Table of Contents
Advertisement
MPC2000+ Technical Manual
14. MPC2000+ Thermal Overload Protection
MPC2000+ Thermal Operating Curves
The curves shown are the time/current operating characteristics
for the MPC2000+ Thermal Overload protection.
Curve 1 :Cold Curve
Overload Setting =105%
Curve 2 :Hot Curve
Overload Setting =105%
Running From 100% FLC
Hot/Cold Ratio = 80%
Curve 3 : Hot Curve
Overload Setting:=105%
Running From 100% FLC
Hot/Cold Ratio = 50%
Curve 4 : Hot Curve
Overload Setting:=105%
Running From 100% FLC
Hot/Cold Ratio = 20%
Explanation
The MPC2000+ simulates the thermal condition of the motor
by means of a thermal register. The heating of the register is
related to the square of the largest of the three line currents.
The rate of cooling of the thermal register is directly related to
the rate of heating. The value of the thermal register is called
thermal capacity and it is used to simulate motor temperature.
100 percent thermal capacity means the motor temperature has
reached the maximum allowed and is the level at which an
overload trip will occur.
When the motor is stopped for a long period of time the
thermal capacity used is zero, this is known as the 'cold
condition', and the motor has 100 percent of it's thermal
capacity available for heating before a trip will occur.
When a motor starts and is running it's temperature increases, after running at normal FLC for a period of time the
motor will have reached a hot condition and a lower value of thermal capacity will be available.
The Hot/Cold Ratio setting determines the amount of available thermal capacity for a motor running at FLC i.e. hot
condition, this is set as a percentage ratio of the amount of thermal capacity available at the cold condition which is
always 100%.
The thermal capacity available for a motor running at normal FLC i.e. Hot condition is the Hot/Cold Ratio setting. For
example if the Hot/Cold ratio setting is 60% and the motor has been running at normal FLC for some time the amount
of thermal capacity available is 60% then the amount displayed by the MPC2000+ is the amount used which is 100 -
60 = 40%.
Providing the motor running current does not exceed the overload setting ( 105% FLC default) the thermal capacity
used will never reach 100% and therefore will never trip on overload
Page 32
200
100
t
10
Operating
Time (secs)
1.5
1
0.2
0.15
0.1
0.01
ISSUE 7 28/9/99
9
8
7
6
5
4
3
2
1
2
3
Multiples Of
P&B Engineering
Curve 1
Curve 2
Curve 3
Curve 4
4
5
6 7 8 9 10
15
Advertisement
Table of Contents
