Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2001-02-09
2003-02-11
Oda, Christine (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S524000
Reexamination Certificate
active
06518769
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for the electrical monitoring of an electrode lead of a bipolar high-voltage d.c. transmission system in which the electrode lead is divided into two lines at a branch point.
BACKGROUND INFORMATION
Systems for transmitting power by means of a high-voltage d.c. current contain two static converter stations that are connected to each other by a d.c. line. In the case of a single-pole d.c. transmission system, both stations are connected to each other by a single d.c. line, the return current being routed through ground. A d.c. pole in each station is then grounded by a good ground connection. Normally, this ground connection is located at a certain distance from the static converter station and connected to the station by an electrical line that is called an electrode lead. It can often be desirable or necessary to locate the ground connection at a great distance of up to one hundred kilometers from the station.
In the case of a double-pole d.c. transmission system, the stations are connected to each other by two d.c. current lines so that in normal operation the direct current does not need to return through the ground. For various reasons, i.e., to enable single-pole operation of the system in the event of a static converter failure, static converter stations in double-pole d.c. transmissions are provided with a ground connection that is connected to the station by an electrode lead.
An electrode lead is insulated from ground and normally is made of a multiple-wire, twisted conductor that is suspended on insulators. Although the voltage between the electrode lead and ground is normally small compared to other voltages in the system, a ground fault on the electrode lead constitutes the danger of personal injuries or damage to other system components, e.g., corrosion. It is therefore necessary to be able to discover ground faults quickly and reliably, including high-impedance ground faults and open circuits.
To locate ground faults on an electrode lead, a differential protective arrangement has conventionally been used. In a protective arrangement of this type, the current is measured at both ends of the electrode lead and a difference between the two measured currents means that a ground fault is present. However, a protective arrangement of this type has various disadvantages. It requires a communication link between the two ends of the electrode lead and therefore is expensive, especially in connection with long electrode leads. A protective arrangement of this type also does not react to a ground fault that occurs in those cases in which the electrode lead is not conducting any current, which is normally the case during operation of a double-pole transmission system without faults. Even in this case, i.e., if no direct current is flowing through the electrode lead, asymmetric currents can lead to the creation of dangerous voltages on the lead.
Ground faults on an electrode lead have also been located by injecting an alternating current signal or alternating voltage signal at a specific frequency into the lead at the static converter station. In this case suppression filters are used at both ends of the line, these filters being tuned to the frequency of the injected signal. An impedance measurement element is used to measure the impedance of the electrode lead opposite ground at the feed point at the injected frequency. A change of the impedance measured in this way is an indication of a ground fault. This method works well in cases of short electrode leads. To detect a line fault, the measurement frequency must be selected so that the length of the line is less than one quarter of the wavelength. For this reason, in the case of long electrode leads, a frequency must be selected that is so low that there is a danger of the measurement being disturbed by the mains frequency or by the lowest harmonics of the mains frequency. Furthermore, at these low frequencies, the suppression filters placed at both ends of the electrode lead—which must be rated for the maximum current on the electrode lead—become very large and expensive.
European Patent No. 0 360 109 describes a protective device for an electrode lead in which a high measurement frequency can also be used in the case of long electrode leads, thereby substantially reducing the dimensions and costs of the suppression filters as well as the danger of interference by the mains frequency or its harmonics. To prevent standing waves on the electrode lead, the suppression filter on the end of the electrode lead farthest from the feed point is provided with resistive elements that have a resistance such that the filter is matched to the characteristic impedance of the electrode lead. This prevents the measurement signal from being reflected at the far end of the electrode lead.
A method for the location of a point of fault in a cable is described in U.S. Pat. No. 5,083,086. According to this method for determining location, a repair technician executes this procedure, according to which the faulty cable is first disconnected, i.e., the cable is not in service. Next, a device used to execute the method for fault location is connected to the end of the disconnected cable. This device feeds a first electrical pulse into the cable and records the received reflections. After that, a voltage applied to the disconnected cable is increased, a second pulse is fed into the cable and the received reflections are recorded. By increasing the feed voltage, the impedance at the fault location in the cable changes so that a reflection that uniquely reproduces the fault location can be received. The recorded echo signals are compared to each other. Using this differential signal and a measured propagation time, the fault location in the cable can then be calculated.
To detect the state of an electrode lead of a bipolar high-voltage d.c. transmission system (HVDCT system), a method is described in German Patent Application No. 196 50 974.2 in which a first electrical pulse is fed to a first end of the electrode lead and an echo signal of this lead is detected. Next, a second pulse is fed into the line on the first end and its echo signal is detected. These two echo signals are then compared to each other. When there is a deviation and/or an agreement between the two echo signals, a corresponding indicator signal is generated. These process steps are continuously repeated until an error signal is generated. This indicator signal is used to stop the state measurement process. The fault location can be determined using recorded echo signals. A comparison of the faulty echo signal with stored echo signals for different operating conditions enables a more rapid determination of the error (ground fault, open circuit. . . ).
A device for performing this method has a pulse generator, an evaluation device and a coupling element. Through this coupling element, the pulse of the pulse generator is fed into the electrode lead and its echo signal is forwarded to the evaluation unit. The device is connected to one end of the electrode lead. The other end of the electrode lead is connected to ground. In order for the electrical pulse not to enter the HVDCT system, but rather only the section of the electrode lead to be monitored, the electrode lead is provided at its ends with attenuators. The evaluation device includes a comparator, a memory and a trigger device. The pulse generator-synchronized to a timer-generates rectangular, pulses with a d.c. offset. These pulses are continuously fed into the electrode lead until there is an error signal.
This method permits simple error detection in the operation of the HVDCT system without the need to use existing measurement signals. The method thus operates self-sufficiently. Since, in the fault-free case, the ground plays a part in conducting the pulse, fluctuating ground conductance affects the echo signals and thus a reliable detection of errors. Moreover, the radiation of electromagnetic energy, which is caused by the pulse in common mode,
Ammon Jörg
Plewka Gerhard
Schaller Gerhard
Benson Walter
Kenyon & Kenyon
Oda Christine
Siemens Aktiengesellschaft
LandOfFree
Method and device for the electrical monitoring of an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for the electrical monitoring of an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for the electrical monitoring of an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3140300