Baker Hughes Apollo 3, Руководство пользователя

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• Overload Time Constant: The longer the time constant, the slower the overload will respond.
For example, a system running at 150% (1.5 on graph) of overload threshold with a 120 second overload
delay will trip in 70 seconds while a system running a 250% will trip in about 20 seconds.
Changing the OL Delay will change the trip time proportionally. For example, doubling the OL Delay will
double the trip time at any overload level.
9.2 Advantages of the I2T Motor Overload Algorithm
An I2T overload algorithm is superior to a fixed threshold/time delay algorithm in several respects.
Advantages include:
• I2T will tolerate light overloads for quite a while. A well tends to pull more current at startup than at steady
state. When using a fixed threshold/time delay algorithm, users tend to artificially raise the overload limit
to accommodate this (for example, by always setting overload to 15% above nameplate), making the
overload less sensitive in steady state conditions. The I2T algorithm can handle the starting current
without compromising protection after the current has stabilized. See
Figure 194: Apollo Overload
Simulator, page 223 .
• I2T will trip faster on heavy overloads. For example, assume we have a fixed threshold overload with
a delay of 30 seconds. The I2T algorithm will trip faster than the fixed threshold algorithm for loads
greater than about 210%. See screenshots below.
• I2T will not forget about the heat buildup just because the load occasionally drops below the overload
threshold. In a fixed threshold/time delay algorithm, the timer is reset each time the load drops below the
overload value. This could allow a system to run in overload indefinitely and damage the motor. See
Figure 194: Apollo Overload Simulator, page 223 .