4.1.6.2 Function block
Figure 228: Function block
4.1.6.3 Functionality
The three-phase thermal overload protection, two time constants, protection
function T2PTTR protects the transformer mainly from short-time overloads.
The transformer is protected from long-time overloads with the oil temperature
detector included in its equipment.
The alarm signal gives an early warning to allow the operators to take action
before the transformer trips. The early warning is based on the three-phase current
measuring function using a thermal model with two settable time constants. If the
temperature rise continues, T2PTTR operates based on the thermal model of the
transformer.
After a thermal overload operation, the re-energizing of the transformer is inhibited
during the transformer cooling time. The transformer cooling is estimated with a
thermal model.
4.1.6.4 Analog channel configuration
T2PTTR has one analog group input which must be properly configured.
Table 442: Analog inputs
Input Description
I3P Three-phase currents
See the preprocessing function blocks in this document for the possible
signal sources.
Improper analog channel configuration causes a validation error if the analog
channels are not completely configured or they do not match with certain settings.
For troubleshooting, check the contents of this chapter and also the preprocessing
blocks in this document. The configuration can be written to the protection relay
once the mismatch is corrected.
4.1.6.5 Operation principle
The function can be enabled and disabled with the
Operation
setting. The
corresponding parameter values are "On" and "Off".
The operation of T2PTTR can be described using a module diagram. All the modules
in the diagram are explained in the next sections.
Protection functions
1MRS759142 F
390 REX640
Technical Manual
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