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.