ABB RELION REX640 Technical Manual page 390

Protection and control

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Protection functions

Function block

Figure 228: Function block

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.

Analog channel configuration

T2PTTR has one analog group input which must be properly configured.

Table 442: Analog inputs

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.

Operation principle

The function can be enabled and disabled with 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.

See the preprocessing function blocks in this document for the possible

signal sources.

Three-phase currents

Operation setting. The

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