The invention of mercury-arc rectifiers and thyratrons, which can convert alternating current to direct current and vice versa effectively and at a reasonable cost, enabled the transmission of electric power over DC networks. Figure 2.1 depicts a single line schematic of a hV DC transmission system. The term "single line" means that the power is transmitted from substation to substation by only a single wire pair. A three-wire system would be called a "three-phase" system. Schematic diagrams like this one are used by power engineers when planning the location of power lines with respect to each other and their environment. They aim to avoid having two lines run into or across each other at right angles.
DC power can be transmitted long distances without loss of voltage because there's no need for large transformers to step up or down the voltage. Transmission lines used for DC power must be thick enough to carry the intended voltage but thin enough so they won't break under their own weight. These constraints don't apply to AC lines because it's easy to increase or decrease the voltage on an AC line by using inductors or capacitors, respectively. Transformers used for interconnecting AC networks have large cores that reduce leakage inductance and allow them to transfer high currents efficiently.
The most common type of DC transmission system in use today is the closed circuit television (CCTV) system.
To address this, a high-voltage direct current (HVDC) transmission technology is typically used for high power transmission. At the conclusion of the DC power system, the DC power is inverted to AC power and synced with the next AC network. As a result, the HVDC system is divided into three sections: the converter station, the transmission part, and the inverter station. The converter station converts the DC power from the nuclear generator to AC power suitable for transmission over long distances. The transmission part consists of large capacitors that store energy for later use if there are fluctuations in load or unexpected events such as a line fault. This allows for continuous transmission even if some components fail. The inverter station converts the transmitted AC power back to DC power for delivery to the consumer. It also includes filters for removing any residual voltage after completion of each cycle.
The HVDC transmission system has several advantages over other types of power transmissions systems. It can transfer power over long distances without loss of efficiency due to major transmission lines. There is also no radiation exposure for operating personnel. The only maintenance required by this type of system is replacement of parts such as transformers, converters, and capacitors. These parts are relatively inexpensive and can last for many years if properly maintained.
However, this type of system does have some limitations when applied to specific applications. For example, it cannot transmit electricity at high rates because there would not be enough time to switch off the current before switching on the next phase of the wave.
The bulk power is sent over a long distance using the DC transmission line. The thyratron transforms DC to AC at the consumer end. The alternating current transmission line sends alternating current over a long distance. At the other end, another thyratron turns the voltage back into DC.
Thyristors are vacuum tubes used for controlling electricity. A thyristor can be turned on and off many times without damage. This makes them useful for switching applications like lighting and heating where repeated on-off cycles are not a problem. A thyristor can also block high voltages so they are useful for protecting other equipment from electrical surges from the power line.
Thyratrons were invented by Harvey Hubbell and first introduced by General Electric in 1951. They are similar to thyristors but use solid-state components instead of vacuum tubes. Both types of switch are activated by applying a small negative voltage to their anodes (minus voltage means electrons flow out of the anode). This causes both switches to turn off, allowing current to flow through the load.
Solid-state switches such as thyratrons have replaced vacuum tubes in many low-power applications such as lamps and heaters. They are more durable than vacuum tubes and do not suffer from radiation damage that would eventually cause lights or heaters made with vacuum tubes to fail prematurely.