Category: Voltage Dip

Earlier this morning, there was a Transmission-level fault that occurred at approximately 10:07AM. PQ monitors in the city-area captured the following waveforms at the 22kV incomer and at the 400V LT incomer side.

Here, the benefit of monitoring at L-N instead of L-L at 22kV is being showed clearly here. It is evident that there was a single-phase fault (L2) and that it originated upstream at higher voltage levels.

Note. A single-phase fault at 22kV will cause the other two phases to swell (not seen here).

There were reports of voltage dips in other transmission blocks from other PQ monitors. With this kind of magnitude observed here at 22kV, it is very likely that this fault originated in the same transmission block as well.

Update: 230kV cable damage along Keppel Road (South Region).

When a 230kV fault occurs, a quarter of Singapore will feel the worst dip magnitude (the region where the fault occurs), with the other 3 regions observing shallow voltage dips. Below is an example (via a Dranetz HDPQ) in the North region of Singapore during this same incident.

Earlier in the week, areas in Tampines, Loyang, Bedok, Pasir Ris will have experienced voltage dips. It was made known later that it was due to a 22kV cable fault in Tampines area.

Few sets of our portable PQ analyzers placed in Loyang was able to capture this event. It registered voltage dips (at low voltage) of about 20%, lasting around 60-80ms. Recorded data showed that it was a three-phase fault.

One may be curious, how could a fault in Tampines result in a voltage dip in places like in Loyang or Bedok?

Our local distribution grid is densely interconnected, resulting in a high-reliability electricity network. Total blackouts are rare. But interconnectivity brings about a small disadvantage. Any fault will be seen/felt (in the form of a voltage dip) by everyone who is connected. The seriousness of this dip will be dependent on the types of faults and the electrical distance between you and the fault point.

Here in our case, the fault was in Tampines area. Based on experience, for a voltage dip ~ 20% to be seen at another 22kV network, it will need to be a significant fault causing a voltage dip in the range of 80-90% in the fault area (Tampines). Loyang (where our PQ analyzers were) is connected to Tampines at 66kV level.

 

Just a while ago, the following waveforms were captured from monitors in Jurong East and in the River Valley area, indicating a transmission fault, likely to be originating from the South block of Singapore. Waveforms captured in the River Valley area indicated a single-phase fault on L1 (Red) at 230kV transmission voltage.

Added the following screenshots obtained from a PQUBE, being monitored in South of Singapore, at Low Voltage. Thanks James!

Earlier this afternoon in the midst of the year-end festive mood, you might have seen your office lights flickered twice in an hour: two transmission-level faults occurred. Tell-tale signs were from the nature of the waveforms and that in general, everyone in Singapore ‘felt’ it, with 1/4 of the island getting the ‘worst-magnitudes’.

One at around 1:46pm and the other at 2:36 PM. The following were captured from an office in Jurong East and in Bedok area (at low voltage).

At 1:46PM, it can be seen that the dips were fairly shallow.  Hence it can be deduced that the origin of the fault were neither in the 230kV blocks that these two sites are located. From the RMS trend of the waveforms captured at Site 2, it can be inferred that it was likely a single-phase 230kV fault on Phase L1 (Red).

At 2:36PM, the dips were much more pronounced at Site 1, suggesting that it resides in the same 230kV block as the fault. Here it is very clear that the 230kV fault was on the Phase L3 (Blue). At the second site at Bedok, the dips were again shallow. These are characteristics of a 230kV transmission level fault in Singapore. Only 1/4 of the island will be most affected with dip magnitudes in the range of 40 to 50% (dip by).

 

Earlier in the morning today, there was a localized voltage dip (dip by ~ 80%) in the Jurong East area. From the waveforms captured, it can be inferred that there was a 22kV L3-L1 fault.
Sensitive equipment was likely to be affected, especially those sensitive single phase LV control circuits taking in on Phase L3.

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.

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.