ZES ZIMMER LMG450, Руководство пользователя

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Z E S ZIMMER Electronic Systems GmbH Chapter 2
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All measuring channels
All channels calculated from sample values (linked channels)
All channels calculating the total values of a group (sum channels)
2.5 Linked values, star to delta conversion (option L45-O6)
If you have installed the option star to delta conversion you can calculate values, which you
can’t measure directly (for example if you have a load in delta circuit, and want to know, how
big is the power in each load, you could use the wiring ‘3+1, U
∆
I*->U
∆
I
∆
’. Then you would
measure the current in the three phases and the voltages between the phases. As linked values
you get the voltage, current, power and all other values of each load, refer the following
figure).
Figure 2: Allocations of the different linked values
Important note!
You can only perform a star to delta conversion, if this is physically possible. For the
calculation we assume following conditions:
•
u1+u2+u3 = 0
•
u12+u23+u31 = 0
•
i1+i2+i3 = 0
•
i12+i23+i31 = 0
This assumption may not be met in following examples:
•
You have a load in star circuit and there is a current flow out of the midpoint. So you can’t
transform this circuit to a equivalent delta circuit, because this would only have 3 wires
instead of 4! This can be a typical problem when using frequency converters: Due to the
high clock frequencies there might be a capacitive earth current which is the fourth „wire“.
•
You have a circuit in a delta configuration. If there are additional sources in one or all of the
three ‘loads’ (e.g. by induction), there can flow a current inside the delta circuit.