GEGenerator Protection System Generator Protection, Control and Asset Management

Overview

The relay features generator unbalance, generator differential, over excitation, loss of 

excitation, 3rd harmonic neutral undervoltage, over and under frequency, synchrocheck 

and other essential functions with a basic order option. Additionally available with an 

advanced order option are overall differential (to protect the transformer-generator 

combined), directional overcurrent elements, restricted ground fault, 100% stator ground, 

out-of-step protection, rate of change of frequency, power factor, harmonic detection, 

frequency out-of-band accumulation and others. An optional RTD module allows for 

thermal protection and monitoring. An optional analog inputs/outputs module allows for 

monitoring of generator excitation current, vibration and other parameters.

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 USB port of any personal 

computer.

A summary of the available functions and a single-line diagram of protection and control 

features is shown below. For a complete understanding of each feature operation, refer to 

the About Setpoints chapter, and to the detailed feature descriptions in the chapters that 

follow. The logic diagrams include a reference to every setpoint related to a feature and 

show all logic signals passed between individual features. Information related to the 

selection of settings for each setpoint is also provided.

Description of the 889 Generator 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 digital 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 offnominal 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 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 through 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