|
General
The SEECO SENSE sensor product
consists of four major system components, a Sensor Unit (monitoring
insulator), an Output Unit, an Enclosure and Power Source and a Communication
Cable. Each sensor unit
requires a Communication Cable, however, a single Output Unit may be
shared by up to three Sensor Units based on the requirements of a
customer's application.
Three distinct sensor unit
configurations (figure 1) are available: current-only, type CS;
voltage-only, type VS; and combination current and voltage,
type CSVS. Type CSVS is identical in external appearance to the
current-only sensor and is not represented by a separate picture.
All three Sensor Unit
configurations share several common design elements. At a high-level,
both the type CS and type CSVS sensors have a current sensing
mechanism, which the type VS sensor
does not require. Similarly, both the VS and CSVS sensor units have a
voltage-sensing mechanism, which the type CS sensor does not
require.
The major system components and
their primary sub-component assemblies are described in more detail below.
Sensor
Unit
The Sensor
Unit is essentially a monitoring insulator. Depending on the
configuration specified, the sensor may include some or all of the
following: current sensing coil, voltage sensing rod, silicone polymer
station post insulator, two or four hole terminal pads, fiber optic cabling and
potting and line and base unit electronic cards.
Current
Sensing Coil (CS, CSVS)
At the high
potential side of the unit is a current sensing coil (Rogowski Coil) which
is used to sense the line current and generate a safe, low voltage
output. The coil (figure 2) eliminates the hazards associated with open
secondary windings of conventional CT's, and the absence of a magnetic
core eliminates circuit loading and saturation concerns.
Line Unit
Electronic Card (CS, CSVS)
The low
voltage output is read by the Line Unit Electronic Card (figure 3), which
is located adjacent and immediately below the current sensing coil. The
card converts the low voltage output from an analog value into a 16 bit
digital value. An extremely high sampling rate insures the current value is accurately
reproduced for both amplitude and frequency.
Fiber Optic
Cabling and Potting (CS, CSVS)
The fiber
optic cabling and potting (figure 4 front view and 4A back view) provides an insulated pathway for the
communication of the current digital signal from the line unit electronic
card to the base unit card. A ½" diameter hole is centered and bored
axially through the insulator core. Three single strand fiber optic
cables are run from the top to the bottom of the insulator. An epoxy
potting material is used to fill all voids and secure the fibers in
place.
Voltage-Sensing Rod/Base Unit Electronic Card (VS, CSVS)
At the low
potential side of the insulator is a voltage-sensing rod located within
the base unit, which transforms the line voltage into a current through
induction. The base unit electronic card (figure 3) converts the current
generated by the rod to a low voltage analog output. This output is then
converted to a 16 bit digital value.
Base Unit
Electronic Card (VS, CS, CSVS)
The base
unit electronic card (figure 5) passes both the voltage digital signal and
the current digital signal to the output unit. The card contains a milspec male connector for the communication cable connection.
Communication Cable
The Communication Cable (figure
6) transfers the output signals from the base unit electronic card to the
output unit, and one cable is required per sensor. Since the
communication is digital, cable burden is not an issue; maximum cable
length is 4,000 feet. The cable has a UV protected black PVC jacket,
which is sunlight resistant,
impervious to moisture and vapor penetration, and suitable for
direct burial in wet or dry locations. Each end of the cable is pre-terminated
with a circular MS connector for quick and easy connection to both the
Sensor and Output Unit devices.
Output
Unit (Control Module)
The output
unit (figure 7) receives and
converts the voltage and/or current digital signals into analog signals
for use by the customer's RTU or other related equipment. One output
unit supports up to three sensors of the same or different voltage/current
configuration. The
output unit includes the following sub-components or features: timing and control crystal, digital to analog conversion,
status indicators, and an enclosure.
Timing and
Control
All timing
and control signals are generated by a crystal source. This maintains constant timing relationships between voltage and
current signals on each phase, and phase to phase.
Digital to
Analog Conversion
The 16 bit
digital voltage and current outputs received from the sensor unit are
converted back to analog signals using digital to analog converters. The
low level voltage signals are converted into either 120-volt or 10-volt outputs,
and each phase voltage output can be field adjusted for scaling. The
analog current output range is factory set, and can be provided as either
.5 ampere, 1 ampere, or 10-volt full scale. The current outputs provide safe outputs,
eliminating the hazards associated with secondary windings.
Status
Indicators
To
facilitate maintenance and trouble-shooting, four status LED's (figure 8) per phase
are provided which indicate the operational condition of all major
components of the installed sensor system. An "active" LED is illuminated
when all system components are functioning properly or normal state. A
failure among any of the system components causes the "active" LED to be
turned off. Three LED's are then used to indicate which major system
component is not functioning properly. A control relay is also provided with two sets of contacts
(control and status). The control contact can be used to disable a local
piece of equipment, such as a motor operator. The status contact provides
remote indication of sensor condition.
Enclosure/Power Source
The Output Unit is typically provided
with an enclosure (figure 9). The enclosure is sized to accommodate
the output device, terminal blocks for output signal wiring connections,
three circular MS connector and power source inputs. A larger
enclosure is also available and is sized to accommodate the above
material, plus the optional 24 VDC or solar power source, or other
customer supplied equipment.
The Output Unit will operate with customer
supplied 24, 48 and 125 VDC or 120 VAC. An optional SEECO supplied
24 VDC power source complete with batteries, charger and battery testing
mechanism can be provided, which requires customer supplied 120 VAC. An optional solar power source is also available.
More Information
For additional information on
SEECO SENSE digital current and voltage sensors, please view the following pages:
|
