Interview Series: Maintenance of Hydroelectric Systems

For this Q&A session I sat down with Sean McNeish who is a mechanical engineer for Ross-shire Engineering. Ross-shire Engineering are a niche engineering service company whose work covers various industries including the renewable energy sector. The goal was to learn a bit more about the maintenance of plant in the renewable sector and to find out what role thermal cameras are used.

Francis Water Turbine Generator and Control Panel

What does your job involve?

My role as a mechanical engineer includes maintaining and servicing of the hydro turbines and repair if needed for faults. There are different types of turbines, all of which run from the same principal of using water which through the turbine which turns a shaft that’s connected to an electric generator. The generator will produce electricity which it will then send to the grid.

How is the hydro-electric equipment maintained?

There are monthly and annual servicing which takes place to ensure the equipment is all running as it should on a number of sites which we maintain. The monthly service is basically just to check things like oil levels, grease levels, noise, pressure levels and a basic service. The annual service however is a much more in-depth service where the machine is stripped down as well as using a thermal camera to check for any defects or temperature anomalies within the likes of the generator, drive end bearings, non-drive end bearings and shaft. Electrical checks are also completed which would cover the likes of the three phase supplies, the tail connections and control board connections, the thermal camera will also be used when conducting these checks.

When carrying out the servicing we will generally use an electronic report connected to the company server which allows us to cross reference month to month or year to year servicing to see if there are any differences over time. This means you can keep an eye out for components which may be deteriorating over time.

What role does the thermal imaging camera play when conducting the servicing of the Hydroelectric equipment?

The machinery only gets stripped down once per year during the annual service so that is our time to complete a thorough check of the machine. One part of this check is to use the thermal camera to look for hot spots throughout the bearings, the non-drive end bearings on both the turbine and the generators. As we know the life expectancy of the bearings which is usually 10 years, I will then know on say year 8 or 9 I will be paying particular attention to these component temperatures to see if these are starting to fail or if there is something that may be causing the bearing to start to fail. The preference is always to repair or replace parts during pre-planned shut downs rather than emergency shut downs as some of the turbines will be going direct to customer supply which if it is an emergency shut down the water going through the turbines will not make it to the service reservoirs and to the customer.

When looking at a generator with a thermal camera talk me through the process of checking it and what you are looking out for.

Before we switch anything off, we are checking temperatures on the likes of the supply cables, compartments and drive end bearing housing and non-drive end bearing housing. If the readings are higher than what is being shown on the HMI (human machine interface) on the control panel we will know that there may be a fault which I will then begin to trace.

When stripping the machine down during the annual service you can also check the shaft to see if this has played a part in the heat transfer. What could happen is if there is a fault and it is showing on the control panel as the generator bearing temperature being high and the turbine bearing temperature also reading high it could be the shaft which is transferring this heat. Using a thermal camera, I will be able to pin point which side the fault is coming from.

Every bearing is different and the lubrication schedule is key to keeping the bearing in good working order. If the wrong grease is used, it won’t properly lubricate the bearing and would cause it to heat up. Also, as water passing through the turbine is from reservoirs, there will sometimes be stones making their way through the pipeline.  This can make its way through the workings of the turbine causing vibrations which can act as a heat transfer to particular components.

Does the thermal camera speed up your job or allow you to source defects that you would not have otherwise found without it?

On one example we received a call out where the bearing temperature was reading high. On arrival to site, the HMI on the panel was showing the temperature to be reading 43 degrees but the temperature of the bearing through the thermal camera was reading 83 degrees so from this we knew that there was a mechanical fault rather than an electrical fault.

Another example is where a rock had become stuck in the spear valve. When this valve becomes stuck and can’t properly open or shut, the control panel will be unsure of what position the spear valve is in as it has not hit the limit switch for the open or close position. So basically, the shaft will try to open and close constantly which will cause friction and that will heat up. The thermal camera could help pin point a defect like this to find out whether it is coming from the electrical component at the back of the spear valve or whether it is coming through the spear valve itself.

The thermal camera can also speed up the job of the electrical engineer by assisting to locate faults with the likes of the control panel. There have been instances where high temperatures have been found within the control panel which could be down to a burnt-out relay or the PLC could be a higher temperature than normal due to a faulty connection.

Hydro Turbine diagram with control panel thermals

How do you know if a component is reaching an unsafe temperature?

The manufacturers literature will explain what temperature the bearing is meant to run at so during the commissioning stages when setting up the hydro turbine we can then put two types of alarm on it to monitor the temperatures. We can place a warning alarm on it say 20 or 30 degrees before it reaches its high temperature and then another warning 15 or 20 degrees below its maximum temperature which will provide us with a warning to show that the temperature is hotter than it is supposed to be. These warnings are all monitored remotely and if reached will prompt a call out.

When the control panel shows a temperature fault, what is the process of confirming this.  

On entry to the site I would check the HMI to see what results are showing on the control panel. Let’s say there was a high temperature on the turbine or generator bearing. I would then use the thermal camera to check the faulty bearing and cross reference the readings shown on the camera to the control panel readings. If both are at a high temperature then it is likely that there is a mechanical fault, If the thermal camera shows a normal temperature through the bearing it would be likely that there is an electrical fault which could be the temperature sensor attached to the bearing housing.

What is the difference in approach between mechanical and electrical faults found on the machinery?  

If an electrical fault is found the turbine would usually need to be shut down to make safe, isolate and work on it. For the mechanical side we can process a fault without the need to shut the turbine down. We use a data sheet which is filled out, weekly, monthly, yearly which will include any faults that have been found. We will be able to assess the issue and know whether it has the potential to affect the process or the turbine. It may be the case that the issue can be safely left until the next monthly service when the faulty mechanical item can be changed out.

Electrical engineers are used when and as needed depending on the fault. The mechanical engineer is usually the first person on scene, the mechanical side can be checked with the thermal imaging camera. If everything is mechanically sound, we will know that there is an electrical fault where an electrical engineer would be needed. This initial visit by the mechanical engineer will bring efficiency savings by not sending two engineers to every visit.

The electrical engineer will however always be required for the annual services as they are checking every terminal and every terminal screw so the annual service is a joint visit between the mechanical and electrical side.

Do you do any repeat thermography over time to see if a component is declining in performance.

We use a traffic light system. Every report will ask for bearing temperatures and everything else that has a temperature sensor. So, what we are looking out for is if a component is coming to the end of its life expectancy, we can then keep an eye on it. If it is still within its working temperature, we will know that is fine but if we start to see this creeping up, we can check back on the monthly reports throughout that year to see if there has been an increase or decrease in temperature for that particular product. It shows on our report as green, amber or red. If the report highlights the component in red it will usually require a replacement of that component.

End of Q&A

From this Q&A session you can really start to get a sense of how important the use of thermal cameras can be during the maintenance of hydroelectric equipment. I had a real sense of how a good thermal camera has the ability to save companies time and money by locating faults quickly and thus reducing the time that equipment is shut down. I felt like I gained a deeper understanding of the maintenance involved in hydroelectric plant and I hope you managed to learn something new as well.

For more on thermal cameras, check out my review of the FLIR One Pro here.

Also for more on learning the basics of thermography check out my educational blog here.

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