Ampcontrol IPD - Page 95

Ampcontrol Pty Ltd – ABN 28 000 915 542
IPD USER MANUAL
IPDB014 Version 14 – SEP/2020
Uncontrolled Copy - Refer to Ampcontrol Website for Latest Version
Page 95 of 96
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– PROPERTY OF AMPCONTROL PTY LTD
– NOT TO BE REPRODUCED IN PART
These two algorithms are mathematically and operationally identical. For purposes of demonstrating
conformance to Curve B of IEC 60255-151, the algorithm has been rewritten for clarity. Equivalence
with the IEC 60255-151 requirements is established with:
TMS = 13.33 x m
k = 13.5, per curve B
c = 0, per curve B
α = 1, per curve B
Resultant values of TMS (based on the range of m values) are 0.066 ≤TMS ≤ 13.33 (0.005 ≤ m ≤ 1.0).
The overall error in tripping accuracy for the Over Current and Short Circuit is 5% (per IEC60355-151
part 6.3).
The transient overreach performance is 35% (per IEC60255-151 part 6.5.2).
The response to time varying energising quantities is < 5% (per IEC60255-151 part 6.5.4).
Motor Overload – IEC60255-8
See “m-OL” Curves (Drawing IPDB019) and Motor Overload Functional Block Diagram (Drawing
IPDB035) in Appendix A – Drawings.
The Ampcontrol IPD implements the motor thermal model in line with IEC 60255 Part 8, represented by
two curves:
 Cold Motor Curves
 Hot Motor Curves
Motor overload is implemented in conjunction with the time independent short circuit functions of the
IPD. The three measured phase currents are squared and added together to provide the heating input
into the thermal model.
The overcurrent time dependent curve is based on a Motor Thermal Model. Using this model, the relay
will trip according to the following formula:
22
2
2
)(
ln
b
p
IkI
II
t


 
Where:
𝑡 is the operate/trip time,
𝜏 is the thermal time constant
𝐼
𝐵
is the basic current. A value of 1.0 is used.
𝑘 is a constant. A value of 1.0601 is used in the IPD.
𝐼 is the relay current
𝐼
𝑝
is the specific load current before the overload occurs.
0
p
I
for ‘cold’,
1
p
I
for ‘hot’.