OMICRON electronics

A New Approach for Testing Generator Protection Systems

The protection of synchronous generators involves the consideration of more harmful, abnormal, operating conditions than any other single piece of power system equipment. Today’s relay manufacturers have responded by improving the reliability of the generator protection, applying digital technology to what used to be a strictly electromechanical environment. Microprocessor-based relays and relay systems have made considerable advances by intelligently protecting the most expensive piece of equipment in the power system, so it is no wonder that their acceptance has grown exponentially. Most projects for new generators now include at least one advanced multifunction generator protection relay.

Depending on the size and type, anywhere between eight to twenty individual protective functions may be required to protect a single generator. These protective functions may be a combination of single function relays, but today it is typical to see these combined in just one or two multifunction relays. Generator protection relay systems typically include other logical control capabilities, such as breaker failure for the main breaker, loss of potential blocking schemes, and automatic load shedding control. Many now have advanced communications capabilities that allow remote operator control using programmable safeguards and user interrogation of various operating characteristics and settings.

The extended capabilities of these new protective relay systems have created a need for new and innovative approaches to testing these latest multifunction relays. One example would be the requirements specified by the Tuas South Power Plant in Singapore. This new automated power system consists of two 83 MVA combined cycle generators, built and constructed by Mitsubishi Heavy Industries, and operated by the Ministry of the Environment, Singapore. The requirements specified by this customer were to provide a complete and automated relay testing process that could be done manually within the power station, or in an automated mode from a remote location.

To do this, new test approach was required, so OMICRON applied its Test Universe capabilities. The precision of OMICRON’s CMC 156 and CMC 256 hardware provides outstanding accuracy, which is most desirable under the strict relay tolerances needed for generation protection. Complete testing of all protective elements and relay logic was easily achieved with OMICRON’s Protection Software, which provides easy to use test modules for testing various protective functions, and the control logic associated with them. These test modules are then combined as a single automated test, using OMICRON’s Control Center software. Since the CMC test set can communicate and operate via the parallel port of the operator’s local test computer, this leaves the local serial communications port available to remotely interrogate the protective relay system, simultaneously. Additionally, it allows the test to be controlled from a remote location, using a standard Windows-based communications program, such as PC Anywhere.

It was the requirement of the customer, to dedicate two OMICRON CMC 156 test sets for each generator, which were directly mounted into the protective relay rack system. This allowed for quick and easy commissioning of the generators during the initial start-up and future periodic testing of the protective relay system during routine maintenance. More importantly, the entire testing process or specific problematic functions can be tested during emergency situations, allowing for quicker re-starts after a disconnect or system alarm. This could now be done from a remote location when operators may not be available to check for a possible relay mis-operation. As a benefit of the automated test plan, all protective functions were tested and validated within a one hour period.

The potential cost of relay failure on a generating system not only includes the possibility of expensive equipment repairs, but also the cost of replacement ?power during unscheduled generator shut downs. Thorough testing is critical?prior to startup to assure relay functions will operate as planned and to provide key performance benchmarks. The ability to retest quickly during an outage allows comparing this information to troubleshoot any potential relay problem. This can minimize the outage time and have obvious cost savings, and improved supply reliability.

OMICRON’s Test Universe, which includes the most advanced hardware, software, and technical support anywhere in the world, provides the means to test any type of protective relay system in this same manner. Whether your testing needs include a new, modern generating system, transmission or distribution substation, or you need to apply new advanced testing methods to older relay technologies, OMICRON is your answer.

Transducer Software

ransducer is a new Windows test module for single-phase and three-phase electrical transducers. It can be used for both regular and multifunction transducers with either a symmetrical or a non-symmetrical operating characteristic of the linear, quadratic or compound type. Transducer functions which can be tested are shown in the table. The single phase mode also supports testing DC transducer types noted with an asterisk(s).

The characteristic is displayed graphically for any test mode used. A manual "static output" mode allows calibration of a transducer while monitoring its output and calculated error. The automatic test mode allows automatic testing of a user defined test point table. Investigation of specific test points may also be done manually.

Error calculation and automatic assessment is based on the ideal characteristic as defined. Graphs for absolute, relative and full-scale errors can be displayed and included in the report. The test repetition setting allows multiple runs of the test table for repeatability testing, with the average error being calculated. As always, reports are generated automatically.

Synchronizer Software

OMICRON’s new Windows Synchronizer Test Module provides the easiest way to test both automatic synchronizing and sync-check relays. Automatic synchronizing relays produce control commands to a generator’s governor and static exciter, controlling the frequency and voltage prior to connecting the generator to the network. When two parts of a disconnected electrical system need to be re-established, such as during auto-reclosing or when closing circuit breakers manually, the sync-check relay performs the required monitoring and supervision.

Complex test definitions or macros are no longer required to test these relays. The Synchronizer uses the relay’s settings to define and emulate the environment where the relay is used. A Function test (for Sync-check) and Adjustment test (for Auto Synchronizers) use the graphical Sync window characteristic to provide simple test point definitions. The circuit breaker close command is detected in all test modes and assessed automatically. A sync-scope graphic shows the system voltages and the ?relay response.

The Adjustment test uses a linear f or V setting or dynamic model based on time constants of the generator. (User defined) The CMC then responds by simulating the generator and testing the relay’s control and synchronization performance. The automated assessment and reporting process completes this highly efficient testing of an otherwise complicated control process.

Ground Fault Software

Transient and steady state ground faults to easily test ground relays used in compensated or isolated neutral systems. The test module allows the use of a reduced network mathematical model for cable or overhead lines and generates realistic fault waveforms.

Models are included for the simulation of both three-phase and two-phase systems, as well as some railway networks. Transformer specific parameters, such as nominal voltage, rating, grounding type, impedance and HV fault level, can be entered and saved for future use. Compensated network models include the actual system operating conditions by specifying an overcompensation factor. Primary capacitive ground fault current of a selected feeder or network may also be taken into consideration.

Compensated network models include the actual system operating conditions by specifying an overcompensation factor.

The ground fault relay can be tested under faulted or non-faulted system conditions and also checked for directionality. The calculated output signals are shown in a separate Time Signal view, which can be displayed or printed from the automatically generated test report. An export option allows the user to save this waveform as a Comtrade file for other test uses. The Measurement view allows for automatic relay assessment based on response time. The test execution can also be GPS synchronized for end to end testing.