FUNCTION CHARACTERISTICS
47
NA30 - Manual - 04 - 2022
Thermal protection with RTD thermometric probes - 26
Preface
The measure of temperature is acquired by means of Pt100 (RTD Resistive Temperature sensing
Devices) probed, connected to the MPT module.
[1]
A direct thermal protection element with eight PT100 thermometric probes (RTD Resistive Thermal
Device) provides protection against premature ageing or breakdown of the insulating materials
through overheating.
Thermal protection using thermometric probes offers greater reliability than Thermal overload-based
indirect protection, since it is not influenced by inaccuracies in the time constant for the thermal
model of the machinery and by variations in the surrounding temperature.
For each thermometric probe an alarm (
Th
ALx
, where x=1...8 points one of the eight probes) and one
trip adjustable threshold is provided (
Th
>
x
), with adjustable operating time (
t
ThALx
and
t
Th
>
x
>);if the
measured temperature overcomes the threshold, the relative alarm and/or trip is issued when the
timer expires.
The adjustments are operable in °C.
The probes should be placed in strategic points around the machinery susceptible to the greatest
overheating, such as for example:
- near the generator stator windings, near the step-up transformer windings and/or in the oil, with the
aim of detecting overheating produced by the overload currents,
- near the generator bearings, with the aim of detecting localised overheating due to worn or non-
lubricated bearings.
The Pt100 probes detect the temperature in the range -50 °C...+250 °C (at 0 °C its resistance is 100
ohm); an alarm indicates any interruption or short-circuiting of the probe or related connections to
the MPT module; the information is available inside the
Read \ PT100
menu:
•
Ptx probe ON
to point a measure inside the range
•
Ptx probe LOW
to point a measure lower the range (short circuit of probe and/or wires)
•
Ptx probe HIGH
ao point a measure higher the range (breaking of probe and/or wires).
Self reset is performed when faults are cleared.
The measure of each probe is updated at 2 s time intervals.
Note 1 The 26 menu is available when the MPT module is enabled
t-int-F26.ai
T
(°C)
t
General operation time characteristic for thermal protection with RTD thermometric probes (26)
Th
>
x
t
Th
>
x
t
ThALx
TRIP
all-F26.ai
General logic diagram of the thermal elements - (26)
P t10 0
Thybus
MPT
AL ARM
TRIP
Trip Element
Alarm Element
ThAL
x
enable
Th>
x
enable
Th
ALx
Th
>
x
t
ThALx
t
Th
>
x
Th>xBF
Trip Th>x
&
Th>xBF
t-refresh-F26.ai
t
Pt1...8 update
P t1
P t 2
P t 3
P t4
P t5
P t 6
P t7
P t 8
P t1
0.2 5s
0.2 5s
0.2 5s
0.2 5s
0.2 5s
0.2 5s
0.2 5s
0.2 5s
2.0s
