Transformer no-load test regulator configuration

Example: The voltage level of the transformer is 10KV/0.4KV, the maximum capacity is 2500KVA, the national standard impedance voltage is 4.5% → Then the actual voltage is obtained: High voltage (10000V) × 4.5% = High voltage (450V) → Maximum capacity (2500KVA) ÷ 1.732 ÷ High voltage (10000V) = High-voltage current 144.3A → High-voltage voltage 450V × High-voltage current 144.3A × 1.732 = Voltage regulator capacity 112KVA, so transformer manufacturers we have 160KVA, if the installation company can be equipped with 100KVA.

1. All power transformers with a capacity of less than 800KVA and a low voltage of 400V can be directly measured without external voltage and current transformers.

Example: Power transformer Se=800KVA, 10KV/400V measurement method.

(1) Select three-phase voltage regulator capacity:

Transformer high-voltage side rated current I1=Se/1.732×U=800KVA/1.732×10KV=46.19A

Transformer low-voltage side rated current I2=Se/1.732×U=800KVA/1.732×400V=1154.73A

The no-load current is generally 1.2~1.4% of the rated current, and the estimated current

I0=1154.73A×1.4%=16.17A

The impedance voltage is generally 4.5% of the rated voltage, the expected voltage

Uk=10KV×4.5%=450V

The voltage regulation range of the voltage regulator is required to be 0-450V and the current is 46A. Therefore, the capacity of the regulator is required to be 35KVA. Considering that the regulator can be overloaded for a short time, therefore:

1. If the short circuit test rises to the rated current (Ik=46.19A), select the 30KVA regulator.

2. If the short-circuit test rises to 40% of the rated current, (Ik=46.19A×40%=18.47A), an optional 10KVA regulator may be selected. The instrument automatically converts the data at 40% of the rated current to the rated value and 75°C.

(2) According to Figure 3 wiring do no-load test. Note: Apply voltage to the low side of the transformer, and leave the high side unconnected.

(3) Turn on the unit and select “No load test”. After confirming, select Se=800KVA, Ue=400V (the rated voltage value of the input pressure side), the data of Se and Ue must be input correctly, otherwise the output calculation result is not correct. Since there is no voltage and current transformer, KCT=1 and KPT=1. After the input is complete, select Test.

(4), adjust the voltage, the LCD screen shows the three-phase voltage, average value and three-phase no-load current value. When the voltage is adjusted to UP=400V, press the “move up” button for 1S, the instrument displays “calculating”, then lock the data and stop the measurement. At this point you can step down to zero.

(5) Press “Confirm” to enter the print menu and press “Confirm” to print out all test results.

(6) The three lines output to the transformer are switched to the high-voltage side, and the low-voltage side is short-circuited using copper bars.

(7) After power on, select “Load Test”. After confirming, select Se=800KVA, Ue=10KV (the rated voltage value of the input pressure side), the data of Se and Ue must be input correctly, otherwise the output calculation result is incorrect. . Since there is no voltage and current transformer, KCT=1 and KPT=1. After the input is complete, select Test.

(8), adjust the voltage, the LCD screen displays the three-phase voltage, average value and three-phase short-circuit current value. When the current is adjusted to IP=46.19A (any value less than the rated value), press the “Up” button for 1S, the instrument displays “Calculating”, then lock the data and stop measuring. At this point you can step down to zero.

(9) Press “Confirm” to enter the print menu and press “Confirm” to print out all test results.

2. Measurement methods for external voltage and current transformers.

Example: Measuring method of power transformer Se=8000KVA, 66KV/6.6KV

(1) Calculated rating:

Transformer high-voltage side rated current I1=Se/1.732×U=8000KVA/1.732×66KV=70A

Transformer low-voltage side rated current I2=Se/1.732×U=8000KVA/1.732×6.6KV=700A

The no-load current is generally 1.1% of the rated current and the estimated current

I0=700A×1.1%=7.7A

Impedance voltage is generally 9% of rated voltage, estimated voltage

Uk=66KV×9%=5940V

(2) Choose booster equipment:

The no-load test requires boosting to 6.6 kV and requires a step-up transformer. Since it is difficult to find such voltage regulating equipment on site, an ordinary distribution transformer can be selected instead (capacity 100 KV, voltage 400 V/10 KV).

(3) Select the voltage regulator capacity:

The no-load current of the transformer during the no-load test is 7.7A, and the low-voltage side current of the boost device is (10KV/400V)×7.7A=192.5A. Therefore, the voltage regulator capacity S=1.732×192.5A×400V=133KVA is selected. Considering that the regulator can be overloaded for a short time, select the 100KVA regulator.

(4) Large-current generator cable fault locator test transformer, according to Figure IV method wiring, three-phase regulator part of the pressure regulator and booster combination. Wiring method shown in Figure 5.

(5) At this time, the voltage and current are high voltage and high current. It cannot be directly measured by the instrument. It must be connected to voltage and current transformers.

(6) During the load test, due to the capacity limitation of the regulator, the current can only rise to about 6A, which accounts for about 8.5% of the rated value.

(7) Since the current range is between 0 and 10A, a transformer of 100A/5A can be selected with 10 turns through, the current ratio is 10A/5A, and the input ratio KCT=2.

(8) Select the three-phase 10KV/100V voltage transformer with the input ratio KPT=100.

(9) The other procedures for the no-load and load tests are the same as those in the previous example.