ABB PR512, Руководство пользователя

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12
t> = K x
b
t> = K
x
b
I
I>
a
– 1
PR512/P UNIT (50-51)
Protection functions
The PR512/P protection unit (50-51)
carries out two independent protec-
tion functions which can be ex-
cluded:
– 51 protection against overcurrent:
• 0.2 < I < 2 In (rms)
• 2 < I < 20 In (peak);
– 50 protection against instantane-
ous or delayed short-circuit
(operation on peak value).
Protection against overcurrent (51)
This function makes four different
groups of protection curves avail-
able, defined as follows (IEC255-3):
– definite time-delay
– normal inverse time-delay
– very inverse time-delay
– extremely inverse time-delay.
The following settings are possible:
• 32 threshold current values (I>) (1)
0.200 0.225 0.250 0.275
0.300 0.325 0.350 0.375
0.400 0.425 0.450 0.475
0.500 0.525 0.550 0.575
0.625 0.650 0.675
0.700 0.725 0.750 0.775
0.800 0.825 0.850 0.875
0.900 0.925 0.950 0.975
1.000 x In
OFF
(1) The unit guarantees non-entry into threshold for
currents under 1.05 x I> set and guarantees entry
into threshold for currents above 1.30 x I> set.
Selection of threshold I> value
Four different time-current relationships can be
selected.
Fixed time curve (
b
= 2)
For protection with definite time (DT), the trip time
is given by the following relationship:
Definite time-delay curves
For definite time-delay protection, the relationship
between trip time and overcurrent is given by the
following formula.
Caption
t> trip time
k parameter set by the user to select the trip curve
a, b
pair of parameters, depending on the type of
protection selectable
I fault current
I> trip threshold selectable by the user
The threshold value of this protection is indicated
by I>, whereas the relative trip time is indicated by
t>.
Start of timing is signalled by the ALARM LED
lighting up whereas circuit-breaker opening
having taken place is signalled on the front by the
magnetic flag I> I>>, turned to the yellow position.
To reset signalling, the FLAG RESET pushbutton
on the front of the release must be pressed,
ensuring one of the following conditions:
a) 24 Vdc auxiliary voltage present (display lit);
b) primary circulating current more than 0.2 x In
(display lit with indication of the circulating
current);
c) application of the TT2 unit to the TEST connec-
tor on the front of the release (optional acces-
sory).
Selection of threshold I> value
Setting of I> threshold is carried out by using the
Dip Switches (see page 13).
The sum of the values selected represents the
fraction of In which corresponds to I>.
32 threshold values are available, defined from
0.2 .... 1 x In with steps of 0.025 x In.
The protection can be excluded by positioning the
first Dip Switch in the OFF position.