Where:
• I
1
= Calculated positive sequence current of the measured RMS phase currents
• I
2
= Calculated negative sequence current of the measured RMS phase currents
• k
NPS
= Correction factor of the NPS current biasing to the equivalent current calculation
• I
MAX
= Measured maximum of the three TRMS phase currents
The thermal image status (θ
t%
, in percentages of the maximum thermal capacity used) calculation is
based on the sum of the long and short time constant thermal image calculation:
The basic operating principle of the thermal replica is based on the nominal temperature rise, which is
achieved when the protected object is loaded with a nominal load in a nominal ambient temperature.
When the object is loaded with a nominal load for a time equal to its heating constant tau (τ), 63% of
the nominal thermal capacity is used. When the loading continues until five times this given constant,
the used thermal capacity approaches 100 % indefinitely but never exceeds it. With a single time
constant model the cooling of the object follows this same behavior, the reverse of the heating when
the current feeding is completely zero.
A
AQ
Q-M257
-M257
Instruction manual
Version: 2.07
224
© Arcteq Relays Ltd
IM00021
Summary of Contents for AQ-M257
Page 1: ...AQ M257 Motor protection IED Instruction manual...
Page 2: ......
