Transformer Life Management Conference

[ TLM 2011]

June 6th ~ 7th, 2011Hannover, Germany

General Knowledge

In the mid-1800’s, Thomas Edison changed everyone's life where he perfected his invention of the electric light bulb.

After 1879, George Westinghouse developed a device called a transformer to send the power over long distance.

The transformer is based on two principles.

- First, that an electric current can produce a magnetic field (electromagnetism),

- Second, that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction).

Summary of TLM 2011

1. Dissolved-Gas-Analysis (DGA): Tool for Power Transformer monitoring

2. New experience in the Transformer Diagnostics

3. Transformers of the Future4. 3-Days stay: Experience at Hannover

1.(DGA) : Tool for Power

Transformer monitoring

Introduction

DGA enables to track the condition & gives an early indication of transformer failures.

Standard guidelines:- IEC 60599: Guide to the interpretation

of dissolved and free gases analysis IEEE Std C57.104™-2008: IEEE Guide for

the Interpretation of Gases Generated in Oil-Immersed Transformers

CIGRE [http://www.cigre-a2.org/]

DGA – Diagnostic limits

• Combustible gasesa.Hydrogen ( H2): < 100 ppmb.Methane ( CH4): < 120 ppmc.Ethane (C2H6): < 65 ppmd.Ethylene ( C2H4): < 50 ppme.Acetylene (C2H2): < 1 ppmf. Carbon Monoxide (CO): < 350 ppm• Non-Combustible gasesg. Carbon Dioxide ( CO2): < 3500

ppm

Partial Discharge

(PD)

Overheated Oil

Arcing in Oil

Overheated Cellulose[ CO2/ CO

<3 or >10]

DGA – Diagnostic limits (2)

Total Dissolved Comb. Gases (TDCG): < 720ppm

CO2/CO <3: indicates excessive paper degradation

C2H2/H2 >2: in main tank indicates OLTC contamination

Roger’s ratio method Duval’s Triangle method

2. New experience in the

Transformer Diagnostics

Introduction

The fault must be located if increased proportions of hydrocarbon gases are found in the oil.

preventative maintenance must be performed in time to avoid an unexpected total failure

The most frequent sources of faults are the tap changers, bushings, the paper-oil insulation and the accessory equipment.

Sources of Transformer faults [ Source: CIGRE International Survey]

Diagnostic test methods

• Turns ratio test and excitation current (no-load) measurement

• Static winding resistance measurement• Dynamic winding resistance

measurement to test the On-Load Tap Changer (OLTC)

• Sweep Frequency Response Analysis (SFRA)

• Di-electric Response Analysis• Partial Discharge (PD) measurement

Turns ratio test and excitation current (no-load) measurement

WHAT? - Transformer Turns Ratio is the ratio of the number of turns in the high voltage winding to that in the low voltage winding.

WHY? - for assessing possible winding damage, such as turn-to-turn short circuits

REASON? - Transformer ratio can change due to several factors, including physical damage from faults, deteriorated insulation, contamination and shipping damage.

Turns ratio test and excitation current (no-load) measurement

WHAT? - The exciting current is the current that maintains the magnetic flux excitation in the core of a transformer.

WHY? - Unwanted circulating currents or unintentional grounds can affect the exciting current and indicate a problem.

REASON? - If the exciting current test shows phase angle deviations, then the cause may be a core failure or unsymmetrical residual flux.

Static winding resistance measurement

To check for loose connections, broken strands and high contact resistance in tap changers.

The deviations between switching upwards and switching downwards are almost same.

High deviations indicates high contact resistances caused by the contacts of the tap selector switches.

Static winding resistance measurement (2)

Dynamic winding resistance measurement on OLTC

dynamic behavior of the diverter switch can be analyzed.

measures the peak of the ripple (Imax–Imin) and the slope (di/dt) of the measuring current, as these are important criteria for correct switching.

If the switching process is interrupted, even for less than 500us, the ripple and the slope of the current change dramatically.

Dynamic winding resistance measurement on OLTC (2)

For tap changers in good condition the ripple and slope measurements for all three phases tapping UP should be similar as for tapping DOWN.

Dynamic winding resistance measurement on OLTC (3)

Sweep Frequency Response Analysis (SFRA) To evaluate the mechanical integrity of

core, windings and clamping structures within power transformers by measuring their electrical transfer functions over a wide frequency range.

5 Hz up to 10 kHz – defect in core & magnetic circuit

10 kHz up to 600 kHz – deformation in winding geometry

600 kHz up to 10MHz – abnormalities on the inter-connection and test system

Sweep Frequency Response Analysis (SFRA) (2)

3. Transformers of the

Future

To Be Consider – Good Transformer

Transportation [ Factory to Site] Design & configuration Installation process especially during

new oil filling into transformer Testing & commissioning Operating condition & condition

monitoring [DGA, Oil & winding temperature, current loading]

To Be Consider – Good Transformer (2)

Recommended testing at factory & site:- DGA testing ( for oil-filled transformer)- Additional Diagnostic testing ( such as

SFRA, static & dynamic resistance test on OLTC )

3-Days stay:Experience at Hannover

Thank you for listening

Discussion

Q & A