Author Archive: Bertie Bezuidenhout

Unbalanced Power Networks in Gauteng South Africa

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It is important to realize that unbalanced networks are not easily manifested in power supplies.

In this document, I am highlighting two cases in which unbalanced networks are perhaps not easily noticeable. In the case of Linden, people may think that the power supply is normal by measuring the phase-to-neutral voltages. In the case of Modderbee, Eskom and officials from the electricity department may think that there is nothing wrong with network when they select the phase-to-phase voltages and notice that it is almost the same.

Perhaps an even more important question is: do the unbalanced networks affect the customers’ electricity bills? The short and simple answer is yes, it does!

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Contravention of Fiduciary Duties

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On the 2nd of October 2023, I published an article with the heading “Phase Imbalance in Distribution Networks” in which I stated that “In a recent unrelated “survey”, I came across a 10-minute averaged voltage unbalance of 327% between Phase 2 and Phase 1”. I also asked the question: is Eskom aware what is happening on the Distribution and Reticulation Networks? I also stated that, since the medium-voltage supply comes directly from an Eskom substation which is probably about 20-metres away, one wonders what is going on at the Eskom substation since it is highly unlikely that the voltage unbalance is as a result faulty equipment at the municipal substation. It is as if one phase is completely missing. The same “missing” phase also show an abnormal high current. The neutral current which is supposed to be at or close to zero is also very high.

In a recent webinar, I posted a question about power quality disturbances. I was then told about the large number of Quality of Supply Instrument that Eskom have installed, assuming that it is regularly maintained and monitored so that poor power quality issues will be detected almost immediately, and action taken to rectify whatever may be causing the issue or issues.

Last week, I reached out to someone at Eskom I believe may be able to help me to have this situation investigated or refer me to someone who can assist me, but that email remained unanswered and the email I sent this morning, “was deleted without being read”. This person’s name appears to be involved in this type of work on the behalf of Eskom, and that is why I reached out to him. So, my question now is: do Eskom or any of the Power Distributors care about Poor Quality of Supply?

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Compensating For Power Quality Issues Caused by Power Electronics Devices

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It is a known fact that there is a growing shift towards renewable energy sources as well as buying and selling electrical power which most often necessitates the use of HVDC transmission systems.

Both the solar power generation and HVDC transmission systems make extensive use of power electronics devices.

In future, more-and-more grid-forming converters (GFMCs) will be introduced as the scale of microgrids also increase. These structural changes would undoubtedly change the system operation paradigms, which in turn, necessitating a deeper understanding how these new devices function and how it would affect network stability and particularly, power quality.

In many studies, it has been found that an extensive use of power electronics devices plays a major role in power quality issues, specifically voltage sags and swells.

The trend of retiring rotating generation plants could lead to grid instability if it is not carefully monitored and actioned well ahead of time before major issues develop. Currently, gas and steam turbine power generation play a vital role in terms of grid inertia and stability.

Thus, with the shift towards renewable energy sources and the trend of retiring rotating generation plants, national grid companies need to consider other alternatives to help compensate for power quality issues caused by power electronics devices. This includes capacitors, static VAR compensators, and static compensators.

The installations of capacitor banks at substations are not new. It is relatively cheap, reliable, and easy to install but it takes up a lot of space and require special controlling devices. An ordinary circuit breaker simply does not work with capacitor banks. Another disadvantage is that they can only supply reactive power and not absorb it. When load rapidly increases and voltage drops, the effectiveness of capacitors diminishes.

Static VAR Compensators (SVCs) consisting of shunt capacitors and reactors and may offer a greater degree of voltage control, but it is of little use for rapid voltage changes.

Although static synchronous compensators (StatComs) with its use of sophisticated power electronics is a far better option, it has a major drawback; it is far pricier than the more basic equipment.

A synchronous compensator is a large piece of machinery. It is spinning generator and flywheel combination. Having it connected to the high-voltage transmission network via a step-up transformer it is kept in sync with grid frequency and thus contributes to network stability, dampening any fluctuations in frequency. Again, this concept is “not new”. In the late 1970s Eskom installed several Synchronous Condensers.

The intermittency of wind energy and the extensive use of power electronics devices, such as found in HVDC transmission systems and solar power generation equipment, emphasizes that grid stabilization and equipped with AC filters to avoid the harmonic impact on the AC network performance, have an increasingly important role in a successful energy transition.

Coal-fired power stations can be repurposed whereby the steam turbine is removed and replaced with a large-mass flywheel and Synchro-Self-Shifting (SSS) clutch. The electrical rotating equipment, such as the existing generators, is then reconfigured to become synchronous condensers. Since it is already connected to the high-voltage transmission network via a step-up transformer, it will become a stabilizing device.

With the rapid shift towards renewable energy sources, we should have started thinking about ways to stabilize the network by installing more synchronous condensers and AC filters to avoid the harmonic impact on the AC network performance. In an article published in the Engineering News of 20 November 2023, it is stated that “Eskom is preparing to introduce 11 synchronous condensers – seven new and four repurposed – across its transmission system to support grid stability as the penetration of variable renewable-energy generators rises”. On 22 June 2023, the Australian Renewable Energy Agency (ARENA) published and supported a report in which the installation of synchronous condensers is also addressed.

A timely commitment to install synchronous condensers is needed because “long queue for new SCs is already forming” [my interpretation based on what I have read about this topic]. Considering that there is already a significant rise in reports about poor power quality issues, my question is: Was this unforeseen by the industry? The large-scale use of power electronics in solar power generation and HVDC power transmission has been around for many years.

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Unfazed Attitude Towards Power Quality Issues

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On September 24, 2023, I posed an article in which I explained how poorly maintained switchgear could lead to long-lasting power quality issues. In that article, which was based on an actual incident in Benoni, Gauteng, South Africa, I mentioned that the voltages of two of the three phases increased by more than 51% while the third phase dropped to a value which was almost zero. I also stated that further investigation was needed “to determine the cause of the voltage discrepancy”. The content of this article was also posted on other media with links sent to several people I believed should be made aware of what could be happening without anyone knowing about it. Amongst them was someone who, from what I was told, sent the information to the municipality. I even placed the pertinent parts of the article in a newsletter that was sent to those on a mailing list, including people at Eskom.

In that same article, I commented that I am not sure whether an investigation will be done. Almost five months later and numerous more attempts from my side to “escalate” this kind of issue, and I have not been contacted. So, I am beginning that believe that the municipalities and/or Eskom is unperturbed about issues of poor Power Quality.

Phase Imbalance in Distribution Networks

On October 2, 2023, I posted another article in which I stated that “In many cases operators and maintenance crews are unaware of the negative consequences that phase imbalances can have on LV networks and electrical equipment. Current imbalances would lead to a reduction in the serviceable loading capacity of LV cables and distribution transformers. Because of the imbalances, some of the phases could carry higher loads while the remaining phase or phases could be lightly loaded but, the limiting factor for the addition of three-phase loads is the current on the highest loaded phase or phases.

“Current imbalances can also cause additional heat losses in distribution transformers and LV cables in both the phase and neutral conductors. These types of losses represent a significant part of the total losses occurring in LV networks.

“When end users, such as municipalities, are supplied by unbalanced voltages, induction machines and power converters face adverse effects such as reduced efficiency, increased losses, potentially dangerous overheating and, in some situations, premature failures. At severe voltage or current imbalance levels, some types of protection relays could malfunction, leading to miscoordination, nuisance tripping and lack of selectivity.”

In that same article, I also said that such issues are usually not restricted to just the one substation. Often it may affect an entire region, depending on where the fault is located. There be many such issues going unnoticed.

Late December 2023, I learned that people in the Magaliesburg area are having to replace electric motors and other electronic equipment quite frequently. Earlier this week, while in the Magaliesburg area, I noticed the signs of an Unbalanced Network. This has probably been going on for many years, listening to those living and running businesses in that area.

Cost of Complacency

On November 7, 2023, I posted an article in which I pointed out how unbalanced voltages, phase-shift variations, and harmonics disturbances would result in enormous economic losses. This was aimed at accountants and financial officers to make them sit up and start to notice how some financial losses at their businesses are preventable. I mentioned how “customers on that feeder [the one in Benoni], are most likely paying around 237.27% more than they ought to”.

Now, the question is: is there an Unfazed Attitude Towards Power Quality Issues?

Judging by the lack of action from all those who have or must have seen these articles, I would say YES, there certainly is Unfazed Attitude Towards Power Quality Issues.

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Cost of Complacency

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In the latest newsletter which would be published on November 14, 2023, I am making another attempt, this time, to catch the attention of accountants and financial officers explaining to them how unbalanced voltages, phase-shift variations, and harmonics disturbances would result in enormous economic losses.

But first, I must go back to a previous blog posted September 24, 2023, in which I referred to unbalanced voltages and currents I “accidently” came across when I analyzed the measurements, I took for a consulting engineer who wanted to know what the maximum loading on a 6.6kV cable feeder is.

On our website, there are two pages which are particularly relevant to understand the consequences of unbalanced voltages, phase-shift variations, and harmonics disturbances. The most recent one explains how unbalanced three-phase quantities are decomposed into their symmetrical components to understand what happens “almost undetected” but have an enormous impact on the power system. In an earlier published, Negative Phase Sequences have a harmful effect on power system equipment and operation.

In the latest newsletter mentioned above and called Financial Losses Resulting from an Unbalanced Network which would be published on November 14, 2023, under the heading Cost of Sales Losses, I explain how some large power users – industrial and commercial – are paying for Apparent Power (kVA) while they can only effectively use the Real Power (kW). In the incident referred to in the blog posted September 24, 2023, the customers on that feeder, are most likely paying around 237.27% more than they ought to. The ratio of kVA to kW is 3.37:1.

The question is: is that restricted only to large power users – industrial and commercial – or do single-phase power users also get charged so much more. The answer is a little more complex and not that straightforward, but the simpler answer is yes, they do. Everyone, single-and three-phase power users is charged per unit and that unit is kVAh and not kWh. So, those power users fed from that feeder are paying approximately 3.37 times for what they are getting.

When you do go and lay a complaint with the power utility company, they will make you pay to have the electricity meter tested, and I can tell you beforehand, there will be nothing wrong with the meter. What happens next is also not going to solve the problem. Someone will be sent out to check the voltages and currents at the substation, and even that will show that there is “nothing wrong”. Why, they check the voltages between phases with a panel meter which is grossly inaccurate. That would then finally “prove” that there is “nothing wrong”.

If anyone believe that this is only restricted to one area, think again. I have had a discussion with someone from Middelburg, Mpumalanga, South Africa since the incident I referred to previously, who also complaint that their account is mysteriously double than it used to be.

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Consequence of Weaknesses in Power Quality

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In the mid-eighties, as part of my function, I was asked to help and solve a problem of one of our client’s constant complaints about “power failures”. This client was the National Accelerator Centre (NAC) in Faure, Western Cape. Today it is called the iThemba LABS. According to their website, this is the largest accelerator facility in the Southern Hemisphere and the only Cyclotron facility on the African continent.

When I contacted them to find out what the issues were, I was invited to visit them and given several private tours throughout the facility so that I could understand the intricacies of their operation. On more than one occasion, I was taken all the way through to the operating room so I could understand the consequences of power interruptions. I was also shown the damages that was caused every time there was a “power interruption” and explained how long it took them to repair the damages. However, after my first visit, I pulled all the daily incident reports and could not find any power interruptions that occurred on the corresponding dates.

I could not argue that there were no “power interruptions” since I saw the damage. I then enlisted the services of our specialist department. At this point, I must stress, that the kind of instrumentation that is currently available on the market, did not exist. Most of it had to specially build and for a particular function.

Approximately a month later, the specialists came back with, what people may describe today, as rudimentary instrumentation. This was installed at the substation with clear instructions that no-one else were allowed to enter that substation without my presence. Wire was strewed all over the floor. Essentially, the main instrument was a high-speed analogue-to-digital converter that could be trigger by set parameters which then records everything on a computer that we bought specifically for this exercise. When an event occurred, everything before and after an event was recorded. Today, this is a built-in standard function of my Power Quality Monitor. The purpose of that instrumentation was to give us a set of data that we could analyze to determine the cause of power distortions.

After collecting the data, I spend a considerable amount of time to find a correlation between the event recorded at that substation, and anything that happened on the entire network which could have been related. This was a mammoth task and I spent long hours going through daily incident reports obtained from both the local and national control centers.

During this exercise, I found that some of the incidents related to the tripping of 400- and 132kV circuit breakers over a thousand kilometers away.

With this information, I went back to the executive of National Accelerator Centre. I told them that my news was not good and there was nothing we could do about the problem. Whatever caused the “power distortions” was within the power supply limits at that time. I did, however, undertook to help wherever I could, and it was then that I contacted a friend at a European company with presence in South Africa, to come up with one or more solutions. One of those solutions was a motor-generator set with a massive sized flywheel. Whether that was implemented, I am not sure since I was promoted shortly afterwards and move to a different part of the country.

The primary reason for this blog is that, at that time, I was supported by all my seniors all the way up the ranks, and they often visited the site to find out how they can be of assistance. Judging by what I see and experience now, I doubt if this will happen today or anytime soon.

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Power Network Disturbances

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Throughout my time in the power transmission and distribution industry I have probably had experiences that many others may never have. In a previous post, I talked about the current and voltage unbalances and how a large factory in the Western Cape in South Africa was severely affected by negative phase sequencing. In this post I want to touch on another incident we have had around that same time.
Without being directly involved, I learnt about a 500kW electric water-pump motor that was ripped out of its foundation, breaking the water pump, and causing major havoc in the pump station leaving a large urban area without water.

The question that should be asked: are those responsible for looking after the factory or mine aware of the influences of voltage / current harmonics and phase unbalances among several other similar negative effect on their plant? Most probably not since many think that if the lights are burning, everything is hunky-dory, and they should not worry about anything. Fact is, it is not and it is worthwhile to read the other blogs.

If you think that this only applies to South Africa, think again. It is happening in Ireland and the USA or wherever you are from: those reading my blogs.

A second topic I want to discuss is how something unexplained is later contributed to something someone think is “fact”. Many years ago, the loss of power transformers connected to overhead power lines were all contributed to lightning damage. When I worked at Eskom Western Cape in the eighties, I used to receive a daily incident report for the entire region. One day, I noticed that twelve 22kV/380V transformers were lost due to lightning in the Calvinia and Williston areas. I would not except what was stated in the reports and instructed the depot to dispatch all those transformers back to the main workshop in Brackenfell. I also instructed the head of the transformer workshop to cut those transformers open as soon as they arrived and let me when it is done. After the top lid of the transformers were cut open, we found that the core of the transformers was “standing” in water that penetrated over time. We would have spent vast amounts of money on additional lightning protection for something that had nothing to do with lightning.

Then, a few years later, I asked one of my subordinates why there was such a large maintenance backlog. His explanation was that the maintenance crews are not maintaining the 22kV/380V transformers. I immediately instructed him and the person reporting to me to remove all those transformers from the maintenance schedule. I then had to explain that one of the maintenance strategies that should be employed is run-to-failure. It cost less to replace those transformers than to maintain them on a regular basis. Obviously, the cost includes all the associated costs.

Now, I am an independent consultant and working for myself, I can do these types of investigations. That means proper Power Quality Investigations and many more similar types of analytical work.

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Power Quality Issues Caused by Distributed Generation

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To mitigate the effects of Load-Shedding, many homeowners have decided to install PV Solar Energy systems. And, as I said before, they are more worried about how much it would cost than the quality of the products. If they can pay the lowest possible price for the entire installation, they are happy and do not care so much about what they get.

During the early stages of Load-Shedding, someone from our neighborhood asked me for advice regarding a PV system, but when I gave him a rough estimate of what it would cost, including the cost of a well-engineered design, I could see that the price was far more important than the quality of the system. Those advertising in the newspaper say that something the with same output would cost far less. Not long after he had his PV system installed, he told me that their washing machine had broken down and that they were compelled to replace it. I did respond since I knew what the cause of it was.

As in many other countries, PV systems with microgrids has become an unavoidable choice. This, in turn, bring along new challenges for utility companies. Naturally, if those employed by the utility companies are awake, knowledgeable, and experienced, they can proactively conduct power quality monitoring exercises. With the ever-increasing expansion of renewable energy systems, the most important power quality challenges that is brought about, is the harmonic distortion which affect the voltage and current quality at the point of common coupling (PCC), and negatively affects the loads.

We are all aware that there is a wide variety of inverter models are available on the market with new ones added constantly. Consequently, the harmonics delivered to the main power grid will thus vary according to inverter types and their control strategies. Utility companies therefore must have the knowledge, skills, and instrumentation to investigate the impact of these components that accompany the renewable (embedded / distributed) generation.

The technical consequences of distributed generation are dependent on the size of the system and its location in relation to the main power generation grid. These influences are reverse power flow, overvoltage along distribution feeders, voltage / current harmonics, phase unbalances, power losses, voltage control disturbances, low power factor, and Electromagnetic interference problem.

To overcome these effects, grid measurements, data analysis, and system modelling are needed for different parameters of grid and electricity generated by the renewable energy suppliers to find solutions and to make this resource more reliable.

Power quality parameters such as inrush current, power factor, total harmonic disturbance (THD), and frequency fluctuation should be recorded and studied regularly.

Inrush Current is a small predictable difference between distributed generating station’s voltage and utility grid voltage which can produce transient inrush currents. This can cause a temporary voltage sag at the neighboring buses, nuisance trips, thermal stress of the power components and several other problems.

With Under Voltage / Overvoltage, the grid connected distributed generating systems only inject active power into the utility grid, which may change the value of reactive power that flow in the system.

Output power fluctuation is one of the main factors that may cause severe operating problems for the utility network. This occurs because of variations in solar irradiance caused by the movement of clouds and may continue for minutes or hours. This may cause power swings, voltage flickers and fluctuations of over / under voltage.

Power factor often decreases to unacceptable levels due to high-powered distributed generation which sits on lightly loaded short distribution lines.

Current and voltage harmonic distortion, voltage and current distortions is generated by nonlinear loads such as power inverters that are used in solar systems where the currents flowing through the impedances of the grid affecting the voltage nodes. Harmonics produced under such circumstances can cause series and parallel resonances, overheating in transformers and capacitor banks, and false operation of protection devices that may reduce the reliability of power systems. A total harmonic distortion voltage (THDu) value of between 5% and 8% indicates significant harmonic distortion. Some equipment malfunctions may thus occur. The acceptable current and voltage harmonic level generated in the microgrid was specified by the IEEE standards 519 and 1547 and IEC-61000-3 standard, and this should not exceed a THDu of more than 8%.

Frequency fluctuation is an important factor in power quality. Any change between the produced and the consumed power may lead to frequency fluctuation. Small sized solar systems may cause frequency fluctuation to be insignificant compared with other renewable energy-based resources. However, this issue may become more severe by increasing the penetration levels of solar systems. Large enough frequency fluctuation may change the winding speed in motors and may damage generators.

Although there may be more solution available to moderate the impact caused by distributed generation, one suggestion is to switch off some or all the PV panels when flowing current is under the critical value, or rather divert the power to charging a battery bank. A second suggestion is the use of passive or active filters.

When new solar farms are proposed for connection to the municipal distribution network where this is perhaps far more critical, neither solution are compulsory, as far as I understand. I recently saw a proposal for a grid-tie solar farm without batteries nor active passive or active filters. But, as I said earlier on, utility companies need employees who are awake, knowledgeable, and experienced to know what to look for. Alternatively, utility companies can contract a company, us, to regularly conduct power quality monitoring exercises on their behalf.

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Rotating Voltage and Current Vectors

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Any repetitive signal, such as three-phase Alternating Current (AC) Voltages and Currents, can be represented as the rotation of a vector around a point. In a balanced three-phase network, the magnitudes of the voltages and currents in all three phases are the same and these phases voltages and currents are shifted symmetrically by 120 degrees to each other. Under this condition, the vector is fixed, and the rate of rotation is constant, and the end of the vector lines will continuously trace a circle. Each pass around the circle represents one complete cycle of the signal.

In the video below, the three-phase waves are displayed with the phase-displacement 120-degrees, but Phase 2 (yellow) voltage is reduced by 6%, which may result in 3rd harmonics disturbance represented by the thinner solid line (5% 3rd harmonic) and dotted line representing a 2% 5th Hamonic.

Positive Sequence Voltage with 6% Dip in Phase 2 (Yellow), 5% 3rd and 2% 5th Harmonies

The harmonic disturbances will cause the fundamental sine wave to be distorted. So, the display is not as accurate as it would be displayed on an oscilloscope.

The three-phases are represented as Phases 1 to 3. In this video, the three-phase vector are not colored as per the IEC standards for the UK & EU and several other countries: Phase 1 = should be Brown but displayed as Red, Phase 2 = should be Black but displayed as Yellow and Phase 3 = should be Grey but displayed as Blue. These are the former colors and still widely used by many countries.

In the vector diagram above, Phase 1 lies along the X-axis with Phase 2 displaced by 120-degrees in a clockwise direction and similarly, Phase 3 is displaced by 120-degrees from Phase 2, also in a clockwise direction. Since the phases would follow a pattern of Phase 1, the Phase 2 and lastly, Phase 3, the normal vector rotation, or more precisely referred to as positive phase sequence, is counterclockwise.

In the vector diagram above, Phase 1 lies along the X-axis with Phase 2 displaced by 120-degrees in a clockwise direction and similarly, Phase 3 is displaced by 120-degrees from Phase 2, also in a clockwise direction. Since the phases would follow a pattern of Phase 1, the Phase 2 and lastly, Phase 3, the normal vector rotation, or more precisely referred to as positive phase sequence, is counterclockwise.

If the magnitudes of the three phases becomes unbalanced or if phases are shifted by something different from the 120 degrees, a negative phase sequence vector is generated. This vector rotates in the opposite direction, which is clockwise.

Because of such voltage unbalances, a common phenomenon found in three-phase power systems which are not well known, additional power losses are being generated. These current and voltage unbalances could damage equipment connected to power system. Again, not always that apparent. In many cases, it happens almost undetected.

Obviously, the greater the unbalances, the greater the risk of damage and more severe it becomes. Another seemingly unknown factor is the substantial financial losses to both distribution network operators and end-customers. This applies to any plant with rotating apparatus and many other user-connected devices. This issue is one of the unrecognisable critical power quality problems which should become a major focal point for utilities and Distribution Generation (DG) industries. But since it is not clearly noticeable, almost no attention is paid to it.

The asymmetry described above, typically appears in the network because of the connection of single-phase customers, which creates uneven load among the phases. This problem, the asymmetry, is further exasperated by large enough single-phase generating devices that are connected to the existing distribution networks. As the non-dispatchable renewable energy systems are being connected to the power systems, the phenomenon of asymmetry will increase to a point where it becomes a major issue, if it is not already the case. Microgrids and charging stations for Electric Vehicles (EVs) are being connected without proper planning or replanning. This has become one of the greatest technical and operation challenges, but hardly any attention is paid to it. Whether that be the so-called third- or first-world countries. Even the best run utilities are not aware of this problem or do not pay enough attention to the phenomenon asymmetry.

It is thus critically important that these issues are mitigated by comprehensive analysis and careful planning. This requires an all-embracing understanding of unbalance propagation and the identification of critical factors that affect such asymmetries.

In a future blog, I will elaborate on the phenomenon of asymmetry and its relation to harmonics.

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Causes of Unbalanced Voltages and Currents

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Practical imperfections which can result in unbalances are:

  • A three-phase equipment such as induction motor with unbalance in its windings. If the reactance of three phases is not same, it will result in varying current flowing in three phases and give out system unbalance.

With continuous operation, motor’s physical environment cause degradation of rotor and stator windings. This degradation is usually different in different phases, affecting both, the magnitude and phase angel of current waveform.

A current leakage from any phase through bearings or motor body provides floating earth at times, causing fluctuating current.

  • Any large single-phase load, or several small loads connected to only one phase cause more current to flow from that phase causing voltage drop online.
  • Switching of three phase heavy loads results in current and voltage surges which cause unbalance in the system.
  • Unequal impedances in the power transmission or distribution system cause differentiating current in three phases.

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