6ra70_hubmagnet_engl.pdf

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A&D LD CS 21/February/2006

FAQ for 6RA70 DC MASTER and SIMOREG CM

Question:How can I calculate the inductance and the required number of additional Alpha W pulses forthe operation of highly inductive loads on a SIMOREG converter?

Answer:

The application note "SIMOREG as a Field Supply" provides information about supplyinghighly inductive loads such as the field circuits of DC and induction motors, and theapplication of solenoids. Supplementary tips about operating the SIMOREG converter safelyare given below.

Inductance L [H]:In order to determine the required number of additional Alpha W pulses and to dimension thesuppressor circuit needed at the DC end of a SIMOREG unit used to supply highly inductiveloads, it is necessary to know the load inductance. A method of calculating the loadinductance using the trace monitor is demonstrated below.The initial linear section of the curve must be analyzed for this purpose.Formal correlation:The following differential equation applies: U – i * R – L * di / dt = 0The following thus applies to the linear range of the current rise: (U – i * R) * ∆t / ∆i = LSee practical example calculated with the trace:U = P078.01 * 1.35 * K0292, with P078.01 = 280 V,and Ua act = K0292 = 65.5% → U = 280 * 1.35 * 0.655 = 248 Vi = r072.02 * K0114 with r072.02 = 105 A and Ia act = K0114 = 28.31%→ i = 105 * 0.2831 = 29.7 A As a result of the linear current rise from i = 0 up to i according to ∆t, i for the i * R drop canbe assumed to be:(i according to ∆t) / 2.R was determined to be 2.30 Ω from the trace, i.e. at the moment of completion of themagnetization process and at which the current had assumed a linear shape.When K0292 = 37 % and K0114 = 57.9 %;R = (280 * 1.35 * 0.37) / (105 * 0.579) = 2.30 Ω. When ∆t = 1 s → L = (248 - 29.7 / 2 * 2.30) * 1 / 29.7 = 7.20 H

Number of additional Alpha W pulses:With high inductance loads, it takes a certain time for the current to decay completely to zerodespite a firing angle of Alpha W (full counter-e.m.f. for current reduction in the inductiveload). In 4-quadrant operation in particular, it is important that the current is reduced to zeroand that the active thyristor blocks reliably before the torque direction is reversed (firing ofinverse-parallel bridge for current reversal). If the inverse-parallel thyristor bridge is firedbefore the previous bridge is reliably blocked, a circulating current will occur and cause fusefailure.



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In motor operation, the low inductance means that it is sufficient to disable the pulses andenable the counter-torque direction after a short delay when the current zero message isactive (current zero in this case corresponds to 1% of the actual rated unit current: parameterr072.02). Motor/generator fields or solenoids often have inductance values of 10 H or higher. As a result, a certain number of additional Alpha W pulses (number can be set in parameterP179) must be output after activation of the current zero message so as to reduce thecurrent to zero.

It is essential to perform an arithmetic check on the result of the trace used to determine thenumber of pulses. This is especially important so as to make allowance for lineundervoltages in operation and, in the case of rated unit currents of > 60 A, for the resolutionof actual-current sensing referred to the thyristor holding current (approx. 100 mA).

Calculation example:U = L * ∆i / ∆t; ∆t = L * ∆i / UU = output DC voltage SIMOREG with line undervoltage threshold and Alpha W: U = P78.01* (1+ P351 / 100) * 1.35 * cos(Alpha W) ∆i = 1% of actual rated unit current r072.02The additional Alpha W pulses are output when the current zero message (1% of r072.02) isactivated. ∆t = minimum period for Alpha W pulses,1 pulse = 3.33 ms at 50 Hz, or 2.78 ms at 60 HzExample:L = 1 H, P78.01 = 400 V (rated line voltage);U = P078.01 * (1+ P351/100) * 1.35 * cos (Alpha W)P351 = -30% (line undervoltage threshold), ∆i = r072.02 * 0.01r072.02 = 1200 A (actual rated unit current), Alpha W = 150 degrees (P151) ∆t = 1 * 12 / [400 * (1 + (-30) / 100) * 1.35 * 0.866] = 0.037 sMinimum number of additional Alpha W pulses at 50 Hz = 37 ms / 3.33 ms = 12 Additional 20 % = 12 * 1.2 = 14.4 → set P179 = 14, P161 = 2 recommended

Tip 1:

The automatic restart function must be deactivated with P86 = 0 for 4-quadrant operation. Alternative settings on request.

Tip 2:The factory default setting for the Alpha G limit on 4-quadrant units is 30 degrees. This canbe increased to 5 degrees (P150) for this application. Necessitates higher voltage reserve forfaster magnetization. Any F043 message can be suppressed via P820 without negative effects.

Tip 3:The firing angle Alpha W must not be shifted to 165 degrees when the current zero messageis activated:Set P192 = 1.



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Recording of magnetization process using the trace monitorfor the purpose of calculating load inductance

K0292:Ua act. = 65 5%

K0114:Ia act. = 28.31 %Delta t = 1 s

100% Ua act. = P078.01 * 1.35100% Ia act. = r072.02

Main line

Delta t

Delta t: t main line minus t aux. lineY value on main line

Aux. line

Click to the select the curve which is todetermine the Y value

6ra70_hubmagnet_engl.pdf

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