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Series Resistance Starters

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Submitted By Toni1204
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Series Resistance Starters
Construction and Operation
In this method, resistors are temporarily placed in series with the motor windings during startup. A voltage drop is created across the series resistors during startup, resulting in a lower starting voltage applied to the motor’s terminals. Once the motor has accelerated to normal operational speeds, the resistors may be “removed” and the motor allowed to operate under normal conditions.
At startup, the start contacts are closed, forcing the starting currents to flow through the series resistors. Once the motor has been allowed sufficient time to accelerate, the run contacts are closed, thus bypassing the resistors. A timer may be utilized within the control circuit to allow the motor to transition from “start” to “run” operation automatically.
Applications
1. Usually on low voltage (less than 600 v).
2. Where current reduction requirements are low, or where load torque during acceleration is minimal.
3. Not often used with large motors because of the high heat loss in the resistors.
4. May be used for full acceleration or for system voltage recovery.

Advantages
1. reduced heat loss
2. greater ease of start
3. (If correctly designed and constructed), this method will cause the motor to accelerate the load to almost full speed with the resistors in circuit before they are bridged out.

Disadvantages
1. The resistors must be cooled in between starts because of the heat build up in the resistors during start, and their temperature dependant resistance characteristics.
2. the resistance may be somwhat difficult to alter
3. If the system is designed poorly, the transition to full voltage will occur at less than 80% full speed, and the current will then step up to almost Direct on Line...

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