PI – Tap Position Indicator
The Tap Position Indicator (PI) consists of a microprocessor based electronic device capable of monitoring and modifying, through the load tap changer (LTC), the positions of power transformer taps.
The PI incorporates the functions of multiple devices that were previously used for controlling the transformers LTC, such as selector switches Manual/Automatic and Local/Remote, manual control switch Raise/Lower and Tap Position Indicator, among others. For this reason, the control wiring and the number of components have been hugely reduced, raising substantially the general reliability and reducing the test and installation work time, in addition it greatly simplifies the maintenance.
The PI is equipped with signalling output contacts, indication of the tap position via a current loop output, dry contacts input for remote command and a RS485 serial port, allowing complete data acquisition and total remote control of the LTC.
The equipment was totally designed and tested for operating in the harsh conditions found in electric substations, such as surges, impulses, electromagnetic interference and extreme temperatures.
Features:
–Intelligent Tap Position Measurement: Automatic compensation of the interconnection cable resistance between the potentiometric position transmitter and PI, allowing longer distances with smaller cables;
– Intelligent Tap Position Measurement: detection and alarming of bad electrical contact in the potentiometric position transmitter or in the interconnection cables;
–Indication of the LTC’s position on display. Type of tap position indication is user-selectable: simple numeric (e.g. 1…33), bilateral numeric (e.g.-8…0…+8) or alphanumeric (e.g. 8L…N…8R);
–Number of positions set between 2 and 50. Programmable resistance values fits all types of LTC. Optional mAcurrent input for position measurement.
–Local/Remote selection made directly on the front panel or through external dry contacts.
–Manual/Automatic operation mode selection made directly on the front panel or through external dry contacts.
–Manual Raise/Lower commands made directly on the front panel or through external dry contacts.
–Current loop output enables the remote indication and/or monitoring of the LTC’s position. Output range selectable by user at front panel: 0…1,-1…+1, 0…5, -5…+5, 0…10, -10…+10, 0…20, -20…+20 or 4…20mA;
–Four output relays to indicate status and/or alarms.
–All parameters can be configured through the PI’s front panel or through the RS-485 communication port. All selections and commands can be performed also through the RS-485 with protocols Modbus RTU (standard) or DNP3.0 (using optional module COMM-04).
–Self-diagnosis: two micro-controllers with reciprocal supervision for detection of failures. Total absence of mechanical parts for parameter definition and calibration.
The Tap Position Indicators PI are universal devices. The PI features are selected by using the programming menus. These adjustments can be made directly on the device’s front panel or by way of the serial communication port RS485. The power feed input is universal (38 to 265 Vac/Vac 50/60Hz).
Therefore, in purchase orders for the equipment only the following need be confirmed:
• Tap Position Indicator PI
– Type of tap measurement input:
Standard – Potentiometric input – state the code PI; Optional – Current mA input – state the code PI-I
• Optional accessories required.
Potentiometric Position Transmitter-Magnetic type
The majority of recent load tap changers, and many of the old ones, are supplied from the factory with a potentiometric position transmitter or dry contacts that allow the creation of the transmitter by means of the appropriate installed step resistors.
However, for tap changers that do not have any of these alternatives, Treetech can provide magnetically operated potentiometric position transmitters, without mechanical contacts, for easy installation in older equipment.