Reverse Power And Underpower Protection P< (32) - Allen-Bradley Rockwell Automation 857 User Manual

3-56
Protection Functions
Reverse power and
underpower protection
P< (32)
857-UM001A-EN-P – July 2009
Reverse power function can be used for example to disconnect a
motor in case the supply voltage is lost and thus prevent power
generation by the motor. Underpower function can also be used to
detect loss of load of a motor.
Reverse power and underpower function is sensitive to active power.
For reverse power function the pick-up value is negative. For
underpower function a positive pick-up value is used. Whenever the
active power goes under the pick-up value, the stage picks up and
issues a start signal. If the fault situation stays on longer than the
delay setting, a trip signal is issued.
The pick-up setting range is from –200 % to +200 % of the nominal
apparent power Sn. The nominal apparent power is determined by
the configured voltage and current transformer values.
Equation 3.3
= ⋅
S VT CT
n Rated Pr imary
There are two identical stages available with independent setting
parameters.
Table 3.32 – Setting parameters of P< and P<< stages
Parameter Value
P<, P<< -200.0 ... 200.0
T< 0.3 ... 300.0
S_On Enabled; Disabled
S_Off Enabled; Disabled
T_On Enabled; Disabled
T_Off Enabled; Disabled
Table 3.33 – Measured and recorded values of P< and P<< stages
Parameter
Measured value P
Recorded values SCntr
TCntr
Flt
EDly
⋅
3
Rated Pr imary
Unit Default
%Sn -4.0 (P<),
-20.0(P<<)
S 1.0
- Enabled
- Enabled
- Enabled
- Enabled
Value Unit
kW Active power
- Start counter (Start) reading
- Trip counter (Trip) reading
%Sn Max value of fault
% Elapsed time as compared to
the set operating time, 100%
= tripping
Description
P<,P<< pick-up
setting
P<, P<<
operational delay
Start on event
Start off event
Trip on event
Trip off event
Description