FREQUENCY MEASUREMENT APPARATUS

• US 20100010762A1
• Filed: 02/19/2007
• Published: 01/14/2010
• Est. Priority Date: 02/19/2007
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Seki, Kempei
• Granted Patent: US 8,190,387 B2
• Time in Patent Office: Days
• US Class Current: 702/75
• CPC Class Codes: G01R 19/2513 Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: G01R 29/18 Indicating phase sequence; Indicating synchronism

Abstract

The invention relates to a frequency measurement apparatus which is arranged in such a way as to obtain an amplitude, chord length and rotation phase angle of a voltage rotation vector by means of an integration method, and furthermore, obtain a change rate of the rotation phase angle, and a rotational acceleration change rate of the rotation vector, and measure a dynamic frequency by determining a frequency change rate for every step.

Claims

1. A frequency measurement apparatus, comprising:

means which calculates an amplitude, chord length and rotation phase angle of a voltage rotation vector by means of an integration method;

means which calculates a rotational acceleration of the rotation vector;

means which calculates a rotational acceleration change rate of the rotation vector;

means which calculates a frequency increment, using an increment of the rotation phase angle; and

means which calculates a dynamic frequency based on an increment between a frequency one step before and a frequency at a present time.

2. The frequency measurement apparatus according to claim 1, wherein the dynamic frequency calculation means includes:

variable acceleration coefficient calculation means, which is arranged in such a way as to introduce a variable acceleration coefficient Nf of which a value changes in accordance with the frequency change rate and, in the event that the frequency change rate is higher than or equal to a predetermined threshold value, determine it to be voltage fluctuation data, and latch the frequency while, in the event that the frequency change rate is low, reduce the variable acceleration coefficient at an initial cycle of an acceleration or a deceleration.

3. The frequency measurement apparatus according to claim 1, comprising:

static frequency calculation means which calculates a static frequency, using the rotation phase angle; and

a frequency identification means which, when the rotational acceleration change rate of the rotation vector is low, determines that there is no effect of a voltage fluctuation or the like, and matches the dynamic frequency with a static frequency measurement calculation result.

4. The frequency measurement apparatus according to claim 1, wherein the dynamic frequency is calculated from a following expression including a variable acceleration coefficient Nf:

$f<br><br>\left(t\right)=f<br><br>\left(t-T\right)+N_f·<br><br>\frac{\mathrm{\delta <br><br>}<br><br>\left(t\right)-\mathrm{\delta <br><br>}<br><br>\left(t-T\right)}{2<br><br>\mathrm{\pi <br><br>}<br><br><br><br>T}$

where f(t) is the dynamic frequency at the present time, f(t−

T) is the frequency measured one step before, δ

(t) is the rotation phase angle calculated at the present time, and δ

(t−

T) is the rotation phase angle calculated one step before.

5. The frequency measurement apparatus according to claim 2, wherein the variable acceleration coefficient Nf is a number between 0 and 1 (including 0 and 1).

6. The frequency measurement apparatus according to claim 1, comprising:

frequency moving average value calculation means which averages the dynamic frequencies, by means of a moving average method, using one cycle or more of dynamic frequency calculation results.

7. The frequency measurement apparatus according to claim 1, wherein, when the dynamic frequency measured by the dynamic frequency calculation means is higher or lower than, or equal to, the predetermined threshold value, trips a breaker CB of a power system, and implements a system protection.