This repeated use means LTCs require careful attention through inspection, testing, and refurbishing. If an LTC fails, the entire transformer will be out of service. This outage will have an adverse effect on numerous distribution circuits and an adverse effect on the remaining power grid due to the need to reroute the load to supply the affected circuits. There are potentially hundreds of LTC designs currently in operating substations.
The most efficient and effective method to keep them working properly is for technicians to have a general understanding of how they operate, how to test them, and how to maintain them.
With that foundational knowledge, it is much easier to understand and adjust for the differences in designs of various LTCs. Please join us at the next Circuit Breaker Seminar. Share this Load Comments. By checking this box, you acknowledge our Privacy Policy and Privacy Notices available here. While tapping, two essential conditions are to be fulfilled. The tap changing employing a center tapped reactor R show in the figure above.
Here S is the diverter switch, and 1, 2, 3 are selector switch. The transformer is in operation with switches 1 and S closed. To change to tap 2, switch S is opened, and 2 is closed. Switch 1 is then opened, and S closed to complete the tap change.
It is to be noted that the diverter switch operates on load, and no current flows in the selector switches during tap changing. The secondary output voltage can be increased or decreased by changing the number of turns ratio using the selector switch and the diverter switch.
Due to the larger power system application, it is necessary to change the transformer taps several times to maintain the required voltage on the system as per load demand. Basically the demand for the continuity of supply does not permit the transformer from disconnecting the supply. Hence an on-load tap changer is employed with a continuous supply. The on-load tap changing transformer using a resistor can be explained as follows. It consists of resistors r1 and r2 and 4 taps t1, t2, t3, t4.
Based on tap position the switches get connected and current flows which are shown in the below case figures. Case I : If diverter switch is connected at tap1 and tap2, the load current flows from top to tap1 as shown below. Case ii : If the diverter switch is connected at tap2, the load current flows from r1 to tap.
Case iv : If the diverter switch is connected between tap3 and r2, then the current flows from r2 to tap. Case v : I f the diverter switch is connected at tap3 the current I is shorted as shown below.
The main objective of using a resistor in the OLTC transformer is to maintain the voltage by controlling the flow of current using switches. In the No-load tap-changing transformer NLTC , the main supply connection is disconnected while changing the tap. Whereas on-load tap changing transformer OLTC there will be continuous power supply even when tap positions change.
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