How To Choose The Capacity Of Test Transformer?

       When carrying out power frequency withstand voltage test or leakage test, power frequency withstand voltage test device is required. Power frequency withstand voltage test device includes test transformer and operation platform. How to select capacity of test transformer? GDZX will explain it to you.

1. The formula for determining the nominal test transformer capacity PN = kvn2 ω CT × 10-9

Where: PN - Nominal test transformer capacity (kVA)

VN -- effective value of rated output high voltage of test transformer (kV)

K - safety factor. When k ≥ 1 and nominal voltage VN ≥ 1mV, k = 2; when nominal voltage is lower, K value can be higher.

CT -- capacitance of test object (PF)

ω - angular frequency, ω = 2 π F, F - frequency of test power supply

2. The capacitance of the tested equipment can be measured by AC bridge. CT varies greatly, depending on the type of device.

Typical data are as follows:

Simple tens of Micromethods for rod or suspension insulator

Simple grading casing 100-1000pf

Voltage transformer 200 ~ 500pf

Power transformer < 1000KVA 500 ~ 1000pf

＞1000kVA 1000~10000pF

High voltage power cable and oil immersed insulation 250 ~ 300pf / M

Gas insulation ~ 60pf / M

Closed substation, SF6 gas insulated 100 ~ 10000pf

3. For different test voltage VN, choose different safety factor K

K values selected for different VNS are listed below for reference.

Vn=50~100kV k=4

Vn=150~300kV k=3

Vn＞300kV k=2

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