ENGINEERING ARTICLES

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...

ADVANTAGES OF PHOTOVOLTAICS: Fuel source is vast and essentially infinite No emissions, no combustion or radioactive fuel for disposal (does not contribute perceptibly to global climate change or pollution) Low operating costs (no fuel) No moving parts (no wear) Ambient temperature operation (no high temperature corrosion or safety issues) High reliability in modules (>20 years) Modular (small or large increments) Quick installation Can be integrated into new or existing building structures Can be installed at nearly any point-of-use Daily output peak may match local demand High public acceptance Excellent safety record DISADVANTAGES OF PHOTOVOLTAICS: diffuse (sunlight is a relatively low-density energy) High installation costs Poorer reliability of auxiliary (balance of system) elements including storage Lack of widespread commercially available system integration and installation so far Lack of economical efficient energy storage

HVDC links may be broadly classified into the following categories: Monopolar Links Bipolar Links Homopolar Links The basic configuration of a monopolar link is shown in figure. It uses one conductor, usually of negative polarity. The return path is provided by ground or water. Cost considerations often lead to the use of such systems, particularly for cable transmission. This type of configuration may also be the first stage in the development of a bipolar system. Instead of ground return, a metallic return may be used in situation where the earth resistivity is too high or possible interference with underground/ under water metallic structures is objectionable. The conductor forming the metallic return is at low voltage.

Figure: A schematic of a bipolar HVDC system identifying main components

1) CONNECTING REMOTE GENERATION Some energy sources, such as hydro and solar power, are often located hundreds or thousands kilometers away from the load centers. HVDC will reliably deliver electricity generated from mountain tops, deserts and seas across vast distances with low losses. 2) INTERCONNECTING GRIDS Connecting AC grids is done for stabilization purposes and to allow energy trading. During some specific circumstances, the connection has to be done using HVDC, for example when the grids have different frequencies or when the connection has to go long distances over water and AC cables cannot be used because of the high losses. 3) CONNECTING OFFSHORE WIND Wind parks are often placed far out at sea, because the wind conditions are more advantageous there. If the distance to the grid on land exceeds a certain stretch, the only possible solution is HVDC - due to the technology’s low losses. 4) POWER FROM SHORE Traditionally, oil and gas p...