Immersion Heaters and Potential Fire Risks

Immersion heater terminal box. (AI enhanced as the original photo was blurry)
© Eugene Brennan

So I was doing some gardening for the sister today and she mentioned a smell that was coming from her immersion. This immediately rang alarm bells in my engineering head, knowing what was likely to have happened—So I investigated.

Loading Data for the Kilcullen 38 kV Substation.

Loading data for the Kilcullen 38 kV Substation, courtesy ESB Networks.

From the ESB Networks document 38 kV & 110 kV Station Special Load Readings. 

The table shows summer and winter loads in megawatt (MW) for transformers T41, T42 and T424.

Available Substation Capacity in Ireland

Information on substations. Image courtesy ESB Networks.

This interesting interactive map on the ESB Networks website shows transformer capacities. A "substation" indicated on the map could be an actual town substation like the one at Sunnyhill, with 1, 2 or more transformers and associated switchgear and circuit breakers, or a transformer in a cabinet or small building (common in the newer housing estates).

What Is the Ground Wire For?

© Eugene Brennan

What Is a Ground Wire?

The hot and neutral cores in a power cable are used to supply current to the appliances in your home. So what about the green wire? Why is it needed? This is known as the "ground" and is an additional wire that is included for the safety of you and your home.

How to Use a Multimeter to Measure Voltage, Current, and Resistance

© Eugene Brennan

What Is a Multimeter?

Multimeters are measurement instruments widely used by professionals in several fields including industrial maintenance and testing, research, appliance repair, and electrical installation. However, a digital multimeter (or DMM) is also an invaluable test instrument for home and DIY use.

What Are the Applications of Multimeters?

The instrument can be used for measuring voltage, current, and resistance and can check the following:

• Battery voltages in equipment
• Current through cables or components
• Vehicle electrics and electronics
• Continuity of cables and power cords
• Home appliances and electronic devices
• Fuses

How to Understand Electricity: Volts, Amps and Watts Explained on Appliances

© Eugene Brennan

This comprehensive guide for consumers and students explains everything about volts, amps and watts and how they apply to home appliances and circuits. The equations are really quite simple, and you'll find some examples on how to apply them to home appliances.

Electricity 101: Understanding the Basics

In this tutorial, you'll learn about:

• Volts, watts, amps
• Power consumption of appliances and kilowatt hours (kWh)
• Ohm's law and resistance
• Resistivity and how it affects the resistance of a material
• Fuses and how they protect wiring and appliances
• How electricity is produced
• Devices used to measure voltage, current and resistance
• The effects of electric and magnetic fields
• Conductors, insulators and superconductors
• The basics of AC and DC
• Arcs and sparks
• Power supplies and voltage regulation
• Tracking electricity usage in the home

Work at Dunstown 400kV Substation

Groundworks at Dunstown 400 kV Substation. Image © Airbus, Maxar Technologies.

On a section of land adjacent-to and SE of the existing substation.

Maybe extra transformer capacity being added or other electrical infrastructure. I'm going to have to visit Google Earth, rather than Google Maps, as the former has historical satellite imagery.

 

Edit: Possibly preliminary groundworks for this: The connection of a "a high-capacity 400 kV (kilovolt) underground electricity connection between Dunstown substation in Co Kildare and Woodland substation in Co Meath." This is part of the Kildare-Meath Grid Upgrade (or Capital Project 966).

High Volume Releases at Golden Falls Dam

Golden Falls dam, Ballymore Eustace. © Eugene Brennan

According to the ESB, a flow rate of 15 m³/s (cubic metres per second) is estimated for today, 13th November, from 00:00 to 24:00. That's 15 tonnes of water per second. The compensation/buffer lake at Ballymore Eustace has risen by 9 m since 14th October. The lake acts as a buffer to cater for larger releases at the Poulaphouca dam. I'm guessing some of this water may be over the spillway, or through a compensation valve, which gives finer control over flow, rather than through the penstock (a large diameter pipe feeding the alternator). I've put in a query to the ESB, requesting answers to some technical questions.

The Golden Falls hydroelectric power station has a single three-phase alternator that generates 4 MW of electrical power. For comparison, onshore windmills typically output 2 to 3.5 MW.

Golden Falls Generator Assembly

Golden Falls G 4 assembly. Main shaft guide bearing and oil pump. July 1948. 

Permission to reproduce image courtesy ESB Archives.

 © ESB Archives

ESB Archives have sent me some photos, dating from the 1940s, of the electrical generating equipment in the Golden Falls hydroelectric power station. The stator assembly of the generator can be seen around the perimeter of the casing in two of the photos. Similar to the alternator in your car, a rotor carrying field coils, driven by a shaft from the turbine, turns within the outer stator. The field coils are excited by DC to create a magnetic field and three-phase AC is drawn off the stator. (The same thing happens in a car alternator, but the three-phase AC at a frequency of several hundred hertz is rectified to DC. Older cars used dynamos, that produced DC directly, but suffered from several drawbacks).

Turlough Hill Transmission Lines

Twin 220 kV lines crossing the mountains from Turlough Hill hydro station. © Eugene Brennan

One of my cycles back in mid-August (the long days of summer seem to be a distant memory now) was from Kilcullen to within a few miles of Turlough Hill. This is the location of Ireland's only pumped storage power station. When there's a surplus of power which the grid can't use, pumps at the station send water to an artificial lake located on top of the mountain. Once there's a demand for power, the motors and pumps switch function and become turbines and generators, the turbines driven by water as it rushes down through penstocks (large pipes) to a natural lake, located at the base of the mountain. Turlough Hill power station is net inefficient (power out is less than power in due to losses in the system).

A Little Ladder Logic

Ladder logic program. © Eugene Brennan

Just found this among documents I was going through after getting the oil boiler serviced last week. I had forgotten all about it. The electrician made a minor cockup when wiring the controls for the dual oil/solid fuel heating system 9 years ago. So I had to go off and look for a CAD package to draw a ladder logic diagram for him, showing how it should have been wired. (He had his own ladder logic diagram, but it made more sense for me to draw a new one, rather than trying to explain the error in English). Ladder logic is a schematic system for showing the wiring in an electrical/electromechanical system, input devices such as switches and sensors and output devices, e.g. motors and relays being shown as symbols on a diagram. It has evolved into a graphical programming language, the graphical program used to control programmable logic controllers (PLCs). These are basically modular, industrial control computers, built into a box, with terminals for connecting inputs and outputs. A computer can be connected for programming and they can be linked-to by various computer networks.

I'm rusty on this stuff. It's a shame when you learn stuff, and then forget it all if you're not applying the knowledge on a daily basis (I never really used this practically, even though I studied industrial automation).

See if you can understand what this does. Hint: MV1, 2 & 3 are zone valves, R1 & R2 are relays. SF is solid fuel.

Two Lifelines to Kilcullen

38 kV line that carries power to Kilcullen. © Eugene Brennan

Today was a busy day! First I had to scoff my dinner quickly (well half of it!) to be up at Dún Ailinne by 1:30 for the site tour. There was an open day today at which archaeologist Dr Susan Johnston of George Washington University gave us an update on what work had been done so far this summer. Dr Johnston has been investigating the neolithic and iron age ceremonial site since 2006, alongside a team of archaeology students. On the walk back, I snapped a picture of the pylon near the motorway bridge, that carries the power lines that supply electricity to Kilcullen. Those lines come from a substation adjacent to the turn for the Glen of Imaal on the N81. Electricity is transmitted at 38,000 volts or 38 kV from the Stratford substation in Wicklow, before being dropped to 10 kV for distribution by the transformers in the Kilcullen substation.

A 19th Century Light Bulb

Oliver F. Brastow, Public domain, via Wikimedia Commons. Image pixel size doubled.

Newer incandescent lighting uses filaments typically made from less fragile tungsten. Materials such as copper or steel aren't practical because the metal has to have sufficient resistance in a short length to dissipate power in the form of light (although incandescent lighting is woefully inefficient: 95% of the power dissipated is heat and only 5% light). Copper or steel could be used, but power dissipated in a resistor is I²R where I is the current and R is the resistance. Since copper and steel have low resistivity, a filament made from these materials would have low resistance and so a much larger current (or longer section of filament) would be needed to create the same amount of power (meaning that supply cables would also have to have to be beefed up).

I just checked a table and actually the resistivity of iron doesn't differ hugely from that of tungsten. It's only around half the value. This would mean that a filament of the same length made from iron rather than tungsten would have half the resistance. For the same voltage applied to the filament, current would be double and the power equation would give a value for power consumption of twice that produced for a tungsten filament. Tungsten however has a higher meting point and can become white hot in a lamp, without melting or losing its integrity on supporting wires.

Transformer Cooling Oil and Heathrow Disruption

A typical power transformer with oil cooling tank. Sensenschmied, CC BY-SA 3.0, via Wikimedia Commons.

You're probably aware of the major disruption at Heathrow Airport this morning because of a fire at a nearby electrical substation. According to the BBC, 25,000 litres of cooling oil in a transformer at the substation (20,000 according to The Guardian) had caught fire. London Fire Brigade said this was due to transformer failure igniting the oil. Transformers are ubiquitous components in electrical and electronic appliances and gadgets, and larger types have to be cooled. Just like the way a car engine has coolant flowing through its core to carry away waste heat, transformers have a similar cooling system. Water can't be used, so the cooling medium is usually a specialised high-grade mineral oil.

 

Why do transformers get hot?

 

All electrical conductors have electrical resistance which restricts current flow. You've probably noticed the phenomenon where a power flex in an electrical extension reel gets hot if the reel isn't fully unrolled. Transformers have thousands of turns of wire wound onto laminated iron cores and this wire gets hot (known as copper loss). The iron core of a transformer also gets hot because of magnetic fields inducing current flow in the core (known as eddy currents). The small transformer in a power adaptor can usually air cool, however room-sized transformers in substations because of their size have issues with heat making its way to the surface and dissipating. Without being cooled, heat can build up and melt insulation on the windings, potentially causing the transformer to short out. Large transformers therefore have a cooling system, and oil circulates through or around the device, either by natural thermal convection or by being pumped. This carries heat to the surface of the transformer casing where a heat exchanger (just like the radiator in your car or home) dissipates it to the ambient air. Sometime fans are used to increase airflow through the cooling fins of the heat exchanger. The cooling system is usually sealed, just like in a sealed, pressurised central heating system, so a tank mounted on the transformer is often used to cater for expansion as temperature changes. Sealing is necessary to prevent the oil absorbing water, compromising its electrical insulating properties.

Counter-terror officers are investigating the fire, so it's not known, or at least no information has been released to the public yet about whether the fire was due to a system fault or sabotage by terrorists.

The image above is of a typical transformer with conservator tank mounted on top.

Arc Flashes

Zaereth, CC BY-SA 4.0, via Wikimedia Commons

Which can cause severe burns. The arc is usually hotter than the surface of the Sun and has the energy of an explosion. A conductive arc can form due to dust, faulty components or shorted terminals in an electrical panel due to a dropped tool. Another cause can be improperly placed test leads which bridge live parts. The huge surge in current through the low resistance arc can lead to catastrophic injuries and damage in the milliseconds before a protective device operates. Personnel working on electrical panels use PPE to protect themselves from the heat and intense UV of an arc flash. See this Fluke guide for more details.

Ardnacrusha to Dublin Transmission Line and Mystery Engine House

Image courtesy Military Archives.

Just noticed the base of one of the pylons of the 110 kV line from Ardnacrusha to Dublin in the top left of this photo of Kilcullen Bridge from the military archives (Click on the link in the image caption to open the image viewer which has a zoom facility). Ardnacrusha hydro-electric power station was commissioned in 1929, and presumably the transmission line dated from then. The line was dismantled in the 60s or maybe early 70s? When the photo was taken, power was delivered directly from Newbridge/Kildare to Kilcullen at 10 kV and there's a transformer in Nugent's field for dropping voltage from that 10 kV to around 230 V. There was no substation in the town at the time, or at least when the last edition 6" OSI map shown was drafted. The map is post-1939 as the Nicholastown housing estate has been built. The 38 kV station at Sunnyhill we have now is fed from the 110 kV substation on the N81 near Stratford-on-Slaney.

The record in the archives at the link below also has an aerial view of the bridge looking south. On desktop/laptop, right click and open the image in a new tab to view at full size. There isn't a zoom facility in the viewer.
I still haven't found out what was housed in the "Engine Ho.", located approximately where Scoil Bhríde is now. A stationary engine for pumping water from a well for the convent? Or maybe a machine for making meal for feeding animals on the convent "farm"? Or did the convent have their own electricity and this was where the engine and generator was located? Maybe someone knows.

Image courtesy Tailte Éireann (OSI)

 

Real-Time Information From EirGrid

Screenshot from the EirGrid website.

Eirgrid's function is to match supply and demand from their control centre in Dublin. As load i.e. demand increases, generating facilities have to be switched onto the grid or increase their output to compensate, and vice versa. They also have to be synced so their voltages match and AC waveforms all start at the same point. One of the results of increasing demand is that generators slow down, and frequency drops. The opposite happens when load reduces. A change in frequency from 50 hertz can affect clocks and timing, motors and other connected equipment, so frequency is usually regulated to within fractions of a hertz (typically 0.03 hz). Anyone who has ever had an electric clock driven off the mains, will know they keep relatively good time, in comparison to a clockwork clock. That's because the speed of the shielded-pole motor used in the mechanism to turn the hands depends on frequency, not voltage.

Eirgrid's Smart Grid Dashboard shows various parameters of Ireland's electricity system, including frequency, daily supply and demand in GW, fuel mix, interconnection imports, and CO₂ emissions. Historical stats and real-time graphs of system parameters are also available on the EirGrid website. At 3 pm today, demand is 5.485 gigawatt (GW) and wind generation provides 21.8% of that. Peak demand is forecast to occur at 6.30 pm today and is expected to be 6.34 GW.

1 GW = 1000 MW (megawatt) or 1,000,000 kW. Think of 1 GW as the power used by one million, one bar electric fires.

Golden Falls Releases Through the Spillways

Golden Falls dam. © Eugene Brennan

High flows at Golden Falls today, which were forecast to be 10 m³/s all day. The releases are due to recent heavy rainfall. I always end up here late in the afternoon on dull days, so the high contrast in the scene means photos aren't the best. So the sky gets washed out if I increase the exposure.

© Eugene Brennan

 

© Eugene Brennan

13 A Fuses Don't Blow Instantly When Current is > 13 Amp

© Eugene Brennan

Did you know that the rating of fuses and MCBs is the current they can carry indefinitely without overheating, not the current they blow at? For instance Type B MCBs, used in domestic installations will trip at a current of 3 to 5 times their rating. A BS1362 13 A fuse, used in 3-pin plugs must allow a non-fusing current of 1.6 times 13 A or approximately 20 A to pass for at least 30 minutes. BS1362 also specifies the fusing current as 1.9 times the rating or 24.7 A for a 13 A fuse. The fuse must blow in less than 30 min when current exceeds this value. The function of fuses in plugs is to protect the power cord, not necessarily the appliance. Lower rating fuses are often incorporated into appliances such as TVs that use smaller gauge wiring internally, to prevent against fire.

 

More info here:

 

BS 1362 Fuse Operation Characteristics

Check your plugs regularly to make sure they're not getting hot, especially when powering high wattage items like electric heaters (warm is normal for such appliances). Hot plugs are a symptom of a loose connection such as screws not tightened down fully in terminals or worn spring contacts in sockets (requiring a socket replacement). Any of these scenarios can potentially cause a fire.

 

Related Reading

Work at Dunstown 400kV Substation

Golden Falls Generator Assembly

Turlough Hill Transmission Lines

A 19th Century Light Bulb  

 

Some Aircraft Have Rats

Ram air turbine on Airbus A320. Image courtesy Curimedia, CC BY 2.0, via Wikimedia Commons.

Ram air turbines that is, or RATs. If main power is lost, the small windmill-like turbine is lowered from the belly of the fuselage and uses ram pressure or force of the moving air to drive an electrical generator or hydraulic pump. This is a last resort scenario though. Usually an aircraft's engines generate electrical power as well as thrust for propulsion. If they fail, an auxiliary power unit (APU) provides power for electrical systems. This also provides system power before the main engines start up, when an aircraft is on the runway. An APU is a mini jet engine, usually mounted in the tail of the aircraft, independent of the main engines and not involved in propulsion.

References:

Naidu, A. (2024, December 29). Redundancy approaches to flight safety: The curious case of the b737’s absence of a ram air turbine compared to the A320". LinkedIn. https://www.linkedin.com/pulse/redundancy-approaches-flight-safety-curious-case-b737s-andrew-naidu

Lomas, C. (2024, March 11). What is the Auxiliary Power Unit (APU)?. Flightradar24 Blog. https://www.flightradar24.com/blog/auxiliary-power-unit/