Troubleshooting old switchgear with partial discharge monitoring

Managing ageing switchgear is an ongoing issue for a growing transmission and distribution network managing rising electricity generation and consumption and evolving industry dynamics. One of the most significant problems with old switchgear is lack of maintenance – and failures are often the result of pure oversight. Carrying out timely repairs is an essential part of keeping switchgear working. But spot-checks risk missing the issues, and traditional monitoring is expensive. What if there was an easier way? Here, we share some insights on the challenges, along with advice on troubleshooting old switchgear with partial discharge monitoring.

The scale of the problem

Firstly, what are the risks? As the UK’s Health and Safety Executive (HSE) points out, and anyone in the industry knows, failure of switchgear due to its age, condition, installation conditions or design (for example, manually operated) could result in death or serious injury. You can download a free copy of the HSE’s guide Keeping Electrical Switchgear Safe here for a full overview of the issues. 

To get a sense of how partial discharge (PD) fits in, here’s the standout statistic: 85 out of 100 disruptive failures in electrical substations are PD related.

Follow guidelines and procedures

As a starting point, it’s vital to understand the guidelines and follow the correct procedures in managing your switchgear. Failing to adhere to the right processes can result in costly damage to equipment and risk to human safety, as well as unplanned outages.

TIP: One of the most critical elements in achieving best practice is making sure that you have comprehensive, up-to-date documentation of your electrical systems, including single-line diagrams (network diagrams).

Monitoring for partial discharge

To understand the state of the insulation within switchgear, monitoring for Partial Discharge (PD) is essential.  PD involves the breakdown of a small area of insulation subject to a high voltage. This breakdown doesn’t entirely span between the two insulated electrodes. The damage is usually small scale – the bigger problem is that once present, PD is always progressive, leading to the failure of the insulation in the long term.

One of the most significant challenges for operators is the scale of the task in spotting potential PD problems – the quantity of low-value assets involved in managing the transformation of HV into LV supply is huge. In brief, these are the main options:

• Time-based maintenance

Time-based monitoring is both expensive and problematic in other respects. Oil-based switchgear was introduced at a time when a time-based approach was the norm – today, we are more aware of its limitations. As the HSE points out, “Where it is known that switchgear will be subjected to variable operating conditions or frequent duty, eg frequent motor starting, maintenance at fixed time intervals may not be adequate, and other techniques may be more appropriate.”^[1]

• Traditional condition-based monitoring

Traditional condition-based monitoring inspections involve ‘getting under the bonnet’ through offline testing – not only costly but with health and safety risks. The outcome is often that the level of monitoring and maintenance being carried out is insufficient. With reduced workforces, in-person inspections by qualified employees become increasingly challenging to implement.

• Remote monitoring

In terms of accuracy, real-time data and ease, monitoring partial discharge remotely comes into its own, allowing you to shift from time-based monitoring to condition-based monitoring without placing onerous demands on maintenance employees.

While online surveys are extremely useful in providing a snapshot, they don’t give the full picture. Using intelligent monitoring and control systems taking information from sensors, you can address problems based on the evidence of permanent monitoring, rather than relying on results gained at a single point in time. Using a predictive maintenance approach, you can upgrade equipment at the optimal time, save unnecessary visits, and ensure that you can make your budget go further.

Repair or replace?

If you monitor for PD issues successfully, you may be able to limit the replacement of ageing assets as you futureproof your network. The choices widen: you can consider the options of reconditioning and refurbishing existing switchgear rather than investing in new equipment. As you modernise your network, ‘sweating the assets’ through forecasting and timely repairs can allow you to make the most of your existing infrastructure while you upgrade to new circuit-breaker technology.

Clearly, there’s a strong business case for getting the most out of PD monitoring to keep your switchgear safe and working. Want to find out more? Download our ebook A Quick Guide to Identifying HV Infrastructure Deterioration through Partial Discharge Monitoring.

(1) Keeping Electrical Switchgear Safe, Health and Safety Executive, Second Edition 2015, p16 para 63