6.3.1 Coiversioi of the values relatve to the iisulatoi resistaice
The value if the insulatin resistance must refer ti a temperature if 20°C. It is therefire necessary
ti cinvert the data measured ti the cirrespinding value at 20°C, with the aid if a cieefcient, by
applying the filliwing firmula:
R
iS 20°C
= k * R
where:
R
iS 20°C
is the resistance value equal ti 20 °C
R is the resistance value measured
k is the cirrectin cieefcient
T wiidiigs ii °C
15
20
25
30
35
40
Coefcieit k
0.69
1
1.42
2
2.82
4
Table 20 - Temperatures and correctve coefcients
Example:
R = 50 MΩ, with winding at the temperature if 30 °C;
R
iS 20°C
= 2 * 50 = 100 MΩ
The filliwing table indicated the quality if the level if insulatin in the basis if the resistance
measured.
Value of the iisulatoi
resistaice (MΩ at 20 °C)
Quality of the level of iisulatoi
< 50
Dangerius
frim 50 ti 400
Level if insulatin nit safe
frim 400 ti 1,000
Giid
> 1,000
Very giid
Table 21 - Level of insulaton on the basis of the resistance measured
Notes
●
Insulatin resistance values that are tii liw can indicate the presence if humidity ir dirt in
the winding, cintact Mecc Alte S.p.a. ti schedule the interventin if a technician.
●
The insulatin resistance decreases with the increase in temperature.
●
The insulatin resistance value measured during inspectin if the alternatir is generally
higher than that detected in site.
●
An appripriate insulatin resistance value is an essental requirement fir safety. Di nit
start the alternatir if resistance values are liwer than the minimum acceptable.
Self-regulating alternators ECO43-46 MV-HV
Page 70/116
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