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Medium Voltage Bus and Switchgear

Partial Discharge Monitoring for smart Predictive Maintenance

Minimize the risk of In Service Failure

During the last few decades, maintenance professionals have grown to appreciate the importance of monitoring medium voltage (4kV to 28kV) metal enclosed bus. Espite best efforts by manufacturers in the design of bus for indoor & outdoor applications, particularly in industrial enviroments, switchgear are not immune to the aging and degradation mechanisms. Documented failures indicate that they are most often a consequence of electrical tracking between phases or phase-to-ground, and across non-metalic insulating components used to support the bus. The failure process involves contaminants (pollution) and moisture ( high humidity). The partly conductive material over the insulation results in the flow of capacitive currents that lead to discharges, and subsequently the carbonization of the organic materials over the insulation results in the flow of capacitive currents that lead to discharges, and subsequently the carbonization of the organic materials of the contaminants. Furthermore, poorly cast current transformers (CTs) and potential transformers (PTs) may have internal insulation voids. These voids result in partial discharge PD) activity that will eventually bore a hole through the insulation and result in a failure to ground.

 

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Product Description

Improve your preventative Time Based) maintenance practices 

Partial discharges (PD) are symptoms of the developing tracking problems, and of the degrading CTs and PTs on the bus rated 4kV and above. PD creates small current pulses, which identify the extent and the nature of the developing problem. Although detection of PD is not a challenge in itself electrical noise might lead to false indications that are critical to the successful diagnosis of the condition of an insulation system. By employing various noise separation tools, Iris Power has been at the forefront of developing on-line PD monitoring systems (instrumentation software and knowledge-base). Periodic measurements (and/or continuous monitors) allow the user to determine if the bus is in need of maintenance and therefore avoid in service failure, the bus should have no detectable PD activity.

Include your Switchgear in your predictive maintenance program

Traditional off-line methods of monitoring switchgear for PD activity required considerable financial resources e.g. an expert to perform the measurement and scheduled outages). The techniques developed by Iris Power for motor and generator PD monitoring have now been extended to provide cost effective and reliable monitoring systems for metal clad switchgear and bus. The advantages to a maintenance department seeking to enhance reliability are as follows:

  • Low testing costs. Once the sensors are installed, plant personnel perform periodic measurements during normal operation. In the case of a continuous monitor, the alarm levels are set to provide a warning of increasing PD activity.
  • Iris Power can provide support to assist in the installation and calibration of systems if requested and help reduce the cost of your planned corrective action, by identifying the section(s) of the switchgear or bus duct that are at risk.
  • Trending of data and support with interpretation from Iris Power, ensures timely and planned interventions and hence minimize related maintenance costs.
  • The instrumentation and hardware required to perform on-line PD testing on large rotating machines (i.e. motors and generators) is compatible with that required for bus monitoring.

Hence owners of the Iris Power TGA-B technology will benefit by applying the same test equipment and procedures to bus monitoring, therefore extending the benefits of their investment.

Periodic partial discharge monitoring

As PD pulses propagate away from the deflect in all directions along the high voltage bus, they are detected by the capacitive couplers. The sensors are strategically located in various sections of the switchgear, and if at least 2 couplers are installed per phase as shown in Figure1. (Refer to brochure), the analysis of PD signals will provide the approximate location of the problem. The sensors installed on each phase are compact poxy Mica Cpacitors EMCs) that block the high voltage and detect the characteristic high frequency PD pulses. The net result is that the measurement allows the user to isolate the origin of PD to a specific location. Furthermore, this diredtional layout and measurement technique helps to separate pulses external to the monitored section of the bus, which may be harmless noise.

Figure 1. (Refer to brochure)

The characteristics of PD pulses recorded by the portable TGA-B  instrument provide the user with results that are trendable over time. The key parameters relevant to the predictive maintenance effort include the rates of increase of the largest magnitude pulses (Qm) and the changes in overall PD activitiy (NQN). Iris provides basic interpretationtraining for clients interested in enhancing their knowledge of PD as a symptom of problems in insulation systems.

Continuous atrial Discharge Monitoring

As an alternative to periodic monitoring, Iris Power offers continuous monitors that take multiple measurements during each hour, and trend the key parameters of PD activity (Qm and NQN). He monitor can be installed at any time after the commissioning of the sensors and helps to minimize the effort of datacollection and trending.

The benefits include:

  • Continuous / Remote PD Monitoring
  • Maximise collection of PD activity
  • Maximise warning of pending problems
  • Create a smoother trend curve (i.e. more data points)
  • Same PD detection/noise separation system as the TGA-B
  • Flexible communication for remote operation and date storage

Implement an online partial discharge diagnostic system

As a user, you have the opportunity to decide on the level of support required from Iris Power.

  • Once the sensors are installed you can choose to have iris power perform a periodic on-site visit to perform the measurement and provide you with a report on the condition of your bus.
  • If you own a TGA –B instrument, or choose to rent periodically, we can train your maintenance personnel to perform the measurements.
  • You can forward the results to Iris Power for interpretation, or you can choose ttend specialised courses that will cover all of the practical aspects of utilising our interpretation techniques.
  • Finally, if you decide on our continuous monitoring system, you can manage trending activity internally and call on our service once PD activity triggers the pre-set alarm levels.

Irrespective of the level of resources you have available for monitoring, Iris Power professionals will be available to discuss your specific needs and recommended an action plan to enhance your maintenance practices for your medium voltage bus and switchgear.

Reduce your maintenance Expenditure

After an initial review of customer drawing of the medium voltage plant distribution system Iris Power will make a recommendation on the optimum quality and positioning of the PD detectors, and the tools to use with them.

  • Depending on the layout of your bus system you may require on e or multiple pairs of 80pF EMCs per phase (6 sensors per kit) rated up to 28kV.
  • TGA-B (requires a laptop) for periodic collection of PD data
  • PDView 3 for data analysis and reporting
  • Continuous monitor as required

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DISCLAIMER: The technical information contained herein is the result of extensive testing in the manufacturer’s laboratories. In addition any application advice given verbally, in writing or by testing corresponds to the best of our knowledge and belief. Since the use and application of any of our products lies beyond our area of control, it remains the responsibility of the user to verify the product’s suitability for their application.

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