KEPCO MST Series - Manual (Page 29)

MST SERIES 061813
2-11
Successful d-c grounding depends on careful analysis of the system operation; only general
guide lines are provided here. One of the major points, however, is to avoid ground loops.
Ground loops are created when two or more points of different ground potentials in the output
circuit are grounded. An undesired signal (noise) is developed that is superimposed on the load
(output potential). A way to avoid ground loops is to check for points of resistance to ground. Dif-
ferences in ground potential can be avoided if the output circuit is completely isolated. A single
point can then be selected along the Power Module output circuit and returned to ground with a
single wire. This method is dependent on the specific application.
2.8 POWER MODULE TO LOAD INTERFACE
The general function of a voltage or current stabilized Power Module is to deliver rated output to
the load. The load may be fixed or variable; resistive, capacitive, or inductive; and may be
located close to or far away from the Power Module. The Power Module is designed for varied
applications. The aim of the following paragraphs is to instruct the user in the interface of the
Power Module to the load.
The perfect interface between a Power Module and load insures optimum performance. To
approach this state of operation, one must be familiar with certain requirements, such as inter-
connection guidelines, Ohm's Law and a-c theory.
Load Wire Selection - A stabilized d-c Power Module is not an ideal voltage or current source
with zero output impedance (voltage mode) or infinite output impedance (current mode): All volt-
age sources have some amount of impedance which increases with frequency and all current
sources have impedance which decreases with frequency (see Figure 2-5).
FIGURE 2-5. OUTPUT IMPEDANCE VS. FREQUENCY