[b]Power frequency voltage dry test[/b] 2

[e119770]

Does anybody know, what is power frequency voltage dry test?
What is the purpose of performing such a test and how is it performed?

 

[DanDel]

Upon which type of equipment is this test to be performed?

 

[e119770]

A generator circuit breaker is subject to test.

 

[cuky2000]

Does anybody know, what is power frequency voltage dry test? Is one of the standard dielectric insulation test voltage withstand parameters performed a low frequency (<500 Hz, usually 48 to 62 Hz) under clean dry conditions for short duration (usually one- minute). There are also power frequency standard for wet and pollution test. (Ex. see insulator wistand voltage rating)

What is the purpose of performing such a test and how is it performed? This test is intended to simulate the normal temporarily overvoltage in the power system network. The maximum overvoltage expected is less than 1.73 the nominal system voltage.

For details, consult the IEEE Stds 4, 857, C57.19 or IEC stds 71, 383

 

[DanDel]

Even though I've been in the power equipment testing business for 13 years, I am not familiar with this particular test description. Can you elaborate?
Are there any more specifications for the test, as in equipment used or results expected?
Any IEEE/ANSI, UL, etc. specifications for the test?
What voltage/current rating is the C/B to be tested?

 

[cuky2000]

[blue]Here is a sample of applicable to generator circuit breaker[/blue]

Manufacturer: ABB
GCB Type HGI 3
Solutions for small power plants.
Technical Data:
Type: HGI 3

Rated maximum voltage [kV]: 21

Rated frequency [Hz]: 50/60

Rated power frequency withstand voltage [kV]: [red] 60 [/red]

Rated lightning impulse withstand voltage [kV]: 125

Rated current [kA]: 3 8

Rated short-circuit breaking current [kA]: 63

 

[scottf]

cuky2000-

Not to split hairs, but I'm not sure I agree with the purpose of the test you listed above.

PFWV testing is not really to simulate overvolages on a system, but rather to overstress the insulation design to ensure that it can properly handle the voltage class for which it is rated. The PFWV (or hi-pot) is typically roughly 1.5-2.0 times higher than the rated system voltage (L-L) voltage. The higher the system voltage, the lower the relationship between PFWV levels and rated system voltage levels.

 

[cuky2000]

Hi Scott,

You have a good point. However we should keep in mind that overvoltage in form of wave amplitude, frequency, duration and wave shape are factor involving “overstress the insulation” in addition to other interrelated factors such as thermal and environment conditions.

The PFWV is the least stress test imposed to any equipment since the overvoltage is <2pu, test frequency is close to nominal, wave shape is regular and max. duration around up to 1 minute.

In the early time of the power system development, the PFWV was the only dielectric test available considering apply voltage around twice the system voltage plus 1000 V. As the voltage increases and other testing techniques available, this is may not be the best present testing practice.

Today, the PFWV has less significance since other tests characterize better the dielectric insulation of electrical apparatus and components.

It should be noted that there might be difference between design tests, production tests, conformance tests, or field tests. PD, impulse, switching and other dielectric test may be preferred than the power frequency test.

 

[scottf]

Cuky2000-

For products that I deal with (HV instrument transformers), the PD test and PFWV are performed in conjunction with one another and are highly interelated. I believe that the PD test for oil/paper insulation systems to be the most telling test in regards to long life in the field.

Of course the BIL test is also quite valid, but not really in terms of insulation stability over time.