ENGINEERING ARTICLES

When carrying out the work of cable laying in the underground transmission line, the trench is to be dug/ prepared. Trench work should be done by following safety precautions. All pits and trench work shall comply with WorkSafe requirements, particularly the WorkSafe Code of Practice: Excavation. They may include but are not limited to: When a pit is to be left open overnight, proper barrier mesh and flashing lights, etc as required or the pit must be covered. Soil must be piled safely back from the edge of the pit. Pits or trenches deeper than 1500mm in normal soil may require a ladder for access and require shoring, benching or sloping of the sides of them. Pits or trenches may require shoring if less than 1500mm deep and the soil is unstable. Undermining walls, foundations, streets or pavements are to be avoided otherwise appropriate shoring is required. All shoring, benching and sloping must be installed. Barriers shall be erected to vehicles inadvertently falling into the excavati...

The transmission lines are used to transmit the power for long-distance. There are two types of transmission lines; Overhead Transmission line Underground Transmission line Overhead transmission line uses bare conductors. These conductors placed at a height from the ground. To maintain clearance between the conductors and ground, supporting towers are used. The voltage of the transmission line decides the height of the tower. The insulators used to provide insulation between the conductor and the tower. As the transmission voltage level increases, the height of the tower increases to provide more clearance between the ground and conductors. In the underground transmission system, the number of conductors bunched together with proper insulation. The underground cable provided with lead sheet and armoring. These provide protection against moisture and mechanical injury. As the voltage level increase, the thickness of insulation increases.   Overhead Line ...

I) PRIMARY SENSING ELEMENT This is the element that first receives energy from the measured medium and procedures an output depending on some way on the measured quantity (measured).  The output is some physical variable e.g. displacement or voltage. An instrument always extract some energy from the measured medium. The measured quantity is always disturbed by the act of measurement, which makes a perfect theoretically impossible. Good instruments are designed to minimize this loading effect.  II) VARIABLE CONVERSION ELEMENT If may be necessary to convert the output signal of the primary sensing element to another more suitable variable while preserving the information content of the original signal. This element performs this function.  III) VARIABLE MANIPULATION ELEMENT An instrument may require that a signal represented by some physical variable be manipulated by some way.  By manipulation we mean specifically a change in numerical ...

Resistive Load Resistive loads can be purely resistive or of the tungsten-heater load type. A resistive load that has no heating element is the easiest for a switch to handle, and the switch’s rating is based on this type of load. A resistive load is one in which 100% of the load is composed of resistive devices. The power factor is high (PF = 1) and contact erosion is low. Consequently, the switch’s electrical life can be anticipated with some certainty.  Lamp Load When a switch closes on a resistive lamp load, the switch sees a short circuit because the cold resistance of the lamp filament is near zero. The surge current as the switch closes can be many times the steady state current. As the lamp filament heats up to operating temperature, the resistance of the filament increases and the current decreases to the lamp’s steady state.  Motor Motor loads present yet another brutal environment for switch contacts. Closing the switch contact on a motor st...

A structural design project may be divided into three phases, i.e. planning, design and construction.  Planning: This phase involves consideration of the various requirements and factors affecting the general layout and dimensions of the structure and results in the choice of one or perhaps several alternative types of structure, which offer the best general solution. The primary consideration is the function of the structure. Secondary considerations such as aesthetics, sociology, law, economics and the environment may also be taken into account. In addition there are structural and constructional requirements and limitations, which may affect the type of structure to be designed.  Design: This phase involves a detailed consideration of the alternative solutions defined in the planning phase and results in the determination of the most suitable proportions, dimensions and details of the structural elements and connections for constructing each alternative structural...

The Hipot Test (Dielectric Voltage Withstand) The Hipot test is the most common type of safety test. This test is designed to stress a product’s insulation beyond what it would encounter during normal use. The reasoning behind this test is that if the insulation can withstand high voltage for short period of time, it will be safe to use at nominal voltage throughout its useful life. One of the main advantages of the Hipot test is its versatility. In addition to measuring leakage currents and detecting breakdowns, you can also use it to detect:  Material and workmanship defects.  Weak points in the insulation.  Small gap spacing between conductors. Air is just an insulator and Hipot voltage will “jump” through the air across gaps that are too small.  Condensation, dirt and contaminants in the insulation. When running a Hipot test, high voltage is applied to the mains conductors (LINE and NEUTRAL). The Hipot return point is connected to the bare metal...

There are several types of the electronic circuitry used within battery chargers for the marine market. FERRO-RESONANT (or CVT) These use a low-frequency MAGNETIC control system, which makes them very HEAVY, very BULKY and is also only available with a poor FLOAT charge characteristic, therefore very SLOW recharging. They can also generate a large magnetic field which can upset other equipment on board. On the plus side, they are CHEAP and RELIABLE due to the low number of components used and they tend to appeal to boat-builders who put the price at the top of their list of priorities.  LINEAR CHARGERS These also use a low-frequency transformer to reduce the input voltage to a lower level but then use transistors to control the current and voltage fed to the battery. This technique can be used for either FLOAT or 3-STAGE chargers but is very IN-EFFICIENT and therefore HOT, HEAVY and BULKY. The biggest drawback is a LIMITED INPUT VOLTAGE range - not ideal for running from a...