CE Technical Discussion 4th Week : Power Transmission,The Journey from Source to Destination.

Replies

• 

  Jeffrey Arulraj

  Hey welcome all CEans for this weeks tech discussion
  
  First as I was going through the previous posts here I wanted to clarify to all one thing
  
  In any transmission device the electric current is transmitted as Voltage over long distances
  
  Never is current transmitted as such through these long cables the reason is a well known fact that electric power losses due to current transmission is very high
  
  Next up is the AC DC war
  
  Most appliances except some industries use only AC supply from generating stations to our house we are wired completely by AC transmission lines as a standard factor.
  
  Do you know why ?
  
  The reason is simple there where no efficient device in the early 1990's to perform suitable operations in the DC transmission this lead to the prevalence of AC over DC in the longer run
  
  Hope this is worth
• 

  pikachu1994

  Whether three phase is used only in industries.?
• 

  Jeffrey Arulraj

  pikachu1994

  Whether 3 phase is used only in industries.?

  Mostly friend
  
  Most of the industries use a higher end Voltage of about 440 V instead of the common house hold 230V
  
  This implies that the Industries commonly use 3 phase supplies
• 

  pikachu1994

  But it is used also in home.Which is prefrable for home?
• 

  Jeffrey Arulraj

  It depends on the load which is being used in your house
  
  If your house has say only a TV and a radio some lights and fan Lesser current will be drawn in by all your appliances and the overall bill will be less in the case of single phase supply itself
  
  But (considering my street in Chennai) well here Each house has the following
  

  • 2 air conditioners
  • fridge
  • then fans
  • computers
  • high power washing machines
  • home theatres
  • more than 1 TV
  • other appliances

  Here the overall current drawn in by each house is rampant in the case of single phase supplies and the bills fly up and so we prefer more of # phase supply to all our houses here
  The reason is in case of single phase we get a supply of about 230 V to our house and as load increases more current will be drawn from the supply lines
  But in the case of 3 phase supplies there is a 400 V potential difference between two phase lines. This ensures that there is a lesser current drawn during high load time also
  This decreases the power consumed by the house reducing EB bills
• 

  pikachu1994

  Thanks.I got some idea
• 

  Jeffrey Arulraj

  pikachu1994

  Thanks.I got some idea

  Most welcome friend
• 

  dossdss

  hi,
  but isn't it like, that many of the appliances are rated up to 230-250V then how come the supply of 440 is fine with houses ?
• 

  dossdss

  power is transmitted in ac rather than in dc form....
  reasons 'may' be
  
  

  1. the losses in transmission process are tremendous.
  2. original form of generated electricity is ac (dc can not be generated using generators)
  3. that ac is first stepped up n transmitted n then stepped down back to required values. (dc can not be stepped up or down).
  4. so even if there are are losses they will appear to be small for the stepped up power.
  5. n as said most of the devices need ac.

  thank you.
• 

  dossdss

  jeffrey samuel

  But in the case of 3 phase supplies there is a 400 V potential difference between two phase lines. This ensures that there is a lesser current drawn during high load time also
  This decreases the power consumed by the house reducing EB bills

  hi,
  but isn't it like, that many of the appliances are rated up to 230-250V then how come the supply of 440 is fine with houses ?
• 

  Jeffrey Arulraj

  dossdss

  hi,
  but isn't it like, that many of the appliances are rated up to 230-250V then how come the supply of 440 is fine with houses ?

  The supply to your house is about 400 V but no device is connected between two phase lines it is always connected between a phase line and a Earth line
  
  The potential difference between these lines are always 230 V which is what is required for every house hold appliance
• 

  Jeffrey Arulraj

  dossdss

  power is transmitted in ac rather than in dc form....
  reasons 'may' be
  
  

  1. the losses in transmission process are tremendous.
  2. original form of generated electricity is ac (dc can not be generated using generators)
  3. that ac is first stepped up n transmitted n then stepped down back to required values. (dc can not be stepped up or down).
  4. so even if there are are losses they will appear to be small for the stepped up power.
  5. n as said most of the devices need ac.

  thank you.

  Sorry to say friend that AC Voltage transmission has lots of loss and is never 100% at any point of time the following losses are present in AC transmission
  

  • Corona loss in the form of violet glow in voltages above 110k some times even in lesser voltages
  • Skinning effect where by the effective resistance of the transmission lines increases a lot
  • Radio interference as power of transmitted AC is always high

  But I will say now for the future DC voltage transmission is possible and It has higher efficiency than the AC transmission
• 

  Ramani Aswath

  Are we not slightly off topic? I thought the discussion was about transmission from source to sink?
  
  There is a little confusion here over 3 Phase domestic supply. The appliances still run at 220-230 V. What Jeff wrote above is relevant here. The power is delivered as three phases and neutral. All loads are connected between one of the phases and the neutral. So the line voltage is always 220-230. What happens is that in houses consuming more power the loads are distributed among the phases leading to better balance on the distribution transformer.
  
  The fridge and microwave at my house is on one phase, while the blender, toaster and induction heater are on another phase with all fans, lights and TV on the third.
  In the industry lot of power is consumed. Balancing loads is easier if most are on three phase supply. Starting currents and power factor issues are also better with 3 phase balanced loads.
  
  About transmission of power from generating station to the distribution centre, very high voltage DC transmission is less lossy than AC for the same power transmitted. The problem arises with conversion to AC at the using end. China transmits lot of power as DC across huge distances.
  
  This has many implications for India. For one thing it is easy to steal AC power. Power theft is the major loss in transmission in India, not line losses. DC transmission may help minimise this as the power thieves will find it difficult to use such power without costly equipment.
  
  CEans on this thread must come up with thoughts on very high voltage DC bulk power transmission in India and elsewhere.
• 

  Jeffrey Arulraj

  Thanks for the Easy clear cut explanation Sir
  
  

  About transmission of power from generating station to the distribution centre, very high voltage DC transmission is less lossy than AC for the same power transmitted. The problem arises with conversion to AC at the using end. China transmits lot of power as DC across huge distances.

  The problem of conversion has also been removed to a great extent by the Invention of High power rated IGBT transistors. Their invention is likely the revolution in the power transmission in DC form I would say the revelutionised this field and made DC transmission very much possible
• 

  Ramani Aswath

  jeffrey samuel

  The problem of conversion has also been removed to a great extent by the Invention of High power rated IGBT transistors.

  I agree. That is clearly the issue. We should look at current technology and not go by what was valid in the early days of electricity generation.
• 

  Jeffrey Arulraj

  bioramani

  I agree. That is clearly the issue. We should look at current technology and not go by what was valid in the early days of electricity generation.

  True once semi conductors came into the picture there was a change
  
  When transistors controlled by current came they said too much heat and loss is much but it was an innovation that proved all things are possible
  
  Then the revolutionary FET completely controlled by Voltage came into the picture . This was the first Semi conductor device which was completely independant of the INPUT CURRENT
  
  The MOSFET IGBT and IGFET all increased the speed of the device and also reduced the depandancy of the devices in input current
  (
  
  These paved way for chopping a DC signal into pulsating DC which can be stepped up or down using a Transformer this proved as the break through which was what we needed
  
  

  AN INDEPENDENCE FROM INPUT CURRENT ​
• 

  Ramani Aswath

  Here are some useful inks:
  This is an overview of HV DC Transmission:
  #-Link-Snipped-#
  
  This gives info from a major power supply industry:
  #-Link-Snipped-#
  
  This was the 11th Plan target forIndia. How much actually got done has to be established:
  #-Link-Snipped-#
• 

  [Prototype]

  The core problem for DC transmission lies in the fact that, it cannot be generated. Besides, there's no PRACTICAL easy (and reliable) way to step up DC voltages, as transformers are not valid for DC supply.
  
  If you actually see, most part of the appliances works on DC supply. However, due to the above fact, its more economical, reliable and simple to convert the AC supply at consumer end instead of transmitting DC.
  
  Lets say we find a reliable way to transmit DC, then, could we like add the 5th wire and send DC separately with the existing AC supply? That way, you can just the 'totally AC' appliances like motors on AC while other DC appliances on DC without need of any conversions that would incur losses.
• 

  dossdss

  what is about this new topic coming in to focus "wireless power transmission" ?
• 

  [Prototype]

  dossdss

  what is about this new topic coming in to focus "wireless power transmission" ?

  Not exactly new, old Palm devices have employed this. However, yes, a lots of interest is being shown in this field. However, this is at very basic stage for transmitting large power over a distance. Don't see it coming anytime soon. Atm, it wastes lots of power.
  
  Actually, the RFID technology is somewhat similar to this. The RFID cards don't have power supply. They derive the power from scanner.
• 

  Ramani Aswath

  dossdss

  what is about this new topic coming in to focus "wireless power transmission" ?

  That is very unlikely for large powers or long distances. Such transmission will have a spherical wave front like other Electro Magnetic radiation. If MASERS (microwave version of LASERS) are used it can be a line of sight transfer. Prohibitively expensive. Wastes too much power.
• 

  Jeffrey Arulraj

  Lets say we find a reliable way to transmit DC, then, could we like add the 5th wire and send DC separately with the existing AC supply? That way, you can just the 'totally AC' appliances like motors on AC while other DC appliances on DC without need of any conversions that would incur losses.

  The existing cables are enough and the newly found IGBT tech which is being primarily experimented There is a probability of transmitting DC and the re conversion of it to AC is also much simpler when compared to older days so this is very much possible
  
  But the implementation time will have to wait for atleast another five years in the minimum
• 

  Jeffrey Arulraj

  dossdss

  what is about this new topic coming in to focus "wireless power transmission" ?

  More power more liability to loss in lower frequency so you need to increase the frequency above Giga Hertz then again in the receiving end you need to bring the frequency down to 50 / 60 this is too lossy to be tried out
• 

  Jeffrey Arulraj

  Dewitt Hunt

  Thanks.I got some idea

  Hope you can participate again in this weekky event and enrich s with more of your post