VAMP Ltd
Motor protection relay
Technical Description
VAMP 150
VM150.EN005
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5
2.
Functions
The individual protection functions of the VAMP 150 motor
protection relay can independently of each other be enabled or
disabled according to the requirements of the application. See
the configuration instructions, Chapter 5 and 7, in the first
part of this manual.
2.1.
Principles of the numerical protection
technique
The VAMP 150 relay is designed using numerical technology.
This means that all signal filtering, protection and control
functions are made by digital processing.
The numerical technology used in the relay is primarily based
on an adapted fast Fourier-analysis (FFT), in which case the
number of calculations (multiplications and additions) required
to filter out the measuring quantities remains reasonable.
By using synchronized sampling of the measured signal (phase
or residual current) and a sample rate according to the 2
n
series, the FFT technique leads to a solution, which can be
realized with just a 16 bit micro controller, without using a
separate DSP (Digital Signal Processor).
The synchronized sampling means an even number of 2
n
samples per period, e.g. 16 samples/period. This means that the
frequency must be measured and the number of samples per
period must be controlled accordingly, so that the number of
samples per period remains constant should the frequency
change.
Figure 2.1-1 shows the main components of a relay using
numerical technology; i.e. the relay comprises input
transformers, digital input adapters, output relays, A/D
converters and a micro controller including memory circuits.
Further the relay needs a power supply and a user interface.
Figure 2.1-2 shows the heart of the numerical technology or the
main block diagram of the calculated functions.
Figure 2.1-3 shows a functional principle diagram of a single-
phase overcurrent function.