Fast distance protection for energy supply networks

• US 9,478,968 B2
• Filed: 07/09/2010
• Issued: 10/25/2016
• Est. Priority Date: 07/09/2010
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Blumschein, Joerg, Dzienis, Cezary, Kereit, Matthias
• Primary Examiner(s): Gami, Tejal
• Application Number:
  US13/809,086
• Publication Number:
  US 20130107405A1
• Time in Patent Office: 2,300 Days
• Field of Search: 361/79, 702/58
• US Class Current: 1/1
• CPC Class Codes: G01R 31/085 in power transmission or distribution lines, e.g. overhead
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: H02H 1/0092 concerning the data processing means, e.g. expert systems, neural networks
• CPC Class Codes: H02H 7/26 Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured locating faults in cables G01R31/08

Abstract

A method for detecting a short circuit on a multiphase electrical energy supply network line includes recording current and voltage sampled values and generating a fault signal upon a fault evaluation performed by an electrical protection device indicating a short circuit. Instantaneous reference voltage values are calculated from instantaneous current and voltage sampled values recorded before the short, and instantaneous comparative voltage values are calculated from instantaneous current and voltage sampled values recorded before the short and instantaneous current and voltage sampled values recorded during the short, to generate a fault signal quickly. Then a rectified reference voltage value is calculated from consecutive instantaneous reference voltage values, and a rectified comparative voltage value is calculated from consecutive instantaneous comparative voltage values. The fault signal is generated if a difference between rectified comparative voltage and rectified reference voltage values exceeds a triggering threshold value. A corresponding electrical protection device is provided.

Claims

1. A method for detecting a short circuit on a line of a multi-phase electrical energy supply network with grounded neutral, the method comprising the following steps:

recording current and voltage sampled values at a measurement point at one end of the monitored line by an electrical protection device;

generating a first fault signal indicating a short circuit on the line if a fault evaluation of the current and voltage sampled values performed by the electrical protection device indicates a short circuit present on the line; and

performing the following steps for fault evaluation of the current and voltage sampled values;

calculating instantaneous reference voltage values for a reference point on the line from instantaneous current and voltage sampled values recorded before an occurrence of the short circuit;

calculating instantaneous comparative voltage values for the reference point on the line from instantaneous current and voltage sampled values recorded before the occurrence of the short circuit and instantaneous current and voltage sampled values recorded during the short circuit;

calculating a rectified reference voltage value from consecutive instantaneous reference voltage values and a rectified comparative voltage value from consecutive instantaneous comparative voltage values;

comparing the rectified reference voltage value and the rectified comparative voltage value;

generating the first fault signal if a difference between the equivalent comparative voltage value and the rectified reference voltage value exceeds a triggering threshold value; and

calculating the rectified reference voltage value by the following equation;

U ref (n)=2 Nk=n−

(N2−

1)n(u ref (k)) ##EQU00011## where U.sub.ref(n);

rectified reference voltage value;

u.sub.ref(k);

instantaneous reference voltage value for the sampled value k;

n;

number of the sampled value after fault occurrence;

N;

number of sampled values per period;

k;

summation index; and

calculating a rectified comparative voltage value in accordance with the following equation;

UV(n)=2Nk=n−

(N2−

1) n(uV(k)) ##EQU00012## where U.sub.v(n);

rectified comparative voltage value;

u.sub.v(k);

instantaneous comparative voltage value for the sampled value k;

n;

number of the sampled value after fault occurrence;

N;

number of sampled values per period; and

k;

summation index.

2. The method according to claim 1, which further comprises calculating the instantaneous reference voltage values by the following equation:

3. The method according to claim 1, which further comprises calculating the instantaneous comparative voltage values by the following equation:

4. The method according to claim 3, which further comprises establishing the instantaneous delta voltage values by the following equation:

Δ

u_f(n)=u(n)−

u_p(n)

where

Δ

u_f(n);

instantaneous delta voltage value after fault occurrence;

u(n);

instantaneous voltage sampled value after fault occurrence;

u_p(n)=u(n−

N);

pre-fault voltage sampled value, a period before the instantaneous voltage sampled value u(n);

n;

number of the sampled value after fault occurrence;

N;

number of the sampled values per period; and

establishing instantaneous delta current values by the following equation;

Δ

i_f(n)=i(n)−

i_p(n)

where

Δ

i_f(n);

instantaneous delta current value after fault occurrence;

i(n);

instantaneous current sampled value after fault occurrence;

i_p(n)=i(n−

N);

pre-fault current sampled value a period before the instantaneous current sampled value i(n);

n;

number of the sampled value after fault occurrence; and

N;

number of the sampled values per period.

5. The method according to claim 1, which further comprises using an end of a monitoring zone on the line monitored by the protection device as the reference point.

6. The method according to claim 1, which further comprises:

detecting a start of a short circuit with the protection device when the recorded current sampled values have a current jump exceeding a jump threshold value;

generating a first initiation signal upon the protection device detecting a start of a short circuit; and

only starting the fault evaluation of the current and voltage sampled values with the protection device once the first initiation signal is present.

7. The method according to claim 6, which further comprises:

upon the presence of a first initiation signal, first examining the current and voltage sampled values with the protection device to establish which phase conductor of the line is affected by the short circuit;

generating a second initiation signal indicating at least one phase conductor affected by the short circuit; and

performing the fault evaluation with the protection device merely with regard to the at least one phase conductor indicated by the second initiation signal.

8. The method according to claim 1, which further comprises dynamically determining the triggering threshold value in such a way that a value of the triggering threshold value decreases at least in steps with an increasing number of the current and voltage sampled values used to calculate the rectified comparative voltage value.

9. The method according to claim 1, which further comprises:

additionally using the instantaneous current and voltage sampled values to calculate a complex impedance value of the line monitored by the protection device; and

generating a second fault signal indicating a short circuit on the line with the protection device if the complex impedance value lies within a predefined triggering area in a complex plane.

10. The method according to claim 9, which further comprises generating a trigger signal with the protection device as soon as the first or the second fault signal is present, to trigger a power circuit breaker defining the line.

11. A protection device for monitoring a line of a multi-phase electrical energy supply network with grounded neutral for short circuits occurring on the line, the protection device configured to perform the method steps according to claim 1.