SE1500277A1 - Power supply - Google Patents

Abstract

It is presented a power supply for supplying power for use at high potential comprising: a first transformer comprising a low voltage winding connectable at its ends at ground level to a mains power supply, and a second winding; a second transformer comprising a low voltage winding connected at its ends at high potential level to an output; a first string comprising a serial connection of a first capacitor and a resistor, the first string being connected between a first end of a high voltage winding of the first transformer and a first end of a high voltage winding of the second transformer; and a second string comprising a serial connection of a second capacitor and a resistor, the second string being connected between a second end of the high voltage winding of the first transformer and a second end of the high voltage winding of the second transformer.(Figi)

Description

15 20 25 otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a schematic drawing illustrating one embodiment.

DETAILED DESCRIPTION The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig. 1 is a schematic drawing illustrating one embodiment. Embodiments presented herein solve the problem of scaling up the transformer solution for higher HVDC levels. They also solve the problem with sensitivity to fast transients when the HVDC side is switched. They also use readily available components for high voltage that avoids complicated technical implementation.

This solution is safer to scale up to high HVDC levels since is uses well tested HV DC capacitors as the barrier between high voltage and ground.

Embodiments presented herein also have the potential of being more cost effective that the transformer solution of the prior art since such a transformer grows disproportionately in size for higher voltage levels.

The components are passive high voltage components with a long expected lifetime and high immunity to overvoltages and transients. The voltage at the output 15 is a normal mains voltage e.g. at 230V and 50 or 60 Hz that can 10 15 20 25 30 power most equipment. At the input 19, the system 1 is powered by a normal 50 or 60 Hz main voltage and requires no active electronics.

Embodiments presented herein relate to a system of high voltage components for a main frequency, 50 or 60 Hz, to transmit electric power up to a high DC potential with the ability to withstand transients from switching.

Two high voltage capacitors 14a-b are used as coupling capacitors for an AC voltage up to the high potential. Each capacitor is series connected with resistive impedance 17a-b and optionally a respective inductive impedance 13a-b to attenuate transient currents during switching events. The AC voltage is a relatively high voltage that enables the series connected resistor to have a high resistance without having significant power losses. In this way, the high resistance attenuates the transient capacitive current during a switching event. This is not possible to implement for the high frequency solution in the prior art since the low AC voltage gave a high current through the capacitors event for low power loads. The relatively high AC voltage comes from a? Rst high voltage transformer 11a with a center tap. The voltage level of each output is in the range of 15 to 50 kV depending on the capacitor value and maximum transmitted power. In experiments, more than 1 kW was transmitted at an efficiency of 75% with a system comprising two 14 kV transformers, two 20 nF capacitors and two 40 kohm resistors.

At the high voltage side 20, the AC voltage is transformed back to a suitable voltage level with a second transformer 11b of the same type as the? Rst transformer 11a used at ground level. Reactive compensation of the series capacitances reduces output impedance and makes the output voltage more stable when load changes. This reactive compensation can be placed in several positions. The resistors 17a-b may be made as wire wound resistors to have a large inductance. This will also help to attenuate transient current during switching. The leakage inductance of the transformers 11a-b may be used as part of the reactive compensation. Finally, one or more low voltage reactors 23a-b may optionally be placed in series to the low voltage windings for one or both of the transformers 11a-b. 10 15 The high voltage windings of the transformers 11a-b may be designed to share the full transient lightning voltage, or cheaper transformers with a lower rating may be used if optional surge arresters 22a-d protect them. The rest of the overvoltage is then applied over the resistors 13a-b.

Compared to the high frequency solution of the prior art, the high AC voltage which is used to transmit the power enables the insertion of the two impedances which reduce the high current peak at switching to a very low value. Moreover, this solution uses the main frequency of 50 or 60 Hz, thus eliminating the need for sensitive electronics in the driving circuit which would be exposed to transients during switching or lightning.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as deñned by the appended patent claims.

Claims (5)

10 15 20 25 30 CLAIMS 1. A power supply (1) for supplying power for use at high potential (20) comprising: a first transformer (11a) comprising a low voltage winding connectable at its ends at ground level to a mains power supply (19), and a second winding; a second transformer (11b) comprising a low voltage winding connected at its ends at high potential level (20) to an output (15); a? rst string (27a) comprising a serial connection of a? rst capacitor (14a) and a resistor (17a), the? rst string (27a) being connected between a? rst end of a high voltage winding of the? rst transformer (11a) and a? Rst end of a high voltage winding of the second transformer (11b); and a second string (27b) comprising a serial connection of a second capacitor (14b) and a resistor (17b), the second string (27b) being connected between a second end of the high voltage winding of the? rst transformer (11a) and a second end of the high voltage winding of the second transformer (11b). The power supply according to claim 1, wherein the first string (27a) further comprises a? Rst reactor (13a) provided as part of its serial connection and wherein the second string (27b) further comprises a second reactor (13b) provided as part of its serial connection. The power supply according to any one of the preceding claims, further comprising surge arresters (22a-b) provided from each of the high voltage winding ends of the? Rst transformer 11a and ground. The power supply according to any one of the preceding claims, further comprising an inductor provided between the low voltage side of the? Rst transformer (11a) and the input (19). 5. The power supply according to any one of the preceding claims, further comprising an inductor provided between the low voltage side of the second transformer (11b) and the output (15).