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# Question on voltage / current in transformers

We use transformer to decrease current and increase voltage at the time of transmitting the AC power to homes, industries etc so that the loss of power due to current is less .now when we will step down the voltage at the receiving end then voltage will decrease and current should increase, but we see that at homes voltage and current both are less
xheavenlyx • Mar 12, 2008
Re: transistor

Current is not exactly less. There is a limit set on the max level of current that comes to our houses. This is because if there is short it would not cause many problems (eg at homes on 10 to 20 Amp lines). If there is a short on 200 Amp line, it can melt concrete and maybe even blow up your fuse box.
Re: transistor

The thread title was a little misleading 😛 biggie, I'm unable to change it somehow.
well,when we transmit HV,then also it consist of high current,sure when we step down voltage,current is also regulated using current transformers,anyhow 2 Amps current is also not so low!!!
At the time step-up the voltage is increased and current is decreased. Losses are directly proportional to the flow of current.
Suppose we want to send the 20MW power to a distance of 100KM.
Power = Voltage x Current
In case of 66 KV,
I = 20,000,000/66,000= 303.03 Amp.
In case of 132 KV,
I = 20,000,000/132,000 =151.5 Amp.

Due to the above voltage level 132KV line having more efficiency than 66KV line.

It is clear that the transformer is not playing any role, the power is constant at the input & output.

In transformer you will find that
Vp x Ip = Vs x Is

Connect
plantate • Jun 2, 2008
AnilKumarTiwari
At the time step-up the voltage is increased and current is decreased. Losses are directly proportional to the flow of current.
Suppose we want to send the 20MW power to a distance of 100KM.
Power = Voltage x Current
In case of 66 KV,
I = 20,000,000/66,000= 303.03 Amp.
In case of 132 KV,
I = 20,000,000/132,000 =151.5 Amp.

Due to the above voltage level 132KV line having more efficiency than 66KV line.

It is clear that the transformer is not playing any role, the power is constant at the input & output.

In transformer you will find that
Vp x Ip = Vs x Is

Connect
Not exactly,transformers lose power,so the output will always be less than the input.Transformers can be very inefficient on bad waveforms,however they are still considered to be about the most efficient electrical device!
To transmit energy any distance you need good conductors,which usually mean big cables,by using high voltage,the current is less so smaller cables can be used watts lose =Current squared resistance.Another bonus is that any volt drop as a result will be a much smaller percentage of the total voltage.Of course high voltage AC does present other losses,which is why DC is sometimes preferred for large transmissions.
4IPacino • Jun 3, 2008
Transformers ARE the most efficient el. devices 99% and even more if they are of greater power (100 MVA, 200 MVA, 500 MVA; The greatest power for which I know is 700 MVA). For example 1% loss in case of 100 MWA is arround 900 kW (when you consider COS(fi)). So the loss is the big problem when we speak of about 100s of MVA because loss=heat. A lot of heat. Such big transformers are used in sending electricity to large distances.

When you talk about losses in power lines, you can almost ignore ohmic losses because they are hardly few percents of inductive losses.

The transformers in cities are smaller. Their power is 10s of MVA. They are called DISTRIBUTIVE transformers, and are used to deliver electricity to your home.
The current that comes out of secundar in real world is allways little smaller than the calculated value because of losses.
You should consider that there is lot of end users so the current out of this transformers is divided to users according to KIRCHOFFS laws.
These are the reasons why the current at secundar is smaller.

AIPacino