Zebras

Clams, mussels, and other bivalves are a serious problem in many cooling water systems. Zebra mussels and freshwater Asiatic clams are relative newcomers to the United States. Because of a lack of natural predators and prodigious reproduction rates, they have rapidly become a serious threat to the operation of many cooling water systems. 

Consider a 400 kV, triple-Zebra line, having a distributed leakage capacitive reactance Xco of 74 x 10 fl/km from Table 24.1(b). Then the charging power per phase per km. 

Recently the development of Na/S batteries for car applications has been abandoned only Na/S batteries for stationary applications (load leveling) are still under development in Japan. Among the high-temperature batteries, the ZEBRA battery is the only system at present which is being commercialized for car applications. 

Because of the less advanced status of the lithium aluminum/iron sulfide battery, only the ZEBRA battery and the Na/S battery are described in this section. 

The ZEBRA battery is a high-energy battery based on a cell with electrodes of sodium and metal chloride. The ZEBRA system was first described by Coetzer in 1986 12J. 

Nickel chloride is preferred and ZEBRA batteries are based today on nickel chloride and sodium. According to the very simple cell reaction... 

ZEBRA cells have a high open-circuit voltage (OCV) of 2.58 V at 300 °C. The temperature dependency of the OCV is shown in Fig. 2. 

Figure 2. Open-circuit voltage of the Zebra cell versus temperature.

The thermoneutral potential is 2.72 V this means that during charging at voltage below this value ZEBRA cells will be cooled thermodynamically. 

The second electrolyte, the melt of sodium aluminum chloride, provides another advantage for the ZEBRA system. This second electrolyte makes the system tolerant to overcharge and overdischarge. In the overcharge reaction NaAlCl4 reacts with nickel to form sodium, nickel chloride, and... 

The molten salt, sodium aluminum chloride, fulfills two other tasks in the cell system. The ceramic electrolyte "-alumina is sensitive to high-current spots. The inner surface of the ceramic electrolyte tube is completely covered with molten salt, leading to uniform current distribution over the ceramic surface. This uniform current flow is one reason for the excellent cycle life of ZEBRA batteries. 

The molten salt electrolyte also contributes to the safety behavior of ZEBRA cells. The large amount of energy stored in a 700 g cell, which means about 30 kWh in a 300 kg battery, is not released suddenly as heat as be expected in a system with liquid electrodes such as the sodium sulfur cell. In the case of accidental destruction of ZEBRA cells, the sodium will react mainly with the molten salt, forming A1 sponge and NaCl. -The diffusion of the NaAICI ... 

The power of the ZEBRA cell depends on the resistance of the cell during discharge. The resistance of the ZEBRA cell rises with increasing depth of discharge (DOD). There is a contribution to the resistance from the fixed values of the solid metal components and of the/ "-alumina solid electrolyte. The variable parts of the resistance arc the sodium electrode and the positive electrode. The increase in internal resistance during discharge is almost entirely due to the positive electrode, as can be seen from Fig. 4. 

Figure 4. Qminbuuun.v to the internal resistance of a ZEBRA cell.

The ZEBRA cell shows the similar behavior during the charging reaction, in which the nickel is converted to nickel chloride within the reaction front. During the charging reaction the reaction front also moves from the / " -alumina into the positive electrode. 

The ZEBRA cells are connected in series to obtain the demanded voltages, and chains of these cells are connected in parallel to obtain the capacity which is requested. At present there is a request from the car companies to obtain battery voltages close to 300 V, which means that about 110-120 cells will be connected in series in one string. The capacity of one... 

The performance of the ZEBRA battery system is shown in Table 3 ... 

Table 3. Data for ZEBRA batteries (including peripheral equipment)...

---