ENGINEERING ARTICLES

An autotransformer is a transformer which has part of its winding common to the primary and secondary circuits. Fig. 1(a) shows the circuit for a double-wound transformer and Fig. 1(b) that for an auto transformer. The latter shows that the secondary is actually part of the primary, the current in the secondary being (I 2 -I 1 ). Since the current is less in this section, the cross-sectional area of the winding can be reduced, which reduces the amount of material necessary. Figure 1: (a)  double-wound transformer (b)  auto transformer ADVANTAGES OF AUTO TRANSFORMERS The advantages of autotransformers over double wound transformers include: 1) a saving in cost since less copper is needed 2) less volume, hence less weight 3) a higher efficiency, resulting from lower I 2 R losses 4) a continuously variable output voltage is achievable if a sliding contact is used 5) a smaller percentage voltage regulation. DISADVANTAGES OF AUTO TRANSFORMERS The ...

The magnetic flux ϕ set up in the core of a transformer when an alternating voltage is applied to its primary winding is also alternating and is sinusoidal. Let ϕm be the maximum value of the flux and f be the frequency of the supply. The time for 1 cycle of the alternating flux is the periodic time T, where T = (1/f) seconds The flux rises sinusoidally from zero to its maximum value in (1/4) cycle, and the time for (1/4) cycle is (1/4f) seconds. Hence the average rate of change of flux = (ϕm/ (1/4f)) = 4f ϕm Wb/s, and since 1Wb/s D 1 volt, the average emf induced in each turn = 4f ϕm volts. As the flux ϕ varies sinusoidally, then a sinusoidal emf will be induced in each turn of both primary and secondary windings. For a sine wave, Form Factor = r.m.s Value / Average Value = 1.11 Hence r.m.s. value = form factor*average value = 1.11 * average value Thus r.m.s. e.m.f. induced in each turn =1.11 * 4fϕm volts =4.44fϕm volts Therefore, r.m.s. value of e....

Some small transformers for low-power applications are constructed with air between the two coils. Such transformers are inefficient because the percentage of the flux from the first coil that links the second coil is small. The voltage induced in the second coil is determined as follows. E=NdΦ/dt10 8 where N is the number of turns in the coil, dϕ/dt is the time rate of change of flux linking the coil, and ϕ is the flux in lines. At a time when the applied voltage to the coil is E and the flux linking the coils is ϕ lines, the instantaneous voltage of the supply is: Since the amount of flux ϕ linking the second coil is a small percentage of the flux from the first coil, the voltage induced into the second coil is small. The number of turns can be increased to increase the voltage output, but this will increase costs. The need then is to increase the amount of flux from the first coil that links the second coil.

Nuclear energy is used to produce electricity. Heat generated from the splitting of uranium atoms in a process known as fission is used to produce steam. This steam in turn powers turbines, which are used to produce the electricity that supplies the surrounding community. Nuclear power stations are set up in a multiple-step process that has been designed to help contain the energy and many of its negative byproducts. This process alone is the base of several advantages and disadvantages for this energy source. ADVANTAGES AND DISADVANTAGES OF NUCLEAR ENERGY EXPENSE Uranium is not subject to the same price fluctuations that oil or coal are. This keeps the cost of nuclear energy stabler than the price of electricity generated by fossil fuels. RELIABILITY When a nuclear power plant is functioning properly, it can run uninterrupted for up to 730 days. This results in fewer brownouts or other power interruptions. NO GREENHOUSE GASES While nuclear energy does ha...

Solid-state Controls systems differ from off-line designs in the following ways: 1. Solid-state Controls offers an on-line, double conversion UPS system. Therefore, the client’s critical load is being powered continuously from the inverter. The battery is always being floated by the fully-rated rectifier/charger and is always connected to the inverter input. As result, all components used in the Solid-state Controls design are fully rated to carry 120% of the load on a continuous basis over a 20-year life. 2. Solid-state Controls’ Ferro resonant design has a built in capacity to supply nonlinear (crest factor) loads of up to 3:1 without oversizing. 3. Solid-state Controls’ on-line UPS design is provided with a make-before-break static switch to aid in downstream fault clearing and to protect against possible system failures. 4. Solid-state Controls’ on-line UPS system is a double conversion type, converts AC to DC and then reconverts DC back to AC. It is also insensit...

The following is an outline of some of the major problems associated with off-line (stand by) UPS designs. INPUT FREQUENCY/ VOLTAGE PASS THROUGH The off-line unit is designed to pass through the input line voltage and frequency to the load. (Note: the power passed through is non-conditioned utility power.) While this may be fine for office environments, it is not acceptable for industrial settings with periodic voltage and frequency deviations. Due to the design of off-line systems, some of the deviations will be passed directly to the loads, causing loads to drop and/or loss of data. Off-line UPS suppliers could tighten input parameters so these levels of voltage and frequency are not passed through. However, this would require the systems’ batteries to assume the load more frequently. BATTERY PICKUP If the input voltage and frequency deviate outside of acceptable limits, the systems’ batteries will automatically assume the supply of the charger/inverter. While this m...

The D-STATCOM is basically one of the custom power devices. It is nothing but a STATCOM but used at the Distribution level. The D-STATCOM is a voltage or current source inverter based custom power device connected in shunt with the power system. It is connected near the load at the distribution systems. The key component of the D-STATCOM is a power VSC that is based on high power electronics technologies. Basically, the D-STATCOM system is comprised of three main parts: a VSC, a set of coupling reactors and a controller. The basic principle of a D-STATCOM installed in a power system is the generation of a controllable ac voltage source by a voltage source converter (VSC) connected to a dc capacitor (energy storage device). The ac voltage source, in general, appears behind a transformer leakage reactance. The active and reactive power transfer between the power system and the D-STATCOM is caused by the voltage difference across this reactance. The D-STATCOM is connected in shunt w...