Electric measuring assembly and a method for continuously monitoring a protective-conductor resistance

Patent metadata

Field	Value
Publication number	US-11500032-B2
Application number	US-202117470536-A
Country	US
Kind code	B2
Filing date	Sep 9, 2021
Priority date	Sep 16, 2020
Publication date	Nov 15, 2022
Grant date	Nov 15, 2022

Abstract

An electric measuring assembly and a method for continuously monitoring a protective-conductor resistance of a protective-conductor connection in a power supply system having a supply station, a supply line, and an electric installation, grounded via the connection. A signal generator generates a signal alternating voltage having a measuring frequency; a first transformer encircles the connection and a first winding inductively couples the voltage into the connection so a loop current flows via first and second leakage capacitors, the active conductors, and the connection, and a second winding for the second measurement of a protective-conductor voltage; a second transformer encircles the connection and has a secondary winding capturing a protective-conductor current flowing in the connection; an evaluation unit determines a loop impedance from the protective-conductor voltage and the protective-conductor current for evaluating the real part of the loop impedance.

First claim

The invention claimed is:

1. An electric measuring assembly ( 2 ) for continuously monitoring a protective-conductor resistance (Rpe) of a protective-conductor connection (PE) in a power supply system (A) comprising a supply station (V), which comprises first leakage capacitors (C 1 , C 2 ), comprising a supply line (K), which comprises active conductors (L, N), and comprising an electric installation (E), which is grounded via the protective-conductor connection (PE) and comprises second leakage capacitors (C 3 , C 4 ) and a load (R), the electric measuring assembly ( 2 ) comprising
a signal generator ( 4 ) for generating a signal alternating voltage (Us) having a measuring frequency (fs),
a first measuring current transformer ( 6 ), which encircles the protective-conductor connection (PE) and has a first winding ( 8 ) for inductively coupling the signal alternating voltage (Us) into the protective-conductor connection (PE) so that a loop current (Is) flows via the first leakage capacitors (C 1 , C 2 ), the active conductors (L, N), the second leakage capacitors (C 3 , C 4 ) and the protective-conductor connection (PE), and has a second winding ( 10 ) for the second measurement of a protective-conductor voltage (Um), a second measuring current transformer ( 12 ), which encircles the protective-conductor connection (PE) and has a secondary winding ( 14 ) for capturing a protective-conductor current (Im) flowing in the protective-conductor connection (PE),
an evaluation unit ( 20 ) having a digital computing unit ( 28 ) for controlling the signal generator ( 4 ), for determining a loop impedance (Zm) from the protective-conductor voltage (Um) and the protective-conductor current (Im) and for evaluating the real part (Zre) of the loop impedance (Zm).

2. The electric measuring assembly ( 2 ) according to claim 1 , wherein the measuring frequency (fs) of the signal alternating voltage (Us) is in the range of 100 kHz.

3. The electric measuring assembly ( 2 ) according to claim 1 , wherein a high-pass circuit ( 22 ) for filtering the protective-conductor current (Im).

4. The electric measuring assembly ( 2 ) according to claim 1 , wherein the evaluation unit ( 20 ) comprises analog-digital converters ( 26 ) for analog-digital converting the protective-conductor voltage (Um) and the protective-conductor current (Im).

5. A method for continuously monitoring a protective-conductor resistance of a protective-conductor connection (PE) in a power supply system (A) having a supply station (V), which comprises first leakage capacitors (C 1 , C 2 ), the power supply system comprising a supply line (K), which comprises active conductors (L, N), and comprising an electric installation (E), which is grounded via protective-conductor connection (PE) and comprises second leakage capacitors (C 3 , C 4 ) and a load (R), the method comprising the following steps:
generating a signal alternating voltage (Us) having a measuring frequency (fs) by means of a signal generator ( 4 ),
inductively coupling the signal alternating voltage (Us) into the protective-conductor connection (PE) by means of a first measuring current transformer ( 6 ), which encircles the protective-conductor connection (PE) and has a first winding ( 8 ), so that a loop current (Is) flows via the first leakage capacitors (C 1 , C 2 ), the active conductors (L, N) of the supply line (K), the second leakage capacitors (C 3 , C 4 ) and the protective-conductor connection (PE),
conducting a return measurement of a protective-conductor voltage (Um) for the second time using a second winding ( 10 ) of the first measuring current transformer ( 6 ),
capturing a protective-conductor current (Im), which flows in the protective-conductor connection (PE), by means of a second measuring current transformer ( 12 ), which encircles the protective-conductor connection (PE) and has a secondary winding ( 14 ), and
controlling the signal generator ( 4 ), determining a loop impedance (Zm) from the protective-conductor voltage (Um) and the protective-conductor current (Im), and evaluating the real part (Zre) of the loop impedance (Zm) by means of a digital computing unit ( 28 ) in an evaluation unit ( 20 ) disposed in the supply station (V).

6. The method according to claim 5 , wherein the measuring frequency (fs) is in the range of 100 kHz.

7. The method according to claim 5 , wherein filtering the protective-conductor current (Im) is by means of a high-pass circuit ( 22 ).

8. The method according to claim 5 , further including analog-digital converting ( 26 ) the protective-conductor voltage (Um) and the protective-conductor current (Im).

Assignees

• Bender Gmbh & Co Kg

Inventors

• Broeckmann Eckhard
• Hackl Dieter

Classifications

• G01R27/18 Primary

  Measuring resistance to earth {, i.e. line to ground} · CPC title

• G01R31/40 Primary

  Testing power supplies (testing photovoltaic devices H02S50/10) · CPC title

• G01R15/18

  using inductive devices, e.g. transformers · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title