Method for selecting the capacity of experimental transformers
来源：本站 点击：38 时间：2021-05-08
How to choose the capacity of the test transformer is a common confusion faced by many power testing personnel. We usually choose based on the recommended capacity in the instructions provided by the manufacturer of the test transformer. However, when conducting power frequency withstand voltage tests, is the capacity of the test transformer appropriate, in its optimal operating state, and can it meet the requirements of other tests? We will share with you the capacity selection method for testing transformers here.
Firstly, based on the experimental requirements, calculate the appropriate capacity.
The formula for determining the nominal test transformer capacity Pn is: Pn=KVn2 ω Ct × 10-9
In the formula: Pn - nominal test transformer capacity (KVA)
Vn -- Effective value of rated output high voltage of the test transformer (KV)
K - Safety factor. When K ≥ 1 and the nominal voltage Vn ≥ 1MV, K=2. When the nominal voltage is lower, the K value can be higher.
Ct - capacitance of the test sample (PF)
ω - angular frequency, ω=2 π f, f - - frequency of the test power supply
The capacitance Ct of the tested equipment can be measured using an AC bridge. The variation of Ct is significant and can be determined by the type of device. Typical data is as follows: Simple bridge or suspension insulators with a thickness of tens of micrometers
Simple graded casing 100-1000PF
Voltage Transformer 200-500PF
Power Transformer<1000KVA -1000PF>1000KVA 1000-10000PF
High voltage power cables and oil immersed paper insulation 250-300PF/m
Gas Insulation-60PF/m
Enclosed substation, SF6 gas insulated 100-10000PF
Select different (appropriate) safety factors K for different test voltages Vn. The following is a list of K values selected for different Vns for reference
Vn = 50–100KV K=4
Vn = 150–300KV K=3
Vn > 300KV K=2
The calculation formula for the capacity of test transformers is applicable to the detection and testing of various test transformers. We should select a suitable test transformer based on the required voltage and safe capacity of the test sample. On the premise of ensuring the safety of the experiment, meet the testing requirements of different capacities.
