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open / closed transition
- Thread starter malz
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Malz,
Open/Closed transition generally is in reference to automatic transfer schemes, where electrical loads can be fed from one of two, or three sources (generator, utility, transformer, etc).
When swtiching loads from one source to another, you can use either an open transition or a closed transition. The Open transition will switch from the preferred source the alternate source by first opening the preferred source before closing the alternate source. The benefit of this scheme is that it is less costly, and involves fewer engineering considerations (such as increased fault current, and more requirement for protective relaying). However, it also means that there will be a temporary interruption of power and can cause potential transient voltage situations which can be damaging to sensitive electronic equipment.
The second option is to use a closed transition where the alternate source closes before you open the preferred source, this means that both sources are feeding the load for a short period of time. The advantage of this is that there is no interruption of power. However, there are a number of engineering considerations that need to be made when implementing a system such as this. Depending on the layout of the electrical system, there will be an increase of the available fault current during the transition. Also, protective relays may need to be used to ensure that the sources are synchronized before the transition is made.
I hope this answers your question. I too have some questions concerning transfer schemes. Does anybody know of a standard I can reference with respect to close transition systems, whether they be IEEE, ANSI, etc?
/Sharmen
Open/Closed transition generally is in reference to automatic transfer schemes, where electrical loads can be fed from one of two, or three sources (generator, utility, transformer, etc).
When swtiching loads from one source to another, you can use either an open transition or a closed transition. The Open transition will switch from the preferred source the alternate source by first opening the preferred source before closing the alternate source. The benefit of this scheme is that it is less costly, and involves fewer engineering considerations (such as increased fault current, and more requirement for protective relaying). However, it also means that there will be a temporary interruption of power and can cause potential transient voltage situations which can be damaging to sensitive electronic equipment.
The second option is to use a closed transition where the alternate source closes before you open the preferred source, this means that both sources are feeding the load for a short period of time. The advantage of this is that there is no interruption of power. However, there are a number of engineering considerations that need to be made when implementing a system such as this. Depending on the layout of the electrical system, there will be an increase of the available fault current during the transition. Also, protective relays may need to be used to ensure that the sources are synchronized before the transition is made.
I hope this answers your question. I too have some questions concerning transfer schemes. Does anybody know of a standard I can reference with respect to close transition systems, whether they be IEEE, ANSI, etc?
/Sharmen
To add to Sharmen: Open or closed transition can also apply to wye/delta starter used on cooling water chillers.
The motor started in wye connection to reduce inrush currents and staring torque, transitions to delta connection is timed depending upon application. When transition ocuurs in the open mode the wye connection is disconnected from the line then the delta connection is connected to the line. During this period of transition a transient is generated. When transition ocuurs in the closed mode, a resistor is connected to the line, the wye connection is disconnected from the line then the delta connection is connected to the line and the resistor is disconnected from the line . During this period of transition a no transient is generated. Note motor is designed for wye/delta operation.
See Hardwood "Control of Electric Motors".
The motor started in wye connection to reduce inrush currents and staring torque, transitions to delta connection is timed depending upon application. When transition ocuurs in the open mode the wye connection is disconnected from the line then the delta connection is connected to the line. During this period of transition a transient is generated. When transition ocuurs in the closed mode, a resistor is connected to the line, the wye connection is disconnected from the line then the delta connection is connected to the line and the resistor is disconnected from the line . During this period of transition a no transient is generated. Note motor is designed for wye/delta operation.
See Hardwood "Control of Electric Motors".
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