isolated current voltage transducers

Other Types of Voltage Transducers Technologies
6 Other types of voltage transducer technologies
Two additional voltage measurement technologies have been
developed by LEM to achieve differentiated measurement
performance compared to Hall (§ 3.4) or Fluxgate (§ 4.4.4)
based voltage transducers. The first technology, OptiLEM,
uses fiber optics for the transmission of the voltage
measurement information, providing a high level of dielectric
isolation. The second technology is the AV-type of voltage
transducer based on electronic isolation circuitry that also
provides galvanic isolation, but at the component level rather
than using discrete fiber optics.
and transmitted to the secondary side through an optical
link. The same is done with the required data
synchronization signals.
On the secondary side the data stream is converted back
into an analog signal and converted into an output current
for high noise immunity and easy scaling. A very critical
function of the transducer is to provide a low voltage supply
for the components on the primary side, requiring a very
high level of voltage isolation and very low capacitive
coupling from primary to secondary. A sine wave signal is
used to minimize noise levels.
6.1 OptiLEM voltage transducers
The OptiLEM voltage transducer has been developed to
provide an optimal solution for higher isolation voltages. The
result is an interesting product containing numerous patented
concepts.
The following key attributes are reached with the first voltage
transducer model:
• isolated voltage measurements up to 12 kV RMS
• 100 V to 6 kV measuring range
• overall accuracy better than 1.5 %
• bandwidth from DC to 12 kHz
• low stray capacitance between primary and secondary
(less than 10 pF)
• low partial discharge extinction level of 5 kV with < 10 pC
Figure 48: OptiLEM voltage transducer
The working principle of the OptiLEM voltage transducers is
shown in Fig. 47. The primary voltage is directly applied to the
transducer primary connections, ±U. An internal resistor
divider network and differential amplifier measure the primary
voltage signal. This output is converted to a serial data string
U+
U-
DIFFERENTIAL
AMPLIFIER
12 bits A/D
converter
A
D
SERIAL DATA
OPTIC FIBER
D
A
U
I
M
OPTIC FIBER
SYNCHRONIZATION
OSCILLATOR
+
VOLTAGE REGULATOR
+V
supply
-
-V
PRIMARY SUPPLY
+
0 -
RECTIFIER/ FILTER
HIGH INSULATION
VOLTAGE
TRANSFORMER
SINE
OSCILLATOR
PRIMARY SIDE
SECONDARY SIDE
Figure 47: OptiLEM working principle
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