Last week I ran a post on a theory why the Electric Train fleet was grounded. The theory’s premise was based on the fact that both only two substations of the planned (four) were ever built and as a possible result we have “dirty power” causing the faults. These faults have now grounded the Electric Train fleet for 10 days and Auckland Transport want to start rolling the Electric Trains out in three weeks time on the Manukau Line. Yet Auckland Transport has no clue.
Yesterday it was raised that the a POSSIBLE source of the dirty power could be the National Grid. That is the 110,000 and 220,000 volt wires on large pylons that either cross or run beside the rail network at certain points in Auckland. To make things more interesting we have the Southdown gas-fired power station next door to the rail network as well. That power station has the 220,000 volt lines running over the rail lines just north of the Westfield junction (where the Eastern and Southern Lines branch off or merge back together (depending which way you are going) as well as large transformers within the plant itself.
Where am I going with this in regards to the power station and the high tension power lines (that are part of the National Grid)?
Harmonics voltages and currents in an electric power system are a result of non-linear electric loads. Harmonic frequencies in the power grid are a frequent cause of power quality problems. Harmonics in power systems result in increased heating in the equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors. Reduction of harmonics is considered desirable.
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Effects
One of the major effects of power system harmonics is to increase the current in the system. This is particularly the case for the third harmonic, which causes a sharp increase in the zero sequence current, and therefore increases the current in the neutral conductor. This effect can require special consideration in the design of an electric system to serve non-linear loads.[2]
In addition to the increased line current, different pieces of electrical equipment can suffer effects from harmonics on the power system.
Motors
Electric motors experience losses due to hysteresis and losses due to eddy currents set up in the iron core of the motor. These are proportional to the frequency of the current. Since the harmonics are at higher frequencies, they produce higher core losses in a motor than the power frequency would. This results in increased heating of the motor core, which (if excessive) can shorten the life of the motor. The 5th harmonic causes a CEMF (counter electromotive force) in large motors which acts in the opposite direction of rotation. The CEMF is not large enough to counteract the rotation, however it does play a small role in the resulting rotating speed of the motor.
Power quality determines the fitness of electrical power to consumer devices. Synchronization of the voltage frequency and phase allows electrical systems to function in their intended manner without significant loss of performance or life. The term is used to describe electric power that drives an electrical load and the load’s ability to function properly. Without the proper power, an electrical device (or load) may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality power.
The electric power industry comprises electricity generation (AC power), electric power transmission and ultimately electricity distribution to an electricity meter located at the premises of the end user of the electric power. The electricity then moves through the wiring system of the end user until it reaches the load. The complexity of the system to move electric energy from the point of production to the point of consumption combined with variations in weather, generation, demand and other factors provide many opportunities for the quality of supply to be compromised.
While “power quality” is a convenient term for many, it is the quality of the voltage—rather than power orelectric current—that is actually described by the term. Power is simply the flow of energy and the current demanded by a load is largely uncontrollable.
To use a household appliance like a computer as an example: our household appliances run on 240 volts and usually 3-10 amps at 50Hz frequency. When you have dirty power the Hz frequency jumps all over the place and as a result it will cause your computer to either blow its fuse (same way when there is too much amps coming through) or damage the equipment.
To make things more interesting I have been told of over voltage issues especially around the Onehunga Line where the trains go from receiving its normal 25,000 volts to all of a sudden 27,000 volts. Again this will cause the train to shut down if not blow its fuses.
Now using the Onehunga Line as the test case (seeming this is where the breakdowns are happening) I note that there is a 110,000 volt line that runs parallel to the Onehunga Line from Penrose Station to Onehunga Station. Like all things electric the 25,000 volt wire carrying the power for the trains and the 110,000 volt line next to it (on pylons) emit electric fields at certain frequencies. No doubt these frequencies will be quite different which leads to the problem (when safeguards like power conditioning or filtering equipment is either lacking in sufficient number or not at all – see below).
Remember what happens when you place your phone next to some speakers and you get that awful sound? That is two difference electric frequencies from two devices interfering each other, the sound being the speakers impaired from normal operations.
Now lets step it up a bit. 25,000 volts for the trains and for the Onehunga Line it is next to a 110,000 volt line – over four times the voltage and most likely operating at different frequencies. This frequency difference from the 110kv (110,000) and the 25kv (25,000) can cause dirty power and upset the harmonics of the electric lines supplying power to the trains. As a result the electric trains do not have clean power and thus in this case shut down or suffer over-voltage issues (which causes shut downs any how).
To make things more interesting the power station down at Southdown with its 220kv line undoubtedly will be giving off interference, along with high tension wires crossing the rail network at Middlemore (110kv), Takanini (110kv) and between Avondale and New Lynn (2x 110kv and 1x 220kv).
So there is a possibility our National Grid could be interfering with our electric trains. The fix? Well pretty straight forward but can get very expensive very fast. The fix is done through what is called power conditioning. Power conditioning being:
An uninterruptible power supply can be used to switch off of mains power if there is a transient (temporary) condition on the line. However, cheaper UPS units create poor-quality power themselves, akin to imposing a higher-frequency and lower-amplitudesquare wave atop the sine wave. High-quality UPS units utilize a double conversion topology which breaks down incoming AC power into DC, charges the batteries, then remanufactures an AC sine wave. This remanufactured sine wave is of higher quality than the original AC power feed.[2]
Modern systems use sensors called phasor measurement units (PMU) distributed throughout their network to monitor power quality and in some cases respond automatically to them. Using such smart grids features of rapid sensing and automated self healing of anomalies in the network promises to bring higher quality power and less downtime while simultaneously supporting power from intermittent power sources and distributed generation, which would if unchecked degrade power quality.
Now to get that power conditioning it would help Auckland Transport and Kiwi Rail to build those other two substations so that the full set of four are running for the entire electrified rail network (only two of the four were built so we have a technical reduction in filtering, power conditioning and power supply points by 50% of what was originally planned). However, with the rail network close to the National Grid in some places extra but smaller transformers might be needed nearby to act as further power conditioners and filters. For those smaller more remote transformers to work though extensive tests and planning would be needed to determine best location for them.
And as I said earlier these fixes are not cheap so it will come back and cost us.
As for what Auckland Transport are saying we have this:
Transport chief more confident after big jump in train use.
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Puzzle stops trains in their tracks
Auckland Transport still hopes to introduce electric trains to eastern suburbs in three weeks, despite a puzzling power problem that has stopped trains running between Onehunga and Britomart.
A spokesman’s assurance that the trains would start running between Manukau and Britomart via Panmure and Glen Innes on August 17 follows a succession of night-time tests of power supply equipment since they were replaced temporarily by old diesel units a week ago on the Onehunga line.
Chief operations officer Greg Edmonds told Auckland Transport’s board that trains had operated with few problems on the line since April before being hit by intermittent power supply problems on Monday and Tuesday last week.
It was not known whether the problems came from the national grid, the local network, equipment on the trains or a combination of factors.
Not known what the problem was and the Manukau Line is meant to go “live” in three weeks. You will have to excuse me Greg Edmonds if I fail to display confidence on both fronts there. This fault should have been worked through in full proper tests IF NOT anticipated in the planning stages if it is deemed the National Grid is causing the issues. As for not building the full set of substations? Well that was just daft looking at the fact the fleet is now at Day 10 in being grounded!
Day 10 folks and no apparent end in sight yet…
Good way to compromise our $1.1 billion investment…
Talking Southern Auckland 