4 - 20
4 - 21
Assessing supply performance
The voltage and frequency maximum and minimums and transient response graphs can
be used to assess the performance of the Supply-on-Test.
ISO8528 defines three classes of generator performance (G1, G2 and G3) and specifies
deviations and recovery times for each class as follows:
The generator class will be indicated on rating plate. For example, in Figure 4-8 the
generating set is rated G3 (ISO8528 - 3 Rating).
Operating Limit Values
Performance class
Parameter
Unit
G1
G2
G3
Transient fre-
quency devia-
tion from rated
frequency
100% sudden
power decrease
%
<= +18
<= +12
<= +10
Sudden power
increase
%
<= -15
<= -10
<= -7
Frequency
recovery time
100% sudden
power decrease
s
<= 10
<= 5
<= 3
Sudden power
increase
s
<= 10
<= 5
<= 3
Transient volt-
age deviation
100% sudden
power decrease
%
<= +35
<= +25
<= +20
Sudden power
increase
%
<= -25
<= -20
<= -15
Voltage recov-
ery time
100% sudden
power decrease
s
<= 10
<= 6
<= 4
Sudden power
increase
s
<= 10
<= 6
<= 4
Chapter Four
