The Empire and the Century/The Nerves of Empire

AC power is used at 60 Hz in North America (excluding the aforementioned 25 Hz network), western Japan, South Korea and Taiwan; and at 50 Hz in a number of European countries, India, Saudi Arabia, eastern Japan, countries that used to be part of the Soviet Union, on high-speed lines in much of Western Europe (including countries that still run conventional railways under DC but not in countries using 16.7 Hz, see above). 2⁄3 Hz to 16.7 Hz which is no longer exactly one-third of the grid frequency. The capacitively loaded antennas used at low frequencies have extremely narrow bandwidths, and therefore if the frequency is changed the loading coil must be adjustable to tune the antenna to resonance with the new transmitter frequency. This has been solved in newer wireless DMX systems by using adaptive frequency hopping, a technique to detect and avoid surrounding wireless systems, to avoid transmitting on occupied frequencies.

These drives can run equally well on DC or AC of any frequency, and many modern electric locomotives are designed to handle different supply voltages and frequencies to simplify cross-border operation. In telecommunications, a broadband signalling method is one that handles a wide band of frequencies. Each wheel set of a powered bogie carries one traction motor. The return of each traction motor, as well as each wagon, is effected by one contact shoe each that slide on top of each one of the running rails. The London Underground in England is one of few networks that uses a four-rail system. If one computer begins to give aberrant results for any reason, potentially including software or hardware failures or flawed input data, then the combined system is designed to exclude the results from that computer in deciding the appropriate actions for the flight controls. In 1970 the Ural Electromechanical Institute of Railway Engineers carried out calculations for railway electrification at 12 kV DC, showing that the equivalent loss levels for a 25 kV AC system could be achieved with DC voltage between 11 and 16 kV.

The cable's male connector attaches to the transmitting, female jack (OUT), and its female connector attaches to the receiving, male jack (IN). The converters turned out to be unreliable and the experiment was curtailed. This solved overheating problems with the rotary converters used to generate some of this power from the grid supply. DC rolling stock was equipped with ignitron-based converters to lower the supply voltage to 3 kV. 6-7 UIC conducted a case study for the conversion of the Bordeaux-Hendaye railway line (France), currently electrified at 1.5 kV DC, to 9 kV DC and found that the conversion would allow to use less bulky overhead wires (saving €20 million per 100 route-km) and lower the losses (saving 2 GWh per year per 100 route-km; equalling about €150,000 p.a.). Also, the energy used to blow air to cool transformers, power electronics (including rectifiers), and other conversion hardware must be accounted for. The higher the voltage, the lower the current for the same power (because power is current multiplied by voltage), and power loss is proportional to the current squared.

The lower current reduces line loss, thus allowing higher power to be delivered. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails, what is control cable which have to be seated on stronger metal chairs to carry the weight of trains. DC voltages between 600 V and 750 V are used by most tramways and trolleybus networks, as well as some metro systems as the traction motors accept this voltage without the weight of an on-board transformer. 420 V DC, and a top-contact fourth rail is located centrally between the running rails at −210 V DC, which combine to provide a traction voltage of 630 V DC. Inside the locomotive, a transformer steps the voltage down for use by the traction motors and auxiliary loads. The Expo and Millennium Line of the Vancouver SkyTrain use side-contact fourth-rail systems for their 650 V DC supply. SEC. 6. RETRANSMISSION CONSENT FOR CABLE SYSTEMS.