Why DC voltage is not Applied in Transformer Input

What Happen if DC Voltage is Applied to Transformer Input?

Considering the importance we can say a transformer is the most efficient electrical machine ever invented on the earth.

The main function of the transformer is to step up or step down the voltage to the desired voltage level keeping the power level the same at both primary and secondary or in simple input power and output power are equal.

So, we can define a transformer as a static device that converts electrical power from one circuit to another without changing its frequency and it Steps up or Steps down the level of AC Voltage and Current.

What is the Advantages and Disadvantages of D.C. and A.C. Transmission System?

What is the Advantages and Disadvantages of D.C. (Direct Current) and A.C. (Alternating Current) Transmission System?

The electrical energy transmission can be transmitted either by means of DC- Direct Current or AC- Alternating Current each system has its own advantages and disadvantages. From that point of view, we want to discuss today the technical advantages and disadvantages of the two electrical energy transmission systems for of electric power network.

D.C. Energy Transmission System

From the couple of years past, engineers in transmission sector are rethinking the DC electric transmission system. DC electric power transmission has been receiving the active consideration due to its numerous advantages as bellow:

Advantages of DC Electrical Energy Transmission System.

The high voltage DC energy transmission has the following advantages over the high voltage AC energy transmission system.

(i) DC system requires only two conductors comparing to three for AC transmission;

(ii) In DC transmission system there is no presence of inductance, capacitance, phase displacement and surge problems comparing AC transmission system;

(iii) In DC electric transmission line has better voltage regulation comparing AC system due to the absence of inductance. For a particular same load the voltage drop in a DC transmission line is less than the AC;

(iv) The total conductor cross section of the transmission line is utilized due to their no skin effect in a DC system;

(v) For the same working voltage, the potential stress on the insulation is less in case of DC system than that in AC system. So, a DC line requires less insulation;

(vi) There in a DC line has less corona loss and reduced interference with communication circuits;

(vii) The high voltage DC transmission is free from the dielectric losses, particularly in the case of cables;

(viii) In DC transmission system, there are no stability problems and synchronizing difficulties comparing AC system.

You may read the another article to know details about D.C. transmission and distribution:

HVDC Transmission and Distribution System Network

Disadvantages of DC Electrical Energy Transmission System

The high voltage DC energy transmission has the following dis advantages over the high voltage AC energy transmission system.

(i) Due to commutation problems the electric power cannot be generated at high DC voltage that is one of the disadvantage of DC system;

(ii) Stepped up or stepped down in electric energy transmission system is an important factor, but in the DC voltage cannot be stepped up for transmission of power at high voltages;

(iii) The DC switches and circuit breakers have their own limitations.

A.C. Energy Transmission System

Now-a-days, most of electrical energy transmission system is in Alternating Current or AC system. Exclusively generation, transmission and distribution system is popular in all over the world.

Advantages of AC Electrical Energy Transmission System

(i) It is easy and can be generated at high voltages AC electric power system;

(ii) The maintenance of AC sub-stations is easy and cheaper than DC transmission system;

(iii) The AC voltage can be stepped up or stepped down by transformers with ease and efficiency that is not possible in DC energy transmission system. This permits to transmit power at high voltages and distribute it at safe potentials in AC electric transmission system.

Disadvantages of AC Electrical Energy Transmission System

(i) An AC transmission conductor copper is required more copper than a DC transmission line;

(ii) The construction of AC transmission electric line network is more complicated than a DC transmission electric line network;

(iii) Due to skin effect in the AC system, the effective resistance of the line is increased;

(iv) The AC line system has capacitance. Therefore, there is a continuous loss of power due to charging current even when the line is open.

HVDC Transmission and Distribution System Network

Transmission and Distribution of D.C. (Direct Current) Power

By the meaning of electrical power transmission and distribution is electrical energy generated in a central power station and carried to the consumers end like- heavy industries, mill-factories, commercial zones, residential areas and so on through transmission and distribution transformers. from the central So far, there are two well known electric power transmission and distribution network systems:

(i) By overhead system; or 
(ii) By underground system.

Overhead power transmission is suitable and costs economic for long-distance and less populated or less obstructed rural or countryside areas.

Underground power transmission is the easiest way to distribute electric lines in cities or densely populated areas where overhead line construction is difficult. Comparing the overhead power transmission, the underground power transmission system is more costly.

In an overhead system, power is conveyed by bare conductors of copper or aluminium which are strung between wooden or steel poles erected at convenient distances along a route. 

The bare copper or aluminium wire is fixed to an insulator which is itself fixed onto a cross-arm on the pole. The number of cross-arms carried by a pole depends on the number of wires it has to carry. 

Line supports consist of (i) pole structures and (ii) towers. Poles which are made of wood, reinforced concrete or steel are used up to 33 kV whereas steel towers are used for higher voltages.

The underground system employs insulated cables which may be single, double or triple-core etc. A good system whether overhead or underground should fulfil the following requirements :

1. The voltage at the consumer’s premises must be maintained within ± 4 or ± 6% of the declared voltage, the actual value depending on the type of load.

2. The loss of power in the system itself should be a small percentage (about 10%) of the power transmitted.

3. The transmission cost should not be unduly excessive.

4. The maximum current passing through the conductor should be limited to such a value as not to overheat the conductor or damage its insulation.

5. The insulation resistance of the whole system should be very high so that there is no undue leakage or danger to human life.

You may be interested to know: 

01. Advantages and Disadvantages of D.C. and A.C. Transmission System

02. Why DC System Is More Dangerous Than AC System?

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