News from the Field : Smart grids play key role in modern energy infrastructure

How do you ensure a steady supply of electricity from fickle renewable sources such as solar, wind and biomass? 'Smart grids' that manage and distribute flows of electricity could be the answer.

     The EU's ambitious goals of a 20 percent increase in energy efficiency, a 20 percent increase in renewables and a 20 percent reduction of carbon dioxide emissions - all by the year 2020 - are a huge undertaking. Experts agree that none of the "20:20:20" goals are achievable without a functional smart grid that ultimately optimizes energy generation.

     That's because simply building more wind plants and solar collectors won't be enough, as renewable energy is hampered by the fact that it's not constantly available – after all, if the wind doesn't blow or the sun doesn't shine, wind turbines or solar cells don't generate energy.
     'Smart grids' on the other hand can manage and distribute intermittent energy supply from small power plants, wind mills or solar systems without a hitch, leading to a steady supply of electricity.   If there's too much electricity in the grid, it can be stored in batteries, for example when an electric car rolls up to a recharging point.

Smart energy draws big players
     Smart grids provide utilities with the information and flexibility required to manage intermittent electricity supply from renewable and micro-generation sources, allowing them to balance this with more traditional, consistent supply.

     Large companies such as Switzerland's ABB, a rival of Germany's engineering giant Siemens, say smart grids are a huge trend in the energy sector.

     "There are lots of solutions that are already available. We could begin with them right away," Peter Smits, the head of ABB Europe said. But Smits says incentives, like feed in tariffs, are still needed to encourage the switch to a bigger pool of renewable energy sources.

     "The more renewable energy we have to feed in the network, the more the utilities and electricity distributors are going to need this solution," Smits said. The International Energy Agency estimates that by 2030, worldwide investments worth several trillion dollars will be needed for modern energy generation and new electricity networks.

     Indeed, the booming market, which promises lucrative returns, has attracted new players to the utilities sector, including IT giants such as Google, IBM, Cisco, Microsoft or telecommunications firms such as Deutsche Telekom.

Various smart approaches
     From the use of smart meters in households in Italy or France, to government-backed pilot-projects in the US, there's a growing momentum for groundbreaking smart energy schemes.  In Germany, too, the government is trialing smart grids in a few hand-picked regions.

     The impression that Germany is lagging behind on smart energy projects is not true, says Hartmut Schmeck from the Institute for Technology in Karlsruhe.  He says selected regions in Germany are testing the entire supply chain - from electricity generation, and distribution to supplying the end consumer.  "Other countries are trying out projects where individual processes are monitored. But comprehensive, holistic approaches like the ones in Germany - they don't exist elsewhere."

Customers needed
     It's expected that in two years, Germany's model regions will have developed their smart energy concepts to the point where they'll be ready for the market and everyday use.  This summer, project organizers set up a model house complete with washing machine, refrigerator and an electric car. The latter plays a key role in the project - both to store electricity as well as consume it.

     Still missing are the thousands of electricity consumers needed to test the whole thing.  "The most important thing is that the customers play along because you can't have a smart grid without customers," said Joern Kroeplin from the energy utility firm EnBW, which is involved in the project.  Kroeplin says it is important to find tariffs and models that will create the necessary incentives.  "We also need the necessary appliances that customers accept and use. Without all that, it won't work," he said.

Not all smooth sailing
     A first intelligent washing machine manufactured by German company Miele was on display at this year's consumer electronics fair IFA in Berlin. It switches on when the electricity price falls below a certain level. But it also needs a smart plug which recognizes what the electricity currently costs.  For smart grids to work, a number of players will need to come together, including industrial and private consumers, to help share the introductory costs.

     Another obstacle remains. Aside from their upfront costs, smart meters also use a lot of energy to maintain, due to all the data flows operating in real time.  The required internet connection alone, which runs 24/7, uses over 100 kilowatt hours of electricity in a year – almost exactly as much as a modern refrigerator.

High Voltage Probes - an Introduction

High Voltage probes are used to measure high voltages which are beyond the range of common measuring instruments.  For instance, ordinary multimeters may not be able to measure the high voltages generated in the Television set.  In these conditions, High voltage probes may be used.  High Voltage probes usually contain resistors in series.
High power probes can be used with multimeters, oscilloscopes, synchroscopes and a wide variety of industrial measuring instruments. 

The instruments which are connected to the High voltage probes usually have a high internal impedance to limit the current.

High voltage probes have a voltage ratio similar to a transformer.  High voltage probes are also rated on the amount of power they can withstand.  Some High voltage probes are designed only for low power application.

Liquid Rheostats - an Introduction

Liquid Rheostats are variable resistors which use a liquid electrolyte.  The electrolyte, usually common salt, is used as the resistor whose resistance value is varied by changing the level.

The construction consists of two electrolyte placed in a container.  The container is filled with a solution of common salt.  There is a provision to vary the level of the electrolyte in the container.

This changes the conductivity and thus the resistance is varied.  At high levels of the electrolyte, the resistanc is very low and increases as the level decreases.

Liquid rheostats are silent and are supposed to have long life.  They are usually only used in AC circuits as DC may cause electrodeposition between the electrodes. 

Liquid rheostats can also be used as load banks to test generator output at testing facilities.  The output of the generator is connected to electrodes which are placed in a container filled with a salt solution.

Liquid rheostats are also used as resistances for starting induction motors.  Some large liquid rheostats have a heat exchanger to control the temperature of the electrolyte. 

Polarity in Capacitors

Capacitors are components which are used in electric and electronic circuits to store charge, to filter dc, to improve power factor and so on.  There are many kinds of capacitors available.  Ceramic, Paper capacitors, electrolytic capacitors and so on.

Electrolytic capacitors are called as one of the plates of the capacitor is made of an ionic conducting liquid, an electrolyte.  These capacitors must be connected in a fixed polarity.  Hence, these capacitors cannot be used in AC circuits without a dc bias.  These capacitors have a high capacitance value.

Polarity is usually indicated in the capacitors with the positive lead longer than the negative lead.  Alternatively, the polarity markings are made in the capacitor body.

Connecting these capacitors in the wrong polarity will cause heating of the electrolyte and lead to an explosion, a catastrophic failure.  Most capacitors are provided with a vent to relieve pressure and prevent explosions.

What are the advantages of wound rotor over a squirrel cage rotor for induction motors

Wound rotors are used in applications where high starting torque is required.  External resistances may be added to these rotors via slip rings shaft.  These resistances serve to increase the starting torque and ensure smooth starts.  

However, these rotors are more expensive than induction motors.  In the wound rotor, the rotor windings are insulated to the ground.  The slip rings and the brushes also require maintenance.

The starting current drawn by a wound rotor machine is lesser than that that of a squirrel cage motor.

The wound rotor is designed to have the same number of poles as the stator winding of the motor.  The windings are designed to with stand high mechanical forces as these motors are used for high-torque applications. 

Wound Rotors are used for applications which require soft-starts and adjustable speeds

Squirrel cage rotors are the most common type of rotors found in induction motors.  These rotors are simple to construct, robust and relatively inexpensive. 

They are particularly suited for low inertia loads.  Their easy construction enables lower rotor weight and lesser centirfugal force and windage losses.

What are the advantages of wound rotor over a squirrel cage rotor for induction motors

Wound rotors are used in applications where high starting torque is required.  External resistances may be added to these rotors via slip rings shaft.  These resistances serve to increase the starting torque and ensure smooth starts.  

However, these rotors are more expensive than induction motors.  In the wound rotor, the rotor windings are insulated to the ground.  The slip rings and the brushes also require maintenance.

The starting current drawn by a wound rotor machine is lesser than that that of a squirrel cage motor.

The wound rotor is designed to have the same number of poles as the stator winding of the motor.  The windings are designed to with stand high mechanical forces as these motors are used for high-torque applications. 

Wound Rotors are used for applications which require soft-starts and adjustable speeds

Squirrel cage rotors are the most common type of rotors found in induction motors.  These rotors are simple to construct, robust and relatively inexpensive. 

They are particularly suited for low inertia loads.  Their easy construction enables lower rotor weight and lesser centirfugal force and windage losses.

Surge Arrestors - An Introduction

A surge arrestor is an electric equipment used in substations and switch yards. The surge arrester is used to protect the substation equipment from surges caused by lightning or by sudden switching. The surge arrestor is an insulator which is a non-linear resistor.

This means that the surge arrestor has high resistance at the operating voltage and low resistance as the voltage increases. Thus when lightning strikes the overhead conductors in a substation, the arrestor acts like a conductor and discharges the surge to the ground.

Surge arrestors are usually constructed of MOV(Metal oxide varistor). Zinc oxide is a widely used non-linear resistor. The zinc oxide is the form of blocks which are stacked inside the arrestor.