Partial discharge
Online Partial
Discharge Testing: ‐
Online Partial
Discharge Testing is performed online without disrupting plant or facility operations.
This non‐destructive, non‐invasive predictive maintenance
tool assesses the condition of switchgear, feeder cables, and bus duct to
provide critical information regarding levels of partial discharge and its
potential impact on the health of the electrical asset. The cost to perform
online testing is relatively inexpensive compared with offline testing that requires
interruption of service and production. For critical facilities that operate
24x7, online testing is considered the single best option for detecting
insulation condition.
Technology:
·
ACOUSTIC METHOD
·
ULTRASONIC DETECTION
·
HFCT
Acoustic Method:‐Acoustic
partial discharge measurement can be easily applied on AIS
without the need
of interrupting the operation. Acoustic Partial discharge measurements rely
on close
acoustic contact of the area producing discharge. This method is also very
effective in
localization of PD.
Ultrasonic Detection: ‐
All electrical
equipment produces a broad range of sound. The basic electrical problems that
produce distinct
ultrasound waves that can be detected by Ultrasonic Testing include partial
discharge,
corona and tracking. Ultrasonic measurement is most powerful on comparative
basis
and will significantly
increase the reliability of correct detection of partial discharge.
HFCT
HFCT is used to
detect high frequency current pulse discharging through earth from system
ground. It is also
helpful in getting PD Pattern.
PD Tolerance Levels for
Switchgear:
‐
mV
Level
|
Condition
and Action
|
<
6
|
Discharge
within acceptable limits*
|
6‐12
|
Monitoring
recommended
(Recommended to conduct PD after 1 year.)
|
12‐32
|
Regular
monitoring recommended
(Recommended
to conduct the PD after 5‐6 months. The
panel having increasing trends in PD value should be monitored with help of
IR thermography immediately.
|
>
32
|
Major
concern, located PD with alternate technology
|
Benefits of On-Line Partial Discharge Field Measurements
·
It is truly a predictive test,
indicating insulation degradation in advance of the failure.
·
It is a nonintrusive
test, requiring no interruption of service and is performed under
normal operating voltage, load and environmental conditions.
normal operating voltage, load and environmental conditions.
·
It is a nondestructive test; it
does not test to failure or adversely affect the equipment under test in any
way.
·
It does not use any
overvoltage, thereby not exposing the tested equipment to higher voltage stresses
than those encountered under normal operating conditions.
·
Trending can be accomplished by
storing baseline measurement results to allow comparison with future
tests.
·
In many instances the site of
the partial discharge occurrence can be located within
the cable/plant under test, so the localised problem can be repaired.
the cable/plant under test, so the localised problem can be repaired.
·
The cost to perform a PD-
survey is relatively inexpensive compared with off-line testing, allowing annual surveys to be performed economically at most facilities.
survey is relatively inexpensive compared with off-line testing, allowing annual surveys to be performed economically at most facilities.
Examples
of HV & MV Plant that can be tested
·
Cables and Cable
Accessories (terminations and joints)
·
Switchgear (AIS, SIS and GIS)
·
Instrument
transformers (voltage and current)
·
Power transformers and bushings
·
Motors and generators
·
Surge arrestors
·
Capacitors