MV design guide - Schneider Electric
MV design guide - Schneider Electric
MV design guide - Schneider Electric
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Switchgear<br />
definition<br />
Voltage transformer<br />
Rated secondary voltage (Usr)<br />
c For phase to phase VT the rated secondary voltage is 100 or 110 V.<br />
c For single phase transformers intended to be connected in a phase to<br />
earth arrangement, the rated secondary voltage must be divided by e.<br />
E.g.: 100 V<br />
e<br />
Rated output<br />
Expressed in VA, this is the apparent power that a voltage transformer<br />
can provide the secondary circuit when connected at its rated primary<br />
voltage and connected to the nominal load.<br />
It must not introduce any error exceeding the values guaranteed by the<br />
accuracy class. (S = eUI in three-phase circuits)<br />
c Standardised values are:<br />
10 - 15 - 25 - 30 - 50 - 75 - 100 - 150 - 200 - 300 - 400 - 500 VA.<br />
Accuracy class<br />
This defines the limits of errors guaranteed in terms of transformation<br />
ratio and phase under the specified conditions of both power and voltage.<br />
Measurement according to IEC 60 186<br />
Classes 0.5 and 1 are suitable for most cases, class 3 is very little used.<br />
Application<br />
Accuracy class<br />
not used industrially 0.1<br />
precise metering 0.2<br />
everyday metering 0.5<br />
statistical and/or instrument metering 1<br />
metering not requiring great accuracy 3<br />
Protection according to IEC 60 186<br />
Classes 3P and 6P exist but in practice only class 3P is used.<br />
c The accuracy class is guaranteed for values:<br />
v of voltage of between 5% of the primary voltage and the maximum<br />
value of this voltage which is the product of the primary voltage and the<br />
rated voltage factor (kT x Upr)<br />
v for a secondary load of between 25% and 100% of the rated output with<br />
a power factor of 0.8 inductive.<br />
Accuracy class Voltage error as ± % Phase shift in minutes<br />
between 5% Upr between 2% between 5% Upr between 2%<br />
and kT • Upr and 5% Upr and kT • Upr and 5% Upr<br />
3P 3 6 120 240<br />
6P 6 12 24 480<br />
Upr = rated primary voltage<br />
kT = voltage factor<br />
phase shift = see explanation next page<br />
62 Merlin Gerin <strong>MV</strong> <strong>design</strong> <strong>guide</strong> <strong>Schneider</strong> <strong>Electric</strong>