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Detection Technology

nterference in partial discharge tests

time:2020/6/27   source:华天电力  reading:309 time

One, the source of the interference

Generalized local emission interference refers to not only the interference that enters the monitoring system with the local emission signal through the current sensor, but also the interference that affects the monitoring system itself, such as the interference caused by grounding, shielding and improper circuit processing. Field local emission interference refers to the former, which can be divided into continuous periodic interference, pulse interference and white noise. Periodic interference includes high - order harmonics, carrier - wave communication and radio communication. Pulse type interference can be divided into periodic pulse type interference and random pulse type interference. The periodic pulse interference is mainly caused by the high frequency inrush caused by the action of power electronic devices. Random pulse interference includes corona discharge on high voltage line, partial discharge from other electrical equipment, discharge from tap switch action, electric arc discharge from motor operation, suspended potential discharge from bad contact, etc. White noise includes coil heat noise, ground network noise, power supply line and various kinds of coupled noises in transformer relay protection signal lines.

Electromagnetic interference generally enters the measurement point by means of spatial direct coupling and line conduction. The interference coupling path will be different with different measurement points, and the influence on measurement will be different. The kinds and intensity of interference vary with different measuring points.

Ii. Classification of local emission interference

The interference caused by various reasons will seriously affect the partial discharge test. If these disturbances are continuous and their amplitude is essentially the same (background noise), they will reduce the effective sensitivity of the detector, i.e. the minimum visible discharge is greater than the theoretical minimum of the test circuit used. This form of interference increases with the voltage and hence the sensitivity decreases proportionally. In other cases, discharges in the test circuit with an increase in voltage may be considered to have occurred inside the test sample. Therefore, it is important to reduce the interference to a minimum and to use a detector with an actual discharge waveform display to identify spurious discharge responses from the specimen's discharge as much as possible. According to the location of the possible interference sources in the test loop, the interference sources can be divided into two types: the first type of interference has nothing to do with the external application of high pressure, and the second type of interference is only generated when high pressure is added to the loop.

The main forms of interference are as follows:

(1) Interference from the power supply may affect the measurement as long as the control part, voltage regulator and transformer are connected (no boost is needed);

(2) Interference from the ground system, usually refers to the interference deflection caused by the potential difference between different connecting points on the measuring instrument when the ground connection is not good or multiple grounding;

(3) Interference detected from other high voltage tests or electromagnetic radiation, which is caused by electromagnetic coupling of the electromagnetic field outside the circuit to the circuit, including radio frequency interference of the radio station, interference of adjacent high voltage equipment, fluorescent lamp, electric welding, arc or spark discharge;

(4) Discharge of test circuit;

(5) Contact noise caused by bad contact in test lines or samples.

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