Electricity: measuring and testing – Electromechanical switching device – Circuit breaker
Reexamination Certificate
1999-06-24
2002-05-28
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Electromechanical switching device
Circuit breaker
C324S418000
Reexamination Certificate
active
06396279
ABSTRACT:
BACKGROUND OF THE INVENTION
The object of the invention is a method and a device for testing differential protective relays and systems. Differential protective relays and systems of such a type are used as protective equipment for the monitoring of the widest possible variety of electrical equipment used in power engineering. Electrical equipment of this type can include, for example, a high-voltage or medium-voltage transformer, a bus bar, a generator, a line or a cable, and other similar kinds of electrical equipment. For safety reasons, these types of electrical equipment used in power engineering are provided with differential protective relays which have the job of disconnecting the electrical equipment to be protected from the power supply network in the event of a fault.
The object of the present invention is a method and a device for testing such differential protective relays and differential protective systems, with the goal of safeguarding the function of such differential protective relays and differential protective systems (guaranteeing their protective function).
In conjunction with that, the function testing of the differential protective relay must be possible with installation-specific parameterizations and settings.
By using the test method that is being introduced, it is possible to verify the correctness of the installation-specific design, parameterization and settings, and wiring of the differential protective relay or differential protective system, as well as its protective function.
A further object of the invention is the replacement and improvement of the primary test methods which have previously been carried out, e.g., the 380-volt method, which, due to the small test values, permit only limited and often unclear information.
The designation differential protective system includes the matching converter circuit, particularly with the use of conventional differential protective equipment.
At the present time, numerical differential protective equipment with software-implemented switch assembly matching and zero current elimination are being tested almost exclusively by means of a single-sided current feed at a single point in the characteristic region, which does not permit reliable information concerning the functional capability of the differential protective relay. A few large utilities are testing differential protective relays by means of a double-sided current feed with two controllable current sources, whereby the current vector calculation and the test wiring is difficult and requires specialized knowledge, and is limited to a single-pole and double-pole fault simulation. Finally, the latter utilities do special testing of the correctness of the design, parameterization and setting, and wiring of the differential protective system on transformers by means of a three-phase primary test method (380-volt method). Tests in the characteristic region are also carried out by manufacturers of protective equipment by using two current generators and parameterized switch assembly Yy0 and Yy6.
Such known test methods can, for example, be found in the “IEEE Guide for Differential and Polarizing Relay Circuit Testing”, IEEE C37.103-1990, ISBN 1-55937-058-0, pages 21 ff.
The known test instructions show that testing is being done with the simplest of equipment. As a rule, several formulas and current tables are shown for a simple testing of the relay. The testing is usually carried out with single-sided current feed. On occasion, a second current generator is used in order to be able to adjust the stabilization current independently of the differential current.
A complete check of the relay and the protective systems without rewiring is completely impossible, as is the testing of the entire stabilization characteristic curve. It is not always possible to carry out the known 380-volt test due to conditions at the site, and the test currents that are available are often too small to be able to provide meaningful results.
SUMMARY OF THE INVENTION
It is therefore the task of the present invention to further development a method and a device of the type mentioned at the beginning, so that all of the parameters relevant to the protective function of a differential protective relay or system can be tested in a simple and exact way, and thus a complete test is possible.
To perform the required task, the invention is characterized by the features of claim
1
.
A test method is suggested which provides for a three-phase circuit for connecting a three-phase current system to the primary, secondary and, if applicable, tertiary side (6-9 current generators), plus, if applicable, the additional connecting of separate zero currents.
The item under test is connected once, and can then be tested in its complete functionality. The checking is not carried by means of any kind of current values that are calculated manually or read from a table, instead, it is carried out directly in the transformed level of the stabilization characteristic curve I
DIFF/I
STAB
(operating characteristic I
DIFF
/I
BIAS
) and/or the matched (virtual) currents I
S
=f(I
P
). The calculation of the current vectors is carried out automatically, taking into consideration the electrical equipment to be protected, the current converter ratios, the fault type and the fault location.
With this new test method, possibilities are provided for the testing of differential protective systems with respect to function and to the object being tested. The method allows the testing of the special parameters of line-differential protective devices and bus-bar protective devices, as well as of transformer, generator and motor differential protective devices which process the measured value “current” of all of the electrically connected protected objects with regard to their current differential or phase angle difference. The complexity of the protected object nodal point is limited to three legs.
The foundation of all stationary test methods is the model of a transformer with three windings. The other protected objects can also be simulated by means of this model through the selection of specific parameters. The allocation of the voltage levels remains fixed. The left winding with feed possibility is always used as the primary side (P). The right winding with feed possibility is always used as the secondary side (S). The tertiary side (T) can be used as pure fault or load side only with a three-winding device or a three-leg device (bus bar).
It is an essential feature of the invention that the protected object is simulated by means of software so that it is simulated with its most important parameters. This simulation of the protected object takes place in the test facility itself The currents calculated in the simulation are then output to the connected differential protective relay or system.
For the test in this case, the test facility with 6 to 9 current generators instead of the current converter is connected directly to the protective relay or system that is to be tested. A simulation of the transformer behavior is carried out in the test facility, and the calculated current vectors are fed into the protective relay or system that is to be tested:
A method for testing the switch assembly matching and the correction of the value will now be explained in the following.
In the case of the transformer, the test currents of the individual windings are dependent upon the effective switch assembly and the numerical index of the switch assembly, and differ in their phase positions. With star or delta transformers, the use of stepping switches, or because of differing I
NConverter
/I
NTransformer
ratios of the windings to be compared, the values of the test currents are also different. The current comparison must thus be traced back to the currents flowing in the individual branches or to a reference winding.
The correct calculation of the currents to be compared from the measured secondary line currents is verified by the test method described here. In addition, a check is carried out with regard to the co
Lackenbach & Siegel LLP
Metjahic Safet
Nguyen Vincent Q.
Omicron Electronics GmbH
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