HVPD awarded international patent for VSD/VFD Partial Discharge solution

High Voltage Partial Discharge (HVPD) have been granted another international patent for our unique Partial Discharge monitoring technology – this time for our solution for monitoring Variable Speed Drive (VSD) fed rotating machines.

The latest patent, UK number: 2536989, follows the patents granted for HVPD’s Queen’s Award-winning solution for monitoring rotating machines located in hazardous gas zones and patent for our HVPD Kronos® Permanent Monitor.

We thought this was the perfect opportunity to take an in-depth look into the technology, and the challenges that HVPD had to overcome to produce our unique solution.

What is a VSD and why do we use them?

By design, most industrial motors run at a fixed speed. In Direct On Line (DOL) motors, the frequency of electrical power is fixed at 50 or 60 Hz, so only one speed is achievable. Many industrial processes require this to be more flexible.

Traditionally, for applications where varying speeds are required, manipulation of the mechanical output is undertaken to alter the performance of the motor, including the use of pulleys, hydraulics, gearboxes etc. This solution can be energy-consuming and not cost-effective and therefore detrimental to a business’ bottom line.

The same result can be achieved in a more elegant and cost-effective way by the use of a Variable Speed Drive (VSD). A VSD – also termed adjustable-frequency drive, variable frequency drive, AC drive, micro drive or inverter drive – controls the AC motor speed by varying the electrical input frequency and voltage.

In many applications, the use of VSDs can lead to a substantial reduction in energy use. Often, reducing the speed of the rotating machine can exponentially reduce the amount of energy used. For example, using a VSD to slow a fan or pump from 100% to 80% can save as much as 50% energy, as explained by ABB in this article.

The global VSD market is expected to reach $33.1bn by 2025, compared with $18.32bn in 2016, according to a study conducted by Grand View Research, Inc.,. Growing awareness and advancement of the technology, as well as the increasing global demand for energy efficiency, are likely to provide a fillip to the market.

Why is it difficult to monitor VSD motors for PD?

A primary challenge is that the pulses generated by a VSD either mask or look very similar to Partial Discharge pulses.

Pulses generated by a VSD have frequency characteristics similar to stator winding PD (a rise time between 0.05 – 2 µs). These pulses are also high in magnitude, so even a small percentage of them can greatly affect the perception regarding the insulation condition of the stator winding.

Another challenge is the frequency; the motor-line-frequency (VSD output) varies, and is different from the power frequency. This means it can be difficult to isolate, and to use as a trigger to synchronise the on-line Partial Discharge acquisition process.

About HVPD’s VSD Solution

High Voltage Partial Discharge (HVPD) are the only Partial Discharge experts that can offer a reliable and robust VSD Partial Discharge monitoring service.

The monitoring solution, developed in collaboration with the former Statoil (now Equinor) and Gassco was presented at the PCIC Europe Conference in Berlin, Germany in June 2016.

Our patented technology includes a number of analysis software tools that are able to distinguish VSD pulses from PD pulses.

Combined hardware and software de-noising technology for the HVPD Kronos® system provides reliable on-line PD condition monitoring of VSD motors.

For the isolation of the line frequency, HVPD developed a unique sensor with two windings that can simultaneously detect the low line frequency and the high frequency PD pulses.

The SMART-TB3™ TriBand sensor (above)is a world first, and utilises the detection capability of the HFCT sensor to detect high frequency PD and incorporates lower frequency bands for the detection of the line frequency. The Low Frequency winding provides a synchronisation signal for the acquisition process and the Phase-Resolved pattern build-up.

Using SMART-TB3™ TriBand sensors along with TEV sensors, the system can effectively monitor PD activity within the stator windings of VSD motors by differentiating PD pulses generated within the HV motor and the switching pulses generated by the VSD drive.

The installation will vary depending on the plant, but we have put together a ‘best practice’ solution for the installation of sensors to monitor PD in twin-winding VSD-fed motors (below).

How does HVPD read the data?

The HVPD Kronos® Permanent Monitor’s data interpretation process is illustrated below. This takes the raw data collected by the monitor (shown on the left) and then analyses it through a number of stages to provide the final denoised measurement on the right. In the example above, only 0.1% of the electromagnetic pulses detected were PD pulses, with the 99.9% remainder being ‘noise’ pulses from the VSD’s power-switching electronics. This illustrates the ‘needle in a haystack’ situation that makes VSD-operated motors the most difficult type of asset to reliably monitor for partial discharge.

We implement a series of Expert System de-noising rules into the software over a 90-day training period, to better separate and identify PD pulses. Analysing data this way also means that trends can be effectively measured, and no false PD alarms are raised.

HVPD’s hardware and software combine to provide the best early warning indicator of Partial Discharge in your VSD-fed rotating machines. Get in touch today to see how to include us in your condition monitoring strategy, and save time, money and energy from day one.

Furthermore, installing sensors at both the VSD and the motor itself (as detailed in the previous section) allows us to better determine the location of any Partial Discharge pulses that are picked up by the HVPD Kronos® Monitor, as demonstrated in the video below:

How did we come up with the solution?

The project to develop a solution to reliably monitor on-line Partial Discharge in VSD-fed motors was undertaken, as mentioned earlier, in conjunction with Statoil (now Equinor), involving a pilot project at one of their gas processing facilites.

As well as helping Equinor to take care of their assets and better monitor the condition of their electrical insulation, developing such a solution was important due to the trend in adoption of VSD-fed motors in the Oil & Gas industry – a trend we still see continuing today.

The project helped to further HVPD’s knowledge on performing reliable PD monitoring on VSD motors whilst rejecting noise pulses, and come up with a solution that has since been granted a patent.


Get in touch

Our VSD solution for Partial Discharge monitoring could save your business money, and help you move towards a condition based maintenance programme. Get in touch today to discuss how we can help you protect your assets: sales@hvpd.co.uk

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