GE 850 Feeder Protection System
Overview
Each relay provides protection, control, and monitoring functions with both local and remote human interfaces. They also display the present trip/alarm conditions, and most of the more than 35 measured system parameters. Recording of past trip, alarm or control events, maximum demand levels, and energy consumption is also performed.
These relays contain many innovative features. To meet diverse utility standards and industry requirements, these features have the flexibility to be programmed to meet specific user needs. This flexibility will naturally make a piece of equipment difficult to learn. To aid new users in getting basic protection operating quickly, setpoints are set to typical default values and advanced features are disabled. These settings can be reprogrammed at any time.
Programming can be accomplished with the front panel keys and display. Due to the numerous settings, this manual method can be somewhat laborious. To simplify programming and provide a more intuitive interface, setpoints can be entered with a PC running the EnerVista 8 Setup software provided with the relay. Even with minimal computer knowledge, this menu-driven software provides easy access to all front panel functions. Actual values and setpoints can be displayed, altered, stored, and printed. If settings are stored in a setpoint file, they can be downloaded at any time to the front panel program port of the relay via a computer cable connected to the serial port of any personal computer.
Description of the 850 Feeder Protection System
CPU
Relay functions are controlled by two processors: a Freescale MPC5125 32-bit microprocessor that measures all analog signals and digital inputs and controls all output relays, and a Freescale MPC8358 32-bit microprocessor that controls all the advanced Ethernet communication protocols.
Analog Input and Waveform Capture
Magnetic transformers are used to scale-down the incoming analog signals from the source instrument transformers. The analog signals are then passed through a 11.5 kHz low pass analog anti-aliasing filter. All signals are then simultaneously captured by sample and hold buffers to ensure there are no phase shifts. The signals are converted to digital values by a 16-bit A/D converter before finally being passed on to the CPU for analysis.
The 'raw' samples are scaled in software, then placed into the waveform capture buffer, thus emulating a fault recorder. The waveforms can be retrieved from the relay via the EnerVista 8 Series Setup software for display and diagnostics.
Frequency
Frequency measurement is accomplished by measuring the time between zero crossings of the composite signal of three-phase bus voltages, line voltage or three-phase currents. The signals are passed through a low pass filter to prevent false zero crossings. Frequency tracking utilizes the measured frequency to set the sampling rate for current and voltage which results in better accuracy for the Discrete Fourier Transform (DFT) algorithm for off nominal frequencies.
The main frequency tracking source uses three-phase bus voltages. The frequency tracking is switched automatically by an algorithm to the alternative reference source, i.e., three-phase currents signal or line voltage for the configuration of tie-breaker, if the frequency detected from the three-phase voltage inputs is declared invalid. The switching will not be performed if the frequency from the alternative reference signal is detected invalid. Upon detecting valid frequency on the main source, the tracking will be switched back to the main source. If a stable frequency signal is not available from all sources, then the tracking frequency defaults to the nominal system frequency.
Phasors, Transients, and Harmonics
All waveforms are processed eight times every cycle with a DC decaying removal filter and a Discrete Fourier Transform (DFT). The resulting phasors have fault current transients and all harmonics removed. This results in an overcurrent relay that is extremely secure and reliable and one that will not overreach.
email:1583694102@qq.com
wang@kongjiangauto.com