MA-040 – DGA 900 Plus - Operator Guide - Rev 1.1 4-Mar-22 Page 26 of 99
8 CARD OPTION #3: OLTC MONITOR
The OLTC card option is designed to monitor one OLTC and integrates data from several
sources. The OLTC tap position is monitored by either measuring the resistance of the
OLTC resistor wheel or by an available 4-20 mA current loop. Two 4-20 mA current loop
temperature sensors provide the transformer main tank top oil temperature and the
OLTC temperature. An active power consumption converter measures power drawn by
the OLTC motor and supplies this data as a 4-20 mA input to the monitor.
DGA 900 Plus products with an OLTC card enabled must undergo OLTC
commissioning as detailed in Section 10.3. The installation and
commissioning of the OLTC monitor must be performed on a non-
energised transformer.
After installing the Motor Power Converter, the OLTC Tap Position and
OLTC Torque models must be left disabled (refer to ‘Section 6.4: Models
Activation and Status’ in the ‘MA-040 – DGA 900 Plus – Operator Guide’)
until commissioning is successfully completed.
8.1 Sensor Input Configuration
Table 8-1 lists all the inputs available to the OLTC Monitor. See Section 8.1.2.1 for wiring
installation details.
Table 8-1: OLTC Monitor inputs
None / CT / 4-20 mA / RTD
Note: The top oil temperature sensor must not be installed if a thermal card top-oil
temperature is already available (from Option 1 Thermal Models as described in
Section 6).
8.1.1 Tap Position Sensor
The tap position input comes from a customer-supplied potentiometer or other 4-20 mA
sensor capable of supplying a position input.
8.1.2 Motor Torque Measurement
Measurement of the OLTC motor torque depends on whether there is a three phase or
single-phase motor circuit.
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