What to do with abnormal transformer local discharge monitoring data? Diagram analysis and fault diagnosis method

• tell the difference between what's real and what's fake: Abnormal local-amplitude monitoring data should first be ruled out interference - substation electromagnetic environment is complex, the sensor may respond to external interference signals rather than the real local-amplitude
• Multi-sensor cross validation: Signals detected by a single sensor are not sufficient to recognize a localized discharge; two or more sensors of different types have diagnostic value when they capture signals in the same time window.
• atlas comparison: Compare the PRPD map of the abnormal signal with the standard map features of typical discharge types to determine which type of discharge it belongs to and its severity.
• Trend Tracking: A single anomaly may be a transient event, but multiple, persistent anomalies signal a failure - Continuously track the trend of discharge amplitude and frequency changes

1. Common causes of data anomalies

2. Diagnostic process

2.1 The first step: rule out equipment abnormalities

Check the system self-test status - whether the sensor connection is normal or not, and whether the acquisition unit has fault alarm. Ultrasonic sensors need to check whether the coupling agent is dry or off. High-frequency current sensors need to check whether the card mounting is loose. Cable connectors and grounding are reliable.

2.2 Step 2: Analyze signal characteristics

Observe the phase distribution of the signal - is it related to the IF? The real local amplifier has a fixed phase relationship with the industrial frequency voltage, and the signal appearing randomly has a high probability of being interference. Observe the characteristic parameters of the signal - amplitude distribution, repetition rate, pulse waveform, etc.. Different types of local discharges and interference differ significantly in these characteristics.

2.3 Step 3: Multi-sensor cross validation

If only a single sensor detects a signal and the others do not respond, the probability is that it is localized interference in the vicinity of the sensor. If two or more sensors of different types capture signals of the same characteristics within the same time window, the confidence level increases substantially.

2.4 Step 4: Trend Confirmation

A single or occasional signal, no matter how strong, cannot be directly recognized as a fault. If the signal is observed for a number of consecutive detection cycles, it can only be recognized as a real local amplifier developing if the signal is present in each cycle and shows an increasing trend in amplitude or frequency.

2.5 Step 5: Develop a Response Plan

The response level is determined according to the type and severity of the local discharge: corona discharge can be included in the planned maintenance, internal discharge needs to be encrypted monitoring, discharge along the surface needs to be arranged for near-term maintenance, and suspended discharge needs to be shut down as soon as possible to deal with.

3. Typical mapping troubleshooting

3.1 Spectral signals are dense and symmetric in the positive and negative half-periods

The signal is densely distributed in both the first and third quadrants of both the positive and negative half perimeters, with moderate amplitude. Characteristics point to internal discharges - typical local discharges generated by air gaps within insulating materials. If the trend is stable you can continue to operate and monitor regularly; if the amplitude or frequency tends to increase, you should arrange for maintenance.

3.2 Spectral signals are concentrated in the region of voltage peaks

The signal is concentrated near the peaks of the industrial frequency voltage (about 90° and 270°) and has a low amplitude but high repetition rate. Characteristically points to corona discharge - usually caused by internal metal tips or sharp edges. Not harmful in the short term, but should be included in planned maintenance to check for concentrated sources of electric fields.

3.3 High-amplitude narrow-phase signals in the spectra

The signal is concentrated in a particular phase interval and the discharge amplitude is significantly higher than other signals. Characteristics point to a suspended discharge - a metal part that is not well grounded discharges with neighboring parts in an alternating electric field. This is the most dangerous type of local discharge and should be scheduled out of service for inspection and treatment as soon as possible.

4. Frequently Asked Questions FAQ

4.1 Q. What if a suspected localized signal appears on the map but the type cannot be confirmed?

A: First confirm whether it is detected by multiple sensors synchronously, and then use the automatic diagnosis function of the system to come up with a preliminary judgment first. If still not sure, send the map and data to the supplier's technical team for remote analysis. In case of serious suspicion, we can arrange power outage to do traditional local discharge test for final confirmation.

4.2 Q. How can local discharge data and oil chromatography data be jointly determined?

A: local discharge found discharge signal but oil chromatography acetylene did not rise - local discharge may be in the early stage, oil chromatography has not responded. Bureau of discharge and oil chromatography acetylene rise simultaneously - discharge has developed to a higher energy level, need to be dealt with as soon as possible. Local discharge is not abnormal, but the oil chromatography acetylene rises - there may be shielding between the discharge location and the sensor, or there are other abnormal reasons.

4.3 Q: How can external interference and real localization be distinguished on a map?

A: External interference signals usually do not have a fixed phase relationship with the IF phase and appear in different phase locations in different cycles. Real local amplifiers have a fixed phase-binding relationship with the IF voltage, appearing in the same or similar phase intervals over a number of consecutive cycles.

4.4 Q. What does the rate of increase in the trend of local-radio signals mean?

A: Slow steady growth (months to years) is usually indicative of progressive aging of insulation. Rapidly accelerating increases (weeks to months) may indicate that localized defects are rapidly expanding. A sudden change to a high amplitude signal often indicates that a new structural problem has occurred (e.g., suspended discharge due to mechanical loosening) and requires immediate attention.

4.5 Q: Do I have to shut down the operation if the local discharge data is abnormal but the oil color spectrum and temperature are normal?

A: Immediate shutdown is not necessarily required, but you should go into encrypted monitoring mode. Localization is usually the earliest of the three monitoring tools to respond. Just because the oil color spectrum and temperature haven't responded yet doesn't mean there is no fault, it may just be that the fault is still in the early stages. Decide by trending - if the local discharge signal is increasing at an accelerated rate, consider scheduling an overhaul even if oil chromatography and temperature are not yet responding.

Disclaimer: The content of this article is for technical exchanges and reference only, and does not constitute any form of procurement commitment or contract offer. Product technical parameters, configuration programs and prices are subject to the actual signed contracts and technical agreements. The technical data and cases involved in this article are from public information and engineering practice, if updated without notice.

Transformer local discharge monitoring data abnormalities need professional diagnosis? Welcome to contact INNOTEC for graphical interpretation and troubleshooting technical support. Service hotline: 13959168359 (micro letter with number).