• Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies
  • Rainbow Technologies

Welcome to Rainbow Technologies

Rainbow Technologies was formed nearly a quarter century ago (1989) to deal with the serious Power Quality challenges inherent with a newly integrated transmission grid at that time.

Introduction

The meshing of the previously islanded Southern African power pools with thousands of kilometres of new transmission lines, subjected to harsh & aggressive climatic conditions, resulted in an initially unstable & poor power supply.


RainbowtechThe new grid was exposed to bush and cane fires, tropical vegetation growth, uncontrolled wildlife, one of the highest lightning incidences in the world (>10 flashes per square km per annum), marine & industrial pollution, temperature inversions, line lengths in excess of 600km, mountainous terrain, deliberate sabotage and temperature extremes.
 
 
 
0002Increased transmission equipment and servitude maintenance were required, with unique insulator "live line" spray washing measures.

All the foregoing created numerous line and equipment faults with consequent voltage dips, frequency excursions and grid separations.
 
 
 
 
 
Added to this, the ever-increasing installation of low-cost and efficient Variable Speed Drives at that time created other problems. The voltage sensitive power electronics combined with their non-linear currents (ie harmonic generators) and low fault levels required new and unique solutions.
 
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There was an obvious & over-riding need for innovative and Africa based designs. Equipment designed in Europe or North America was (and still is) ill-suited for these rough & ready supply conditions.
 
Reliability of equipment operation was paramount, incorporated with simplified maintenance since the equipment manufacturers call-out times were measured in days or weeks.
 
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Incorporation
 
Rainbow Technologies rose to these unique challenges and was formed to provide a much needed, home-grown analytical & design service.
The company was incorporated in 1989 to develop the Specialist Engineering services required for measuring, analyzing and designing improvements & enhancements to the power supply and the sensitive loads.
 
The combined specialist expertise in various power quality areas listed below exceeds 300 man-years.
Rainbow's specialist electrical expertise is broad and covers:

Rainbowtech• Generation
• Transmission
• Substation Design
• Industrial plant design
• Materials Handling
• Earthing
• Lightning Protection
• Protection Grading
• Control & Instrumentation
• Transient & Steady state measurement
• Modelling
• Predictive failure systems
• Tariff Optimisation & negotiation of Power Supply Contracts
• Power Factor Correction
• Harmonics
• Voltage dips
• Voltage Unbalance and
• Flicker
 
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Client Base Summary

The much needed local expertise provided by Rainbow, has resulted in a large Blue Chip client base in Southern, Western & Eastern Africa (more specific detail in Client base section).

African Client Base
 
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Rainbow's dedication to engineering excellence & innovative designs resulted in various successful projects outside the African continent including;
Australia, Mainland China, Italy, Germ any, United Kingdom, Canada & USA.
 

International Client Base
 
worldwide
 
 
 
Engineering challenges faced by Rainbow Technologies
 
South Africa's mining and metallurgical industries are large power consumers and require special engineering to function productively with the prevailing adverse electrical supply conditions.
 
Mine Winders
(Large time variant Loads, Harmonic Generators)

South Africa has the deepest gold mines in the world (depths of 4km or more), requiring massive mine winders in excess of 10 000kW. (Ward Leonard sets initially, then DC Drives and finally Cycloconverters).

Vast amounts of Chilled water (ie MW pumps) are required to reduce the intolerant underground temperatures of >600 Celcius for safe human working conditions.
 
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A typical large Gold Mine has an installed load of around 200MW, of which 20% is 4-6 mine winders and about 40% pumping (previously large synchronous motors, now soft-start 4-8MW induction motors).
 
The grid supply is typically at 132kV, with the mine load network at MV 6,6kV or 11kV. Because of the shaft depths, the MV cable network is tens of kilometres, creating another potential harmonic resonance with now significant distributed cable capacitance.
 
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Single Phase AC Traction
(Large unbalanced space variant loads, Harmonic Generators)
 
The longest bulk freight line in the world (860km) transports iron ore to the Western seaboard of South Africa. The trains consisting of 350 wagons & 8 locomotives have a length in excess of 3800m and a total payload of 41 000 tons. The locomotives are 50kV single phase AC (phase-phase from the grid) VSD's and draw up to 40MW total per train.
 
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South Africa also has a 600km bulk coal line transporting 80 million tons of coal per annum from the inland coal-mines to the Eastern Seaboard. The trains are made up of over 200 wagons, with length around 2500m and payload per train of 21 000 tons. The 8-10 locomotives are 25kV single phase AC and draw up to 25MW total per train.
Special precautions have to be taken to protect other consumers from the excessive voltage unbalances caused by these Traction loads (Voltage unbalance in excess of 5% vs motor tolerance levels of 2%).
 
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Challenges faced were measuring & modelling several moving spatial loads over the rail lengths. Each spatial load (ie individual trains) has varying magnitude during acceleration, constant speed, climbing, descending and deceleration.

Combined with the analysis, were the mitigation requirements including system strengthening, Static VAr Compensators (single phase control), Grid Operating regimes, Improving other load immunity etc.

Large Induction Motor Starting
(Large startup currents, Transient Under-voltages)

Because of the extended transmission network and remoteness of large (eg pumping) loads from the generating pool, there is a special problem associated with starting these motors with low supply fault levels.

Typical MV motor starting currents are 5-7 times full-load current and are mainly reactive in nature (low power factor during the set-up of the magnetic field). If the motor is large in relation to the fault level, then the transient under-voltage, if switched Direct on Line (DOL) will be large and delay or prevent the motor from starting.
Special starting techniques are required in these cases to reduce the under-voltage to acceptable levels, including tolerance levels of the other loads in that area.
 
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Accurate modelling of the motor and network is required, with special attention to supply contingencies. The versatile ERACS modelling suite is used for time based Motor Start Computations.

Load & motor inertias are critical here, and loads with high inertia (conveyors, Ball Mills, Gearbox driven fans etc) need extra attention and proper specification of motor parameters (eg Start Torque, Breakdown torque, Start Current etc).

Successfully designed & cost-effective Starting solutions (apart from soft-starters & star-delta starters) are autotransformers with switched START & RUN Capacitors.
 
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Voltage Dips
(Impact on Sensitive Plant, Loss of Production)

The increased exposure of the extended transmission network resulted in numerous voltage dips due to line (and terminal equipment) faults.
Typical Southern African transmission statistics are in the region of 3-7 faults/100km/year (versus typical 1-3 in more hospitable terrains such as Europe). For a network extending more than 25 000km, that implies something like 1000 – 1500 line faults which will be seen as dips everywhere because of the interconnected network.

The vast majority of these dips will be insignificant due to the remoteness of the faults, but the geographically/electrically closer-in faults will be much larger in dip magnitude.
Below is a 1 month recording of voltage dips at a 132kV substation, graphed according to SANS042 definitions. By classification a dip has to be greater than 10% and lasting from 20 milli-seconds to 3 seconds – under-voltages with duration longer than that are defined as short term under-voltages, or interruptions if voltage is zero. (the hundreds of small dips <10% are therefore excluded).
 
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The effects of dips on serial industrial processes (eg Pulp & Paper production, Steel Mills, Textile Mills etc) and processes that cannot tolerate drive stoppages (eg uphill Slurry Pumping) are significant.

The stoppage is normally not the cause of the extensive financial consequences, but rather the time to cleanup and restart the process – sometimes up to 4 hours. http://youtu.be/hxB30vREBO4
 
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Extensive research was carried out by Rainbow, in conjunction with the local utility Eskom, on the nature of voltage dips.
The vast majority of dips (>85%) are due to phase-earth faults in the HV transmission system. Passing through the normally star/delta configured step-down transformers to the Load MV networks, converts this reduction in 1 phase to a reduction in 2 phases. Transforming to LV is normally via a delta/star transformer, and the HV dip is then re-created at LV.
This behaviour makes it difficult to compare the same event at different voltage levels.

Furthermore, the faults can develop into 2 & 3 phase faults if un-cleared fast enough, the load may increase the dip magnitude during the fault time and will hinder the full voltage recovery because of increased loading by motors re-accelerating.

Assessing load performance for this non-ideal voltage dip is always difficult and never easy to simulate under manufacturer routine & type tests.
 
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Rainbow patented the Dip Doctor to provide global, cost effective voltage support for large loads (>10MW) and has installed 5 units to date.

In addition to the consumer improving the load ride-through capability during voltage dips, the supply utility can often implement relatively low cost network modifications, to reduce the frequency and/or duration of voltage dips.
 
Large Open Arc Furnaces
(Rapidly varying Load, Harmonic & Flicker Generation)

South Africa's metallurgical Industry is large, with about 20% of total generated electricity used for smelting.
The closed arc and DC furnaces do not have that significant an impact on the supply network, the arc is "milder" and the charge is generally auto-fed. These are typically Manganese, Aluminium, and Gold smelters.

Be that said, all these smelters are rated in the 50MW plus range and require significant Power Factor Correction to improve the very low power factors (as low as 0,6 lagging), and these are normally harmonic filters tuned as low as the 2nd harmonic. Flicker can also be a problem, depending on the supply fault level and the furnace short circuit ratio.

Open arc furnaces (Steel, Titanium, Iron ore) are typically AC supplied, with furnace currents in the +50kA range at very low voltages (50V-500V). Because the smelting is done in discontinuous batches, and because the charge is not homogeneous, the furnace arc current is erratic, sometimes extinguishing completely.
 
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The voltage deformity is clearly visible and analysis of the frequency components gives a weighted value of Flicker using various algorithms.
Flicker is mainly "annoying" to humans as incandescent light bulbs glow & dim. It can also initiate fits in persons with epilepsy (It has no serious damaging affect on equipment)..
Typically Static VAr Compensators with predictive controllers are required to dampen the rapid furnace current fluctuations if the Short Circuit ratio is below around 30.
 
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Increasing Fault Levels is often not cost effective for remote furnace loads, and SVC's have to be installed (also not such low cost solutions).


 
 
 
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