MR MESSKO MT-ST Compact RM - Setting Temperature Gradients

5 Installation and commissioning
64 BA5831400-00 EN
5.6 Setting temperature gradients (winding temperature)
Since the temperature sensor is located in a thermometer pocket instead of
directly in the winding, the temperature difference between the winding and
insulating fluid must be taken into account. The temperature difference at
nominal load is called the temperature gradient. This is specified by the
transformer manufacturer. The temperature difference is reproduced in the
thermometer by a heating resistor that is supplied with the secondary trans-
former current of the transformer.
Setting the temperature gradient is necessary for thermome-
ters to display the winding temperature. Perform this setting
before commissioning the transformer and before connecting
the current transformer [►Section 5.7, Page 73].
The pointer thermometer is set at the factory as follows:
Parameters Setting
Nominal secondary transformer current 2A
Temperature gradient 17K
Nominal heating current for MT-ST160W 1A
Nominal heating resistance for MT-
ST160WR
6Ω
Table6: Factory settings
If the temperature gradient of the transformer deviates from this factory set-
ting, you must adjust the temperature gradient of the thermometer. Depend-
ing on the device variant, there are two different processes to do this:
▪ MT-ST160W(/RM): Gradient setting by heating current
– You need a constant current source and a voltmeter.
▪ MT-ST160WR(/RM): Gradient setting by resistance value
– You need an ohmmeter and, for a second calibration before commis-
sioning, a calibration bath and a current source.
5.6.1 Gradient setting by heating current
For the MT-ST160W and MT-ST160W/RM device variants, set the tempera-
ture gradient by adjusting the heating current.