Last week, two of our portable PQ analyzers captured a voltage dip of about 13% (at 22kV) lasting almost 200ms. It was made known later that it was due to a fault in the Tuas South area.
Our PQ analyzers were in the Tuas West Drive area.
Based on experience, for a voltage dip of about 10 to 20% to be seen in 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 (Tuas South).
A voltage dip was reported in the Jurong-Pioneer area at around 6:10PM, due to a 22kV cable fault.
Our office, a 15-20mins drive away (Jurong East – Boon Lay Way) recorded a drop in voltages of about 13% (from 420V to 366.5V) or about 8% (if referred to nominal voltage of 400V), as seen below.
One may wonder how could a fault in Pioneer area affects the voltages in Jurong East?
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.
Based on past experiences, for a voltage disturbance of about -10% to be seen at another 22kV network, it will need to be a significant fault causing a voltage dip in the range of 70-80% in the fault area.
Our office is in another 22kV network, which is connected to the fault area via the 66kV network path, as illustrated below.
Such drop in voltages usually do not cause much problem(s) to the equipment-end (especially typical office loads), as observed in the following Irms trends during this voltage disturbance.
What happens if a voltage dip occurred, and for some reason(s), you had not set the PQ analyzer to capture it or that the PQ analyzer had ran out of memory for capturing of events? (Note: some brands of PQ analyzer do have a limitation on how much event(s) it can record).
The short answer is that you will not be able to get detailed waveforms (and trend) of that particular event. Hence, information such as how long was the dip would not be known.
But not to worry. Not all is lost. You will still be able to get the lowest (minimum) RMS voltage(s) recorded. Depending on the brand/model/software used, one will need to plot out the ‘per-cycle’ RMS voltage minimum trends.
Dranetz, for instance has incorporated these per-cycle trends automatically in their voltage/current trends. So the minimum/maximum value(s) that one see on a Drantez voltage/current RMS trend is really the lowest and highest value(s) recorded.
For others, you need to find things like “Detailed RMS trends”. Typically they termed this as the Vrms 1/2 trends, as seen here.
Vrms 1/2 Trend – Showing The Voltage Dip That Occurred on 14/11/2021 1600hrs (V1: 146V, V2: 198V, V3: 140V)
One must be careful not to plot the ‘normal’ RMS trends, which calculate out the RMS values based on sets of 10-cycle waveforms, as shown below. Values here will not show the true worst-case min/max values. Short events like a voltage dip which lasts 3-4 cycles, will get ‘diluted out’ here in a 10-cycle RMS calculation.
What is seen on the second trend graph here is also what is usually obtained when one uses a standard power logger. Hence the difference (in capability) between a PQ analyzer and a power logger, is clearly illustrated here.
Trend Analysis
Without an event capture, it will be impossible to ascertain the actual duration of this voltage dip. However, based on the differences in the two trends (Vrms 1/2 vs Vrms) minimum values, we can tell that this dip was definitely less than 10 cycles ( < 200ms).
This monitoring was done at Low Voltage (monitored at 3P4W) in a commercial complex along Orchard Road, with V1 and V3 dropped significantly (dip by about 40%) and V2 slightly lesser (dip by about 17%). Comparing with its loading/current trend suggests this was an event upstream of the monitoring point.
Looking upstream at 22kV, dip magnitudes at 22kV will be similar (i.e 22kV dip magnitude V12 will be similar to LV V1). At 22kV, for a voltage dip of such characteristics, it was likely an event originating from a higher voltage level (you may refer to other voltage dip posts on this).
Feedback from other PQ monitors island-wide supports this. This was a transmission-level voltage dip event. The trend results suggest that it was a single-phase (L1) transmission level fault.
On October 13, 2000, the Public Utilities Board announced, “New Measures to Control Voltage Dips”, which went effective on 1 November 2000.
The new measures include reviewing a licensed electrical engineer (LEE)’s performance if the electrical installation(s) under his charge had caused a total of 3 voltage dips, within a period of 2 years.
This was the beginning of having all voltage dip incidents (date, site, LEE-in-charge) published on the Authority’s website.
Then, the utility’s (PowerGrid) power quality section, the Power Quality and Load Analysis (PQLA) section, was just being formed. The island-wide power quality monitoring system (PQMS) was still in the works. It became operational somewhere in 2001-2002 with 80+ PQ monitors monitoring voltage levels from 22kV to 230kV.
Singapore’s 230kV transmission network was just being split into two networks, effectively minimizing the impact of a 230kV voltage dip from one another.
Voltage dip, then and now is still a costly affair for sensitive industries. While just lasting in terms of milliseconds, it can have a detrimental impact on production processes, especially those in the semiconductor-related industries.
The utility via its subsidiary (SP Systems) introduced (shortly after in October 2002), a voltage dip mitigation device, known as the Dynacom. It was a single-phase ultra-capacitor-based device meant to compensate voltage dips as low as 40% of nominal and for up to 1 second. It was targeted at protecting sensitive control circuits.
Fast track to today and the number of PQ monitors has more than doubled. The PQMS has enabled the utility to keep track and map out its voltage dip performance (System Average RMS Frequency Index – SARFI map) to the various regions of the island.
Singapore’s 230kV transmission network has since being split into 4 parts, limiting the significant impact of a 230kV voltage dip to just 1/4 of the island.
With inter-connectivity to our ASEAN neighbours being the talk of the town these days to improve the reliability of the electricity grid, we must not forget it does come with some downside as well.
Being inter-connected, any fault that occurred in one country’s electrical network can be seen in another. For instance, right now, Singapore is connected to Malaysia at 230kV. Any faults on either side of the network will be seen by both.
Here, in a recent event whereby a Tenaga Nasional Berhad (TNB)’s transformer was reported to have tripped. It had caused a voltage variation here in the eastern part of Singapore.
“Does frequency changes during a voltage dip?” – A favourite question among many. The answer is “Yes”.
This will be quickly followed by “But why our power quality monitor did not show significant changes in the frequency values even though a voltage dip event was captured?” The general answer is that the standard (IEC 61000-4-30) does not require it to measure such detailed changes in frequency values.
With the voltage waveforms captured, it is technically possible to calculate the frequency values during a particular event (say a voltage dip). Here’s an example, where the event waveforms were post-processed (via the Dranetz Dranview 7 software).
Such post-processing feature is very useful especially in generator load-test applications, where one will be interested to know both the voltage and frequency changes during every step-load change. An example is shown below. One just need to ensure that the pre/during/post event waveforms were set to be captured properly (i.e enough cycles). The software will do the rest.
Earlier this evening, there was a voltage dip that occurred just before 7pm. The following is a waveform captured at Low Voltage (monitored at L-N), located in the city area.
Reports of voltage dips from other PQ monitors in other transmission blocks suggest this was a Transmission-level fault.
Voltage waveform seen here was at LV (L-N). It mirrored what was seen at 22kV and above (at L-L). From here, it can be inferred that there was a transmission level single phase fault (Phase L1).
A shallow voltage dip was recorded this afternoon in the city area at approximately 3:01PM.
Most equipment will not be affected by this shallow ~12% dip.
Earlier this evening, there was a Transmission-level fault that occurred at approximately 7pm. The following is a waveform captured at 22kV incomer (monitored at L-N), located in the city area.
Here, it suggests that there was a Single-phase fault (L2) and that it originated upstream at higher voltage levels. There were reports of voltage dips from other PQ monitors in other transmission blocks as well.
Update: Suspected fault originated from Genco facilities in the west.
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.