Volt/Hz Characteristic
1.0
10.0
100.0
1000.0
100%
105%
110%
115%
120%
125%
130%
135%
140%
Percent of Nominal V/Hz
Ti
m
e
in
S
e
c
onds
Transformer Limit
Generator Limit
Inverse
105%, TD=1.9
Definite
118%, 6s
Figure 4-33. Time Shown on Vertical Axis
Volt/Hz Characteristic
100%
105%
110%
115%
120%
125%
130%
135%
140%
1.0
10.0
100.0
1000.0
Time in Seconds
P
er
cen
t
o
f
N
o
m
in
a
l
V
/H
z
Transformer Limit
Generator Limit
Inverse
105%, TD=1.9
Definite
118%, 6s
D2871-43
02-12-04
Figure 4-34. Time Shown on Horizontal Axis
Assuming a Vnom of 69.3 volts phase-neutral, 1 pu volts/hertz = (69.3 *
3) / 60 = 2.00. Using
IEEE/C37.102, "
Guide for AC Generator Protection
" as a guide for setting overexcitation protection, the
following example demonstrates how to set the BE1-CDS240 to provide a composite V/Hz characteristic
for protection of a generator and a step-up transformer:
• Alarm = 105% @ 1 second time delay; V/Hz = 2 * 1.05 = 2.10
• Inverse time pickup = 105%; Time Dial = 1.9; Inverse Trip Curve = (M-1)^2; V/Hz = 2 * 1.05 = 2.10
• Definite Time #1 = 118% @ 6 seconds time delay; V/Hz = 1.18 * 2.0 = 2.36
In BESTCOMS, the 24 graphing capability can be used to verify the composite shape as shown in Figure
4-35. Secondary V/Hz is shown.
4-40
BE1-CDS240 Protection and Control
9365200990 Rev F
Summary of Contents for BE1-CDS240
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