# OLTC Modeling

I have a transformer 115/11.5kV controlled secondary voltage between 0.97 and 1.03 Tap setting max 1.1 and min 0.9, tap size = 0.00606.

I am having troubles setting the tap size? Which field is that? and the setting for the current tap? Which field is this?

I would appreciate instructions what is the PSS/E input record for modeling the OLTC. How to obtain the resultant current tap setting after running the loadflow?

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In addition to @acd1's answer I want to clarify that the number of steps are:

Nsteps = (Rmax-Rmin))/STEP = (1.1-0.9)/0.00606060606 = 33.

The number of tap changer positions are always Nsteps+1, i.e. NPOS = 33+1 = 34 in this case. Normally, the number of positions are odd numbers so there may be something wrong with the given data here. With 33 tap positions the steps size would be: STEP = 0.2/(33-1) = 0.00625!

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You are correct - my calculation (and I believe the poster's data) misrepresent the situation. The number of tap positions is different from the number of steps (= taps - 1). 33 tap positions, or 32 steps of 0.625%, are very typical of LTCs.

( 2023-01-26 11:06:41 -0600 )edit

Hi! If “550kV/220kV+-2*2.5%/66kV" is the only information for an auto transformer, what is the tap range and tap step? And how do I calculate the Tap Position in PSS/E? Thx!

( 2023-03-25 01:44:08 -0600 )edit

For 220 kV winding: Rmax=1.05 pu, Rmin=0.95 pu, Tap positions=5. Winding I/O code=3.

( 2023-03-25 06:04:04 -0600 )edit

Thank you for ur help. But in PSSE, the other two windings also need to be filled with the tap position for a three-winding transformer, what should I fill in and how to change the tap position for 220kV winding?

( 2023-03-25 06:50:30 -0600 )edit

Enter Winding Nominal voltage in kV for all three windings. Enter Winding Ratio = 1 for all windings..Ratio for 220 kV winding may have values 0.95, 0.975, 1.0, 1.025 or 1.05 depending on the tap changer position.

( 2023-03-26 06:52:50 -0600 )edit

The tap size is actually controlled via the "Tap Positions" field. So with a tap range of 0.9 ~ 1.1, you have a range of 0.2. With each tap step of 0.00606, the number of tap positions is 0.2 / 0.00606 which is 33.

The current tap setting will either be "Winding 1 Ratio (pu)" or "Winding 2 Ratio (pu)" depending on your control settings. You can also use the "xfrdat" routine from the psspy API to programatically retrieve the tap ratio for two winding transformers.

Here is a series of batch commands to add a 2-winding zero-impedance transformer between a hypothetical bus 1 and bus 2, as generated by PSSE. The winding 2 ratio is one tap off the nominal ratio, at 1.00606.

BAT_TWO_WINDING_DATA_6,1,2,'1',1,1,1,0,0,0,33,0,1,0,0,1,0,1,1,1,0.0, 0.0001, 100.0, 1.0,0.0,0.0, 1.0,0.0, 1.0, 1.0, 1.0, 1.0,0.0,0.0, 1.1, 0.9, 1.1, 0.9,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0," ",

BAT_TWO_WINDING_CHNG_6,1,2,'1',,,,,,,,,,,,,1,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,;

BAT_TWO_WINDING_CHNG_6,1,2,'1',,,,,,,,,,2,,,,,,,,,,,,, 1.00606,,,,,,,,,, 1.03, 0.97,,,,,,,,,,,,,,,,,,;

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