Seg HighTECH MRU3-2, Руководство пользователя

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TB MRU3-2 12.00 E 9
4.4 Voltage supervision
4.4.1 1-phase/3-phase supervision
The voltage relay MRU3-2 protects electrical genera-
tion systems, consumers and appliances in general
against over- and/or undervoltage. The relay is
equipped with an independent, 2-step over- (U>, U>>)
and undervoltage supervision (U<, U<<) with sepa-
rately adjustable tripping values and delay times. Volt-
age measuring is 3-phase. In this process there is a
continuous comparison of the line conductor voltages
in case of a delta connection and of the phase volt-
ages in case of a star connection with the pre-set limit
values.
With the MRU3-2 the highest voltage is always evalu-
ated for overvoltage supervision and the lowest volt-
age for undervoltage supervision.
A distinction is made between 1-phase and 3-phase
tripping. (1/3 – Parameter)
With 1-phase tripping the voltages are evaluated as
follows:
U</U<</U</U>>: Activation cum tripping takes
place if
at least one phase has fallen short of the trip-
ping value.
With 3-phase tripping the voltages are evaluated as
follows:
U<: Activation cum tripping takes place if all three
phases
have fallen short of the tripping value.
U<<: Activation cum tripping takes place if one phase
has fallen short of the tripping value.
U>: Activation cum tripping takes place if
all three
phases have exceeded the tripping value.
U>> Activation cum tripping takes place if one phase
has exceeded the tripping value.
4.4.2 Principle of the voltage unbalance
protection
The principle of this procedure is to detect faults which
effect an asymmetry of the voltage vector.
A single-phase line interruption can for instance cause
voltage unbalance in the mains which does not guar-
antee that the voltage will be zero in the faulty phase.
Especially in higher impedance networks the missing
phase can partly be rebuilt through running engines or
transformers. A pure undervoltage protection cannot
detect this condition, however, the rebuilt phase does
not coincide with its old position in amount and phase.
So an asymmetrical voltage vector system is formed.
In a compensated or isolated grid a single-phase
earthfault will hardly cause a significant earth current.
Because, however, the faulty phase takes on the earth
potential the entire voltage vector system is shifted by
the amount of the faulty phase and does not rotate
anymore around the initial star point (earth). The rela-
tive position of the voltage vectors between each other
is hereby not changed. Also this vector system is not
symmetrical anymore in relation to the earth potential.
The MRU3-2 can detect such asymmetry.