Ashida ADR241B, Instruction Manual

Page: 104 / 272

ADR241B
Doc ID : ADR241B-DO_IM_01
Ref ID : ADR241B/IM/PLF
Rev No. : 06
Page No. : 104 of 272
Definite Time Reset Characteristic
Start Time
Energising
Quantity > Gs
Start (Pick-up)
Signal
Operated
Signal
Value of
Internal Time
delay counter
tr Reset time settings
Reset Time
Restart Time
Time Delay setting
Tripping
Disengaging
Time
Figure 15: Definite Time Reset Characteristic
4.8 Cold Load Protection Function
Cold Load Pickup function is provided to avoid mal operation of relay due to high inrush
current after the closing of circuit breaker. If Clod Load function is enable, whenever a circuit
breaker is turn ON relay sense through CB auxiliary contact (CBNO) and start internal timer
known as “t_CLP Timer”. During this time period relay will activate separate group of setting
specified in cold load settings menu and inhibits all other protection function for a set
duration. When the set “t_CLP Timer” is elapsed, all the relevant settings will revert to their
normal protection setting values or become unblocked.
4.9 Thermal Overload Protection Function
The thermal withstand capability of the power system equipment is affected by overheating
prior to a fault. The temperature should not exceed the thermal withstands capability of
power system equipment. The RMS currents are measured and analyzed to monitor the
thermal state of power system equipment. In case of thermal overload function the
calculation of the trip time is given by:
t =
τ
x ln ((K²- A)/(K²- 1))
Where
t : Time to trip
τ
: Thermal time constant T of the equipment to be protected
K : Thermal overload capacity (Irms/ k* Ith>)