RLIB100 ABB RK682007-BA optional measuring unit

The optional measuring unit RLIB 100 includes the negative sequence current
protection function Insc - with inverse time characteristic to comply
with the generator capability curve. A separate independent time delayed
alarm stage is included.
From the analogue bus the RLIB 100 picks up the signals needed to perform
the Insc> protection function (see fig 2.8).
The signal paths for each phase current are identical. Hence only the path
of phase R will be described.
The current signal is filtered and fed to the variable gain amplifier G 1.
The gain of G 1 is controlled by the microprocessor. Different gain factors
are needed to adopt to the wide range of the current input signal and ` achieve correct measurement over the full dynamic range. The signal from
G 1 is fed to a full wave rectifier and a squaring amplifier. The output of
the full wave rectifier is connected directly to one of the four AID - con- t
verter channels of the microprocessor, which samples the signal at a rate
of 12 samples/cycle of the power frequency.
The output signal of the squaring amplifier is fed to an edge triggered
input of the processor. The square wave is used to determine the sign of
the sinusoidal input, i.e. the sign of each sample, and to measure the frequency.
The sampled data are used to calculate the negative sequence current.
See chapter Theory of measurement for details regarding the
algorithm.
The output signals of RL田100 are all controlled by the microprocessor
and connected to the output signal bus via drivers.
The program package of the unit is built up by five major parts, the protection
program, the timebase routines, the communication driver routines, t
the phase data collection routine and the command interpreting and executing
routines (see Fig. 2.9).
The command interpreting and executing program is cyclic. Each cycle it
checks if any commands have been received in the input buffer. The routine
receives commands from the MMC unit RLSClOO, interprets and
executes the command, and initiates the communication driver routines to
send a prepared answer to the MMC unit when applicable.