Load bank

Subcell Approach Stumper et al.135 presented the subcell approach to measure localized currents and localized electrochemical activity in a fuel cell. In this method a number of subcells were situated in different locations along the cell s active area and each subcell was electrically isolated from each other and from the main cell. Separate load banks controlled each subcell. Figure 8 shows the subcells in both the cathode and anode flow field plates (the MEA also had such subcells). The current-voltage characteristics for the... 

The numerical model is implemented for the three current collector configurations previously mentioned. Since the model uses semi-empirical parameters, this is first calibrated and then validated, through a comparison with experimental data. For collecting the current, a silver wire is wrapped around the cathode, while a nickel spring is placed in contact with the anode (case 3 previously defined). The tests are performed using pure hydrogen at a constant flow rate. Voltage is varied by the use of a load bank, and the relative current is measured. The temperature of 800°C is... 

The impedance can be measured using various instalments and techniques, ranging from a simple oscilloscope display to a fast Fourier transform (FFT) analyzer. The most common instrument used is a frequency response analyzer (FRA), e.g., the Solartron FRA. A potentiostat or a load bank combined with a frequency response analyzer can perform the EIS measurements. The electrical connection between the FRA, the potentiostat (or the load bank), and the fuel cell is illustrated in Figure 3.19. 

There are two options for controlling the perturbation to the measured system one is to control the current perturbation then record the voltage response from the system the other is to control the voltage perturbation then record the current response. For a current control measurement, when the leads are all connected the electrical load is set to a DC constant current. The FRA will generate an AC current perturbation and interrupt the fuel cell through a load bank or a potentiostat. The response to the interruption from the fuel cell will enter into the FRA for analysis to obtain the AC impedance spectra. 

Figure 3.20. AC impedance measurement by TDI RBL 488 load bank and Solartron 1260 [21]. (Reproduced by permission of ECS—The Electrochemical Society, from Tang Y, Zhang J, Song C, Liu H, Zhang J, Wang H, Mackinnon S, Peckham T, Li J, McDermid S, Kozak P. Temperature dependent performance and in situ AC impedance of high-temperature PEM fuel cells using the Nafion-112 membrane.)...

When fuel cells work under heavy load conditions, it becomes more difficult to carry out the same measurements of AC impedance. One limitation on the application of EIS to large fuel cell stacks is that most commercially available load banks operating at higher currents do not have good frequency responses (ca. 10... 

The STAR fuel cell stack, shown in Figure 5, was characterized via H2/air operation (Figure 6). Figure 6 data are limited to 66 kWe although the stack is capable of higher power - load bank limitations have prevented us from higher power operation. 

Figure 7.4. The anode and cathode bi-polar plates, the gas plenums, the membrane, and the gas diffusion layer. The Plenums are slowly replenished from an external feed. The black arrows indicate direction of electron flow and of proton counterflow. The external circuit between anode and cathode is completed through a load bank with variable resistance Rg. The voltage between anode and cathode plates is denoted by V and the external current by 7. ...

Switching of harmonic filter banks or capacitor banks on loss of utility power can allow a standby generator to operate at a suitable output power factor when supplying load. Installation of a reactive load bank can provide a further sink for system reactive power if a standby generator is not capable of absorbing the power present in the system. 

A portion of a typical mine site power distribution system is shown in Figure 3. This example shows the application of a diesel generator on an emergency power distribution system bus that includes a drum-type auxiliary hoist and other equipment that is also used for emergency egress, air compressors for underground supply air, and resistive load bank used to absorb excess regenerative power from the hoist, if necessary. 

The benefits of AFE PWM variable frequency drives coupled to mine hoists indicates that this will be the preferred application for the foreseeable future. When powered by off-grid diesel generation systems, particular attention paid to design specifications of drive transformer or input reactors, generators, load banks, harmonic filter banks, and power system controls can avoid potential power system problems and ensure a successful system implementation. Individual equipment manufacturers need to have an understanding of overall system design... 

Ordinary potentiostats are limited to a highest current of approximately 1 A. To study higher currents, either booster potentiostats [695] or so-caUed load banks should be used [696, 697]. In load banks, the ac current may be modulated externally and the potential drop on a load resistor (proportional to current) and potential difference at the studied object are applied to the frequency response analyzer to measure the impedance. Analysis of the impedance of fuel cells with the separation of impedances of the anode, cathode, and load were presented by Diard et al. [698, 699]. A similar correction procedure was also described in Ref. [700]. 

All tests were conducted on a Fideris 100 W fuel cell test station, and a fresh MEA was employed for each contamination test. The steady-state polarization curves were recorded using a load bank controlled in a constant-current pattern. The relative humidity (RH) of the fuel cell was set at 80% for both anode and cathode sides. The cell temperature and backpressure were held at 80°C and 30 psig, respectively. 

FIGURE 8.4 Load banks to discharge large battery systems for a performance check. The capacity of critical standby batteries is often measured by applying a full discharge. Such a test can take more than a day to perform. 

FIGURE 5.9 Connections between a Solartron 1260 FRA, RBL 488 load bank, and fuel cell for EIS measurement [47]. 

Loads AC and DC load banks, load profile controller... 

PLR - Parasitic Load Regulator and associated Resistive Load Bank Radiator EP - Electric Propulsion... 

Current interrupt technique is also commonly used to determine ohmic losses across the membrane electrode assembly (Buchi et al, 1995). A load contactor/relay switch is in series with the load bank and fuel cell. This relay is latched off while operating at a particular current. This along with an oscilloscope in line can help separate ohmic losses from the total losses in a fuel cell. The switching speeds of the relay switch are to be of the order of milli-seconds and a gigahertz oscilloscope is required to record the waveform when the contactor is open. 

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