power frequency test in MV switchgear 3

[Netsky]

hi
acc to IEC 62271-200 / 6.2.5
for insulated test in MV switchgear should be power frequency test voltage of 150% of the rated voltage for 1 min at an altitude of 1000 meters above sea level. that in 20kv it will be 50kv for 1 min.
my question is here ,altitude of above see level in our city is 1200 meter . how many voltage should we use in power frequency test voltage in MV 20kv?
What is its calculation formula that?
Thanks for guiding me

 

[che12345]

Dear Mr. Netsky
[COLOR=]"...acc to IEC 62271-200 / 6.2.5 for insulated test in MV switchgear should be... for 1 min at an altitude of 1000 meters above sea level. that in 20kv it will be 50kv for 1 min...my question is here ,altitude of above see level in our city is 1200 meter . how many voltage should we use in power frequency test voltage in MV 20kv? What is its calculation formula that?...".[/color]
1. See IEC 62271-1 sub-clause 2.2.1 Altitude . See also note 2 For LV auxiliary and control ....
2. For altitude of 1200 m the factor Ka = 1.01 approx. See standard for full detail the formula etc. etc.
3. Attention: a) This Ka factor is to be applied when testing the gear in the lab; where the lab is located =<1000m[/b].
b)It is NOT intended to be applied on tests carried out at site; where the site is at 1200 m.
Che Kuan Yau (Singapore)

 

[Netsky]

thanks che12345 for your help

I checked out that standard (IEC 62271-1 sub-clause 2.2.1 Altitude ) And I calculated Ka factor completely acc to the full formula. it is Ka=1.02 in altitude 1200m .
my test is in lab.

I want to know what should I do with this Ka now ??
1) test MV 20kv in altitude 1000M = 50KV in 1 min
2) test MV 20kv in altitude 1200M with Ka=1.02 = ???? How should I calculate this part?
Thanks in advance for your guidance

 

[che12345]

Dear Mr.Netsky
"...I checked out ...calculated Ka factor ... Ka=1.02 in altitude 1200m. my test is in lab. I want to know what should I do with this Ka now ??
1) test MV 20kv in altitude 1000M = 50KV in 1 min
2) test MV 20kv in altitude 1200M with Ka=1.02 = ???? How should I calculate this part?... "
1. If the lab is located =<1000m, the test voltage shall be Ka * 50kV = 1.02 * 50kV =51kV for 1 min.; in order for it to be suitable for 1200m location. Ask the lab for the altitude datum. See also other climatical requirements per the IEC standard.
2. If the lab or the site where you are carrying out the site test is at 1200m, the test voltage = Ka * 50kV = 1.02 * 50kV = 51kV for 1 min.
3. General guidelines are: air insulation properties go down when increase in altitude.
a) testing it to 51kV at =<1000m will be about equal to 5okV at 1200m.
b) a gear tested to 50kV at =<1000m shall withstand the lower insulation air at 1200m. Therefore, it shall be tested to 51kV at 1200m locations.
Do they make sense?
Che Kuan Yau (Singapore)

 

[Netsky]

Dear che12345
Thank you very much for your attention.
it was very useful for me.

 

[RRaghunath]

I think there is an error in what Mr. Che Kuan Yau mentioned.
If the test lab is located at 1200m, there is no need for applying any factor (Ka) over the stated PF withstand voltage. It is relevant when the test lab is located < 1000m elevation.

 

[che12345]

Dear Mr. Netsky
@ Mr. RRaghunath
"...I think there is an error in what Mr. Che Kuan Yau mentioned. If the test lab is located at 1200m, there is no need for applying any factor (Ka) over the stated PF withstand voltage. It is relevant when the test lab is located < 1000m elevation..."
1. I am thinking if the lab is =<1000m, the test voltage is 50kV. If the gear is intended for installation at 1200m, the test voltage shall be higher i.e. 51kV.
2. When the lab or site test is conducted at a location 1200m; if the gear is tested at 50kV, i.e. without Ka or Ka=1.00; it is inadequate. It shall be conducted at 51kV.
Do they make sense? Please advise.
Che Kuan Yau (Singapore)

 

[LionelHutz]

Yes, when testing at 1200m just test to the same voltage as you would at 1000m.

If you are testing air insulation then you do need to worry about this since it is the air properties that change. If you are testing solid insulation then you really don't because the insulation still has the same insulating properties at 1200m as it has <1000m.

150% of the rated voltage of 20kV is 30kV too. Did you mean 250% of rated voltage? I don't do IEC, but in NEMA it is 225% + 2000.

 

[Netsky]

Rated voltage values according to IEC 60071-1 (Insulation co-ordination – Part 1: Definitions, principles and rules)
(see Fig. B5)

Ur = rated voltage, rms value, kV. It is the maximum rms value of voltage that the equipment can withstand permanently. 24 kV rms for example.
Ud = rated power frequency withstand voltage, rms value, kV during 1 mn. It defines the level of rms over-voltages that the equipment may withstand during 1 minute. 50 kV rms for example.
Up = rated lightning impulse withstand voltage, peak value, kV. It defines the level of lightning over-voltages that the equipment may withstand. 125 kV peak for example.
Un = service voltage, rms value, kV. It is the voltage at which the MV utility distribution network is operated. For example, some networks are operated at Un 20 kV. In this case, switchgear of at least 24 kV rated voltage shall be installed.