Online CT Diagonistics Without Contact of Primary

Online CT Diagnostics Without Contact of Primary
by swipower @ 2009-08-01 – 08:08:53
Keywords: CT, Online Diagnostics,Error, failure
The below summary and attached product information focus on two major issues:
1. Insulation
2. Metering
The first is realized through an online equivalent loop admittance diagnostic methods, which can be a complement to other methods like Dielectric loss,PD and oil analysis, actually the admittance response features with frequency vary design, which zooms out the defects parameter.
The latter, metering error, most important for income of power utilities, will be a trends for a non-offline test.
Based on experience.....

The research started from year 2006 and initiated project in year 2007. a sample product being finished in the end of year 2008.
Application Background:
Current Transformer, Voltage Transformer, Secondary wirings and Electronic energy meters are components of metering loop, among which high-voltage electronic energy meter is online calibrated periodically 6 to 12 months, and even shorter in some substations. But Current Transformer (CT) keeps running for several years until a power off accuracy calibration, metering loss will be difficult to compensate if error runs out of limits. Traditional methods employ offline comparison techniques to verify the accuracy and healthy condition of current transformer, which requires large amount of efforts on both labor and time. Power utilities also try their best to get family data that relates to accuracy or potential fault in order to avoid or decrease sudden power losses. Most common adopted techniques are active ratio, phase error test, burden measurement and harmonics. But burden measurement can only determine if secondary load is within allowed limit, which is just one of several factors that affect metering error. Ratio and phase error measurement require operator to contact primary high-voltage line for an online verification, which adds extra danger and in most cases infeasible. Harmonics gives results which are not easy for decision making of whether CT is running healthily. TM01 is an innovative CT analyzer that focuses on active composite error for metering verification and potential faults that cannot be detected through traditional ways. It also features on low-voltage injection methods that avoid high-voltage contact. Test methods are well in accordance with IEEE CT application Guide and IEC standards.

Features:
Internal Insulation Diagnostics
Exciting magnetics shortcomings
Potential Faults
Burden Influence
Trends data analysis
Portable Design
Avoid High Voltage Contact
Active CT background
Factors that influence CT metering error (under active conditions):
1. Turns ratio
2. Load conditions (primary and secondary)
3. DC magnetizing (Remanence)
4. Magnetizing Characteristics
Factors that influence CT operation (Fault):
1. Primary short circuit or abnormal impedance
2. Insulation (Turn to Turn) breakdown
3. Secondary burden (multipoint grounding, joint corrosion, burden out of limit)
4. DC magnetizing (Remanence)
5. Mechanical problem (Gap, vibration)

Functions and features for reference
Major Function of TM-01-X Online CT Analyzer(Also named active ct analyzer,admittance response analyzer)
¨ Active composite error test (going to be announced)
¨ Active magnetizing characteristics test
¨ Active internal wiring insulation analysis
¨ Active loop impedance (admittance) test
¨ Active load/current characteristics
¨ Fault characteristics and trends analysis
¨ Current Harmonics(Optional)
Application Area
¨ Onsite accuracy verification without need to contact primary line
¨ Internal wiring short-circuit/insulation abnormality
¨ DC magnetizing (Remanence abnormal)
¨ Permeability decrease
¨ Contact point corrosion
¨ Multipoint ground/ ground abnormality
¨ Primary line to ground insulation abnormality
¨ Wiring displacement/vibration
¨ Linea (magnetizing) zone Assessment

The above info is considered free, but should be agreed by the author for transfer or quote.