Formula for determining the nominal capacity Pn of the test transformer: Pn=KVn2ωCt×10-9
Where: Pn----nominal capacity of the test transformer (kVA)
Vn-----rated output high voltage effective value of the test transformer (kV)
K------safety factor. K≥1, when the nominal voltage Vn≥1MV, K=2, when the nominal voltage is lower, a higher K value can be taken.
Ct-----capacitance of the test object (PF)
ω----angular frequency, ω=2πf, f----frequency of the test power supply
The capacitance Ct of the test equipment can be measured by an AC bridge. Ct varies greatly and can be determined by the type of equipment. Typical data are as follows:
Simple bridge or suspension insulators: tens of microfarads
Simple graded bushings: 100 – 1000PF
Voltage transformers: 200 – 500PF
Power transformers: < 1000kVA - 1000PF
> 1000kVA: 1000 – 10000PF
High voltage power cables and oil-impregnated paper insulation: 250 – 300PF/m
Gas insulation: - 60PF/m
Enclosed substations, SF6 gas insulation: 100 – 10000PF
For different test voltages Vn, different (appropriate) safety factors K are selected. The K values selected for different Vn are listed above for reference.
Vn = 50–100kV K=4
Vn = 150–300kV K=3
Vn > 300kV K=2
Working Principle
1. AC, AC/DC test transformer: Input the power frequency power into the operation box (or operation console), adjust the voltage through the auto-transformer and input it to the primary winding of the test transformer. According to the principle of electromagnetic induction, power frequency high voltage can be obtained on the secondary (high voltage) winding. This power frequency high voltage can be rectified by a high voltage silicon stack and filtered by a capacitor to obtain DC high voltage, whose amplitude is 1.4 times the effective value of the power frequency high voltage. However, when using DC, the short-circuit rod should be pulled out; when using AC, insert the short-circuit rod. 2. Test transformer with taps: In order to simultaneously satisfy the contradiction between higher voltage and lower current, and lower voltage and higher current, the high voltage winding is divided into two windings, one with larger current and the other with smaller current, and then the two windings are connected in series and led out separately. Schematic diagram 3. Cascade test transformer: To obtain a higher voltage test transformer, the cascade method can also be used to obtain higher voltage. Figure 2 shows the principle wiring diagram of a three-stage cascade test transformer. The capacity and voltage relationship of the three transformers satisfy: P1=2P2=3P3, U(total)=1U+2U+3U.
Supporting Products
(Select according to customer's own needs, not standard products)
1. Operating system:
XC, series operation box: capacity: 1KVA – 5KVA input voltage: 0.22KV.
TC, series operation console: capacity: 10KVA – 300KVA input voltage: 0.22KV, 0.38KV.
2. Protective digital microammeter MSA. –
3. Resistive-capacitive AC/DC voltage divider RCF – 50, 100, 150, 200KV.
4. High voltage DC discharge rod FZ – 70, 140, 210KV.
5. High voltage silicon stack 2DL – 150, 300, 450KV.
6. Insulation support 50, 100, 200, 300KV.
7. High voltage filter capacitor 0.01uF – 0.1uF, 40 – 100KV.
8. Grading ring.
9. Protective sphere gap Q – 50, 100, 150, 200, 250, 500.
10. Standard oil test cup 400ml.
11. Dielectric oil cup.
12. Folding trolley 150, 300 type.
13. Water resistor.
14. High voltage tester 10KV 35KV.
15. High voltage phase detector 10, 35, 110KV 220KV.
16. Various multimeters, megohmmeters and test leads.
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