Load Shedding
Description
The LTMT main unit provides load shedding, which you can use to deactivate non-critical loads if voltage level is substantially reduced. For example, use load shedding when power is transferred from a main utility supply to a backup generator system, where the backup generator system can supply power only to a limited number of critical loads.
The LTMT main unit only monitors load shedding when Load Shedding is selected.
With the load shedding function enabled, the LTMT main unit monitors the average phase voltage and:
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Reports a load shedding condition and stops the motor when voltage falls below a configurable voltage dip threshold and stays below the threshold for the duration of a configurable load shedding timer.
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Clears the load shedding condition when voltage rises above a configurable Voltage dip restart threshold and remains above the threshold for the duration of a configurable load shedding restart timer.
When the LTMT main unit clears the load shedding condition:
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In Maintained start configuration, it issues a Run command to restart the motor.
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In Momentary start configuration, it does not automatically restart the motor.
If your application includes another device that externally provides load shedding, the LTMT main unit load shedding function should not be enabled.
All voltage dip thresholds and timers can be adjusted when the LTMT main unit is in its normal operating state. When a load shedding timer is counting at the time it is adjusted, the new duration time does not become effective until the timer expires.
Functional Characteristics
The load shedding function includes the following features:
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Two thresholds
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Voltage Dip Threshold
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Voltage Dip Restart Threshold
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Two time delays
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Load Shedding Timeout
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Voltage Dip Restart Timeout
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One status flag
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Load Shedding
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One counting statistic
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Load Sheddings Count
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Parameter Settings
The load shedding function has the following parameters:
|
Parameter |
Setting range |
Default value |
|---|---|---|
|
Function |
|
Disable |
|
Load Shedding Timeout |
1–9999 s in step of 1 s |
10 s |
|
Voltage dip threshold |
20–90% of nominal voltage in step of 5% |
90% of nominal voltage |
|
Voltage Dip Restart Timeout |
0–9999 s in step of 1 s |
2 s |
|
Voltage dip restart threshold |
20 -95% of nominal voltage in step of 5% |
95% of nominal voltage |
Technical Characteristics
The load shedding function has the following characteristics:
|
Characteristics |
Value |
|---|---|
|
Trip time accuracy |
+/– 0.1 s or +/– 5% |
Timing Sequence
The following diagram is an example of the timing sequence for the load shedding function, for a maintained start configuration with automatic restart:
