Basler Electric DECS-400 - Manual (Page 52)

40 9369700990 Rev R
Figure 7. Generator Capability Curve Versus 40Q
Response
Figure 8. Motor Capability Curve Versus 40Q
Response
Field Overtemperature
Field overtemperature is annunciated when the field temperature exceeds the Field Overtemperature
Pickup Level setting for the duration of the Field Overtemperature Delay setting. The Pickup Level setting
is adjustable from 0 to 572
°C in 1°C increments. The Delay setting is adjustable from 0.1 to 60 seconds in
0.1 second increments. The DECS-400 calculates field temperature based on the generator main field
resistance, the field ambient temperature, and the voltage drop across the generator main field brushes.
Field overtemperature protection is intended for static exciter applications supplying a generator’s main
field or for rotary exciter applications where the field voltage and current is measured at the slip rings and
main field current shunt on the brush-type rotary exciter.
Volts per Hertz (24)
Volts per hertz protection is annunciated if the ratio of the per-unit voltage to the per-unit hertz
(volts/hertz) exceeds one of the Volts per Hertz Pickup Level settings for a definite amount of time. If the
Volts per Hertz Pickup level is exceeded, timing will continue until the Volts per Hertz ratio drops below
the dropout ratio (95%). Volts per hertz protection also guards against other potentially damaging system
conditions such as a change in system voltage and reduced frequency conditions that can exceed the
system’s excitation capability.
Several volts per hertz settings enable the DECS-400 to provide flexible generator and generator step-up
transformer overexcitation protection. An inverse square timing characteristic is provided through the 24
Volts/Hertz Pickup Setpoint setting and 24 Volts/Hertz Pickup Time Dial. These settings enable the
DECS-400 to approximate the heating characteristic of the generator and generator step-up transformer
during overexcitation. The Pickup Setpoint has a per-unit setting range of 0.5 to 6.0 with increments of
0.01. A Pickup Time Dial setting of 0 to 9.9 may be entered in increments of 0.1. A linear reset
characteristic is provided through the 24 Volts/Hertz Reset Time Dial setting. A Reset Time Dial setting of
0 to 9.9 may be entered in increments of 0.1.
Two sets of fixed-time, overexcitation pickup settings are available through the 24 Volts/Hertz Definite
Time Pickup #1, #2 and Definite Time Pickup #1, #2 settings. Both pickup settings have a setting range of
0.5 to 6.0 with an increment of 0.01. Both time delay settings may be set over a range of 0.50 to 600
seconds in 0.05 second increments.
The following equations represent the trip time and reset time for a constant V/Hz level. Volts per hertz
characteristic curves are illustrated in Figure 9 and Figure 10.
Functional Description DECS-400