GISmonitor - Partial Discharge Monitoring System

Q: GISmonitor FAQ 1

Certain features set the GIS monitor apart in its abilities as a specific PD monitoring system for GIS. These differentiating features include: The unit accommodates a customised system layout for each installation The flexible system design due to frequency conversion allows a centralized structure and limits the number of acquisition units on site reducing drastically also the number of possible failure points during operation Due to the modular concept of Power Diagnostix the PDMS can be easily extended with more channels in case of extension of the GIS Advanced and dedicated software features for sensitivity verification and HV Test developed with feedbacks of on-site and commissioning engineers from GIS OEMs High levels of redundancy and self-monitoring Highest cyber security standards (hardened system, encrypted communication, user authentication, integration to superordinate systems) Continuous and parallel PD measurement on all channels, no PD pulse gets lost All PD measurement data is saved and stored through an optimized memory saving algorithm on the control cabinet. In-depth review and analysis is therefore facilitated The provided PD database for automatic recognition is extendable, therefore the system gets stronger and more efficient with every new PD pattern saved The operator has various options to interact with the PDMS, including remote access facilities, IEC61850, or web based access. More features often necessitate more hardware. When choosing between multiple PD monitoring systems for your GIS, look closely at the prospective systems' specific capabilities to ensure they are comparable.

On-line PD monitoring of gas-insulated switchgear

The GISmonitor is a fully automated, continuous on-line partial discharge (PD) monitoring system for Gas-Insulated Switchgear (GIS)

Parallel UHF PD measurement on all channels

Centralized architecture

High level of redundancy

Highly extendable

Automatic recognition of PD defect and noise separation techniques

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About the product

When it comes to Partial Discharge (PD) monitoring, Power Diagnostix’s GISmonitor is the perfect choice for the job. The main task of the GISmonitor is to provide the user with a reliable Partial Discharge Monitoring System (PDMS) capable of detecting defects hidden inside the Gas Insulated Switchgear (GIS) such as hopping particles, floating potential, cracks in insulators, protrusion or other degradation in the insulation system.
The system’s hardware has been optimised for continuous, parallel and real-time PD acquisition in order to record each signal coming from the pre-installed UHF sensors inside the GIS enclosure, no PD activity is left undetected.

The Frequency Converter Units (FCU2) pick up the UHF signal from the embedded UHF sensor and demodulates it into a lower frequency band for easy transmission over longer distances. Special Input Protection Units (IPU2B) placed at the output of the UHF sensors block strong signals, such as very fast transients (VFT), and protect the PDMS.

Each UHF sensor is connected to an acquisition cabinet (PDMAR) that process the data before sending it to the control cabinet (PDMCR): each of these acquisition units can be connected up to 120 UHF sensors. With very few acquisition cabinets, Power Diagnostix’s GISmonitor can therefore cover even the largest GIS and thanks to its modular approach it is highly extendable in case of future extension of the switchgear.

The acquired and processed data is sent through fiber optic ring network to the control unit (PDMCR) where the user can directly operate and have a complete overview of the status of the GIS. In order to ensure that a proper analysis of the measured PDs can be conducted, the GISmonitor software provides the user with a various set of features and options. Through a monitoring mode the operator can access to the historical and live analysis of years of measured data in just a click while also checking the PD event list that summarizes the most critical acquired signals. All the data is collected, stored and automatically analysed in one central server and a database for automatic recognition of particular defects is provided (ICMexpert).

Dedicated features for pre-energization activities are part of the GISmonitor software. A Sensitivity Verification mode, with CIGRE TBA 654 compliancy, reduces to a minimum the requested time for the commissioning of the PDMS and automatically generate a report for the customer. The sensible HV Test that is performed before the energization of a GIS is supported by a dedicated HV Test mode that allows the user to record PD levels and applied voltage simultaneously creating therefore a replay that can be viewed anytime: this constitutes a fingerprint of the substation at the moment of the test.

The PDMS generates and forwards alarms to the subordinated system, such as SCADA, in the exact moment as they are raised, through different interfaces such as potential-free relays or IEC61850 communication protocol.

In case the GIS to monitor is not provided with embedded UHF PD sensors, Power Diagnostix can offer also a series of accessories and external sensors optimized for retrofitting.

To receive software updates or user guides, please contact [email protected] or call +49 241 74927. Please have your device serial number ready or state your reason for interest.

FAQ / Frequently Asked Questions

Which special features or capabilities of a GISmonitor make it more suitable for detecting PD in a GIS than other PD monitoring solutions?

Certain features set the GISmonitor apart in its abilities as a specific PD monitoring system for GIS. These differentiating features include:

The unit accommodates a customised system layout for each installation
The flexible system design due to frequency conversion allows a centralized structure and limits the number of acquisition units on site reducing drastically also the number of possible failure points during operation
Due to the modular concept of Power Diagnostix the PDMS can be easily extended with more channels in case of extension of the GIS
Advanced and dedicated software features for sensitivity verification and HV Test developed with feedbacks of on-site and commissioning engineers from GIS OEMs
High levels of redundancy and self-monitoring
Highest cyber security standards (hardened system, encrypted communication, user authentication, integration to superordinate systems)
Continuous and parallel PD measurement on all channels, no PD pulse gets lost
All PD measurement data is saved and stored through an optimized memory saving algorithm on the control cabinet. In-depth review and analysis is therefore facilitated
The provided PD database for automatic recognition is extendable, therefore the system gets stronger and more efficient with every new PD pattern saved
The operator has various options to interact with the PDMS, including remote access facilities, IEC61850, or web based access.

More features often necessitate more hardware. When choosing between multiple PD monitoring systems for your GIS, look closely at the prospective systems' specific capabilities to ensure they are comparable.

What criteria should make me consider a GISmonitor over a GISmonitor Portable?

The continuous data acquisition, storage, and analysis provide a complete overview of the development of PD activity within your switchgear. You can track ageing mechanisms and evaluate the urgency of taking action based on continuous data acquisition. Furthermore, a permanent PD monitoring system provides an instant indication in case PD activity occurs. Manual measurements with a portable instrument can be weeks or months apart, possibly delaying detection after PD's inception.

What do I have to do if I have more than 120 UHF sensors to connect?

The GISmonitor is based on a scalable and modular architecture. The number of channels can be increased by adding more acquisition cards in the PDMARs and, if required, more PDMARs themselves. With this approach, systems with more than 1000 channels are possible, and a system design customised and optimised for a specific GIS can be provided.

I am relatively unexperienced in PD testing. How can I become proficient in detecting PD activity when using the GISmonitor?

The detection of the problem is done by the GISmonitor system autonomously. You will not be required to determine if there is PD activity. The software algorithm continuously analyses all measured data and detects whether PD activity is present. Regarding a deep analysis of a PD defect, our ICMexpert software comes with a database of known defects. The software automatically takes the phase resolved partial discharge (PRPD) that triggers an alarm, compares it to a database of known defects and finds the best match within our database. Accordingly, it will give you an indication of the most likely type of defect you are facing. If you want you can also store the just measured PD pattern and add it to the database itself: next time you are on site you will have one more measurement to use as a reference for the automatic recognition! In this way you can build your own database that will come in hand each time you have to perform an on-site measurement/activity.

When it comes to GIS monitoring I don’t see any measured value in pC. What am I missing?

According to the extremely important CIGRE TBA654 “UHF partial discharge detection system for GIS: application guide for sensitivity verification” document: “For the UHF method a calibration to “apparent charge in pC” is not possible due to the complex PD pulse propagation characteristics”. Therefore the measurement data is reported either in dBµV or dBm. Power Diagnostix suggests to everyone who is approaching UHF measurement on GIS for the first time to download such a document from CIGRE website.

Troubleshooting

Connection to module PDMAR is not establishing

Check that the power is on for the cabinet and make sure there is power to the plug-in board.

Connection to module PDMAR has been lost

Make sure the cabling is properly connected.
Check that the plug-in board is indicating that the initialisation is correct - green LED will be lit up if so
Reset the alarm in the GISmonitor control software

The miniature circuit breaker (MCB) has tripped

Check the cabinet for damage or visual signs of any problems. Reactivate the MCB and reset the alarm in the GISmonitor control software.

The MCB keeps tripping

You should:

Bridge out the uninterrupted power supply (UPS) on the back of the cabinet.
Measure the insulation resistance of the cabinet power supply.
Disconnect all components from their terminals until the insulation resistance is acceptable. The criterion is R > 0.2 MΩ.
If possible, reset the alarm in the GISmonitor control software (this depends on the component).
Report the affected component to Power Diagnostix.

The fibre optic (FO) ring network connection, which connects all cabinets, is open

You should:

Check that the power is on for all cabinets
Check the switches on the hat rail of the cabinets to identify the open connection
Ports 7 and 8 must show a green LED
Check the FO cabling between the affected switches
Repair the FO cable
Check the system for normal operation
Reset the alarm in the GISmonitor control software

The lightning protection has triggered

The cabinet’s overvoltage (OV) protection module has activated, and it needs replacing.

You should:

Check the cabinet for damage and adequate function
Unplug the OV protection module
Plug in a new module
Reset the alarm in the GISmonitor control software

What does the message “UPS on battery” mean?

This means the uninterrupted power supply (UPS) is using the battery, due to a missing power supply.

You should:

Check if the MCB has tripped
Measure the power supply
Check all cables to ensure the connections secure
Reset the alarm in the GISmonitor control software

The UPS is not working

You should:

Check the back of the UPS and find the thermal fuse
Reset the thermal fuse by pressing the red button
Test if the system has returned to normal functionality
Reset the alarm in the GISmonitor control software

Getting the message “Replace Battery”

This message indicates that you must replace the UPS battery.

You should:
Contact the UPS manufacturer or Power Diagnostix for a new battery and follow the manufacturer’s battery replacement instructions.

Interpreting test results

Evaluation of phase-resolved partial discharge (PRPD) patterns

The evaluation of a PRPD pattern, enables you to determine the kind of fault within the test object. Most partial discharge (PD) faults, such as insulation damages, voids, surface discharges, or floating points, will have completely different PD patterns. The typical criteria for classifying these patterns are:

Phase position of the maximum partial discharge
Phase position of the starting electron
The gradient of discharges
The shape of discharges in the positive and negative half-cycle
The absolute value of discharge in pC or nC
Short-time or continuous discharges

For successful interpretation, it is also necessary to get as much information as possible about the test object and its environment. Such information could include temperature, installation condition, age of the test object, previous faults, or weather conditions.

It is useful to store typical PD patterns of known faults in an archive. This, can be done by using the GISmonitor software in combination with Power Diagnostix’s ICMexpert software. This customer-specific database will be helpful for later evaluation on other test objects.

FAQ / Frequently Asked Questions

If a Sensitivity Verification has not been conducted, how do we know what voltage to inject from the CAL2B pulse generator?

The CIGRE TBA654 Sensitivity Verification step 1 determines the voltage that should be applied during step 2 with the same type of GIS, type of sensor, measurement instrument, and pulse generator. If we do not know that information for a particular GIS, we can rely on experience with a comparable known one: even though it is impossible to prove it is 100% correct, this can be considered an acceptable procedure by many and can give a fair performance evaluation.

Do I need to check my GISmonitor PDMS periodically?

The PDMS by Power Diagnostix includes an extensive self-monitoring functionality that will detect issues automatically. Any problem then raises a “Maintenance Request” or a “System Fault” indication to the operator. If the PDMS is integrated to any superordinate systems via one of the available interfaces, such notifications are forwarded automatically. The same works also for PD High and Low level warnings.

Do I need to test my GISmonitor system periodically?

The PDMS includes an extensive self-monitoring functionality that will detect most issues automatically. Any problem then raises a “Maintenance Request” or a “System Fault” indication to the operator. If the PDMS is integrated to any superordinate systems via one of the available interfaces, such notifications are forwarded automatically.

How do I know if I have a sufficient number of sensors on my GIS system?

The GIS manufacturer usually have a wide knowledge regarding the number and placement of their UHF PD sensors and through the years have also developed experience and know-how. Anyway, the CIGRE TBA654 “UHF partial discharge detection system for GIS: application guide for sensitivity verification” document provides further information on how to access a 5pC sensitivity on a GIS. The process consists of two steps, one in laboratory and one on-site before the HV Test: while the latter is typically done by our commissioning engineers, the former requires a close collaboration between the GIS and PDMS manufacturers.Power Diagnostix and Megger strongly suggest to read this document in order to fully understand the Sensitivity Verification process, but for the sake of simplicity we will say that the main goal of the first step is to determine the voltage amplitude output on which the CAL2B has to be set on-site to simulate a 5pC defect during the second step.