point in time.

Claim 12

Dependent Claim 52 words

Apparatus as defined in claim 10, and further including a normally open capacitor discharge switch (S 2 ) connected in parallel across said peak voltage capacitor, said capacitor discharge switch being momentarily closed to discharge said peak voltage capacitor upon each operation of said first switch means from one condition to another.

Claim 13

Dependent Claim 47 words

Apparatus as defined in claim 11, and further including alternately operable third (S 3 ) and fourth (S 4 ) switches for transferring the charge from said peak voltage capacitor to said storage capacitors when said first switch means is in its closed and open conditions, respectively.

Claim 14

Dependent Claim 21 words

Apparatus as defined in claim 1, measurement voltage applying means (18) comprises a source of constant-amplitude measurement current (i M ).

Claim 15

Dependent Claim 34 words

Apparatus as defined in claim 2, and further including (d) safety circuit means (S) connected with the output of said rectifier and filter means (64) for indicating maximum possible contact current (I E max).

Claim 16

Dependent Claim 79 words

Apparatus as defined in claim 14, wherein said safety circuit means comprises (1) means including a low pass filter (70) for detecting the maximum amplitude (V E max) of the interference pattern envelope; (2) divider means (74) for determining the ratio between maximum envelope amplitude (V E max) and the measurement voltage (V EM ); (3) display means (78) for displaying the output of said divider means as an indication of maximum possible conductor contact current (I E max).

Claim 17

Dependent Claim 42 words

Apparatus as defined in claim 15, and further including (4) alarm means (82, 84) including threshold detector means (80) connected with the output of said divider means for operating an alarm when the maximum possible conductor contact current exceeds a given value.

Claim 18

Independent Claim 155 words

The method for measuring the magnitude of the leakage impedance (Z E tot) of an ungrounded alternating-current power supply system having a given system frequency (f N ), comprising the steps of (a) applying between the conductors of the system and ground a measurement voltage (V M ) having a measurement frequency (f M ) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i M ) in the system which produces across the total leakage impedance a voltage drop (V EM ) that is superimposed on the system component voltage (V EN ) to produce an interference pattern having an envelope (FIG. 3); (b) detecting from the interference pattern envelope the total leakage voltage drop (V EM ); and (c) displaying the total leakage voltage drop (Z E tot) as a function of the total leakage voltage drop (V EM ).

Claim 19

Independent Claim 155 words

The method for measuring the magnitude of the leakage impedance (Z E tot) of an ungrounded alternating-current power supply system having a given system frequency (f N ), comprising the steps of (a) applying between the conductors of the system and ground a measurement voltage (V M ) having a measurement frequency (f M ) which differs slightly from system frequency by a ratio that is other than a whole number, thereby to inject a measurement current (i M ) in the system which produces across the total leakage impedance a voltage drop (V EM ) that is superimposed on the system component voltage (V EN ) to produce an interference pattern having an envelope (FIG. 3); (b) detecting from the interference pattern envelope the total leakage voltage drop (V EM ); and (c) displaying the total leakage voltage drop (Z E tot) as a function of the total leakage voltage drop (V EM ).

Claim 20

Dependent Claim 87 words

The method as defined in claim 17, wherein said total leakage voltage drop (V EM ) is initially detected from the interference pattern envelope associated with a first system conductor (10) when the amplitude of the voltage component thereof (V EN1 ) exceeds a given value, said total leakage voltage drop (V EM ) being subsequently detected from the interference pattern envelope of a second system conductor (12) when the amplitude of the voltage component of the first conductor (V EN1 ) drops below a given value.

Claim 21

Dependent Claim 119 words

The method as defined in claim 17, wherein the measurement voltage is periodically connected with the system; and further wherein the leakage voltage drop (V EM ) is detected by storing in a first capacitor (C 2 ) a charge corresponding with the maximum amplitude (V E max) of the interference pattern envelope when the measurement voltage source is connected with the system, storing in a second capacitor (C 3 ) a charge corresponding with the system component voltage (V EN ) when the measurement voltage source is disconnected from the system, and subtracting the system component voltage (V EN ) from the maximum envelope value (V E max), thereby to produce the measurement component voltage (V EM ).

Claim 22

Dependent Claim 51 words

The method as defined in claim 17, and further including the steps of dividing the maximum amplitude (V E max) of the interference pattern envelope by the measurement component voltage (V EM ), thereby to produce a signal that is a function of maximum possible conductor contact current (I E max).

Claim 23

Dependent Claim 29 words

The method as defined in claim 20, and further including the step of actuating an alarm when the magnitude of maximum possible conductor contact current exceeds a given value.

Claim 24

Dependent Claim 18 words

The method as defined in claim 17, wherein the measurement current (i M ) has a constant amplitude.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1987-09-18	1988-03-19	1988-09-18	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1991-09-18	1992-03-19	1992-09-18	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1995-09-18	1996-03-19	1996-09-18	$7700.00	Window Closed / Lapsed

Leakage impedance measuring system including a superimposed measuring voltage having a frequency differing slightly from system frequency

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