Generally speaking, the dc high voltage generator under the condition of meet the power frequency cable under 220 kv voltage class of dc withstand voltage test, but some special cases, some cable, electrical rated voltage level is have special requirements, such as the coal industry in our country the underground cable, electrical voltage is different from the ground pressure rating, only 6 kv, so in this case, how to set the test voltage dc high voltage generator system?

According to the regulation, different cable needs to test voltage and time pressure is not the same, crosslinking polyethylene cable, for example, the 6 kv cable, dc test voltage needed for 25 kv, lasts for 5 minutes,

General experiment need from 40% full, full voltage start slowly increase the voltage to the voltage, lasts for 5 min, if it is less than a year of new cable line, power cut just a month, can do 50% specified test voltage, the last 1 min, the need of power a year according to the general test requirements,

Specific test voltage and time pressure regulation, different cables and specific test requirements, in the power cable well specified in the preventive test procedures,

Dc withstand voltage related knowledge links:

Solid dielectric breakdown forms are: electric breakdown, thermal breakdown and electrochemical breakdown, the same kind of the dielectric in different external conditions, can occur in different breakdown form,

(1) electric breakdown

Because of the existence of external electric field ionization electron accumulated enough energy in the strong electric field, the mutual collision led to the electric breakdown, its characteristic is process is fast, high breakdown voltage,

(2) thermal breakdown

Breakdown voltage with the temperature and voltage drops rapidly with the extension of time, then the related with the thermal process of dielectric breakdown process, known as thermal breakdown, ambient temperature and voltage duration increased, thermal breakdown voltage drop; The dielectric thickness increases, the average breakdown voltage to drop,

(3) the electrochemical breakdown

Under the effect of electric field, the dielectric, may produce chemical changes in the irreversible to gradually increase the conductivity of the dielectric, causing breakdown, known as electrochemical breakdown, dielectric loss due to chemical changes usually increases, thus the electrochemical breakdown of the final form is often thermal breakdown,

(4) along the surface breakdown

In the insulation of the actual structure, solid medium gaseous or liquid medium, tend to have two dielectric breakdown often along the interface and in the side of the lower dielectric strength, called breakdown, along the surface along the surface is lower than single dielectric breakdown voltage, breakdown voltage capacitor electrode edge, motor line (rod) end insulator creeping discharge is easy to occur, the damage to the insulation is large,

Dc high voltage generator of the common faults and processing:

Dc high voltage generator fault 1. Open the power switch, power light and green light is not bright?

Failure analysis:

Check the power fuse, the power cord and the power switch;

Solution:

If any one case of damage, please change in time,

Fault 2. After open the power switch of dc high voltage generator, the power indicator light flashing and at the same time accompanied by hum,

Failure analysis:

A. no grounding;

B. grounding is not reliable;

C. use the generator power supply or switchgear of isolation transformer, power supply

Solution:

A. grounding;

B. check reliable grounding line, to ground;

C. if power supply by 1/1 isolated or field with spontaneous power, it must be artificially with the power supply is connected to the earth,