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Publication Title | Supercapacitors Energy Storage System for Power Quality Improvement: An Overview

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The reason behind overview of supercapacitors energy storage system is that supercapacitors are less weighty than that of battery of the same energy storage capacity, a fast access to the stored energy, Charging very fast than battery, Charge/discharge cycle is 106 time, storage capacity independent of number of charging/discharging cycles, energy density for Supercapacitor is 10 to 100 times larger than of traditional capacitors(typical 20-70 MJ/m3), capacities up to 5F/cm2, life cycles 25-30 years, high efficiency (95%),power density 10 times greater than batteries, Charge and discharge time very less, rated capacitance value ranging from 0.043-2700F,nominal voltage ranging from 2.3 to 400 V,rated current ranging from 3-600 A, operating temperature ranging -40°C to 85°C,Maintenance free, very low leakage current, also non polar [4, 5, 6, 7].

2. Power Quality Issues

a) Voltage flicker

DG may cause voltage flicker as a result of starting a machine or sudden change in the DG output which results in a significant voltage change on the feeder. In case of non dispatchable source, the output fluctuates.

The voltage flicker can be reduced by controlled voltage starting of Induction generators, tighter synchronization; Inverters are controlled to limit inrush currents and the change in output levels so that it must follow the IEEE standards 519-1992[8, 9, 10].

b) Voltage sags

The most common power quality problem is voltage sag; the DG may or may not help. However, the ability of DG to reduce sags is very dependent on the type of generation technology and interconnection location, during voltage sag, DG might act to counter sag. Large rotating machines can help support the voltage magnitudes and phase relationships. Although not a normal feature, Inverter-based distributed generators can be controlled to supply reactive power for voltage support during sag [8, 9, 10].

c) Sustained Interruptions

To improve the power system reliability and to provide backup power, incase of power interruption, or to cover for contingencies when part of delivery system is out of service. Unfortunately, with an uncontrolled-inverter and lack of storage capacity might not be capable of operating in stand-alone mode. When the DG is interconnected in parallel with the utility distribution system, some operating conflicts might arise that affect the system reliability. An example is the interference with utility relaying and reducing the devices reach. Therefore; DG has the potential to increase the number of interruptions in some cases [8, 9, 10].

d) Voltage regulation

Alternators are capable of providing active and reactive power and, hence, can be used to regulate the voltage in the distribution system to which they are interconnected. Initially it seems that DG should be able to improve the voltage regulation on the feeder. Some technologies are unsuitable for regulating voltages like simple induction machines, most utility interactive inverters that produce no reactive power. Also, the most utilities do not want the DG to attempt to regulate the voltage because that would interfere with utility voltage regulation equipment and increase the chances of supporting an island. Generators controls are much faster than conventional tap-changing transformer and switched capacitor banks larger DG greater than 30% of the feeder capacity that is set to regulate voltage will often require special communications and control to work properly with the utility voltage regulating equipments [8, 9, 10].

e) Harmonics

There are harmonics concerns with both rotating machines and inverters, although concern with inverters is less with modern technologies; based on IGBTs that use PWM

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reason behind overview supercapacitors energy storage system weighty battery capacity
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