Onload Tap Changer (OLTC) is used with higher capacity transformers where HT side voltage variation is frequent and a nearly constant LT is required. OLTC is fitted with the transformer itself. Multiple tappings from HV windings are brought to the OLTC chamber and conacted to fixed contacts. Moving contacts rotates with the help of rotating mechanism having a spindle. This spindle can be rotated manually as well as electrically with a motor. Motor is connected in such a way that it can rotate in both the directions so as to rotate the OLTC contacts in clockwise and anticlock-wise direction. Two push buttons are fitted on the LCP (local control panel) to rotate the motor and hence the OLTC contacts in clockwise and anti-clockwise direction. This movement of contacts thus controls the output LV voltage of the transformer. So rotating of OLTC contacts with spindle or push buttons in this way is a manuall process. In case this process of rotating the OLTC contacts and hence controlling the LV side voltage is to be done automatically then a RTCC (Remote Tap Changer Controller) is installed with the transformer HT Panel. The RTCC sends signals to LCP and LCP in turn rotates the motor as per the signals received from the the RTCC.

	Microprocessor Based - Remote Tap Changer Contoller (RTCC)
	Dimensions: 96mm x 96mm x 165mm		Panel Cutout: 91mm x 91mm
	Front View		Back View
	RI Raise Indiactor   LI Lower Indicator   AI Auto Indicator   MI Manual Indicator   UV Under Voltage   P Panel   L Lower - Push   R Raise - Push   S Set   TIMER Time Delay Control   L-SET Lower Level Setting Control   R-SET Raise Level Setting Control

Automatic OLTC Panel consists of a LCP & a RTCC. System uses an AVR (AVR-MA9) to sence the LV voltage and a comparator circuit to compare the sencing voltage with a preset value. Any difference in two sends a corresponding signal to OLTC pane to lower or raise the LV voltage of transoprmer. The OLTC control panel also has the provision to operate two or more transformers in parallel. One transformer is taken as the master and the remaining as the followers so that they follow the master's LV voltage set values.

An OLTC control panel panel is fitted with various indications to visually show the various operations being performed by the OLTC as forward and reverse movement of OLTC contacts, upper limit and lower limit indications, fault indications, interlocking indications between manual and automatic mode of the OLTC and many more.