P&B MPR3E5 - Tolerances

14/1/98 Page 29 Issue H
10.4 Tolerances
Function Tolerance
Thermal curve
Overload Pickup
time delay at 6x FLC
+6%, -0.0%
±5.5% or ±0.5sec
Low Set
Overcurrent Pick up I>
time delay t
I>
at 2x setting
±3% of setting
±3% or ±40ms
High Set Overcurrent
Pick up I>>
time delay t
I>>
at 2x setting
±3% of setting above 2.0 x In
±10% of setting at 2.0 x In
±3% or ±40ms except "instantaneous"
setting of 0.0sec (50-90ms)
Earth Fault
Pick up Io
time delay t
Io
at 2x setting
±3% of setting
±3% or ±40ms
Measuring Ranges
Current measurement is effected in two ranges for phase currents i.e. 0-1.45 x I
FLC
and 1.1 x I
FLC
to
16 x I
n
. Measuring range of I
n
= 6 × for thermal characteristic, above which time delay is definite
time. Measuring range for display of thermal capacity = 143%
Measuring range of In for other faults i.e. low set, high set and earth fault is 16 x In unless inhibited
for contactor applications.
Measuring range of earth fault input is 0.4 x In.
Current measuring errors ±1% of range.
Thermal Current / Time Curves.
The thermal curves shown overleaf are given by the following formula, used by the MPR3E5:-
(Starting/Cold Condition)
(Running/Pre-load Condition)
where
'p' is multiple of motor FLC (per unit value)
'a' is setting of t6x in seconds
't
c
is the operating time (Cold)in seconds
t
H
is the operating time (Hot) in seconds
s is the overload pick-up in per unit eg 1.05
Where 'I
L'
is the steady state load prior to overload condition divided by motor FLC, e.g. if motor is
running at FLC, I
L
=1
'H/C' is the hot/cold ratio in per unit value e.g. 40% hot to cold ratio = 0.40.
)(
)(
log..32
22
2
sp
p
at
eC
−
=
(
)
(
)
)(
)/1(
log..32
22
2
2
sp
ICHp
at
L
eH
−
−−
=