American Magnetics 05100PS-430-601 Integrated Power Supply System - Manual (Page 190)

172 Rev. 5
Appendix
Model 601 and Energy Absorption
A.12.2
Model 601 Energy Absorber Functional Description
The Model 601 provides a constant reverse voltage source of 5 Vdc. With
this configuration, as the power supply voltage is reduced below 5 Vdc, a
net reverse voltage allows controlled, active discharge of the magnet.
This requires power supplies capable of voltages higher than 5 Vdc for
charging, a requirement that is met by the basic 0 to +10 Vdc rated
08150PS Power Supply unit. The following paragraphs discuss basic
magnet charging, discharging, and application of the Model 601 with
unipolar power supplies.
A.12.2.1 Magnet Charging
Whenever the current flowing in an inductor changes, whether due to an
external influence such as a power supply or from natural decay of the
field, the inductor always presents a terminal voltage in the direction that
would preserve the former current rate of flow (i.e., oppose the change).
The magnitude of this opposing voltage is equal to the current rate of
change (Amperes per second) multiplied by the inductance (Henries). In
mathematical symbols, V = L x (di/dt)
1
.
In charging a magnet, the power supply must provide this voltage plus
additional voltage to overcome loop IR (V = i x R) voltage drops 2 (due
primarily to lead/cable resistance); thus V = L x (di/dt) + V
lead
(refer to
1. Refer also to “Ramping Functions” on page 77
2. Lead and other small circuit resistances are on the order of one or
two hundredths of an Ohm. V
lead
varies with current but is depicted
in the drawings arbitrarily as 0.5 Vdc (superconducting magnet resis-
tance is essentially zero so there is no inductor IR drop).
Figure A-4. Loop Voltages - Actively Discharging (with Model 601)