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