IMPORTANCE OF VOLTAGE OPTIMIZATION OF ENERGY

IMPORTANCE OF VOLTAGE OPTIMIZATION OF ENERGY

IMPORTANCE OF VOLTAGE OPTIMIZATION OF ENERGY

IMPORTANCE OF VOLTAGE OPTIMIZATION OF ENERGY EFFICIENCY AND HIGH-SPEED PARALLEL REDUNDANT SOLUTIONS

Süleyman Topçu

EDİT ELEKTRONİK SİSTEMLERİ SAN. ve TİC. LTD. ŞTİ.

SUMMARY

Line voltages are set higher than the nominal value to provide sufficient voltage to users at the end of the distribution line and to reduce transmission losses.  Voltage received by a company from the mains depends on the place of the facility in the distribution line, electricity consumption graphics of other subscribers, the time of day , the season and electricity consumption graphics of the facililty’s own equipments.

The usage of the electrical machines which are designed and manufactured to work with the highest efficiency and best performance on the nominal supply voltage value, on the low voltage values, high voltage values and for 3 phase machines with unbalanced voltage, causes significant productivity and performance losses.

To make voltage optimization in facilities  will reduce direct power consumptio and will improve the performance and lifetime of machinery and equipment. Investment costs  in voltage optimisation can be brought back in a short time such as 5 years with taking into account the direct energy savings, effects such as the increase of operational efficiency and stimulations given by the government due to the reduction of carbon emissions.

In voltage optimization / regulation solutions, maintenance-free, long-lasting, increasable power with parallel connections, adjustable output parameters according to different voltage and load characteristics, making high-speed voltage regulation and suitable for industrial applications products should be preferred.

 

INTRODUCTION

 

The most important visions of  all manufacturers on the world and in Turkey in the last 20-30 years, is to develop more efficient and longer-lasting products. Manufacturer companies make long time R&D projects to increase the efficiency of the products %1.  This projects are to get the best results at the nominal voltage supply. For this reason the information like efficiency, energy consumption and other performance characteristics that are in the products’ technical documentation are the informations those are measured when the products are supplied with the nominal voltage. Manufacturer companies design their products to work with a wide range of supply voltage, considering the different distribution lines. But this equipments and machines do not work with the same efficiency and performance on all supply voltages. As you get farther from the nominal value of supply voltage the efficiency and / or performance drops. This applies to all industrial products.

Manufacturers of electrical devices prepare all performance and efficiency tables based on the nominal voltage. Therefore, unless a special measuring is not done, it is not exactly possible to determine loss of performance or energy of machines and instruments in different supply voltages.Bu nedenle, işletmelerin herhangi bir enerji tasarruf uygulamasına başlamadan önce profesyonel bir enerji analizi ölçümü yaptırmaları bir zorunluluktur. Therefore, the companies must do  a  professional energy analysis measurements before starting any energy conservation practices. The companies which manufacture devices for energy analysis and measurements with the new softwares that they supply, can prepare reports about the total energy loss and the increase in bills that is paid because of the bad energy quality. The same products can also prepare reports and results based on the measurements for the efficiency increase and energy saving ratios for the before and after energy saving applications. This measurement and the other measurements those are done with the analysis devices, will supply information about the results of the voltage optimisation in advance and will give enough information about the energy saving levels that they will get with the voltage optimisation.

The extra consumption that occurs on the machines and equipments because of the losses, mostly comes out as heat. This extra heat must be taken away to keep the machines go on with the same performance. So the energy that is used in the cooling and ventilating systems of the industrial products or most commonly of the whole facility must be added to the total energy loss.

As a last thing; the voltage optimisation and regulation(VOR) units are not only used for energy saving applications. VOR is also needed to prevent the machines and the equipment from the harms that can occur because of the instable voltage. This decreases the facility expenses and increases the production efficiency. Because any pause in the planned working hours because of any voltage problem or any machine harm, will decrease the production quantity and the efficieny. For a city grid that supplies electricity for thousands of users at the same time, is not possible to continuously supply the optimum voltage value for all users and electrical equipments.

In Turkey, in most of the cities including Istanbul, it was measured that in the high consumption hours, grid voltage decreases in %15-%30(%60 in some of the cities) band levels and in the low consumption hours it increases in %10-%15 band levels. In similar way, the grid voltages changes according to the transmission conditions in summer and winter time. These problems which are because of many reasons like the weakness of the distribution lines, overloading and illegal usage, are not expected to have a solution in the near future. Therefore facilities need to have their own VOR systems.

Voltage optimisation and regulation(VOR) system are the AC voltage regulation units and the management softwares for this units which adjust AC grid voltage to nominal voltage value that is determined according the special conditions of the facilities.

VOR units are designed and manufactured specially according to the load chracteristics, the total load and the grid voltage chracteristics. acVoltaj Below there is a drawing that shows the general structure of a VOR unit.

                                                             

Fig.-1. Voltage optimisation and regulation unit.

 

SPECIFICATIONS OF VOR UNITS AND THEIR EFFECTS ON ENERGY EFFICIENCY

1.- Voltage Increasing : VOR unit increases the voltage to the nominal voltage level which is most appropriate for the facility. This feature is called voltage boosting (boost). This is done by the booster transformer which is connected in serial way between the load and the city line. Load voltage is increased and stabilized to the nominal levels with the variable voltage that is applied to the control windings of the booster transformer. At this time more current is taken from the grid line which is lower than the nominal voltage. As the grid line voltage decreases, the current increases but the total power that is taken from the grid line is the sum of the total output power and the lost power on the VOR unit itself. The total lost power on a well designed VOR unit should be around %2-%3. The machines those are supplied by a lower voltage value than the nominal voltage, have much more loss than this. When the supply voltage of the electrical equipment whic are designed to work on nominal voltage with the highest efficiency, goes down, the power losses increases proportionally.   This extra loss comes out as heat.

The current on the line at low voltage will go up with the increase of power consumption of the machines. The increasing current on the line will increase the line losses proportionally. This loss on the line also comes out as heat.

For example at a %20 low voltage value , the sum of efficiency loss of the electrical equipment and the line losses  will make the electrical consumption %10-%15 higher. In a facility like that by voltage optimasing a %8-%12 energy saving can be done directly. ( The %3 difference is the loss on VOR unit.)

Considering the manufacturing losses that will be caused by the problems on the machines, and the service costs that will occur because of the low voltage and the shortening lifetime of these equipment, the total energy saving will be more than %15.

2.- Voltage Decreasing: This is to decrease the high grid line voltage to the nominal values(Buck). When the city line continiously supplied at high levels or increases in different times, the facilities should have VOR units those have the voltage decreasing(buck) feature.

VOR units can be manufactured as “ only voltage increase(boost), only voltage decrease(buck) or voltage increase/decrease(buck&boost) . As the cost will go up by adding each feature, the determination of the actual load and grid conditions and to design the system according to this will effect the initial cost and refunding time of that The increase on the supply voltage of the electrical equipment doesn’t make the current decrease with the same ratio. As explained above, the increase on the supply voltage of the electrical equipments those are designed to give the highest efficiency at the nominal voltage, makes the losses increase.  This extra consumption comes out as heat. The energy loss may occur %5-%10 on a supply voltage of %15 more than the nominal. Using a VOR unit, considering the increase on expenses of the facility and the losses because of the cooling systems, can make an energy saving approxiamately %10.

3.- Voltage Balancing: The imbalances on the grid line distribution and usage, makes the voltages on the 3 phases different from each other. This is called phase asymmetry. Another reason of the phase asymmetry is the start/stop of the machines on the facility in different times randomly. Each machine that is connected to the line which has a phase asymmetry, has an effect on the increase of  the imbalance, because the high current that is used by the 1-phase machines those works through the lower voltage phase will  make the voltage even lower.  Most of the 3-Phase machines will act in the same way and will use more current through the low voltage line and will make decrease the voltage more. The lines that have the higher voltage will have less effect comparing with the low voltage line, as they will have less current. And finally it must be mentioned that the imbalance on the lines that have phase asymmetry is not permanent but changes continiously according the the changes on the loads.

When the 3-phases machines those are manufactured to work with the highest efficiency on nominal and balanced voltage, are supplied with an unbalanced 3 phase, high voltage losses and also imbalance losses will occur. Another negative effect of the phase asymmetry is the increase on the neutral  current. The neutral current is “0” when a 3-phase machine is supplied with nominal and symetric voltage. When phase asymmetry happens, parallely neutral current also increases. The increase on the neutral current is proportional with the voltage imbalance. The increased neutral current goes through all the building’s line. The line losses on a facility without phase asymmetry is the sum of all the losses on 3 phases, the line losses on a facility with phase asymmetry is the sum of all the losses on the 4 cables as 3 phases and neutral.

 

VOR units can be designed to balance the phase asymmetry. A good designed VOR unit which can manage each phase and power units completely indepent, can work with %100 unbalanced load and %100 unbalanced voltage with full and same performance. We explain this with an example: Let’s imagine a scenario like this, R phase is %60 lower than the nominal voltage, S phase is %40 higher than the nominal voltage, T phase is %20 lower than the nominal voltage,, and the loads are %100 on R phase, %0 on S phase , %30 on T phase.   VOR unit will keep the supply voltage always on the nominal voltage value and will work with the highest efficiency without any performance lost. The change on the imbalance of  loads and the grid voltage will not effect the performance of the VOR.

The design of the VOR units will effect the manufacturing cost so the system features must be determined by making detailed measurements of voltage and load on the facility that it will be used.   

In case of imbalanced phase voltages, the loss on 1 phase machines those are supplied from high and/or low voltaged phases must be added with the losses on the 3 phase machines caused by phase asymmetry and the losses on the facility lines. %10-%15 energy saving can be done where the voltage is %15 lower and the phase imbalance is %10. 

4.- The effect of VOR system on reactive power compansation: The performance of reactive power compansation systems on a facility with phase asymmetry, decreases. Because the compansation capacitors in the standart reactive power compansation systems are started and stopped with 3 phase. The capacitors groups’ effects those are on a facility with phase asymmetry, changes from phase to phase.  This makes to establish a successful and stable reactive power compansation harder. As the VOR unit will keep the phases equal and on nominal voltage, reactive power compansation will be more effective and successful. 5. The effect of VOR Systems on manufacturing efficiency and facility costs:

The machines on the facilities where there is low or high voltage value then the nominal, or phase asymmetry, will be shut down by the protection units.  Most of the machines and electrical equipments which are manufactured according t ot the standarts, have a voltage tolerance of %10. If the supply voltage goes out of this limitation then the machines will automatically stop.

The stopping of the machines and systems which in most cases  followed by each other as  a manufacturing process, will make a big loss on raw material and labor work. A VOR unit which can keep manufacturing process run, will increase the total efficiency of of the facility and will make energy saving.

 

Some machine and electrical equipment manufacturing companies let their products to work in inappropriate voltage levels but in any problem they don’t accept the warranty. In such cases user companies have to accept the additional facility costs those occur because of working with inappropriate voltage conditions.

VOR units can be equipped with additional protection features in order to maintain safe work of both themselves and loads those are connected to them. All the machines and the equipments can be protected against high voltage, low voltage, phase asymmetry and phase lost, with the protection features that are adjusted according to the facility’s own conditions. These protection features will not maintain extra energy saving but they will decrease the facility costs.

 

THE STRUCTURAL AND TECHNICAL SPECIFICATIONS OF VOR SYSTEM

 

1.- Efficiency:

First of all the VOR unit that will be installed must have at least %97 %98 efficiency. The efficieny values must also be effective for different voltage and load conditions rather than being effective for only nominal working conditions. Even it works with the lowest input voltage, highes input voltage, %100 load or %50 load, it should work with full performance and %97 efficiency.

Additionally it must not have any wearing and consumable parts to keep the facility cots low. Standby working losses have to be small and when necessary it should be shut down with remote management easily. 

2. Fast And Independent Voltage Management

In VOR system, the transformers on each phase, power control and switching elements and the elements those control and manage these parts have to be completely independent for each phase from the other phases. This is a must to maintain the full performance work of the system even with %100 unbalanced voltage and %100 unbalanced load. The other important parameter is speed. VOR system must regulate the voltage fast. Most of the protection and control boards of the high tech machines measure the deviation on the supply voltage very fast and they shut down the machines to prevent from any harm.   This fast protection feature of the electrical machines is preferred because it keeps the fault ratios low. But the shut down of the machines becaue of these  fast protection functions, means the pause or stop of the manufacturing process in the facilities. A stop of a machine for a couple of minutes can be the reason of a pause of a couple of hours or production faults, related with the production process which is connected to multiple processes. To solve this problem, a VOR unit with high speed voltage stabilisation, has to be used. With the VOR units those are  thyristor technology based, the voltage drops can be measured in ½  period and in 3 periods can be adjusted to its nominal value. Figure-2  

                                                                              

Figure-2. Correction Speed

 

 This is fast enough to stabilise the voltage before the fast protection units of the machines are on. It is not possible to get this performance with the electro mechanical voltage regulation devices those have the regulation times which are measured in seconds.  

3.- The Parallel Connectivity and Redundant Working Features:

 

One of the biggest  problems in a facility’s electrical system is, any fault or pause in one of the electrical control and management devices that causes a production stop.  To keep the facility running in such cases, more than one power transformer are connected parallely to get the total power or alternative supply sources are maintained with diesel generator systems or spare power transformers which can be started in any fault case. Automatic or manual transfer units are installed in order to start these alternative supply sources. In facilities where more than one transformer are used or in facilities where there is  a back-up transformer, VOR units must also been used more than one quantity and with parallel connection in order to maintain the facilities’ security and the sustainability.

In parallel redundant system, VOR system is manufactured as multiple(N pieces)  units which have the same technical specifications instead of being manufactured as one, and these VOR units are parallely connected by shortcurcuiting the outputs. The total power requirement of the facility is supplied by N pieces of VOR units with an automatic sharing. According to the project specifications, all VOR units’ outputs and inputs can be connected paralelly as well as each VOR unit can also be supplied by a different transformer. These parallely connected units which works synchronously with the help of a special management unit, share the total power equally

Figure-3.

                                                                                              

Figure-3. Parallel Redundant VOR Unit

 

On this system, if any VOR unit breaks or stops with any other reason, the faulty unit shuts down and the other units keep working by sharing the total load without any energy outage or instability. If the facility’s total power equals to the VOR units’ total power and the facility works on full load, then in any case of fault, the total load of the facility must be decreased.   Because the remaining VOR units can supply the overload only for a limited time. If  it is required to maintain the full load work of the facility even in a fault situation then 1 piece of additional VOR unit is added to the parallel system. This system is called N+1 Parallel Redundant System. In parallel redundant systems VOR units’ total power is %20-%25 more than the total facility’s load power. Facility’s total load power can be supplied with N pieces of units and +1 is used as the redundant. In any case of failure of one unit, the remaining N pieces units will keep the facility to run with full load uninterruptably. After starting back the faulty unit, load will again be shared between N+1 pieces of units. If more than one units have a failure then some of the machines or equipments in the facility must be turned off and running of the facility can go on with low capacitity.  In similar way if the facility is wanted to run under low capacity on purpose then some of the VOR units can be turned off to keep the energy losses down.

 

Another application area of the parallel redundant VOR is the high power requiring facilitities. Generally switching equipments and semiconductor switching equipments those are used in applications which have more than 1 MVA, are more expensive. The reason of this is, high power switching is harder and they are manufactured in low quantity as they are used less. Even on more powered applications like 4MVA, switching equipments are not standart.  Also these high power switching equipments and semiconductor power switching parts, so the delivery time is long.

Using parallel redundant VOR units on high power facilities , will maintain the facility secure and the initial cost will less.

On parallel redundant systems, different transformers can be used for each VOR units. For example for a 4MVA facility, 4 pieces of 1MVA power transformers can be used. Thus the diffuculty of supplying a 4MW transformer with a single VOR unit  and the risk of shutting down all the facility in any case of failure, are eliminated.

As more than 3MVA VOR units and transformers are not manufactured,  these distribution units are manufactured as more than one group and each group is supplied by a seperate transformer. If any unit breaks down in a system like this, then some parts of the facility will have energy outage. Parallel redundant units produce flexible solutions for high powers.

 

Finally, facilities those are projected to be enlarged, parallel redundant VOR units can be used. At initial investment cost it can be started with one unit and as the facility needs more power, more units can be added to the system.

 

4.- Protection Functions:

Uninterruptable automatic bypass system is required to keep the manufacturing lines running in any case of break down because of a failure or or overload of the VOR units which are supplied to increase the facility efficiency.As an additional protection caution, by this function facility loads are transferred to the city grid with an interrupt. After the fault is fixed or the overload situation disappears then the system will come back on again without  any interruption.

Also additional protections like electronic overload, short circuit, high voltage and high temperature can be suggested for the VOR units for the system security. 

For easy management and visualization, remote management and visualatization modules like MODBUS, ETHERNET and etc. can also be suggested for the VOR units that will be installed.

 

 

 

 

Conclusion

Installing voltage optimisation and regulation systems for energy efficiency, will keep the electriticity consumption of the facilities low and will increase the general facility efficiency. For voltage optimisation and regulation applications, maintenance free, parallel connectable, fast voltage regulating, new technologies must be chosen.   

Sources

Parallel redundant voltage stabilizer technical documents and energy saver user manuals of Edit Elektronik ltd.sti.
“Fluke 430 series II three-phase power quality and energy analyzers” brochure.
Gamak standart asenkron motor specifications.