COLD LOAD
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bphgravity
Senior Member
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- Florida
Re: COLD LOAD
Cold Flow comes to mind but not Cold Load.
Cold Flow is an expansion and contration characteristic of terminals and connections due to the torqueing and over-torqueing of conductors.
What is the scope of the reading material that brings up this term? Does it imply a certain condition?
Cold Flow comes to mind but not Cold Load.
Cold Flow is an expansion and contration characteristic of terminals and connections due to the torqueing and over-torqueing of conductors.
What is the scope of the reading material that brings up this term? Does it imply a certain condition?
Re: COLD LOAD
I am reading "Protective Relaying: Principles and Applications" by J. Lewis Blackburn.
I quote, "... Small tap 5 is selected. The ratio above load 5/4.5 =1.1 . This provides a small margin more than any potential increase in the continuous load, but a large margin with inverse-type relays for transient overcurrents, such as a COLD LOAD... " (Blackburn pg.143)
I am reading "Protective Relaying: Principles and Applications" by J. Lewis Blackburn.
I quote, "... Small tap 5 is selected. The ratio above load 5/4.5 =1.1 . This provides a small margin more than any potential increase in the continuous load, but a large margin with inverse-type relays for transient overcurrents, such as a COLD LOAD... " (Blackburn pg.143)
Re: COLD LOAD
Cold load pickup is the all the load on a circuit being energized at the same time when the breaker is closed. The system will see a larger than normal load current when this happens. You can imagine all of the motors on the circuit trying to start at the same time and the breaker trying to hold until the motors are up to speed.
[ December 06, 2005, 12:38 PM: Message edited by: bob ]
Cold load pickup is the all the load on a circuit being energized at the same time when the breaker is closed. The system will see a larger than normal load current when this happens. You can imagine all of the motors on the circuit trying to start at the same time and the breaker trying to hold until the motors are up to speed.
[ December 06, 2005, 12:38 PM: Message edited by: bob ]
Re: COLD LOAD
The term could also refer to resisters (baseboard heaters and incandescent lite bulbs). At start resistance is low as heat up resistance increases current drops. On large incancescant lite circuits slow blow fuses were used for the higher initial current.
Dan Bentler
The term could also refer to resisters (baseboard heaters and incandescent lite bulbs). At start resistance is low as heat up resistance increases current drops. On large incancescant lite circuits slow blow fuses were used for the higher initial current.
Dan Bentler
rcwilson
Senior Member
- Location
- Redmond, WA
Re: COLD LOAD
This is a utility term "Cold Load Pickup". After an outage, especially a winter outage, most of the utility loads are all set to start at once. All of the electric heat, water heaters, furnaces, lights, industrial machines, transformers, etc. will all try to turn on at one time as soon as the utility feeder breaker is closed.
These loads are usually scattered in time, turning off and on randomly so the inrush currents and operating current don?t all coincide. (Load diversity).
But when everything has been off for a while, all of the thermostats are calling for heat and all of the motors want to start at the same time.
The total inrush current and then the load current for the first few minutes may be greater than the normal feeder line overcurrent protection causing an unwanted trip on the utility feeder breaker. Modern relays have a feature that detects when load has been off for some programmable time and implements a temporary higher overload trip setting to allow cold load. Some relays can have their settings changed to Cold Load Pickup remotely by the system operator.
When designing overcurrent protection for utility feeders and substation, we have to consider the impact of cold load pickup and still protect the equipment.
This is a utility term "Cold Load Pickup". After an outage, especially a winter outage, most of the utility loads are all set to start at once. All of the electric heat, water heaters, furnaces, lights, industrial machines, transformers, etc. will all try to turn on at one time as soon as the utility feeder breaker is closed.
These loads are usually scattered in time, turning off and on randomly so the inrush currents and operating current don?t all coincide. (Load diversity).
But when everything has been off for a while, all of the thermostats are calling for heat and all of the motors want to start at the same time.
The total inrush current and then the load current for the first few minutes may be greater than the normal feeder line overcurrent protection causing an unwanted trip on the utility feeder breaker. Modern relays have a feature that detects when load has been off for some programmable time and implements a temporary higher overload trip setting to allow cold load. Some relays can have their settings changed to Cold Load Pickup remotely by the system operator.
When designing overcurrent protection for utility feeders and substation, we have to consider the impact of cold load pickup and still protect the equipment.
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