Overload And Overcurrent Relay

[Shahid Hafeez]

Hi Guys,

 

Could any one tell me, the difference b/w Over current and overload relay.

 

What the difference b/w Permissive under reach and Over reach Protection .

 

what is the stub protection.

 

what is the SOTF protection.

 

 

Regards,

 

Shahid Hafeez

 

[jraef]

Could any one tell me, the difference b/w Over current and overload relay.

 

An Over Load relay measure the current over time, also known as I^2t. It is not a linear current threshold, but rather a buildup of heat as measured by the energy (amps only) going into a load throughout a period of time. So a short duration but very high increase in current is not necessarily cause for tripping, but a low amount of extra current over a long period of time might be.

An Over current relay would look for just a specific current level and act upon that as a threshold response.

 

What the difference b/w Permissive under reach and Over reach Protection .

Not absolutely sure of the terminology (not used here in the US), but if I had to guess, I'd say that Permissive under reach would be a low limit threshold for an Current Sensing Relay, for example, a way to turn off a motor controller if a shaft or belt breaks and the motor stops drawing some minimum level of current. Over reach to me sounds like the opposite; a threshold that would be used to detect a jammed motor or some other condition that makes the running current exceed a set value.

 

what is the stub protection.

 

what is the SOTF protection.

 

No idea on either of these.

[chinni]

 

The over current is ,it is the current excess than specified current ie,by over load,short circuit.

 

Over load current is the current only that it is under the specified max.current. If exess than max.current it is called as Over load current.