Electra

Thermostat

A thermostat is an electro-mechanical on/off switch that is activated by temperature changes. It is typically used to control a heating or cooling system. The sensing element is usually a spiral bimetallic strip that coils and uncoils in response to temperature changes because of differential expansion of the two bonded metals. The switch element is either a set of electrical contacts or a glass-encapsulated mercury switch that controls a low-voltage relay. The relay can actuate a motor starter and igniter for an oil burner, a heavy-duty switch for electrical units, or a solenoid-operated valve on a gas furnace. The thermostat may also control a house-type air conditioner or heat pump. To reduce temperature swings, a small electrical heater unit is energized during the warming period, causing the switch to break prematurely in anticipation of room-heater override.

Emergency stop switches

Emergency stop switches are devices that users manipulate to initiate the complete shutdown of a machine, system, or process. Unlike regular stop switches, emergency stop switches are not solely dependent on springs. Instead, they generate electrical signals that latch the actuator. Several types of emergency stop switches are available. Pushbuttons are relatively large devices that close a switch when pressed. Trip wires or rope pulls can be actuated at any point along a line that continues to operate even if the cable breaks or goes slack. Combinations of pushbutton and trip wire switches are also available. Typically, these devices incorporate a trip wire for actuation along any point of the cable and a pushbutton for emergency stopping at the end of the installation. By contrast, emergency stop switches that use a telescopic antenna are actuated by the movement of the antenna in any direction.

Emergency stop switches provide many features. Some devices are labeled to indicate their purpose. Others provide illumination for visibility in low light situations. Visual indicators such as light emitting diodes (LEDs) are commonly available. Hermetically sealed devices provide a vacuum or leak-tight seal such as a brazed glass-to-metal seal. Lockable and tamper-resistant devices can be used only by authorized personnel. Explosion-proof emergency stop switches provide a rugged housing that can withstand sparking and flames.

Filters

An electronic filter separates signals of different frequencies from one another. For example, an audio signal could also be carrying a radio frequency (RF) signal on it. A low-pass filter could be used to pass audio frequencies below 20 kHz and stop RF signals, which are well above 20 kHz. A low-pass filter is also used to separate DC power from AC ripple passed by the power source. A simple RC circuit can be used as a filter. The product RC is referred to as the time constant. A time constant is the time it takes a capacitor to charge to 63% of DC voltage applied through a resistor. The cutoff frequency is the point that the amplitude of the output signal is half the value of the input signal. Comparing input to output is the standard method of defining the cutoff frequency of a filter. A second method is to simply compare the amplitude of the signal output in the pass band to the signal output above the pass band. This second method allows you to find the cutoff frequency with only a single meter or scope connection. Simply connect probe to output of filter and adjust frequency roughly to where you get highest output. This puts you in the band pass range of the filter.

Power Generation AC

Rotating a coil in a magnetic field creates alternating current, and is the method that is used to create most of the world’s electricity. Even DC generators create a sinusoidal voltage that is rectified by a commutator. AC electricity is better suited for long distance power transmission than DC electricity. Alternating current voltage can be stepped up to over 100,000 volts, making it possible to transmit power for hundreds of miles over High Voltage transmission lines. The voltage can then be reduced to 120 volts (US single phase) or 220 volts (European single phase) for safe home use. The transformers that you see on poles or behind chain link fences are used to step down high voltage to a safer level.

Most Common DC Generator Types

           Machines can be altered according to the certain requirements.

The types for the DC Generator can be obtained based on connecting field and the armature as well as by means of excitation. The main two categories are the Self excited and the separately excited classified based on the excitation.

The self excited is one which does not need separate source for exciting its own field winding. It is further classified in to three types based on the connection of field and the armature.

1) The series wound Generator is a type in which the field is connected in series with the armature. Here field made of thick wire as it has to pass the entire armature current.

2) The shunt wound Generator can be build by connecting the field across the armature. Here it is not necessary to have field made of thick wire.

3) Compound wound Generator is simply the combination of series and the shunt wound generator.

            In the separately excited generators the field winding is connected to the separate source of supply other than the armature.

CONSTRUCTION of a TRANSFORMER

               Transformer consists of two coils that have got mutual inductance and a laminated steel core, at which the coils are wound. The coils are insulated from each other and also from the steel core.

 This construction has to be kept in a suitable container with proper insulation for the core and the windings from the container.

 The terminals of the coils are taken out through suitable bushings, which are also used for insulation purpose. The bushing used can be porcelain, capacitor-type or oil-filled depending on the application.

Core in the transformer has got greater strength as they are made of steel. The steel sheets are arranged with a minimum air gap between them. The core is laminated to minimize the eddy current loss. The sheet laminations are insulated from each other using varnish.

 Lamination needs to be of certain thickness, it is varied from 0.35mm for 50Hz frequency to 0.5mm for a 25Hz frequency. The steel laminations are alternatively joined through staggered joints. These staggered joints are said to be imbricated.

Transformer is of two types based on the construction – core type and shell type. In core type, core is surrounded by the coil whereas in shell type, windings are surrounded by core but only a considerable portion of the coil.