Relay Testing for Industrial Power Producers
The variety of Industrial Power Producers, in size and type, is as vast as the products they make and sell, and their production ranges from small emergency generators to complete generation, transmission, and distribution systems. In fact, some large refineries can produce enough electricity to meet the needs of an entire city. One thing that remains constant, regardless of size and type of the power system, is the critical need for protective relays within the power system to perform as required. Therefore, relay testing requirements can vary from the most minimal to the most extreme.
Industrial Power Producers may choose to test their relays themselves or hire an independent qualified testing company. In the past, this decision has mostly been based on economics. Today, advanced technology in microprocessor based relays, combined with greatly advanced software driven relay test systems, provides the Industrial customer greater opportunity to do their own relay testing effectively and cost efficiently.
The BASF AG industrial power grid in Ludwigshaven, Germany, covers a 7 square kilometer area, providing 700 MW seven days a week, and is one of the largest of its kind in the world. BASF is supplied by several 220 kV lines from the public power grid. There are also three power plants on the site which produce steam and electrical energy, increasing the security of supply in case of faults in the public power grid. The energy is distributed using 130 switchgear units at the 110, 20 and 6 kV level, and about 1000 low-voltage switch-gear units. The largest generator on site is a combined-cycle unit with a rating of 400 MW.
In cases of severe faults "outside" BASF's facility, the connection to the public power grid will be cut and the BASF grid will go into insular operation in order to maintain the power supply of important parts of the factory, fed by BASF's own power plants.
There are two main objectives in controlling the disconnection:
- selectivity, because unnecessary disconnection has to be avoided, and
- reliability, because quick separation is necessary when a fault occurs in order to keep the plant in service.
The control rack integrating these functions has to be tested thoroughly, especially in conjunction with the commissioning of BASF's new combined-cycle power plant. These tests have been performed using the general functions of the OMICRON CMC 156 test set with the new Windows based software.
OMICRON's Software Makes Difficult Tasks Simple
Using the CMC 156 test set, the general functions of the OMICRON Test Universe windows software are very well suited to satisfy the requirements of these tests on BASF's control rack.
QuickCMC software allows for manual testing by putting out analog or binary testing signals and monitoring the reaction of the relay. The stepping and ramping function of QuickCMC makes it perfect for determining the thresholds of the disconnection criteria, including the tripping times.
The State Sequencer software is used to automate the tests manually performed with QuickCMC, making it easy to investigate the disconnecting element's behavior by varying the fault's voltages, currents, frequencies, phase changes, duration, etc. The State Sequencer has been used to check the selectivity in coordination with superimposed protective systems outside in the public power grid. Its high-performance graphical user-interface makes test results easily seen and is well-suited for results processing.
These tests are then integrated into the overall OMICRON Control Center report document. Because this document contains all the information necessary for performing the test (hardware management, relay data, and the testing functions), it provides a template for the next test. This is particularly helpful to BASF when the disconnecting element B with identical parameter settings is tested. By clearing the results the document becomes the template for the next test, and can be executed once more with little effort.
At OMICRON, we provide the technology flexible enough to meet present and future needs of the Industrial Power Producer. The reliability and ease of operation of OMICRON's Test Universe, combined with the most advanced testing methods available, provides the opportunity for our industrial customers to test their own power systems quickly and with confidence. BASF has shown that the user-friendliness of the new OMICRON Windows Software proves itself in the field.
Testing Differential Relays: The OMICRON Difference
Although the principle of differential protection is the simplest to understand, the practice of applying these relays and testing these protection systems is a challenge. Until now, differential protection testing has usually resulted in compromise. Historically, relays had a single curve for a single function. Testing two or three points along that curve was a reasonable compromise to assure proper relay operation. Today, relays have multiple curves per function and multiple functions per relay. Therefore, testing two or three points is no longer adequate to prove the relay will fulfill the task(s) for which it was installed.
OMICRON's new Differential Software is a family of test programs which, for the first time ever, provide a complete testing solution for differential protection systems, with up to 3-phase, 3-winding transformers. These test modules allow the user to automate tasks that are time consuming, repetitive, and involve complex calculations. The new software provides automatic calculation and automatic setting of the test currents, thereby avoiding error-prone manual calculations and manual settings. The CMC software then provides the automatic recording of all settings and test results into a final test report, eliminating this time consuming task also.
This new software provides the user with full testing control. Manual control using point-and-click tests allows testing to be performed as desired, customizing the test routine allows the user to test the relay with a specific module or sequence, and the capability to customize the test report format adds flexibility to the user's document handling requirements.
OMICRON's Differential Software allows the user to easily:
- Test fault types of differential relays (up to 9 currents) with a single relay hook-up.
- Execute simple point & click manual tests or automatic evaluation tests with the same ease of use.
- Evaluate and assess the tripping characteristics, timing and tolerances of the relay's operation.
- Automatically generate comprehensive test reports including wiring connections, all test settings, impressive graphic displays and the actual test results. This eliminates an error-prone, time consuming, and frustrating task.
- Automatically repeat the same test in the future using an easily configured test report which becomes the template for the next test.
Automatic calculation of currents are based on the same data used to establish the relay settings. From these data the software provides user friendly test screens for defining the tests (fault loops, testing points, test times), executing the tests, and assessing the actual relay behavior automatically.
OMICRON's Differential Software allows automated testing and report generation, easy evaluation of the essential elements of a relay's operation, and full testing control with a helpful graphical user interface. All of these characteristics result in a great deal of benefits. Users will have increased efficiency with more productivity, and their test and report generation will be reliable without errors. With its new Differential Software, OMICRON sets the standard for testing differential relays in a way that is quicker, more reliable, and less costly than other test sets on the market.
The Differential Software contains the following 4 test modules:
Diff Configuration
This test module tests:
- Interposing transformers and secondary wiring (Electromechanical and electronic relays)
- Correct parameter settings of digital relays (specific to the protected object)
- Zero-sequence elimination of ground faults 'outside' the protected zone. Faults outside protected area assure proper trip restraint, with selectable fault currents and fault loops.
Diff Operating Characteristic
This module checks the relay's ability to determine if a fault is inside or outside the protected zone. The test currents are automatically calculated based on the ratio of the differential current, Idiff, to the restraint or 'bias' current, Ibias. The relay's operating characteristic are determined from the relay settings for the specific differential relay under test. This characteristic is then displayed on the screen. The specific test points are marked on the characteristic display after testing for easier analysis.
Diff Trip Time Characteristic
Short tripping time is a basic benefit of differential protection. This module measures the tripping time of the relay and provides a plot of this time vs. the differential current, Idiff, in the Trip Time Test Plane. The application of a pre-fault current for a user specified time, as required by many relays today, is also available with the Diff Trip Time Test Module. Other relay functions, such as backup overcurrent protection and overload protection, can also be tested within this module.
Diff Harmonic Restraint
This test module verifies the correct operation of the harmonic restraint function of the protective relay. The specific harmonic desired can be selected along with its magnitude in percent relative to the magnitude of the nominal current. This may be applied per phase or three phase to the primary windings. Both search and shot tests are possible.