Post on 15-Oct-2021
Underground System Design
TADP 547
Commissioning
Tests
Presentation 6.2
Instructor: Frank Frentzas
Commissioning Tests
After cable installation the system must be tested to
prove system integrity before it goes into service.
Commissioning, or after laying, tests are typically
performed on transmission cable systems.
Since cables are all factory tested, commissioning
tests are performed to detect installation and work-
manship defects, along with possible shipping
damage.
Fluid Filled and Solid Dielectric cables are tested
using different equipment and procedures.
Commissioning Tests (cont.)
Cable systems are tested at a higher voltage level than
the normal operating voltage to identify defects.
To avoid cable damage the applied test voltage level is
limited by the manufacturers design criteria.
Fluid Filled cables are usually tested using a DC Hi-pot
test.
Solid Dielectric XLPE cables can only be tested using
an AC Hi-Pot test.
Test voltage and duration typically follow AEIC CS2,
and IEEE 400 and IEEE 400.1 recommendations.
Test Equipment (Solid Dielectric, XLPE)
Significant improvements have been made in AC Hi-
Pot test equipment in the past 3 to 5 years.
Commercial development of high-voltage test sets,
truck mounted variable-frequency-resonant tests has
changed testing practice on XLPE high voltage cables.
The AC hi-pot tests are costly since large equipment
must be transported to the site.
AC Hi-pot tests are usually performed on 230 kV and
higher on XLPE cable systems and typically a partial
discharge (PD) test is performed during the AC test.
As variable-frequency-resonant test sets are costly and
not readily available, most utilities choose a 24 hour
electrical system voltage test no load.
The voltage applied with a variable-frequency resonant
set is based on the units capacity, which is driven by
the cable length.
Although voltages from 1.25U0 to 1.7U0 are generally
used, utilities may apply their own test criteria and
requirements as long as the values follow supplier
recommendations and do not damage the cable.
Test Equipment (cont.)
AC Hi-Pot Test Set
A partial discharge test is performed to identify defects
in cable, accessories, and workmanship.
Some higher voltage joints and terminations are
designed with internal PD sensors - which provide
excellent sensitivity since they are located inside joints.
AC Hi-Pot tests are performed at voltage levels above
the normal operating voltage (usually 1.25U0 to 1.7U0)
for a duration of one hour maximum.
A phase check is performed on cables prior to returning
line back to service.
Partial Discharge Test
Internal Inductive Type PD Sensor
Internal Inductive Type PD Sensor (cont.)
PD measurement data
and plot report.
PD Test Report
Other voltage tests performed are the jacket (or sheath) test,
and the electrical soak test.
A jacket test involves applying a 5 - 10 kV DC voltage to the
sheath for 1 - 5 minutes to verify the cable jacket integrity.
A cable jacket breach will indicate a high leakage current or
cause the equipment to trip.
A soak test involves applying system voltage to a cable end
with the other end open to eliminate any current load.
A soak test has a duration of 24 to 36 hours. If the test is
successful the circuit can go into service.
Other Voltage Tests
In some cases, baseline Distributed Temperature
Sensor (DTS) measurements are performed using
optical fibers built into the cable or a separate fiber
optic cable in a spare duct. The test is used to
locate and identify external hot spots or heat
sources before the cable system is energized and
loaded.
Another test that can be performed is sheath
current measurements on single phase cables
using a clamp on ammeter to verify the bonding
system was installed per design and is functioning
properly.
Other Tests
Fluid filled cables are tested using DC Hi-Pot, sheath test (for
LPFF cables), fluid samples, and in some cases a 24 hour AC
electrical soak test.
For fluid filled cables a good practice is to pressurized the
system at the normal operating pressure for 24 hours prior to
applying any voltage to the cable insulation.
AEIC CS2 contains a table with recommended values and
duration for DC-Hi-Pot tests for HPFF and HPGF cables.
LPFF or SCOF use similar test values.
For LPFF cables the sheath test is performed similar to XLPE
cable systems.
Commissioning Tests - Fluid Filled Cables
Hi-Pot Test Sheet Sample
Some utilities also collect fluid samples from joint and
termination sampling ports and perform dissolved gas
analysis (DGA) and fluid quality tests prior to placing
the cable system in service. Results from these tests
provide a baseline for future diagnostic testing and
trending.
For pipe type systems, a corrosion system check is
performed to ensure the corrosion system is
functioning properly. The test checks pipe potential
with respected to a reference cell and pipe. A coating
resistance test may also be performed.
Fluid Filled Cable Tests