Backup electricity

The converse of taking electricity off the grid is supplying electricity to the grid. Building owners have used standby generators, fuel cells, and battery banks to provide backup electric power to applications that are especially sensitive to disruption. These include hospitals, attended care facilities and health clinics, banks and credit data processing centers, and even homeowners. 

Fuel cells are being developed for stationary use at either the small residential or commercial level or at the larger commercial level to provide a power source as well as supply backup electricity. In addition, much of this development uses excess heat from electricity production in combined heat and power (CHP) fuel ceU systems. These stationary applications are being tested in real-world applications in hopes of marketing them in the near future. 

Simultaneous failure of two essential independent instrument or mechanical systems Failure of both crane automatic stop safety device and crane magnetorque braking device Simultaneous loss of main electric service power and backup electric generator power Facility destruction due to uncontrollable external events... 

Loss of electrical power can occur suddenly, and it can damage or undermine equipment. To prevent damage, motor-generators can be tied to flywheels which can provide uninterrupted electrical power to equipment for a brief period of time in the order of 30 s. Often they are used to provide electrical power until the plant electrical supply can be switched to the batteries and/or diesel generators. Batteries often form the onsite redim-dant backup electrical system and are also capable of providing sufficient electrical power to shut down a plant. The DC power generate by batteries can be converted to AC power to nm AC devices such as motors using an electrical inverter. 

Simultaneous loss of main electric service power and backup electric generator power... 

I C architectures are probably at their most complex in nuclear power stations. Here, the levels of hazard and the accordingly high reliability requirements mean that diverse high-integrity protection systems are required. Furthermore, the need for extremely high-reliability removal of decay power from the reactor core postshutdown means that there has to be very high-reliability backup electricity supplies. A simplified schematic of a modem I C architecture for a nuclear power station is presented in Fig. 2.7. 

There should also be clear definitions regarding the availability of essential or safety-related plant - e.g., emergency shutdown systems, fire detection equipment, fire suppression equipment, or backup electricity supplies. These types of procedures and definitions are usually called operating rules or site safety policies (Fig. 10.3, top right). 

So-called essential equipment, such as fire-fighting equipment or smoke or fire detection equipment, or backup electricity supply equipment, can only be taken out of service when suitable alternative arrangements have been agreed and are in place. 

A normal electric power system and a backup electric power system shall be provided to support the functioning of structures, systems, and components important to safety. The safety function of each electric power system (assuming the other system is not functioning) is to provide sufficient capacity and capability to assure that (1) the reactor can be shutdown, (2) maintain necessary cooling, confinement, and other safety functions, and (3) provide essential monitoring. 

A performance test shall be performed to demonstrate in an overall integrated manner that the Backup electric power systems can accommodate a complete loss of all Normal ac power to the reactor area, without any concurrent plant transient or accident. This test shall demonstrate the capability of the GM EDGs to accept the initial [tg] automatic loads for the non-accident case. 

Fuels ndEfficiency. Natural gas, oil, and electricity are the primary sources of energy propane is used as backup reserve in emergencies. Natural gas is the least expensive and most frequently used fuel, with heat content ranging from 34—45 MJ/nf (900—1200 Btu/ft ) for raw gas and approximately 3 MJ/m (80 Btu/fT) for air-gas mixtures. Fuel oil has heat content between 39—43 MJ/L (139,600—153,000 Btu/U.S. gal). Fuel oil is viscous at low temperature and must be heated before being fed to atomizing burners where it is mixed with air for combustion. 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

Eliminate common cause electrical failures for supply and backup... 

A breaker, usually an MCCB or an MCB on an LT system, can be provided with backup HRC fuses to enhance their short-time rating. This may be done when the available MCCBs or MCBs possess a lower short-time rating than the fault level of the circuit they are required to protect, and make them suitable for the fault level of the circuit. But this is not a preferred practice and is seldom used. As a rule of thumb, the device that is protecting must be suitable to withstand electrically and endure mechanically the system fault current for a duration of one or three seconds, according to the system design. 

Now let us consider utility failure as a cause of overpressure. Failure of the utility supphes (e.g., electric power, cooling water, steam, instrument air or instrument power, or fuel) to refinery plant facihties wiU in many instances result in emergency conditions with potential for overpressuring equipment. Although utility supply systems are designed for reliability by the appropriate selection of multiple generation and distribution systems, spare equipment, backup systems, etc., the possibility of failure still remains. Possible failure mechanisms of each utility must, therefore, be examined and evaluated to determine the associated requirements for overpressure protection. The basic rules for these considerations are as follows ... 

The control and snpervision of a snppression system is achieved rising an electrical power/control unit with 24-horir (minimum) standby battery backup power. The unit supplies sufficient energy to accomplish the following (NFPA69 1997) ... 

The term rechargeable consumer product (a) means a product that, when sold retail, includes a regulated battery as a primary energy supply and which is primarily intended for 1 kW personal or household use, but (b) does not include a product that uses only a battery as a sole source of backup power for memory or program instruction storage, timekeeping, or any other similar purpose that requires uninterrupted electrical power, in order to function if the primary energy supply fails or fluctuates momentarily. 

Flaving had over 150 years of technical development behind them, lead-acid batteries can be custom-tailored to specific applications, such as those requiring deep discharge cycles (e.g., where the batteries are used as the sole power source for electrical equipment) and for battery backup uses such as in large uninterruptible power supply systems in data centers. Moreover, lead-acid cells not only have low internal resistance but also experience no memory effect as do some more exotic cell designs, such as NiCads. This enables these cells to produce enormous currents and have a moderately long, predictable life.1... 

The magnitude of this accident could have been reduced with (1) improved pipe design, (2) improved deluge system design, (3) backup or more secure electrical supply, and (4) installation of detection analyzers and block valves. 

---