Transcript Transformer Tests Oil tests and on-line monitoring can increase transformer life expectancy

MORGAN TM
SCHAFFER
Transformers – The Inside View
Transformer Tests
Oil tests and on-line monitoring can
increase transformer life expectancy
By: William Morse
Morgan Schaffer Inc.
Transformers

The heart of a
substation
 Needed to transmit
electricity over long
distances
 Steps up or steps down
voltage
The Inside View
Ready to work again
Ready for repair
Oil, the Blood of the Transformer

Part of the Insulation
System
– Excellent dielectric
properties

Cools the transformer
– Excellent heat transfer
properties

Ease of access
Standard ASTM Tests for Insulating Oil
Description
Dielectric Strength
Acidity
Interfacial tension
Color
Water Content
Density
Visual examination
Power factor
Dissolved gas analysis
Inhibitor content
Furan Analysis
Metals Analysis
ASTM Number
D-877/D-1816
D-974
D-971
D-1500
D-1533
D-1298
D-1524
D-924
D-3612
D-4768
D-5837
ICP
Dielectric Strength
Acceptable limit for serviced aged oil:
25 kV
Interfacial Tension
Acceptable limit for serviced
aged oil:
18 dynes/cm
Water Content
The Past
And
Limit for serviced aged oil:
The Present
35 ppm
Dissolved Gas Analysis
The most important test you can perform on your transformer
Dissolved Gas Analysis

High vacuum gas
extraction apparatus
– Extracts all dissolved
gases found in the oil
sample
– Determines dissolved
water in ppm as well
– Extraction of all gases
in less than 2 minutes
Gas Chromatographic Analysis
CO2
CH4
CO
C2H4
C2H6
C2H2
Oil Breakdown Products
Partial Discharge
Overheating
Arcing
Two More Important Tests

Furan analysis
– Determines the state of the solid insulation

Metals analysis
– Used to pin point the location of a fault
Predictive Maintenance

On-site analyzers
– Increase the frequency of testing
– More data points – Better decisions

On-line monitors
– Needed for critical transformers
– Warn of developing problems between routine
maintenance
PHA-1000 Hydrogen Analyzer
Fastest way of
screening transformers.
Analyzes Hydrogen - A
key gas produced by
all fault types
High sensitivity and
wide range
Simple operation
Accurate H2 readings in 60 seconds
Analysis of H2 only = No cross contamination
No special training required
MYRKOS Fault Gas Analyzer
A Full DGA Lab in the field
Typical Gas Extraction
Apparatus

High vacuum gas
extraction apparatus
– Fragile
– Not very portable
– Special training
required
The Shake Test Syringe
Completely portable
No special training
required
Syringe must be filled so that
metering pin is completely
outside of syringe cap.
An exact amount of oil is measured using a metering
pin located on the syringe piston shaft.
Eject the excess oil by pushing the piston
until the metering pin hits the syringe cap.
Mixing the oil with CO2 free ambient air:
Ambient CO2 free air is pulled into the
syringe which is then vigorously shaken to
speed up gas diffusion from the liquid
phase to the gas phase.
•
•
•
•
•
Connect syringe to CO2 trap
Open syringe and CO2 trap
Slowly pull syringe piston to the end
Close syringe and CO2 trap
Disconnect CO2 trap
Method accepted by IEC 60567
and ASTM D-3612
Complete DGA in 2 minutes on-site
Once the test is initiated, automatic sampling occurs and outputs are obtained
from both modules (A & B) simultaneously. Calibration is then performed at a click
of the mouse button.
On-line Monitors

Continuously measure gas concentration
 Store data and trigger alarms
Calisto
Dissolved Hydrogen and Water Monitor
Intelligent Electronic Device IED
Highly Accurate and Precise
Monitors Oil-Filled Transformers
Designed for Extreme Environments
Communicates with the World
Oil circulation and gas extraction circuits
Gas Extraction Technology
H2 detection cell
Specially designed thermal
conductivity detector
Specific to Hydrogen
No interference from other gases
Gas extraction chamber
H2 detector port
Oil
circulation
pump
Water sensor
Primary Heat exchanger
Calisto
Dissolved Hydrogen and Water Monitor
Continuous Hydrogen measurement
Two alarm levels
H2
Data storage and trending software
Why Hydrogen?
Hydrogen is produced in all transformer faults. Calisto will detect
the fault before the Bucholz relay is tripped.
Calisto
Dissolved Hydrogen and Water Monitor
Continuous dissolved water measurement
Two alarm levels
Data storage and trending software
H2O
Reported in ppm or %RS at 25C
Why water?
Along with polar compounds and acids water can adversely
affect the dielectric properties of the solid insulation
Installation
Salt River Project Phoenix, Arizona, USA GE 20 MVA 69 Kv
Installation
Installation
Installations
MPEB Bhopal, India
DUBAL Dubai, UAE
Communication
Ethernet
RS-232
Modem
Fiber Optic
Wireless
RS-485
Gas Trending
Case Study 650 MVA GSU Transformer
failure and Repair
DGA results as of November 11th, 2001
Table 2: H2 generating rates from May 30th to Sept. 26th 2002
Dissolved water
Sudden increase in hydrogen generating rate
Source of incipient fault
Nov. 2001
Initial source of high electrical resistance (e.g. bad connection)
May 2002 to Sept. 17th 2002
Resistive hot spot of increasing resistance (H2, CH4, and C2H4)
Between Sept. 17th and Sept. 30th (Sept. 27th ?)
Additional energy probably through circulating currents
Burned high voltage lead
Overheated
Connector
Burnt Lead
Mirant GSU – Update as of February 19th, 2003
Constant H2 level at approx. 30 ppm
Preventive Maintenance It Pays
Thank you