Arcteq AQ-F210, Инструкция по эксплуатации

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Instruction manual –AQ F210 Feeder Protection IED 117 (292
)
4.2.8 T
HERMAL OVERLOAD PROTECTION FOR FEEDERS
T
F
> (49F)
Thermal overload function for feeder (TOLF) is used for cables and overhead lines thermal
capacity monitoring and protection. Also this function can be used for any single time
constant application like inductor chokes, certain types of transformers and any other static
units which don’t have active cooling in addition to the cables and overhead lines.
TOLF function constantly monitors phase TRMS currents (including harmonics up to 31
st
)
instant values and calculates the set thermal replica status in 5 ms cycles. TOLF function
includes total memory function of the load-current conditions according to IEC 60255-8
TOLF function is based into thermal replica, which represents the protected object or cable
thermal loading in relation to the current going through the object. Thermal replica includes
the calculated thermal capacity used in the “memory” since it is integral function which tells
apart this function from normal overcurrent function operating principle for the overload
protection applications.
Thermal image for the TOLF function is calculated according to equation described below:
θ
t%
= ((θ
t-1
- (
I
MAX
I
N
× k
SF
× k
AMB
)
2
× e
-
t
τ
) + (
I
MAX
I
N
× k
SF
× k
AMB
)
2
) × 100%
, where

t%
= Thermal image status in percent of the maximum thermal capacity available

t-1
= Thermal image status in previous calculation cycle (the memory of the function)
I
MAX
= Measured maximum of the three TRMS phase currents
I
N
= Current for the 100 % thermal capacity to be used (pick-up current in p.u., with this
current t
max
will be achieved in time  x 5)
k
SF
= Loading factor (service factor) coefficient, maximum allowed load current in per unit
value depend of the protected object or cable/line installation
k
AMB
= Temperature correction factor either from linear approximation or settable 10 point
thermal capacity curve.

= Thermal time constant of the protected object (in minutes)
e = Euler’s number
t = Calculation time step in seconds (for AQ 2xx IED:s 0.005s)
The basic operating principle of the thermal replica is based into that the nominal
temperature rise is achieved when the protected object is loaded with nominal load in
nominal ambient temperature. When the object is loaded with nominal load for time equal