Technology Literature

How to shorten the test time of transformer winding resistance?

The voltage drop method and the bridge method are generally used. For large transformers, the inductance is very large. To speed up the measurement, a fast measurement method can be used.


Transformer winding are complex circuits that consist of distributed inductors, resistors, and capacitors. The DC winding resistance is measured by direct current between the tested terminals of the winding. After the transient process ends and the current reaches a stable state, the resistance value and the winding temperature are recorded. The key issue in measuring DC resistance is to minimize self-inductance effects. There are two ways to solve this problem.

1. Magnetic assist method

The magnetic assist method is to force the core flux to quickly become saturated, thereby reducing the self-inductance effect, which can shorten the time constant, and generally has the following methods:

(1) Use a large-capacity battery or a steady current source to measure the current.

(2) The high and low voltage windings are connected in series to measure the current, and the high voltage windings of the same phase and the same polarity are used for magnetic fluxing. Since the number of turns of the high voltage winding is much higher than that of the low voltage, the core can be saturated with a small current by means of the number of ampere turns of the high voltage winding.

(3) A DC resistance tester using a constant voltage constant current source method. When used, the high and low voltage windings can be connected in series, and the dual channel is used to measure the high and low voltage windings at the same time, which better solves the difficulty of the DC resistance test of the three-phase five-column large-capacity transformer. Generally test a 360MVA, 500kV or 220kV transformer winding DC resistance takes about 30 ~ 40min, the measurement wiring shown in Figure 1-1.



2. Degaussing method

The degaussing method is opposite to the magnetically assisted method in that the magnetic flux passing through the core is made zero. There are two ways to use it:

(1) Zero-sequence impedance method. This method is only applicable to transformers with a three-column core Y-N connection. The three-phase windings are connected in parallel and energized at the same time. Since the magnetic flux needs to be closed by the air gap, the magnetic resistance of the magnetic circuit is greatly increased, and the inductance of the winding is reduced, so that the time for measuring the resistance is shortened.

(2) Magnetomotive force cancellation method. In the test, in addition to the current flowing through the measured winding, the current is also passed through the non-measured winding, so that the magnetomotive force generated by the two is equal in magnitude and opposite in direction, and cancel each other, thereby keeping the magnetic flux in the core close to zero. The inductance of the winding is minimized for the purpose of shortening the measurement time. The measurement wiring is shown in Figure 1-2.

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DC winding resistance tester with 500 times tests on a single charge -JYR9310

The test items are required for 110kV/220kV substation acceptance and maintenance testing(with corresponding tester types):

Test Object

Testing Item

Tester Type

Cable

Cable AC Hipot Testing

JYCX

Details

Cable Insulation Resistance Testing

JYM KYORITSU

Details

Transformer

Insulation Resistance of Winding

    JYM KYORITSU

Details

DC Leakage Testing in 1min

JYDHV

Details

Winding Resistance Testing

JYR50S

Details

Winding Deformation Testing

JYP

Details

Turns Ratio Testing

JYT-A

Details

AC Hipot Testing

JYCX

Details

Short Circuit Impedance Testing

JYW6300

Details

Dan Delta Testing

JYC

Details

Oil Breakdown Voltage (BDV)Testing

JY6611

Details

Oil Tan Delta Testing

GTD-61A

Details

Switchgear

Circuit Breaker/Disconnector Resistance

JYL-200B

Details

Relay

Relay Performance

JY7003G

Details

On-load

On-load Switchgear Testing

JYK-I

Details

Tap Changer Dynamic Testing

JYK-I

Details

Instrument   Transformer

Current Transformer (CT)Testing

JYH-C

Details

Potential Transformer (PT)Testing

JYH-C

Details

Surge Arrestor

Zinc Oxide Characteristics Testing

JY6800

Details

1mA DC Reference Voltage

JYDHV

Details

Capacitor

Capacitor Current

JY6700

Details

Capacitor Inductance

JY6700

Details

Ground Grid

Grounding Down Lead Earth

JYD

Details