Implementation of Parallel Synchronization Method of Generators for Power & Cost Saving in University of Gujrat ()
1. Introduction
Today Pakistan is facing disastrous power crises. The demand is much higher than supply so energy supplied to consumers is not continuous and load shedding of 12 - 16 hours badly affects the consumers. The University of Gujrat (UOG) is also affected by this load shedding, to carry on educational activities without any interruption; University of Gujrat has its own standby power system. In UOG for every one or two blocks there is a separate generator. These generators run on almost 30% or less load in 10 months of the year and run on almost 50% load in remaining two months i.e. May and June. In case if any of the generators becomes out of order, the relevant block faces total black out. So to provide continuous supply to all of the blocks, it is better to operate generators in parallel (synchronized generators operation). In this way if any of the generators goes out of order, the blocks will still avail electricity supply from parallel connected generators. This is the main idea of this research work.
UOG is facing financial losses in aspect of standby power system. These losses comprise of fuel cost, higher maintenance cost and lubrication oil cost. Therefore by implementing this method, these losses can be reduced to a great extent. Furthermore UOG can also avail many advantages of this configuration like a lot of savings in terms of diesel cost. For example in synchronized operation of generators, there may be a need to run only two generators instead of three or four, hence fuel and maintenance cost is reduced.
Heavy load of blocks for example machinery, medical lab equipment, and other such sort of massive loads can be operated easily by parallel synchronization method because all the generators are synchronized and bulk load can be managed. But in existing system to operate such load, a separate generator has to install as it is done in Medical Block in recent months. Synchronized generators method also has the ability to meet future expansion of the load. For example, if all the blocks have to build a new computer lab in future then to meet this demand, there is a need to install a single generator in parallel. But if generators are not synchronized, we have to install a generator for all of the blocks instead of one. In parallel operation of generators efficiency of the system will be improved. Less number of personnel is required [1] .
2. Power System of UOG
2.1. Transformers
The power entering into the UOG power system is distributed using distribution transformers of different KVA ratings. These transformers step down the voltage from 11 kV to 400 volts line to line. There are a total of about 36 transformers of total 4700 kVA. Their number and kVA ratings, the location of each transformer with the load it is serving, the current output of each transformer and the voltage at each of them given in Table 1.
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Table 1. Transformers location and rating.
2.2. Generators
The power input source of UOG is behind the main gate of the university, which is provided by WAPDA. It also has thirteen mobile diesel operated generator sets of different capacity. All these generator sets are made by SMJ company. The generation voltage of these generators sets is 380 V, which is directly fed to the different department of UOG. Location and kVA rating of these generators is shown in Table 2.
3. What Is Synchronization
In today’s world of technology, a separate generator is found very rare supplying the load independently. Very often on small places where the emergency power is required for a short while the synchronous generator is used independently. As in any Electrical system, the loads are not constant load is varying with time, Electrical systems are interconnection of large number of alternators operating in parallel and supplying large number of loads. During the process of synchronization of generators the magnitude of voltage, frequency and phase angle is kept constant this process of paralleling of one alternator to another or to the bus bar is called the synchronization. Figure 1 shows the block diagram of the synchronized system, where three generators are connected to the same load and any time these can be used together to address the load demand [2] .
3.1. Need of Synchronization
In any power system it is preferred that instead of supplying power with one big unit, use one or more units at
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Table 2. Generators location and rating.
different load conditions, there are number of benefits that are given below when we run alternators in parallel.
1) As we know the efficiency of any machine is maximum at its full load and we can run any machine when it is required and doing this efficiency can be increased.
2) Using several generators can supply a bigger load.
3) Reliability of the system is increased since if one generator is failed than the other is used for the operation and whole system will not be shut down.
4) Having many generators that are working in parallel we can remove one or more generator for the maintenance purpose.
5) If load demand increases than more generators can be connected.
6) Instead of placing generators at different locations it is better to place all of them at one place it will ease the maintenance.
7) Standby losses and per unit price is reduced because our generation is according to our demand [3] .
3.2. Conditions for Synchronization
The conditions for the generators to be paralleled are given below:
1) The RMS value new coming generator voltage should be equal to the bus bar voltage.
2) The phase sequence of new coming generator should be same to that of bus bar. The phase angle must be the same.
3) The frequency of new generator called the incoming frequency of the generator should be slightly higher than that of running frequency of the bus bar.
The first condition can be found by using the volt meter and the second and 3rd can be found by using lamp method or Synchroscope [4] .
3.3. Techniques for Synchronization
Different techniques are being used for the synchronization of the alternators, the purpose is to check the all four conditions listed above and then different schemes are used to connect the generators to the system. These methods are given below:
1) The bright lamp method.
2) The dark lamp method.
3) The Synchroscope method.
These methods are not preferred today due to less accuracy and manual operation; these methods required a very experienced person and also reliability and security of these methods is not enough. So, Synchroscope method is used now a day and microprocessor based systems are used for the automatic synchronization of the alternators, these methods are reliable and easier to manage [5] .
3.4. Synchronization Using Synchroscope
If the phase angle between the two voltages is different than the pointer of Synchroscope will move, it will move to slower point when the incoming machine is slower and move towards the faster point if then incoming machine is faster and pointer will stop when the incoming generator frequency is same to that of bus bar if this situation is attained then the switch is closed [5] .
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Figure 2. Schematic diagram of Synchroscope.
4. Existing System of UOG and Its Drawbacks
4.1. Power Requirement of UOG
Annual power required for UOG is increasing day by day; energy requirement for UOG from year 2009 to 2013 and expected increase in energy demand after 2013 is given in Table 3.
4.2. Prime Power
As the energy crisis in Pakistan is almost at its peak, approximately there is 12 - 16 hours of load shedding per day. So that’s why the prime power supplied by the electric company is almost 30% - 40%. Due to this severe problem, UOG requires a lot of stand by energy to fulfill out electricity requirements. In the compensation of this problem UOG is using generators to accomplish their stand by power. The per unit cost of electricity is given below:
Present cost of WAPDA/Kwhr (Unit) = 13 Rs./Kwhr [6] .
4.3. Standby Power
In order to fulfill the standby power requirements, UOG is using number of generators at different locations. Per unit cost of stand by generators are: Cost of unit produced by diesel generator/Kwh (Unit) = 33 Rs./Kwhr. The total generation capacity of these generators is 1500 KVA.
5. Drawbacks of Existing System
5.1. No Reliability
For every system reliability is one the most important factor. It means supply of energy should be consistently available at any time. The current system is not reliable as it should be. For example academic blocks are fed by separate generators and in case of maintenance issue or if any generator is out of order for a time, the respected block is black out, and the minimum maintenance time for a generator is at least one day, it means the respected block should remain without electricity for a long time.
One another example is of the generator which is installed for water pump is of 100 kVA, if this generator is out of order the water supply for the entire university is disturbed, on the same time all the generators are running properly and generating extra electricity which is not entertained. According to current system there are blocks which are fed by a generator of high kVA rating which is large enough to entertain two blocks at once. In case one generator for a block is out of order and at the same time the generator of adjacent block generates enough electricity which could entertain both the blocks, but the current system does not allow doing so.
5.2. Higher Cost
For any engineering system lower cost and maximum output is always preferred, so first and foremost priority for an engineer is to reduce the cost of the system. As in existing case numbers of circumstances are available when load requirement is less to an extent that one or two generators are enough to meet the demand of aca-
demic blocks. For example in winter season and after 4 PM. the total demand of the academic blocks is reduced to 25% of the peak demand, it could be fed by one generator and separate generator for each block is not required. But use of all generators as in the case of existing system to provide the electricity increases the cost in terms of diesel and maintenance requirement.
5.3. Less Efficiency
Efficiency is one of the most important factor of the system. Smaller input and greater output is the first preference. A more efficient system provides more stability and reduces cost and losses. In UOG all of the generators are running at 25% - 50% of the maximum load. The optimal operational point for synchronous generator is 75% - 80% load of its rated value. At this optimal point the synchronous generator will be at its maximum efficiency. At evening the generators are operated at 25% of the load in order to reduce diesel cost, its mean generators are operating at lower efficiency that is not good for the life of the generator. Using one generator running at 80% of the load will increase the efficiency of the system and reduces the fuel and maintenance cost as well [7] [8] .
5.4. No Future Extension
An Electrical system is designed in such a manner to provide electricity for the loads introducing in future. This increases the reliability of that system. If a system is designed according to the prescribed condition it will be long lasting. It is noticed that electricity demand is increasing annually in UOG so in case of future expansion same generators will not be able to feed the system. For this compensation there is requirement to install new generators or replace the existing one by a higher kVA value, but both of the things are difficult to evaluate.
5.5. Annual Diesel Cost of Existing Generators
Annual costs of diesel generators have been calculated. Calculations were shown in Table 4.
Total diesel cost per year is Rs. 3,780,100/—excluding lubrication cost.
6. Fuel Cost Comparison for Existing & Proposed System
In this section calculations were done for the fuel cost of various months and the savings obtained by connecting the generators in parallel combination (Synchronization). For these calculations an average of 5 - 6 hour load shading is taken into account. Fuel cost and savings in the month of March is given below in Tables 5-7.
Fuel Cost Comparison in Month of March
Avg load at Generator 1 per day = 42.66 kVA.
Avg load at Generator 2 per day = 41.86 kVA.
Avg load at Generator 3 per day = 26.91 kVA.
Avg load at Generator 4 per day = 40.70 kVA.
So savings in the month of March is = Rs. 441,575.
Similarly calculations were done for the months of April, May, June and July. Saving for these months are rupees respectively.
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Table 4. Diesel cost of existing generators.
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Table 5. Generators operating at 25% load.
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Table 6. Generators operating at 50% load.
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Table 7. Generators operating at 80% load.
7. Real Time Reading of Generators
Generators Reading in Different Months
Several real time readings were taken from the Generators in different months at different times using clamp meter and load of each generator is calculated. The readings of all four generators at different times are given in Tables 8-11 at different times and days.
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Table 8. Generators reading in March.
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Table 9. Generators reading in April.
8. E-Tap Simulations
Using previous mentioned readings of loads two E-Tap models one for synchronized system and for un-syn- chronized system were made for the power system of UOG. In these models real time values of load were used. The ETAP Load Flow Analysis module calculates the bus voltages, branch power factors, currents, and power flows, throughout the Electrical system. Newton Raphson method is adopted to find the optimum results and five iterations were required for this method. Following are the equations used in Newton Raphson calculations.
(1)
and 
are real and imaginary parts of voltage in equation (1).
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(2)
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(3)
δ is the phase angle and Pi and Qi denotes the real and active power in Equations (1), (2) and (3) respectively.
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(4)
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(5)
Active and reactive power mismatch can be calculated from equations (4) and (5) respectively.
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(6)
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(7)
Voltage is the sum of square of real and imaginary parts of voltage and can be calculated using equation (7).
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(8)
Voltage mismatch can be calculated using equation (8).
8.1. Un-Synchronized System Simulation
In un-synchronized system all the generators are working separately at different locations in UOG. There are four generators for seven academic blocks. First generator feds Engineering and Medical Block, second generator feds Academic and Business Blocks, third generator feds Science Block, while the fourth generator feds P and BS Blocks. Real time readings of load in E-Tap were used to take the load flow calculation. E-Tap model for un-synchronized system and load flow report shown in Figure 3 and Figure 4 respectively.
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Figure 3. Un synchronized generator operation.
8.2. Synchronized System Simulation
In synchronized system which is the proposed solution, all the generators are connected in parallel and then load flow calculations are performed on this system. In this system all the generators give supply to a main bus bar, and then different cables execute from this bus bar and reach the academic blocks. The E-Tap models include two different schemes, i.e. once using aluminum conductor and once using copper conductor. E-Tap model & load flow report for aluminum and copper conductor have been shown in Figures 5-8.
9. Synchronized Generator Operation
For this solution all the generators for the academic blocks have to be placed on one place then they will be synchronized through a synchronization panel. In this manner all the generators will supply power on a bus bar. Academic blocks will get supply from this common bus bar through cables of different gauge depending upon the respective load. Generators will get start according to the load demand, for example if load of all the blocks is 300 KVA, then only two generators of 200 KVA and 150 KVA will run to meet this demand. In this manner only two generators are required for the total demand instead of four generators as present. In winter season for reduced load only one generator is enough to meet the load demand. This solution will result in minimum cost.
The diagrammatic representation of our proposed solution is given in Figure 9. In this figure the cables which are shown in bold are pre-installed, while the cables shown in light lines are to be installed. The length and gauge of all the cables have been shown. Cable of gauge 400 mm2 which is to be installed has a length of 200 meters, while the cable of gauge 240 mm2 has a length of 135 meters.
9.1. Existing Equipments
1) Four Generators (200 kVA * 3 + 150 kVA * 1) = 750 KVA.
2) ATS switches.
3) Bus bars.
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Figure 5. E-TAP model with aluminum conductor.
9.2. Equipment Required for Proposed Solution
1) Synchronization panel.
2) Cables of gauge 240 mm2 and 400 mm2 to be installed.
3) ATS switches.
4) Generators to be synchronized.
5) Main bus bar.
6) Circuit breakers.
9.3. Synchronization Panel
Synchronization panel is automatic Electrical device which synchronizes various generators. It is better to use a synchronization panel which must have properties like automatic and manual synchronization, load sharing at generators according to the power; it should automatically start and stop generators according to the load, automatically balance work hours (co-aging) etc. For this proposed solution refer synchronization panel is TEKSAN. Generators made by company which produces generators and synchronization panels. Model: TJPS10 Synchro-
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Figure 6. Load flow report with aluminum conductor.
nization Panel.
9.4. Cables Price & Length Calculation
For this solution proposed, there is requirement to install some new cables of different gauge at different locations as shown in the Figure 9. Cables at some locations are already installed. The length, gauge and location for the new cables are shown in the Table 12.
For this solution, cables of two different gauges i.e. 240 mm2 and 400 mm2 have to be installed. The total length of 240 mm2 is 125 meters, which includes 33 meters from A Block to M Block and 92 meters from S Block to P Block. The total length of 400 mm2 is 195 meters which includes 105 meters from B Block to A Block and 90 meters from B Block to S Block. The cost comparison for these lengths of 3 & half core non-armored copper, aluminum and copper aluminum conductor given below in Tables 13-15.
9.5. Total Cost for the Solution
For the proposed solution we have to put all the generators at one place and then synchronize them through a synchronization panel. Then we have to install some cables that are mentioned above. The total cost comparison for this solution including panel and cable cost is given below in the Table 16.
Hence the total cost for this solution is Rs. 4.13 million Rs.
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Figure 7. E-TAP model with copper conductor.
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Figure 8. Load flow report with copper conductor.
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Figure 9. Proposed model for synchronized operation.
9.6. Pay Back Period
As have been seen from the real time calculations that diesel cost can be save every month in a good manner. Adding all the diesel savings and approximated savings for coming months can be helpful to obtain the payback period. Total saving in current year have been shown in Table 17.
The approximated savings in the up-coming months are estimated below in Table 18.
It is clear from calculations that 18 months are required to compensate these costs. So if Synchronized net
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Table 15. Price for copper aluminum conductor.
work is being installed in December 2013, the amount can be getting back in June 2015. Hence the payback period is approximately 18 months.
10. Conclusion
From the preceding analysis one can conclude that implementing parallel Synchronization technique can bring advantages in the form of power and cost saving. Total cost of the solution is 4.13 million and total annual expenses of old system is 3708100 Rs. Total approximated cost saving in 18 months is 4236550 Rs. with average monthly saving is 235363.9 Rs. Hence payback period of this solution is 18 months.