QUALITROL AKM345 GEN3 OTIWTI
TM
Instruction Manual
40-08847-00-Rev001
www.qualitrolcorp.com
Page 26 of 34
7.1
Adjusting the Internal Matching Resistance
–
TD50 & TD76
The procedure for adjusting the TD50 or TD76 internal matching resistance is as follows:
Step 1)
Check or calculate the secondary current (I
s
) in Amps from your bushing current transformer (BCT) at
100 % transformer load.
Step 2)
Check the required winding hottest spot temperature gradient in °C.
a.
NOTE:
this should be available from the transformer manufacturer
Step 3)
Use the below
Temperature Gradient Adjustment Graph
to determine the required parallel
resistance of the heating element and the matching resistance TD50 or TD76 setting in Ohms using
the CT current and temperature gradient as inputs to the graph. Take note of this value.
Step 4)
Connect a multi meter, set to measure resistance, to terminals 5-5 inside the Winding Temperature
Indicator (WTI)
Step 5)
Loosen the lock nut on the TD50 or TD76 potentiometer and adjust the matching resistance until you
reach the required resistance value
Step 6)
Secure the lock nut on the matching resistance for this setting
Step 7)
Check operation and make final adjustments if necessary
a.
To check operation, keep cover fitted on the device and feed a constant and stable current to
terminals 5-5 and wait 45 minutes before reading the winding temperature gradient.
For example, with CT current of 1.9 A and temperature gradient requirement of 30°C, resistance = 1.4 Ohm.
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