Pressure Transducers

Pressure is an important physical quantity to be measured in industrial systems.  

Transducers are one of the popular means of measuring Pressure.   Pressure Transducers work by converting the pressure signal into an analog electric signal usually a 4...20 mA signal. 

Pressure Transducers can be designed using many principles.  The most widely used of these are the capacitive and the Piezo-resistive transducer. 

Capacitive Pressure Transducers
The capacitive transducer consists of a diaphragm which works as one of the plates of a capacitor.  A fixed conductive surface acts as the other plate.  The permittivity of the space in between these plates varies as the diaphragm moves in response to the measured pressure. 

This change in capacitance is measured as the process pressure.  

The capacitive transducer is used to measure very low pressure values.  Very Accurate measurements are possible using the capacitive pressure Transducers. 

Piezo Resistive Pressure Transducers

Piezo Resistive Transducers work on the principle of the piezoresistive effect.  The piezo resistive effect refers to the change in the resistivity of a material in response to force or pressure.  The piezo resistive sensor is used widely in biomedical applications as well as in the automobile industry. 

Piezo Resistive Pressure Transducers

These sensors are low in cost and have high sensitivity.  They can be manufactured for a wide range of pressure measurement.

Piezo Resistive Pressure transducers consist of a diaphragm which is made of silicon.  The diaphragm bends due to the pressure of the system to be measured. 

Mounted on the diaphragm are four piezo-resistors which are usually arranged in the form of a Wheatstone bridge.  When the diaphragm bends due to the pressure, the piezoresistors are subject to either tensile or compressive stress.  This results in a change in resistance values which is measured through the Wheatstone bridge formation and is scaled as a pressure measurement

Inductive Proximity Sensors

Inductive Proximity sensors find wide application in the field of industrial instrumentation.  These sensors are extremely popular as they are reliable, robust and have a simple construction.  Inductive Proximity sensors are used to measure speed, detect motion and sense the position of objects.

The inductive proximity sensor consists of an oscillator, a coil and a detector.  The oscillator develops a high frequency signal which is fed to the coil. 

The high frequency signal develops a corresponding high frequency magnetic field at
the tip of the sensor.  When a metallic object comes in front of the sensor, eddy currents are induced in the object.  This acts as a load on the oscillator and the amplitude of the high frequency output drops.  This drop in the voltage is detected by the detector unit which causes the switching on or off of a transistor.  This results in a change of voltage level which is interpreted as a digital signal 0 or 1.

The inductive proximity principle can also be applied to speed sensors.  In speed measurement, the inductive proximity sensor is placed near the rim of a rotating object. The rotating object has a number of teeth along its rim.  When a tooth passes near the inductive proximity sensor, a pulse is produced. 

This sequence of pulses can be converted into an analog signal can be measured as the speed of the device.

Sympathetic Tripping

Sympathetic Tripping refers to the phenomenon in Electrical Systems when a protective device in a healthy section of the system operates for a fault in another section of the system.  Sympathetic tripping results in unnecessary loss of power for healthy equipment. 

There are many causes for sympathetic tripping.  The most common reason is undervoltage which occurs across the system when there is a heavy current due to a short-circuit or an earth fault. 

Another reason for sympathetic tripping can be the flow of capacitive currents in the healthy feeders when one of the feeders gets grounded. 

In Transformers and Generators the Differential relay sometimes operates for an overcurrent which is outside its zone.  This is due to the dc component of the earth fault current.

Preventing Sympathetic Tripping   

Sympathetic Tripping can be prevented by designing smaller feeders with the total loads equally balanced across the different feeders

Reducing the fault level can result in lesser currents in the event of faults.  The fault level can be reduced by the use of current limiting reactors which increase the impedance.

Extreme Inverse settings in IDMT relays can also help the relays discriminate between sympathetic overcurrents and genuine faults. 

Increasing fault clearing times in the faulty feeders reduces the duration of the undervoltage across the system. 

Modern Differential relays have an inbuilt dc filter which prevent sympathetic tripping due to dc components during earth faults.

Videos on Power Transformer Testing

Useful Videos on Power Transformer Testing by OMICRON

Your Guide to Energy Saving Lighting

Lighting within the home currently accounts for about 8% of energy bills in the UK. Incandescent and tungsten bulbs have been a standard feature of electrical use since the 19th century, but are gradually being phased out in favour of more energy saving options that save consumers money and benefit the environment. A number of different options are available from online electrical wholesalers or high street retailers, from energy saving bulbs to compact fluorescents, LEDs and dimmers that can help to cut costs and generate more efficient energy. Moreover, these bulbs can be combined with a number of simple energy saving practices that can be followed within the home.

Types of Bulbs and their Benefits

Early incandescent and halogen bulbs relied on a tungsten filament, and remain the norm for most homes. Halogen bulbs are more efficient than incandescent forms, but still lag behind energy saving bulbs in terms of efficiency. The UK Government have promoted schemes to gradually phase out the use of older bulbs, while encouraging a switchover to energy saving lighting options. Energy saving bulbs and lights remains fairly expensive compared to older bulbs, but have the benefit of lasting longer, and reduce electricity bills.

A basic energy saving bulb is 5 times brighter than a standard bulb, and uses 80% less power. If used responsibly, some energy saving bulbs can have a 10 year life span. This length is based on using certain bulbs for three hours a day in parts of the home, and can be an ideal solution for rooms that are not used very often. Energy saving bulbs can result in 75-80% energy savings, and use 4 times less of the wattage of standard bulbs.

Other energy saving bulb options include compact fluorescents. These bulbs use an alternative gas charging method to standard bulbs, and use 20 to 25% less electricity. Again, higher costs for initial purchases can be offset by their long lasting potential and greater energy efficiency.

Another option is to invest in LEDs, or light emitting diodes. These represent strips of about 36 to 48 lights, which when installed can generate 50,000 hours of capacity. Representing 50 times as much capacity as a standard incandescent light, small LED arrays also act as a stylish alternative to hanging fittings, bulbs and lamps within rooms, and are particularly recommended for kitchens.

These lights emit less carbon dioxide than standard incandescent lights, and can consequently help conserve energy and the environment. When looking for energy saving bulbs always check for an Energy Saving Trust Recommended label, or an Energy Related A tag. Energy saving bulbs can also be recycled, and form part of the EU’s Waste Electrical and Electronic Equipment Initiative.

Other Tips

As well as investing in energy saving bulbs, you can also follow some simple steps when using lights in the home. The most basic solution remains turning lights off when they are not being used. Moreover, try to use lights for particular roles, with bulbs being turned off when watching a brightly lit television or computer. If reading, a single lamp is more efficient than keeping a whole room’s lights on. Dimmer switches are also useful in this regard for regulating the amount of light in a room, and can result in 4-9% of electricity savings.

About the author
Serena is a copywriter for a leading supplier of energy saving discount electrical supplies at Discount Electrical. In her spare time she writes various other blogs online on numerous other subjects such as automotive, health and the theatre.

Capacitor Trip Modules.

Capacitor Trip modules are used in breaker circuits to provide a source of back up power for trip operations in the event of the failure of the breaker control supply.  The capacitor Trip device is usually used in switchgear systems which use an AC control supply. 

If the control supply of a breaker panel fails during operation, the operator will not be able to operate the breakers from a remote location.  This would also compromise the protection scheme as the breaker will not trip even if a command is sent by a protection relay. 

The capacitor trip module consists of a capacitor which stores charge.  This charge is enough to trip the breaker for a certain number of times, say 5 times.  This ensures that the breaker can trip even if the control supply fails during operation.  Capacitor Trip modules are available for both AC and DC control systems. 

Grounding Transformers

Grounding Transformers are used in Ungrounded systems to provide a earth point.  Grounding Transformers are classified into two types

1) Zig Zag Transformers and

2) The Star-Delta Grounding Transformer with secondary unloaded.

We had looked at the Zig-zag Transformer in an earlier Post (Click here). 

Let us now look at the Star-Delta Grounding Transformer

The Star-delta grounding Transformer has a primary which is star connected and a delta secondary.  The phases of the star primary are connected to the busbar while the neutral is grounded.  The secondary of the transformer which is delta connected is usually left unloaded, though it can also be used to supply power.  The delta serves to provide a return flux path for unbalanced loads.  

During an earth fault, the zero sequence currents can flow through the grounded neutral of the transformer.  If the current is to be limited, a resistor can be added in series to the neutral of the transformer primary.