Method and apparatus for measuring the impedance of a line

• US 3,904,859 A
• Filed: 09/24/1973
• Issued: 09/09/1975
• Est. Priority Date: 09/29/1972
• Status: Expired due to Term

• Current Assignee: Robert Poncelet
• Original Assignee: Robert Poncelet
• Inventors: Poncelet, Robert
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US05/399,845
• Time in Patent Office: 715 Days
• Field of Search: 235/151.3,31,180 324/57R 317/23,27R
• US Class Current: 702/65
• CPC Class Codes: G01R 27/16 Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
• CPC Class Codes: G01R 31/08 Locating faults in cables, transmission lines, or networks
• CPC Class Codes: H02H 3/40 responsive to ratio of voltage and current
• CPC Class Codes: H04B 3/46 Monitoring; Testing

Abstract

A method and apparatus for measuring the impedance of a line in which the resistive and inductive component of line impedance are determined from measured instantaneous values of voltage, current and the rate of current change using a digital computing circuit.

Claims

1. a third adder;

2. Apparatus for computing the impedence of a line for use in a system protective device comprising:

a. means for providing a first output signal proportional to the line voltage;

b. means for providing a second output signal proportional to the line current;

c. first means for sampling and storing said first output signal at first time interval;

d. second means for sampling and storing a plurality of instantaneous values of said second output signal during said first time interval;

e. first means for computing a mean current from said plurality of instantaneous values;

f. second means for computing from said instantaneous values a first current rate of change corresponding to the current rate of change during said first time interval;

g. third means for sampling and storing said first output signal at a second time interval;

h. fourth means for sampling and storing a plurality of instantaneous values of said second output signal during said second time interval;

i. third means for computing from said plurality of instantaneous values a mean value of current during said second time interval;

j. fourth means for computing from said plurality of instantaneous values the current of rate change during said second time interval;

k. means to sequentially operate said first, second, third and fourth means for sampling and storing and said first, second, third and fourth computing means;

l. a first multiplier having as inputs the output of said fourth means for sampling and storing and said fourth means for computing and providing as an output a first product;

m. a second multiplier having as inputs the output of third means for sampling and storing and said second means for computing and providing as an output a second product;

n. a third multiplier having as inputs the output of said third means for sampling and storing and said fourth means for computing and providing as an output a third product;

o. a fourth multiplier having as inputs the output of said third means for computing and said second means for computing and providing as an output a fourth product;

p. a fifth multiplier having as inputs the output of said third means for sampling and storing and the output of said first means for computing and providing as an output a fifth product;

q. a sixth multiplier having as inputs the output of said first means for sampling and storing and the output of said third means for computing and providing as an output a sixth product;

r. a first substractor having as inputs said first and second products and providing as an output the difference therebetween as a first intermediate value;

s. a second substractor having as inputs said third and fourth products and providing the difference therebetween as a second intermediate value;

t. a third subtractor having as inputs said fifth and sixth products and providing as a third intermediate value the difference therebetween;

u. a first divider having as inputs said third intermediate value and said first intermediate value and providing as an output said first intermediate value divided by said third intermediate value, said output representing the resistive component of line impedance;

v. a secoNd divider having as inputs said third intermediate value and said second intermediate value and providing an output which is said second intermediate value divided by said third intermediate value, said output representing the inductive component of said line impedance;

w. first storage means coupled to the output of said first dividing means for storing said resistive component; and

x. second storage means coupled to the output of said second dividing means for storing said inductive component.

3. means coupling the output of said fourth subtractor to said fourth output storage means;

j. said third means for computing comprises;

4. means coupling said fourth and sixth voltage storage means to said first adder and said second voltage means to said ninth multiplier;

5. fifth output storage means;

and

6. second output storage means;

and

7. means coupling the output of said tenth multiplier to said second output storage means;

f. said fourth means for sampling and storing comprises fourth, fifth and sixth current storage means;

g. said means to sequentially operate said first, second, third and fourth means comprises means for sequentially coupling said voltage and current transformer to the respective ones of said voltage and current storage means at uniform time intervals;

h. said first means for computing comprises;