Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
sumed that the real-time clock in the REF542plus will continue to run for a period of at
least 2 hours at the required accuracy.
The initial temperature for continuing the thermal monitoring of the motor is calculated
with the equation below:
enveenv)-off(ini
off TC
td
-
TTTT +=
(14.)
Where:
Tini Initial temperature for continuing the calculation
Toff Temperature in the moment of the failure of the DC supply
Tenv Setting for the ambient temperature
td Duration of the power down of the auxiliary voltage
TCOff Setting for the cooling-off time constant after switching off the mo-
tor
4.4.1.3 Setting the temperature after reset
For functional testing purposes, another temperature setting "T rst“ is provided. If a
reset signal is present at the input of the function block, the motor temperature is re-
set to the preset reset temperature.
For instance, if a tripping characteristic without preloading is to be checked, tempera-
ture setting T rst has to be equated to the setting of the environment temperature
T env. For checking a characteristic with 100% preloading (hot curves), temperature
setting T rst has to be set equal to the setting of the rated motor temperature T nom.
4.4.2 Tripping characteristic
The following paragraph deals with a tripping characteristic where the tripping time is
specified as 6 times the basic current I
B
which is to be equated to the rated motor cur-
rent. In this context, it is assumed that the setting constant k is 1.1. This means that
with the above setting the setting constant for the memory contents is expanded to
121%.
In accordance with [DIN3], blocking time t
E
should not be below 5sec. Based on
equation 11.1, the setting of the time constant for the REF542plus is:
s146
21,136
36
ln
s5
=
⎟
⎠
⎞
⎜
⎝
⎛
−
=
τ
(15.)
Tripping characteristics with a time constant τ = 146sec corresponding to a setting of
t
6IB
equal to 5sec - without (cold curves) and with 100% preloading (hot curves) - are
illustrated below in graphic form. 100% preloading means that the motor operates un-
der nominal condition at rated current. If there is an overload, the motor can be
switched off quickly due to the fact that the thermal capacity contents or the rate of
the preloading is being taken into consideration.
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 24 / 66
Valid from Version V4D02
To Next Page
Loading...
