Earlier at 2:25PM, there were voltage dips reported all over the island.
This is the waveform captured at low voltage in Jurong East, typical of a 230kV transmission level fault.
This small dip in voltage here suggests that the transmission fault did not originate from this particular 230kV block, where this PQ monitoring device is located.
Learnt a great deal from Amir Boshi of Satec and Powerqualitydoctor.com earlier today.
Thanks to Adrian Teo of Efunity for the kind invitation.
To many of you in Singapore, you will only probably observe lights flickering either when 1) the light bulb itself is due for replacement or 2) during the very brief moment where there was an electrical fault in your area.
You will also not find the word ‘flicker’ in Singapore’s Transmission Code. but that does not mean there are no flicker limits imposed for Singapore’s electrical network. In Section F2.1, it states that “…………shall be in accordance with the requirements set out in Engineering Recommendation P28 of UK.” Based on this old ER P28, the limits are 1.0 and 0.8 for short (PST) and long term (PLT) severity values respectively.
So what is flicker, you may ask?
Flicker is a power quality problem primarily concerning human’s perception of changes to the output of the light bulb. These changes are caused by voltage fluctuation due to electrical loads with rapid variations in its loadings. An arc furnace is often cited as an example.
PST 1.0 refers to the level of voltage fluctuation that will cause more than 50% of you to notice and complain. It is based on the changes of the light output of a 60W incandescent light bulb. One can measure these flicker values either using a Flicker meter or a modern power quality analyzer.
So are there flicker issues (exceeding limits) in Singapore? I will say, there are flicker issues here but not necessarily a problem. Remember, the limits set upon was based on the incandescent light bulb, which you hardly come across today.
An interesting study (Cigre 449) conducted by Cigre Working Group C4.108 revealed in a limited test of their own that modern lighting are less sensitive as compared to the 60W incandescent lamp, when tested under instantaneous flicker value of 1.0.
So there could very well be flicker issues in your area. It’s just that modern lighting have saved you from being irritated.
Below are some of flicker trend values in Singapore from my past work. Yes, flicker do exists here.
I had the privilege in toying around with the new HDPQ Xplorer earlier today, thanks to Terry Chandler of Power Quality Thailand. Definitely re-affirmed my belief that Dranetz PQ instruments and Dranview (especially) are at least one notch higher against its competitors.
p/s: Thanks Terry for visiting us today.
Mr. Harmonics is frequently being blamed when an equipment failed (or when a cable burnt, capacitor bank blown, or a circuit breaker tripped without an obvious fault). Some without due consideration of other simpler factors will blame Mr. Harmonics and his cousins like Mr. Resonance (or perhaps his friend, Mr. Transient – story for another day) straightaway.
Surprisingly, it is a fairly easily accepted reason here. And with power quality instruments getting more affordable these days, it has been becoming quite common to see someone using this new toy, measure current harmonics in percentages of 50-80%, and straightaway concluded that it is indeed a harmonics problem.
Firstly, when it comes to harmonics, we need to know; is it voltage or current harmonics? While there is a common indicator to measure both of them – using the Total Harmonic Distortion (THD) formula (RMS value of the harmonic content expressed as a percentage of the fundamental), one needs to know the pros and cons of using such indicator when applying to voltage/current harmonics.
Usefulness of THD
Limitations of THD
Here in Fig1, is the current waveform and spectrum of the common switched-mode-power supply to our PC/laptop at work or home. Looking at just its THD% current, one will be extremely alarmed (162%!!). So should all of us purchase harmonic filters for all our homes/offices then? (fact: the actual amperes of this circuit is less than 0.6Amps, and VTHD is only 1.52%)
When it comes to current harmonics, it will be more meaningful to use other alternative indicators such as Total Demand Distortion (TDD), or use absolute amperes (my personal recommendation).
Fig 2 and 3 shows the trending results of current harmonics, presented in THD%, Harmonic Amps and TDD%.
Total Demand Distortion
It was reported that the voltage disturbance (lasting about 100ms) yesterday at about 1418hrs was caused by lightning affecting the inter-connector link between Singapore and Johor, Malaysia. Link from the statement by SP PowerGrid.
(FYI: Singapore is inter-connected to Johor at 230kV – a transmission level voltage; any disturbance at this level will typically be ‘seen’ by everyone in Singapore with 1/4 of the island ‘seeing’ the worst dip values).
While there is hardly any blackout moments in Singapore due to how the grid is designed and operated here, voltage dips like the above can actually be quite common. In the last 6 months, there has been 3 of such transmission level-originated voltage disturbances (as taken from our monitoring records; 5/11, 10/9 and 27/7). As electrical faults in the grid (be it caused by cable damage, customer’s installation fault, utility equipment fault or lightning) cannot be totally eliminated (only reduced thru rigorous maintenance, regulations/enforcement etc), customers with sensitive equipment should take measures in protecting their equipment adequately. They should also be aware of this Clause in the Transmission Code (which is also in their Connection Agreement with the Utility).
This clause basically rules out any ‘compensation claim’ from the Utility due to losses sustained arising from voltage dips. To some, this may seem ‘cruel’, but I believed this clause is fair as the electrical network is interconnected and everyone (Customers, Utility, Gencos) has to play their part. From my experience, the awareness on the need and know-how for protection against voltage dip is still very much work-in-progress here in Singapore. The key to solve voltage-dip related problems is not to seek compensations, but rather to undertake a proper assessment on the vulnerabilities of their equipment against voltage dips and then invest in the right mitigation solutions / methods.
“Explaining the outage, SGX said power is supplied to the data centre from two separate substations, which is then connected to the individual UPS systems. A “momentary fluctuation in power supply from the substations” caused the UPS systems to switch to its internal power source, but these power sources malfunctioned.” – ChannelNewsAsia.
In the early afternoon today, there was a voltage dip recorded at approximately 1418hrs (2:18 PM). A snapshot of this dip waveform captured in one of our sites in Bedok area is shown below. We also received several calls from various sites scattered over the island, reporting chiller operations being affected, etc. These could only mean one thing; a transmission level (eg. 230kV) fault had occurred.
Coincidentally, a report from ChannelnewsAsia reported an incident at SGX at approximately the same time, as shown in the following news snapshot. Without knowing further detailed information, I cannot really confirm / comment if these two incidents are related.
Voltage dip, while it typically occurs for just a slight fraction of a second may result in serious consequences when critical sensitive equipment are not being adequately protected. Usually, semiconductor plants suffer the most in these type of incidents, as their process equipment etc are very sensitive to variations in the power supply.
Voltage dip mitigation comes in various forms; some are battery-based like the the UPS (which is also a mitigation against a total blackout), while others are batteryless like the SoftSwitching MiniDysc (which caters for variation in the power supply for a few seconds only). The latter is preferred for dip mitigation as batteries require a rigorous maintenance and replacement programme, to ensure the batteries do work when they are called for.
Earlier, our office recorded a ‘shallow’ dip at approximately 1919hrs. Tell-tale signs from other neighbouring monitoring sites show this could be a transmission-level fault. Shall await for the report from the utility tomorrow.
Update 15/9/2014 from the Utility: Customer installation fault at Jurong Island
Noting how this dip due to a ‘customer installation fault’ can be seen in many areas, those ‘in the know’ will know who is the Customer here.
Just awhile ago, if you are one of the facilities’ guys, you probably had to scramble around because of dip alarms, standby generator cutting in or chiller drop-off.
Another 230kV fault was registered; affecting the South side of Singapore the most, suggesting a 230kV fault in the South block.
Here is a voltage waveform from one of our sites in the South.
Voltage waveform is taken at Low Voltage (L-N). It will mirror what is seen at 22kV and above (L-L).
(i.e L1 phase at LV is equivalent to L1L2 at 22kV).
The waveform here shows that there was a single phase fault (L2) at 230kV.
Here it was registered; worst case dip of more than 50%. Other blocks in Singapore (North, West, East) would also have seen this fault, albeit at less severe values.
On a happier note, Selamat Hari Raya Aidilfitri (in advance) to my fellow Muslims. Maaf Zahir Batin.
As a fan of powerXplorer Px-5 and Dranview, I got a little excited when Dranetz made this announcement.
Hope to get my hands on these ‘toys’ soon. 🙂
Go to dranetz.com for more info or visit their video link here.
p/s: If you have not used Dranview before, you don’t know what you have been missing.