Transformers control

Potential/control transformers must be provided with current limiting fuses at both ends. 

Specification for control transformers for switchgear and controlgear for voltages not exceeding lOOOV a.c. Specification for high voltage busbars and busbar connections... 

Tappings are generally not necessary, as a transformer is designed for a particular voltage system. If and when such a need arises (as in a control transformer (Section 15.4.5)) they can be provided on the primary side of the transformer. 

To damp the transient voltages on the primary side. For markings refer to Section 15.10.1 and Figure 15.35. 15.4.5 Control transformers... 

Figure 15.9 A typical outdoor type oil-filled 11 kV control transformer...

Figure 15.8 Typical single-phase and three-phase control transformers...

For brevity, only the more relevant aspects are discussed here. For more details, refer to lEC 60044-2 and lEC 60186. for instrument voltage transformers and lEC 60076-3 for control transformers. 

The following may be ascertained w hen selecting the rating of a control transformer ... 

The control transformer to be selected may have a rating nearest to the maximum hold-on VA burden so calculated and must be suitable to feed the required inrush current at the p.f. so calculated without affecting its regulation.. So long as these two points fall below the inrush curve of the control transformer, its regulation... 

The actual values us worked out above must fall below the inrush curve of the selected control transformer of 500 VA. as illustrated in Figure 15,12,... 

Figure 15.12 Checking the suitability of the 500 VA control transformer for the required duty tor Example 15,1...

Instrument and control transformers application and selection 15/495 Relevant Standards... 

Figure 16.7 Phasor diagrams for QDC, referred to the secondary side of the control transformer...

---