Method for monitoring of tap changers by acoustic analysis

• US 6,157,196 A
• Filed: 11/12/1998
• Issued: 12/05/2000
• Est. Priority Date: 03/11/1996
• Status: Expired due to Term

• Current Assignee: ABB Research Ltd. (ABB Ltd.)
• Original Assignee: ABB Research Ltd. (ABB Ltd.)
• Inventors: Bengtsson, Tord, Martinsson, Lars, Kols, H.ang.kan
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): DEB, ANJAN K
• Application Number:
  US09/142,379
• Time in Patent Office: 754 Days
• Field of Search: 324/536, 324/547, 324/127, 324/726, 324/76.38, 324/420, 73/584, 73/587, 340/646, 340/635, 702/115, 702/183, 702/48, 702/76, 702/199, 381/56, 327/420
• US Class Current: 324/420
• CPC Class Codes: G01R 31/3274 Details related to measuring, e.g. sensing, displaying or computing; Measuring of variables related to the contact pieces, e.g. wear, position or resistance measuring contact resistance G01R27/205
• CPC Class Codes: G01R 31/3275 Fault detection or status indication
• CPC Class Codes: G05F 1/14 using tap transformers or tap changing inductors as final control devices
• CPC Class Codes: H01H 2009/0061 Monitoring tap change switching devices

Abstract

A method for monitoring an on-load tap changer wherein the recording of sound and its conversion into a sound signal are initiated at the beginning of a connection operation of the tap changer and the sound signal is rectified, converted into a signal envelope, sampled digitally and continuously evaluated with respect to the condition of the tap changer by comparing the envelope with at least one fixed or one continuously updated reference envelope. The comparison is carried out selectively by calculating a dimensionless comparison figure T_i which is based on a quantity measure and a variation measure.

Claims

1. A method for monitoring an on-load tap changer, comprising:

initiating recording of sound and conversion of the sound into a sound signal at a beginning of a connection operation of the tap changer;

rectifying the sound signal;

converting the sound signal into a signal envelope;

digitally sampling the sound signal;

continuously evaluating the sound signal with respect to a condition of the tap changer by comparing the envelope with at least one fixed or one continuously updated reference envelope, wherein the comparison is selectively carried out by calculating, at each sample point with index I, a dimensionless comparison figure T_i that is based on a quantity measure and a variation measure, where the quantity measure and the variation measure relate to a statistical distribution; and

releasing an alarm or a warning when the comparison figure T_i for one or more sample points exceeds a predetermined value.

2. The method according to claim 1, wherein the dimensionless comparison figure T_i is calculated according to T_i =|(S_i -M_i)/s_i |, where S_i is a current sample with index i, M_i is a arithmetic mean value with index i and s_i is the standard deviation with index i for a last N₀ recorded sample values.

3. The method according to claim 1, wherein the dimensionless comparison figure T_i is calculated according to T_i =|(Sl_i -Ml_i)/sl_i |, where Sl_i is the natural logarithm of a current sample with index i, Ml_i is a arithmetic mean value with index i and sl_i is a standard deviation with index i for logarithms of a last N₀ sample values.

4. A method according to claim 3, wherein the dimensionless comparison figure T_i is limited by an upper limit value T_x according to T_i =min (T_i, T_x).

5. The method according to claim 2, wherein in that a running mean value Tm_i is formed from the last number N_t of dimensional comparison figures T_i and that this running mean value Tm_i is used as a dimensionless comparison figure.

6. The method according to claim 5, wherein in that the number N_t is chosen so as to correspond to a time between 3 and 20 milliseconds.

7. The method according to claim 2, wherein the number of N₀ lies between 3 and 30.

8. The method according to claim 1, wherein a sampling frequency of the signal envelope lies between 0.1 and 100 kHz.