Uncovering Generator Failures: The Power of Partial Discharges (PD)

Table of Contents:

1. Introduction
2. Case Study 1: Generator with Sudden Change in Partial Discharge
   • Background
   • Routine Testing and Monitoring
   • Sudden Change in PD Levels
   • Machine Failure
3. Case Study 2: Generator with Dangerous Partial Discharge
   • Maintenance and Inspection
   • Offline Partial Discharge Measurement
   • Commercial vs Technical Aspect
   • Live View PDA2 Monitoring System
4. Analysis of Case Studies
   • Impact of Partial Discharge on Machines
   • Importance of Information and Online Monitoring
5. Conclusion
6. FAQ

Introduction

Partial discharge monitoring is essential for maintaining the performance and reliability of high voltage machines such as generators and motors. Over the past 35 years, Quartz Tech in Switzerland has built a strong expertise in this field. In this article, we will explore two case studies that highlight the importance of proper monitoring, interpretation of results, and preventive measures to avoid machine failure.

Case Study 1: Generator with Sudden Change in Partial Discharge

Background

In this case study, we examine a generator rated at 11 kilovolts, which had been running for several years. The power station operators performed routine tests for partial discharge and ozone monitoring every 9 to 12 months.

Routine Testing and Monitoring

The test results revealed a sudden change in PD levels over a period of just nine months. The PD value almost doubled during this time, indicating a significant increase in partial discharge activity.

Sudden Change in PD Levels

The test results showed a sudden and exponential increase in PD levels, which hinted at potential problems with the generator's insulation system. Unfortunately, the significance of this increase was not fully understood at the time.

Machine Failure

A few months later, the generator experienced a catastrophic failure, resulting in damage to both the stator insulation system and the stator core. Had the information from the PD monitoring been properly interpreted and acted upon, this failure could have been prevented.

Case Study 2: Generator with Dangerous Partial Discharge

Maintenance and Inspection

In this case study, we encounter a similar generator with a rated voltage of 11.3 kilovolts. The generator was brought to Quartz Tech's facility in rugby for maintenance of the generator rotor. During a visual inspection, engineers discovered signs of partial discharge between the stator core and the stator winding.

Offline Partial Discharge Measurement

Based on the visual inspection, the engineers recommended performing offline partial discharge measurements. The results of these measurements confirmed the presence of a dangerous partial discharge in the slot section of the generator.

Commercial vs Technical Aspect

Despite the recommendation to repair the machine before putting it back online, the operator decided to prioritize commercial reasons and proceeded to install the live view PDA2 monitoring system developed by Quartz Tech. This decision was made based on the operators' awareness of the partial discharge problems.

Live View PDA2 Monitoring System

The installation of the live view PDA2 monitoring system provided valuable insights into the PD levels of the generator. A clear change in PD values, particularly on face U, indicated an exponential increase in partial discharge activity.

Analysis of Case Studies

Partial discharges can affect almost every high voltage machine, making monitoring and preventive measures crucial. The first case study highlighted the lack of timely and accurate information, resulting in machine failure. In contrast, the second case study showcased the benefits of online monitoring systems like the live view PDA2, providing the necessary information to prevent insulation breakdown.

Conclusion

These case studies emphasize the importance of proper partial discharge monitoring, interpretation of results, and preventive measures. Timely action based on accurate information can help avoid catastrophic failures and extend the lifespan of high voltage machines.

FAQ

• Q: How often should routine tests for partial discharge and ozone monitoring be performed?

  • A: Routine tests should be conducted every 9 to 12 months to detect any changes in PD levels and identify potential problems.

• Q: What are the dangers of partial discharge in high voltage machines?

  • A: Partial discharge can lead to insulation breakdown, which can cause machine failures and damage to critical components.

• Q: How can online monitoring systems like the live view PDA2 help in preventing machine failures?

  • A: Online monitoring systems provide real-time data on PD levels, allowing operators to take timely action to prevent insulation breakdown and machine failures.