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Capacitive Transfer System (CTS)

Capacitive Transfer System (CTS) is a new concept in power cables. Aimed initially at MV distribution networks, it uses a “linear capacitor” as the cable to transfer power leading to lower losses and the capacity to deliver more power than legacy cable systems. Originally presented as a flat multi-layered cable, Enertechnos has refined the CTS to be manufactured on conventional cable-making equipment; developed a jointing system; and designed a cable protection system.

Capacitive Transfer System (CTS)

Capacitive Transfer System (CTS) is a new concept in power cables. Aimed initially at MV distribution networks, it uses a “linear capacitor” as the cable to transfer power leading to lower losses and the capacity to deliver more power than legacy cable systems. Originally presented as a flat multi-layered cable, Enertechnos has refined the CTS to be manufactured on conventional cable-making equipment; developed a jointing system; and designed a cable protection system.

Comparison: Conventional Cable and CTS

Conventional Cable

CTS Cable

With a legacy cable, an electrical connection is made to the conductor core at both ends and power “flows through” the cable. With DC power, that flow is impeded by the resistance of the metal conductor, with AC power the resistance impedes and so does the reactance, typically due to magnetic fields and called inductive reactance.

To combat this inductive reactance, CTS cable is designed to form its conductor into two “electrodes” along the entire length. One electrode is connected to the generator and the other is connected to the load. In this way the CTS cable acts as a capacitor and provides capacitive reactance which offsets most of the inductive reactance, leaving very nearly only the resistance.

Voltage Drop

Voltage-drop means that less power can be transferred from the generation side to the consumption side leading to poor performance of motors, dimming of lights and potential “brown-out”. With reduced voltage a given load will draw greater current which in turn increases losses due to heating. Untreated, reactance makes voltage drop worse than it needs to be. That is, along the length of the cable the voltage becomes lower than the supplied voltage. The result is the system must supply more amps of current to deliver the same amount of power.

Voltage Drop

Voltage-drop means that less power can be transferred from the generation side to the consumption side leading to poor performance of motors, dimming of lights and potential “brown-out”. With reduced voltage a given load will draw greater current which in turn increases losses due to heating. Untreated, reactance makes voltage drop worse than it needs to be. That is, along the length of the cable the voltage becomes lower than the supplied voltage. The result is the system must supply more amps of current to deliver the same amount of power.

Losses and Reactance

Losses, mostly through heating, increase with the square of the current, so a 5% voltage drop, leads to a 5.3% increase in current to compensate, which in turn leads to a 10.8% increase in losses. These may seem like relatively small percentage numbers, but on a typical 800A cable in a 33kV system, 5.3% more amps flowing means 1.4MW, or almost half the output of an average onshore wind turbine, being lost in a single 3-phase cable run. By reducing the reactance, CTS can reduce the voltage-drop and therefore reduce the current required to supply the load.

Losses and Reactance

Losses, mostly through heating, increase with the square of the current, so a 5% voltage drop, leads to a 5.3% increase in current to compensate, which in turn leads to a 10.8% increase in losses. These may seem like relatively small percentage numbers, but on a typical 800A cable in a 33kV system, 5.3% more amps flowing means 1.4MW, or almost half the output of an average onshore wind turbine, being lost in a single 3-phase cable run. By reducing the reactance, CTS can reduce the voltage-drop and therefore reduce the current required to supply the load.

Typically, when dealing with cables, capacitance is to be avoided, so why is CTS adding it? The capacitance referred to in cable specifications is the capacitance between the core and the earth shield outside the cable’s insulation. This capacitance leads to current leaking to earth and is detrimental to performance. The longer the cable the worse this “shunt” capacitance problem becomes. CTS capacitance is inside the core and rather than leaking current, it is the means by which the current is delivered to the load, so the longer the cable the higher the capacitance of a CTS cable and the more “series capacitance” it can supply.

Value and Impact of CTS

Although CTS started off by helping to reduce losses, we have established additional key advantages and impacts that it can have on grid efficiency.

Increases quantity of power

Increasing the quantity of power that can be delivered through the cable – potentially increasing the current rating

Reactive Support

Providing reactive support as non-synchronous (wind and solar renewables) make up a greater percentage of the grid

Longer cable-runs

Longer runs underground which is especially useful in areas of outstanding beauty where overhead power lines can run into years of objections