Losses Reactive power

The dissipation factor is a ratio of the real power (in-phase power) to the reactive power (power 90° out of phase). It is also defined as (1) IT is the ratio of conductance of a capacitor in which the material is the dielectric to its susceptance, (2) IT is the ratio of its parallel reactance to its parallel resistance it is the tangent of the loss angle and the cotangent... 

In an electrical system, if the power factor is 0.80, 80% of the apparent power is converted into useful work. Apparent power is what the transformer that serves a home or business has to carry in order for that home or business to function. Active power is the portion of the apparent power that performs useful work and supplies losses in the electrical equipment that are associated with doing the work. Higher power factor leads to more optimum use of electrical current in a facility. Can a power factor reach 100% In theory it can, but in practice it cannot without some form of power factor correction device. The reason why it can approach 100% power factor but not quite reach it is because all electrical circuits have inductance and capacitance, which introduce reactive power requirements. The reactive power is that... 

All reactive power requirements are not necessary in every situation. Any electrical circuit or device when subjected to an electrical potential develops a magnetic field that represents the inductance of the circuit or the device. As current flows in the circuit, the inductance produces a voltage that tends to oppose the current. This effect, known as Lenz s law, produces a voltage drop in the circuit that represents a loss in the circuit. At any rate, inductance in AC circuits is present whether it is needed or not. In an electrical circuit, the apparent and reactive powers are represented by the power triangle shown in Figure 6.1. The following relationships apply ... 

Where the factor 1.015 is an allowance for the PX reactive power losses in the transformers. 

The control rod system provides for automatic control of the required reactor power level and its period reactor startup manual regulation of the power level and distribution to compensate for changes in reactivity due to burn-up and refuelling automatic regulation of the radial-azimuthal power distribution automatic rapid power reduction to predetermined levels when certain plant parameters exceed preset limits automatic and manual emergency shutdown under accident conditions. A special unit selects 24 uniformly distributed rods from the total available in the core as safety rods. These are the first rods to be withdrawn to their upper cut-off limit when the reactor is started up. In the event of a loss of power, the control rods are disconnected from their drives and fall into the core under gravity at a speed of about 0-4 m/s, regulated by water flow resistance. 

The reactive power Wr is pumped to and from the capacitor each quarter period, but the net supplied energy is zero. The capacitive, quadrature current just pumps electrons charging the plates. The quadrature current causes no heating of the dielectric, but the current in the wires is real and causes heat losses if the wires are nonideal. 

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. 

The distortion of the output waveform in a thyristor-based system is therefore at least as great as the distortion caused by a diode system. Fortimately, the reactive power compensation that accompanies most large rectifier installations also tends to absorb some of the harmonics. Configuring the added capacitance as a harmonic filter therefore offsets some of the loss. 

Dissipation factor Equal to the ratio of power loss to the reactive power stored when a sinusoidal voltage is applied to the capacitor. 

A third charge sometimes imposed is a penalty for poor power factor. This charge is made to cover the cost of generating the unusable portion of electricity consumed in reactive power losses. 

Control of core reactivity is maintained by control rods, which drop into the core upon receipt of a signal from one of several diverse monitoring and actuation systems, or loss of power. Any water subsequently added to the core to control heat removal contains boron, which maintains the low levels of reactivity. 

To ensure the function of reactor power control, two independent systems based on diverse drive mechanisms are provided for reactor shutdown. One system acts as an accident protection system, while the actuated second system is designed to provide guaranteed subcriticality for an unlimited period of time and to be able to account for any reactivity effects including those in accidental states. Either system can operate under the failure of a minimum of one rod with maximum worth. In case of loss of power to the reactor control and protection system (RCP), all rods of this system can be inserted in the core under the effect of gravity. 

The reactivity incidents of concern in shutdown operation are mostly the fast dilution incidents, which result in a rapid reactivity increase in the core. These are usually related with the transport of the slug of unborated water in the core after starting up a RCP. The prevention against such an event could be made by administrative barriers but also by hardware changes or an operational procedures. An example of an administrative barrier is the requirement for the isolation of a CVCS injection flow in a case of the loss of power event. Similar requirement is covered at other plants by a procedure (an operational improvement )... 

Unique operating characteristics of fuel cell power plants are as follows. Beneficial operating characteristics of fuel cells saves cost and other benefits include load following, power factor correction, quick response to generating unit outages, control of distribution line voltage and quality control can control real and reactive power independently control of power factor, line voltage and frequency can minimize transmission losses, reduce requirement for reserve capacity and auxiliary electric equipment fuel cells have an excellent part load heat rate and can respond to transmission loads. 

Loss factor is the product of the dielectric constant and the power factor, and is a measure of signal absorption. The dissipation factor is a measure of the conversion of the reactive power to real power, showing as heat. The mode of heating can be by electron or ion flow and by dipole rotation. It is variable with frequency, temperature, conditioning, and potential. The test method is ASTM D150, and the conditions of the test and frequency must be specified. 

The next step is to apply a number of loss control credit factors such as process control (emergency power, cooling, explosion control, emergency shutdown, computer control, inert gas, operating procedures, reactive chemical reviews), material isolation (remote control valves, blowdown, drainage, interlocks) and fire protection (leak detection, buried tanks, fire water supply, sprinkler systems, water curtains, foam, cable protection). The credit factors are combined and appHed to the fire and explosion index value to result in a net index. 

The declared efficiency and power factor of a motor are affected by its loading. Irrespective of the load, no-load losses as well as the reactive component of the motor remain constant. The useful stator current, i.e. the phase current minus the no-load current of a normal induction motor, has a power factor as high as 0.9-0.95. But because of the magnetizing current, the p.f. of the motor does not generally exceed 0.8-0.85 at full load. Thus, at loads lower than rated, the magnetizing current remaining the same, the power factor of the motor decreases sharply. The efficiency, however, remains practically constant for up to nearly 70% of load in view of the fact that maximum efficiency occurs at a load when copper losses (f R) are equal to the no-load losses. Table 1.9 shows an approximate variation in the power factor and efficiency with the load. From the various tests conducted on different types and sizes of motors, it has been established that the... 

To provide reactive support for any power system or network, suffering from voltage fluctuations or high line losses or when it is felt that the system cannot transfer the required load it is important to carry out a field study first, to identify areas and suitable locations where reactive support would be more appropriate. A procedure along the lines of Example 24.3 to determine the amount and type of reactive support should then be adopted. 

---