30/03/2016

Monitoring the Effective Delivery of Energy

 - Should Be Part Of Your Supply Chain Management

To most manufacturers the management of the supply chain is the ‘just in time’ stock control system of the components required to produce their end product.  Effective energy management, whether electricity or gas, is often assessed by the facilities management department on a simple cost to supply basis.

Therefore isn’t it time for you to reassess your energy supply by viewing it as an essential component, whose security of supply is as important as the key elements of your production schedule?  After all your contracts with  suppliers are likely to include service level agreements covering delivery, stock levels and potentially penalties for the lack of supply.  Electricity is the ultimate  just in time component; you hold no stock, its delivered to site as need arises and if it fails so does your entire production effort.

It’s down to risk management, it’s down to criticality, and it’s down to the fact that without the high voltage (HV) power grid your factory grinds to a halt.

There are two key constituents to the HV grid; cables and switchgear.  Both sit there, slowly deteriorating over time until they are either replaced or fail.  There is though a way of identifying those elements that are in danger of failing - Partial Discharge.

 

 

 

 

Partial Discharge is an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes. This is commonly known as Partial Discharge (PD) activity and can occur at any point in the insulation system where the electric field strength exceeds the breakdown strength of that portion of the insulating material. PD can also occur in voids within solid insulation, across the surface of insulating material or within gas bubbles in liquid insulation.

Realistically you do not need to fully understand what PD is, but you do need to understand the benefits that active PD monitoring of your assets can give you.  It can give you early warning of potential network failures as well as providing you with a method of justifying your investments and decreasing negative consequences to your business, as illustrated by the following case studies:

1. Switchgear

In November 2014, EA Technology, working in conjunction with a UK Distribution Network Operator (DNO), installed a transient earth voltage (TEV) monitor with prototype software at one of their high risk sub-station sites. As the instrument was on a longterm soak test there were no communications and the system was not monitored during the test period.

The site was judged as high risk due to its location near a river’s edge, together with the type of switchgear operated at the location.

On 28 July 2015 EA Technology received a phone call from the DNO informing them that the sub-station switchgear had blown (see the right hand edge of the trace shown in Figure 1) and asking if they would be able to help investigate the reasons for the failure.

Findings

The failure investigation team reviewed the historical data and found that the sub-station had been running at a normal reading from installation in November 2014 until March 2015, but from this date there was a marked increase in PD activity. Over a week-long period, PD avtivity rose to a level which, had the alarm system been active, would have triggered the automatic alarm notifi cation by text and email. This spike continued to be maintained until 28th July 2015 when the switchgear failed.

The TEV monitor also recorded slight changes in temperature and humidity over the test period, however, these were proven to be unrelated to the increase in PD levels.

Results

The switchgear failure resulted in a large part of a city being left without power for approximately eight hours and, as a direct result, the DNO received customer minutes lost (CML) and customer interruption (CI) fi nes totalling over £300,000, in addition to the direct costs of replacing the failed assets.

Conclusion

If a non-intrusive, expertly assessed, remote condition monitoring system had been installed to monitor the high risk switchgear, the DNO would have been made aware of the irregularity on the day that the PD levels started to rise, potentially giving it approximately three months to take remedial action.

2. HV Cables at Electricity North West

Electricity North West (ENW) is a distribution network operator that owns, operates and maintains the North West’s electricity network, connecting 2.4 million properties and more than fi ve million people to the National Grid.

The project

A data collector was used to carry out a PD assessment of nearly 200 high voltage cables over a two year evaluation period.  The assessment was undertaken with the cables energised and tested in a non-intrusive manner, and since this was an evaluation trial, ENWL chose not to perform any remedial action on the cables tested, but instead to wait and see what happened to the cables’ performance.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results

The chart (Figure 2) shows the results of the testing that was conducted on the cables over the fi rst 18 months of the evaluation period. These are broken down into three categories:

Green – a test where no partial discharge (PD) was found and the cable does not need to be tested for another two years.

Amber – some levels of PD were detected and the cable should be retested in six months’ time to see if the levels have increased.

Red – PD levels indicate signifi cant degradation: the cable should be taken out of service for immediate repair or replacement.

The chart also shows that of the seventeen cables that were categorised Red, over 40% developed a fault inside of two years. Of a further fourteen cables that were categorised Amber, 20% of them failed within two years but, importantly, less than 2% of the cables that were categorised Green had any issues within the two year period.

Going Forward

ENWL now intends to incorporate cable data collection and testing into their outage planning procedures and any long-term 33kV planned outages will also include a pre-outage check on the adjacent circuits which will be carrying all the load during the outage.

Summary

The key with all of this is to get the technology to do the work for you.  Periodic inspections give you a snapshot of the asset health at that discrete moment in time: continuous and remote monitoring provides greater peace of mind due to detailed trend analysis give you early warning of potential failure.  This not only decreases your financial outlay but also releases your inspection teams to undertake more productive tasks.

When you assess the cost-benefit for the financial justification, do not forget to account for the cost of lost production, the cost to brand reputation as well as the cost of the replacement equipment.  Far better to try to avoid the crisis in the first place.