The disclosure relates to an arrangement and a method for determining a measurement value for a power cable.

Background

Cables, in particular power cables, can degrade over time. In particular, temperature has a significant influence on the properties of a cable. Thus, monitoring a thermal condition of the cable is desirable.

It is known to measure a temperature of the cable on the surface of the cable. With a thermal model of the cable, conditions in the cable may be estimated from the surface measured values. For example, a temperature of an inner conductor may be computed.

Alternatively, a fiber optic cable can be inserted in the cable to determine properties of the cable. A polarization of laser light coupled in the fiber optic cable changes with temperature. This approach is expensive. Further, the fiber optic sensor can be a kind of impurity in the power cable which may cause a partial discharge.

Document DE 10 2014 101 156 Al discloses a device for determining a measurement value of an electrical site. The device comprises a measurement sensor which is coupled to a thermo-electrical generator. Measurement values are transmitted to a receiver by a transmitting unit. The device can be arranged on a cable.

Summary

It is an object to provide improved technologies for monitoring power cables. An arrangement according to claim 1 and a method according to claim 10 are provided. Further embodiments are subject matter of dependent claims. In one aspect, an arrangement comprising a power cable and a measurement system is disclosed. The measurement system comprises an energy harvesting unit which is adapted to generate electrical energy, a sensor for determining a measurement value, and a transmitting unit which is adapted to transmit the measurement value to a receiver. The sensor and the transmitting unit are coupled to the energy harvesting unit. The measurement system is integrated in the power cable.

In another aspect, a method for determining a measurement value for a power cable is provided. The method comprises steps of: providing a power cable, and providing a measurement system. The measurement system comprises: an energy harvesting unit which is adapted to convert thermal energy to electrical energy, a sensor for determining a measurement value, and a transmitting unit which is adapted to transmit the measurement value to a receiver, wherein the sensor and the transmitting unit are coupled to the energy harvesting unit. The method further comprises arranging the measurement system such that it is integrated in the power cable, and measuring, by the measurement system, a measurement value of the power cable.

By integrating the measurement system in the power cable, accuracy of the measurement value is increased.

The sensor can be adapted to determine a measurement value of the following types of measurement values: temperature, humidity, gas pressure, gas and light radiation. The sensor can be formed as temperature sensor, humidity sensor, gas pressure sensor, gas sensor and / or light sensor. The measurement system may comprise several sensors, wherein each sensor can be adapted to determine one of the before mentioned measurements values. Several sensors may be coupled with each other.

The energy harvesting unit is used to supply electrical power to the components of the measurement system, in particular to the sensor(s) and the transmitting unit. The energy harvesting unit may be adapted to convert thermal energy in electrical energy (so-called thermo-electrical generator). The energy harvesting unit may comprise two different metals using the Seebeck effect to generate electrical energy. Alternatively, the energy harvesting unit may comprise two different semiconducting materials using the Peltier effect. A temperature difference between the two materials of several Kelvin (K) is sufficient to generate a thermo voltage of several millivolt (mV). The energy harvesting unit may be adapted to sense temperatures in the range from -30 °C to 140 °C. The energy harvesting unit may be adapted to generate an electrical voltage in the range from 2 mV to 1,5 V or more. In other embodiments, the energy harvesting unit can be adapted to convert magnetic field energy and / or electrical field energy to electrical energy.

The measurement system may comprise several energy harvesting units. Several energy harvesting units may be operated in parallel configuration or in series. The measurement system may further comprise a DC-DC converter (also called DC-DC booster). The DC-DC converter can be adapted to transform a small input voltage (e.g. some mV) to a high output voltage (e.g. 1 ,5 V). A resistor may be coupled to the DC-DC converter in order to limit the input voltage. The transmitting unit may be adapted to transmit the measurement value with a frequency of more than 100 MHz, e.g. 305 MHz, 868 MHz, 902 MHz or 2,4 GHz. The transmitting unit may be a radio module of the company EnOcean. The transmitting unit may be adapted to encrypt the measurement value prior to its transmission. The measurement system may comprise a processor, which may be adapted to convert the measurement value in a digital value prior to the transmission. The processor may also be coupled to the energy harvesting unit for power supply.

The power cable may comprise a conductor which is surrounded by a shield, and the conductor and the shield may be surrounded by a jacket. The jacket may be some millimeters up to several centimeters thick, e.g. 8 mm, 2 cm, 3 cm or 5 cm.

The measurement system may be arranged between the shield and an outer surface of the jacket. The measurement system may be arranged directly on the shield. The measurement system may be arranged such that an outer surface of the measurement system finishes with the outer surface of the jacket. In one embodiment, the measurement system may be arranged directly on the shield extending through the jacket such that the outer surface of the measurement system finishes with the outer surface of the jacket. The measurement system may comprise a base plate on which the energy harvesting unit, the sensor and the transmitting unit are arranged. The measurement system may further comprise a heat conductor which is arranged above the base plate. The heat conductor may be connected to the base plate. The heat conductor may be made of a metal or a metallic alloy. The energy harvesting unit may be arranged on the base plate and connected to the heat conductor such that a temperature difference between the base plate and the heat conductor can be converted to electrical energy.

The measurement system may be molded in the jacket of the power cable.

The measurement system may be arranged between the conductor and the shield, e.g. the measurement system may be arranged directly on the conductor.

The measurement system may be arranged in the conductor, e.g. the measurement system may be arranged directly in the conductor.

The measurement system may be surrounded by a closed housing. The housing may surround all components of the measurement system. The housing may be made of a metal, e.g. aluminum or copper, or of a thermally conductive plastic. The housing may be fluid tight, e.g. according to IP class 68 or higher. The housing may be corrosion-resistant.

The features disclosed in context with the arrangement are also applicable for the method and vice versa. Description of embodiments

Following, exemplary embodiments are described. Here show:

Fig. 1 a schematic representation of a measurement system,

Fig. 2 a schematic representation of another measurement system,

Fig. 3 a schematic representation of a power cable,

Fig. 4 a schematic representation of a further measurement system, and

Fig. 5 a schematic representation of a power cable with a measurement system. Fig. 1 shows a schematic representation of a measurement system. An energy harvesting unit 1 is connected to a sensor 2 (e.g. a temperature sensor) and a transmitting unit 3. Electrical energy is supplied by the energy harvesting unit to the sensor 2 and the transmitting unit 3. Measurement values determined by the sensor 2 are transmitted by the transmitting unit 3 to a receiver (not shown).

Fig. 2 shows another embodiment of the measurement system. In addition to Fig. 1, the system comprises a processor 4 which converts the measurements values of the sensor 2 before they are transmitted by the transmitting unit 3. The processor 4 is also supplied with electrical energy by the energy harvesting unit 1.

The measurement systems shown in Fig. 1 and 2 may be surrounded by a housing (not shown). Fig. 3 shows a schematic representation of a power cable comprising a jacket 5, a shield 6 and a conductor 7. Several arrangements of measurement systems integrated in the cable are shown. The measurement system can be arranged between the shield 6 and the jacket 5 (position 10). The measurement system may be arranged on a top end of the jacket 5 such that an outer surface of the system finishes with an outer surface of the jacket 5 (position 11). Alternatively, the measurement system can be arranged directly on and in contact with the conductor 6 (position 12). In another embodiment, the measurement system is arranged on the conductor 6 such that the outer surface of the system finishes with the outer surface of the jacket 5 (position 13). The measurement system may also be arranged inside the shield 6. Position 14 shows an embodiment, where the measurement system is arranged between the shield 6 and the conductor 7. Finally, the measurement system can be arranged directly on and in contact with the conductor 7 (position 15).

In Fig. 4, another embodiment of the measurement system is shown. An energy harvesting unit 22, a sensor 21, and a transmitting unit 23 are arranged on a base plate 20. Above the base plate, a heat conductor 24 is arranged. The heat conductor 24 is connected to the base plate 20 and the energy harvesting unit 22. The energy harvesting unit 22 converts a temperature difference between the base plate 20 and the heat conductor 24 in electrical energy. Fig. 5 shows a power cable, wherein the measurement system 30 is arranged in the conductor 7. The measurement system 30 may be surrounded by a closed housing.

The features disclosed in the specification, the claims and the figures can be relevant for the implementation of embodiments either alone or in any combination with each other.