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4.2 THROUGH FAULT MONITORING LOGIC

V03201

TF I> Trigger

IA magnitude

TF I2t> Alarm

TF I> Trigger

IB magnitude

TF I2t> Alarm

TF I> Trigger

IC magnitude

TF I2t> Alarm

Any Diff Start

Throu fault Alm

TF Recorder trig

Figure 63: Through-fault alarm logic

4.3 APPLICATION NOTES

4.3.1 TFM SETTING GUIDELINES

According to IEEE Std. C57.109-1993, values of 3.5 x normal base current may result from overloads rather than

faults. Accor

ding to IEEE C57.91-1995, the suggested load limits depend on the type of transformer and are as

follows:

● For distribution transformers: Loads above the nameplate specification with 65°C rise is 300% of rated load

during short-time loading (0.5 hours or less).

For power transformers: Loads above the nameplate specification with 55°C rise is 200% of rated load.

To set TF I2t> Alarm you should consider the recommendations given in IEEE Std. C57.109-1993 for transformers

built from the early 1970s onwards. For transformers built before this time, always consult the transformer

manufacturer concerning the short circuit withstand capabilities.

Example

The through fault monitoring element can monitor either the HV, the LV or the TV winding. In three winding

applications, you should monitor the winding through which the highest current would flow during an external

fault. Fault studies are required to determine the maximum through fault current and which winding carries the

most current. For example, consider the following autotransformer:

P64x Chapter 7 - Transformer Condition Monitoring

P64x-TM-EN-1.3 155

GE P643 User Manual

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